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Thread: 78 280Z - no injector pulse

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    HLS30-454423 3/78 Virto's Avatar
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    Default 78 280Z - no injector pulse

    I'm starting this thread as a bit of a placeholder, moving this issue out of my old exhaust manifold/status thread since it's likely I'll need help.

    The background is listed in the exhaust thread, so I'll keep it focused on the EFI here. Bottom line, car hasn't run in a year, head was pulled and tanked, and the car is back together now. The car will crank easily but not fire. Injectors show 12V but no pulse via NOID light.

    Zed Head has helped give me some places to start - I'll likely only have access to the car over the weekend, so I can't just run out and mess around, as much as I'd like to.

    I'll add to this thread as time goes on with status and results. If anyone else has any questions or direction (/wave FastWoman, lol) I welcome your input.
    Kelly R. Johnson
    1978 280Z...yes it's automatic...but I'm fat.

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    You got sparks at the plugs?

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    Hey Kelly,

    Good question from Captain! No sparks means no triggering of the ECU.

    You also need connectivity from the negative side of the coil to the #1 terminal on the ECU to sequence it. You've got 12V at the injectors, which means you've got continuity through the drop resistors. All that's left is for the ECU to ground the injectors.

    Got power to the ECU, BTW?
    My last three sports cars while I still owned all three:

    2001 BMW Z3 Roadster 3.0i soft/hard top (sold)
    1966 Ford Mustang Coupe (sold)
    1978 Datsun 280Z (enjoying very much )

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    ZH mentioned checking for spark and also mentioned the coil to pin 1 connection (blue wire, I believe). I was told that it had spark, but I'll verify for myself when I get over to look at it.

    I'll check to see if there's a break in the connection from the coil, as well.

    I would *assume* there's power to the ECU, but I can't be entirely sure until I go over there. I'll have to pull out the EFI bible and see what pins on the harness I need to check for power.

    Thanks, you two. I'm making a little list - it helps, really.
    Kelly R. Johnson
    1978 280Z...yes it's automatic...but I'm fat.

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    Z geek at large FastWoman's Avatar
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    No problem...

    Obviously check that the ECU has a good ground also!
    My last three sports cars while I still owned all three:

    2001 BMW Z3 Roadster 3.0i soft/hard top (sold)
    1966 Ford Mustang Coupe (sold)
    1978 Datsun 280Z (enjoying very much )

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    HLS30-454423 3/78 Virto's Avatar
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    The ECU grounds via the harness, correct? Not the case being mounted to the body.

    The EFI bible says to test pins 5, 16, 17 and 35 for continuity to ground. Not sure if there were any changes in pin-out from 75 (last revision date) to 78, when the car was built.
    Kelly R. Johnson
    1978 280Z...yes it's automatic...but I'm fat.

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    There is a second version of the "Bible" (New Testament?) published for 1980 that has all models covered. It's a little harder to work with because there are so many choices, but it will have specific tests for your 1978 car.

    XenonS130 - S130 Reference

    Yes, the EFI system ground wire is that black one that has its own connection to the battery negative terminal. It may be extra but you can't have too many.
    1976 280Z, with some minor modifications

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    HLS30-454423 3/78 Virto's Avatar
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    Very cool, thanks - I had no idea there was a newer version.

    This one seems to have a few more tests that can be run and it's generally more well-written and clear as to what you're looking for and why.
    Kelly R. Johnson
    1978 280Z...yes it's automatic...but I'm fat.

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    HLS30-454423 3/78 Virto's Avatar
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    Mmk, minor update - the car has spark for sure - it'll run on starter fluid, there's just no fuel coming in since the injectors aren't firing.

    Spoke with the garage owner and let him know I'd swing by on Saturday to test the ECU and see what I can find - turns out the city just updated codes and notified him this week. If anyone is caught working on a car in the parking lot (ie, not a garage bay) it's punishable by a fine/court appearance. Makes no sense to me, but Elgin is super-big right now on making everything look nice and shiny to attract more well-to-do homebuyers. So I'll be the somewhat cripped, super fat guy sitting on the pavement out of sight trying to multimeter my ECU, lol.

    So, with spark confirmed, is there anything we can rule out?
    Kelly R. Johnson
    1978 280Z...yes it's automatic...but I'm fat.

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    Make sure that there is 12 volts on each pin of the injector connectors, removed from the injector, with the key On. It will seem weird from an Electricity 101 perspective, but one side is power and the other side is the transistor circuit. Probably a pull-up circuit of some kind (unresolved in other threads). Both pins in each connector will show voltage if the ECU has power and things are correct.

    If you have that, then check that Pin 1 has continuity (zero or almost zero resistance) to the coil negative. Make sure that the tachometer is connected. I think that the needle should at least jump when you turn the key On or crank the engine if not show a few RPM.

    If you can get on the forum while you're there somebody can probably walk you through some steps once you get a few results. Take a lap top, maybe there's free wi-fi nearby.
    1976 280Z, with some minor modifications

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    HLS30-454423 3/78 Virto's Avatar
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    As I recall from all my fuel delivery issues, the tach will bounce when the engine is cranking. Should be fairly obvious if it's not connected, at that point.

    He stated that he verified 12V on the injectors, but I'll pull all 6 and test both leads. Checking that coil wire physically will probably be the first thing I do, as well as the ground wire on the battery negative terminal.

    I'll take my phone with me, just in case - not ideal for typing, but it can do the job.

    I just need to get her going so I can get it back home into the garage, where I can cut off the rust before winter comes. After that, I'm going to teach (hopefully) myself to weld. Seems like a vital skill with these cars unless you have countless thousands to pay body shops.
    Kelly R. Johnson
    1978 280Z...yes it's automatic...but I'm fat.

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    Welding... I tried that once! Well, at least I tried. I'm sure it's a learnable skill, just like any other skill.

    I have nothing to add about the ECU. If it has power, ground, and ignition pulse to #1, then it should be grounding your injectors. If not, then you might have a bad ECU.

    I'll mention one thing, though: You should be able to fire your ignition manually by connecting a wire to the (-) side of your coil and tapping it to ground somewhere. Every three taps/sparks should get you an injector pulse. It might be easier than cranking your engine. Don't touch the bare wire, because the flyback could give you a jolt.
    My last three sports cars while I still owned all three:

    2001 BMW Z3 Roadster 3.0i soft/hard top (sold)
    1966 Ford Mustang Coupe (sold)
    1978 Datsun 280Z (enjoying very much )

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    HLS30-454423 3/78 Virto's Avatar
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    I sure hope it doesn't come down to a bad ECU. Those things are too much money, even if you have a rebuildable core!

    Hopefully I find a loose connection or something and it's a fast fix - I don't want to risk getting the garage owner in trouble by poking around under the hood in the parking lot.
    Kelly R. Johnson
    1978 280Z...yes it's automatic...but I'm fat.

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    Kelly, I only know of one bad ECU that cropped up on this list. It was a cold solder joint, and it was fixed by re-flowing. So these things are pretty robust. If you do end up needing one, they sometimes show up on ebay relatively cheaply.
    My last three sports cars while I still owned all three:

    2001 BMW Z3 Roadster 3.0i soft/hard top (sold)
    1966 Ford Mustang Coupe (sold)
    1978 Datsun 280Z (enjoying very much )

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    HLS30-454423 3/78 Virto's Avatar
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    280ZX computers look to be dime a dozen. Hopefully it's a non-issue. We'll see what I can come up with while I'm with the car.

    Do I need to pull the ECU from its mounting location to remove the cable? I've never tried before - I've never even had that trim panel off.
    Kelly R. Johnson
    1978 280Z...yes it's automatic...but I'm fat.

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    No, you leave the ECU in place. If I recall correctly, the big connector is held down with a screw on one end (??). Free up that one end, and the connector hinges away from the box. It's very quick/easy to get into the thing.
    My last three sports cars while I still owned all three:

    2001 BMW Z3 Roadster 3.0i soft/hard top (sold)
    1966 Ford Mustang Coupe (sold)
    1978 Datsun 280Z (enjoying very much )

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    The connector is under the black plastic kick panel left of the driver's feet. Three screws hold the panel. Then the connector actually has a spring clip that is pressed up (I think), allowing the top, cable, end of the connector to swing out (you have to tug on the wires, they'll be okay), far enough to pull the other end of the connector off of it's little pin pivot/hinge. Then it's free. You need to pull the top end out a ways before the bottom will release. This part might require having the door open. Once you get it free you should be able to get to the pins with your meter while inside. Might be cramped though.
    1976 280Z, with some minor modifications

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    In addition to pulling off the cover over the ECU, I think you'll want to remove the small trim strip that runs horizontal above the driver's knees. I don't think there's enough room to swing the big ECU connector off it's bottom hook if you don't take out that trim panel as well.

    Before you start poking around at the ECU connector... Have you checked the big fusible link(s) that feeds the whole fuel injection system? Goes right from the battery to the FI harness? Spade connectors on both ends to facilitate replacement if necessary. You should have 12V on both sides of that link at all times.

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    Quote Originally Posted by Zed Head View Post
    Make sure that there is 12 volts on each pin of the injector connectors, removed from the injector, with the key On. It will seem weird from an Electricity 101 perspective, but one side is power and the other side is the transistor circuit. Probably a pull-up circuit of some kind (unresolved in other threads). Both pins in each connector will show voltage if the ECU has power and things are correct.
    There's no pull ups on the injector outputs inside the ECU. However, unless you pull all the injector connectors off at the same time (at least all the ones that share the same transistor) you'll read 12 back feeding through the other injectors and their dropping resistors.

    In other words, for example... If you pull the connector off injector #2 and probe the contacts for voltage WRT ground:

    One side will read 12V because it's pulled up to Vbatt through it's dropping resistor.
    The other side will ALSO read 12 volts because it's pulled up through the solenoid coils of injectors #1 and #3 through THIER dropping resistors to Vbatt.

    If you pull all the injector connectors at the same time, you should be able to determine which side is hot and which side is pulled to ground by the ECU.

    Does that make sense? Did I say that right?

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    HLS30-454423 3/78 Virto's Avatar
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    I haven't checked any of the links yet. I did replace all the links on the fender before I dropped the car off last year. I haven't checked any other links but those four.
    Kelly R. Johnson
    1978 280Z...yes it's automatic...but I'm fat.

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    Quote Originally Posted by Virto View Post
    I haven't checked any of the links yet. I did replace all the links on the fender before I dropped the car off last year. I haven't checked any other links but those four.
    CO is right, the links could be a factor. No power to the ECU. On your 78 car, there are two green fusible links in line in a small power wire directly from the positive post of the battery. If they haven't been messed with they'll be attached to the metal framework that holds all of the relays in the engine bay. Right in front of the battery. It's possible also that the links just came unplugged, they're held in place by plastic connectors that get old and break. So, overall, you have 6 fusible links. Even if the links look good, the power checks at the ECU connector will tell you if they're working.

    The EFI relay is also a possibility although they really don't go bad often. It's described in the Guidebook also.
    Last edited by Zed Head; 08-29-2014 at 10:06 PM.
    1976 280Z, with some minor modifications

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    Quote Originally Posted by Captain Obvious View Post
    There's no pull ups on the injector outputs inside the ECU. However, unless you pull all the injector connectors off at the same time (at least all the ones that share the same transistor) you'll read 12 back feeding through the other injectors and their dropping resistors.

    In other words, for example... If you pull the connector off injector #2 and probe the contacts for voltage WRT ground:

    One side will read 12V because it's pulled up to Vbatt through it's dropping resistor.
    The other side will ALSO read 12 volts because it's pulled up through the solenoid coils of injectors #1 and #3 through THIER dropping resistors to Vbatt.

    If you pull all the injector connectors at the same time, you should be able to determine which side is hot and which side is pulled to ground by the ECU.

    Does that make sense? Did I say that right?
    I can't say myself, because I generally describe the 12 volts on each side as "transistor weirdness". Not an authority. Sounds reasonable though, I think that you're saying the 12 volts is "backfeeding" through the transistor that controls those injectors. So it should be groups of three then. Added a diagram just for ambience. Of course, it doesn't show the transistor circuits but it does show how all injectors are powered and feed back the ECU.

    Added another diagram. I had a 78 that had the combined EFI/Fuel Pump relay, like 1976. Just for reference. Virto will probably not need to go that deep.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by Zed Head; 08-29-2014 at 10:05 PM.
    1976 280Z, with some minor modifications

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    You don't backfeed through the transistor. You backfeed through the other injector(s). Maybe these sketches will help with the weirdness.

    Here's why you would see +12 on both sides of the injector connector if you pull just one:


    And here's why you should be able to determine which side is which if you pull all of them (or at least the ones that share a transistor):

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    Well, no joy at the moment. The shop is closed, at least for the morning - one man operations have random hours, I've noticed.

    It's also raining, which isn't conductive to my working on the car outside. I did get a few minutes of dry with it, but the battery is flat. I turned it over one time om battery power and swear I saw the tach needle bounce, but now that the battery is completely drained it won't do anything beyond weakly ring the seat belt buzzer.

    It's stuffed in too close to another car for me to get into the driver's side, so no continuity tests for the moment. I did pull a couple of the injector plugs but got no movement on my old multimeter. It might also have a shot battery, so I'll replace that before trying again. Granted I tested after I murdered the battery by turning the car over.
    Kelly R. Johnson
    1978 280Z...yes it's automatic...but I'm fat.

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    Captain, my faith in automotive manufacturing has been restored. I suggested long ago that there's no way a manufacturer would waste 6 pull-up resistors in the design of a circuit. We had speculated that it might have been just one of those charming '70's things or that the hypothesized pull-up resistors might have been for diagnostic purposes (e.g. to be able to test both sides of an injector plug to confirm power to the ECU). However, a Deutschmark is a Deutschmark (Bosch), or a Yen is a Yen (Hitachi). Anyway, yes, the backfeed through a common transistor connection would explain the +12 on the ECU side of an injector connector without indicating anything about whether the ECU has power.

    Kelly, if your fusible links are in typical condition, they're probably pretty awful. I, too, would begin my diagnostic efforts with regard to power to the ECU. However (and this is important), I would not start pulling apart the fusible links to do it. Start methodically at the ECU connector to see if you have power. If you don't, then move back to the EFI relay. If you don't have power there, move back to the fusible links. The reason is that if you have a marginal connection somewhere, you can make it good (for the moment), just by jiggling it around. However, sometime when you're out on the highway, it might decide to go bad again, leaving you stranded. Faulty connection gremlins are sometimes very skittish, so to catch them, it's better to diagnose from afar and to sneak in on them -- catching them by surprise before they can clean up their acts.

    [voice of Elmer Fudd] Be veeeewy veeeewy quiet! I'm hunting gwemlins! Eheheheheheh!
    Last edited by FastWoman; 08-30-2014 at 08:01 AM.
    My last three sports cars while I still owned all three:

    2001 BMW Z3 Roadster 3.0i soft/hard top (sold)
    1966 Ford Mustang Coupe (sold)
    1978 Datsun 280Z (enjoying very much )

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    These Z-Cars don't go off unless you hit them juuuuusst right.
    Last edited by Captain Obvious; 08-30-2014 at 11:15 AM.

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    Your diagram makes it all clear. Thanks. Should have spent some thought on it before. I've been lazy all these years. It seems so Obvious now.

    Virto, if the key was On when you tested the injector plugs then you really want to go directly to the EFI fusible links, the two green ones, right off the battery positive. Look at the 1978 diagram I posted above. They feed the EFI relay and the power to the dropping resistors, which CO has shown supply both sides of the injector connectors. If you have enough juice for the buzzer, there should be enough to register on your meter at the injector connectors.
    1976 280Z, with some minor modifications

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    Quote Originally Posted by Zed Head View Post
    It seems so Obvious now.
    Why yes... Yes it is. Haha!! Glad to help!

    Of course, if you have an Ohmmeter that is capable of truly working down in the low ohm area, you should be able to tell what went where just by checking resistances. My meters aren't that good... I have one that might work for that, but it eats batteries and seems like every time I grab it, the battery is dead.

    Honestly, I almost always find myself reaching for my cheap (disposable) HF meters. I've got one in every room of the house. Cheap and good for reality checks, but I wouldn't trust it to tell me the difference between a half an Ohm and one Ohm.
    Last edited by Captain Obvious; 08-31-2014 at 07:03 AM.

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    Update time.

    Injectors have 12v
    Tach bounces when cranking
    ECU pin 1 has 12v, key on
    ECU has power, pin 10, key on
    ECU grounds, pins 5, 16, 17, 35 all have continuity
    12V leaving the green fuse links
    Relays click when key on
    Fuel pump runs, there is pressure at the rail

    We pulled the EFI main relay and tore it apart. Remarkably clean inside, seems to be doing its job.

    When you first crank the car, it sputters and wants to fire, but there's no fuel. It very nearly catches, so it seems the cold start injector is working.

    I'm going to print out and drop off copies of the EFI wiring diagram on my way to the office tomorrow. I'm hoping I can get her home soon - she looks like hell.
    Kelly R. Johnson
    1978 280Z...yes it's automatic...but I'm fat.

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    You're absolutely certain you have no pulse? Is your noid functioning correctly? It should be a VERY brief flicker once every rotation.

    If you turn on the ignition with the ECU unplugged, can you ground the individual injectors at the ECU plug and hear them click?
    My last three sports cars while I still owned all three:

    2001 BMW Z3 Roadster 3.0i soft/hard top (sold)
    1966 Ford Mustang Coupe (sold)
    1978 Datsun 280Z (enjoying very much )

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    per sage direction from others on this site, i keep a set of christmas lights with the ends cut, stripped & twisted for easy insertion into the injector plugs - they work great as a little test light to check for pulses.
    '78 280z - Daily driver/work in progress...

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    Quote Originally Posted by FastWoman View Post
    You're absolutely certain you have no pulse? Is your noid functioning correctly? It should be a VERY brief flicker once every rotation.

    If you turn on the ignition with the ECU unplugged, can you ground the individual injectors at the ECU plug and hear them click?
    These are two good ideas. You're about to the point where it might be the ECU. The FSM and maybe the Guide Book will show which pins are the grounding pins for the injectors. You can ground those directly since the injector solenoids have resistance. I have made little copper probes to insert in to the ECU connector to make it easy to attach alligator clips, by smashing a piece of solid copper wire flat. With the key on, and power verified at the injector pins of the ECU connector, a quick tap to ground should cause the injector to click. That will show you that things should work if the ECU transistor does its job. If you do that a few times for each one, the engine will probably start and run for a second or two.

    A probe in pin 1 across your voltmeter leads - pin 1 to meter - other side to ground - should show a flicker when cranking the engine over. Or the christmas tree light should show it.

    I have had an ECU go bad to where the engine would not start anymore. First it flooded the engine then it just quit doing anything. So they do go bad. If you can borrow an ECU it might be worth a shot to just go directly to that. Seems like you've done enough to justify it. If you were close by, I'd loan you one.
    1976 280Z, with some minor modifications

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    Honestly, no. I didn't run the noid myself, but I'm pretty confident that I can believe him when he says it wasn't lighting.

    So, key on and then just a length of jumper wire from the ECU plug to ground? Is there any way to test the dropping resistors? That seems to be the only thing in the path I haven't looked at.
    Kelly R. Johnson
    1978 280Z...yes it's automatic...but I'm fat.

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    When you ground the injectors via the ECU plug, current has to flow through both the drop resistors and the injectors for you to hear clicking injectors. So if you can ground the ECU contacts and get clicks, you know that... (1) Your injectors have power, I believe through the ECU circuit, (2) Your drop resistors are good. (3) Your injectors are good, at least mechanically. That's not to say that they aren't clogged. (4) Your wiring is good. (5) If the ECU is also operational, then you should get an injector pulse.
    My last three sports cars while I still owned all three:

    2001 BMW Z3 Roadster 3.0i soft/hard top (sold)
    1966 Ford Mustang Coupe (sold)
    1978 Datsun 280Z (enjoying very much )

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    Quote Originally Posted by Zed Head View Post
    If you can borrow an ECU it might be worth a shot to just go directly to that. Seems like you've done enough to justify it.
    If only. Most of these cars have long since rusted away in Chicagoland. Windy City Z club is almost entirely new model Z cars, from what I've seen these days. I've run across plenty of people that say "hey, I remember these" or "I had one of these in the 80s" but they are an extreme rarity to actually see on the road. I guess I'll start keeping an eye on eBay - I don't really want to send MSA 350 bucks if it's not the issue. That having been said, is there a difference between the M/T and A/T computers, or was that only in the S130?

    If anyone has a good one they want to loan out for a week, I'd be happy to pay the return shipping and then slip some cash into the box with it to cover your time and assistance.

    I'm going to jot some notes down and deliver them tomorrow when I drop off the wiring diagram. If I can just get her to start, we can hang the rest of the exhaust, slap the fan back on and get it into the garage at home. I really do feel pretty sad when I look at it now, thinking of the time I wasted while the car was in better shape.
    Kelly R. Johnson
    1978 280Z...yes it's automatic...but I'm fat.

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    You know I kind of lost track of the problem and its symptoms since you switched threads. But, going back to Post 29, if you're getting some activity from the engine like it wants to start, I would pull a plug or two and see if they're wet or dry. Also, consider that the gas may have gone bad.

    If you're getting signs of life from the engine try some starting fluid. Maybe you just need to purge the bad gas from the injectors and get things flowing and moving again. Actually, I would probably just try starting fluid right now.

    Could also be water in the gas. Where has it been sitting?
    1976 280Z, with some minor modifications

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    I'll see about pulling the plugs. The engine will start on starting fluid. The initial sputter I'm getting now seems to be fuel from the cold start injector - not sure how that's tied into the fuel system, really. Unless I'm totally wrong, it's basically another injector that dumps some extra fuel where, past the maf?

    I suppose it could be bad gas. Back before I knew about how gas will varnish it had run on fuel that was probably 3 years old. It had half a tank of same-day gas when I dropped it off last July. It had last run sometime in November, I believe, when we made the call to have the head sent out for work. I'll mention draining the fuel. Water, have to drain it to be sure - it was kept both inside and outside at various points as it was shuffled around to make room for other cars. It has certainly been exposed to weather, hence the rust growth.
    Kelly R. Johnson
    1978 280Z...yes it's automatic...but I'm fat.

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    In general, old/bad gas can be deadly for a flat tappet, OHC, interference engine. If it's bad enough, varnish goo will form on the valve stems, and then it will solidify when the engine cools. When you go to start it again, your valves are stuck in place and collide with the pistons, while your rockers come loose. It makes a delightful, snappy-klink-klink sound. DAMHIK

    Anyway, I wouldn't do any serious diagnostic work without some known good gas. in the system.
    My last three sports cars while I still owned all three:

    2001 BMW Z3 Roadster 3.0i soft/hard top (sold)
    1966 Ford Mustang Coupe (sold)
    1978 Datsun 280Z (enjoying very much )

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    I threw the gas idea out there on the assumption that the ECU and injectors are actually working correctly. A big problem here is that nobody really knows if the garage owner knows how to test that the injectors are getting grounded or not. Since it runs on starting fluid, seems like there are two feasible possibilities - the injectors aren't opening or they are opening but they're squirting bad gas. Hard to say which is more likely. But the fact that it does run with starting fluid is significant, since it means that the plugs aren't fouled. Overall, it's still looking like the ECU is not properly grounding the injectors.

    There is a test that you can do that will tell pretty surely if the circuit to the ECU is correct and if the injectors are opening. Connect a jumper wire to the negative post of the coil, leaving one end free. Turn the key On. Tap the free end of the jumper to ground quickly. Every three taps the injectors should click, all six of them. With no engine cranking and no extra noise, it will be easy to hear the injectors. If you get a spark at the wire on every tap, which you should, but no noise from the injectors, then something is wrong. At least you'll be back to a focus on the ECU and the Pin 1 circuit.
    1976 280Z, with some minor modifications

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    He did mention that he thinks it's a ground problem, and that's why he wanted a copy of the EFI wiring diagram. I'll drop it off tomorrow and mention everything we've discussed so far.

    Thanks much, seriously. It means a lot.
    Kelly R. Johnson
    1978 280Z...yes it's automatic...but I'm fat.

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    Quote Originally Posted by Virto View Post
    The initial sputter I'm getting now seems to be fuel from the cold start injector - not sure how that's tied into the fuel system, really. Unless I'm totally wrong, it's basically another injector that dumps some extra fuel where, past the maf?
    Yes, it's basically another injector that dumps fuel in, and it's located just behind the throttle body. You should be able to find it by following the fuel lines. The fuel line that shoots over towards the throttle body goes to the cold start injector.

    The cold start injector is not under the control of the fuel injection ECU in any way other than it's connected to the same fuel source. If there's fuel pressure, the cold start injector should spray even if the fuel injection ECU has been completely removed from the car.

    Assuming it's cold enough to warrant needing the cold start injector, the cold start injector should spray when the engine is CRANKING, and it won't do that forever. There's a temperature controlled switch (known as the thermotime switch) that will cut off the cold start injector after a few seconds of spraying regardless if the engine has started or not.

    Take a look in the FI literature about the thermotime switch. That's what controls the cold start injector. The ECU has nothing to do with it.

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    I'll just mention that another tool in your diagnostic arsenal could be to unplug the coolant temp sensor (injector-styled connector going to the SMALLER sensor in the thermostat housing). That should result in the delivery of LOTS more fuel, as though you were trying to start the car during the winter in Antarctica.

    However, try triggering the ECU manually without cranking, the way Zed and I suggested (posts 12 and 39). I bet your ECU is really working.
    My last three sports cars while I still owned all three:

    2001 BMW Z3 Roadster 3.0i soft/hard top (sold)
    1966 Ford Mustang Coupe (sold)
    1978 Datsun 280Z (enjoying very much )

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    Sorry FW I thought that you had mentioned the "grounding the negative post" test but I couldn't find it when I looked back. It doesn't seem very sophisticated, creating sparks and ozone, but it does test a big chunk of the system, in series and connected. Seems like it should be an FSM test.
    1976 280Z, with some minor modifications

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    I dropped off a copy of the wiring diagram, the pinout for the ECU connector and instructions on how to ground the coil to test the injectors. He was out driving a customer car, so I'll have to call him later today and give him the details.

    So, if we do this test and the injectors don't click, we're looking at some kind of issue between the ECU pin 1 and the coil, be it the drop resistors or the wiring, or perhaps the ECU itself?

    Alternatively, if we test and the injectors DO click, what's the next logical step?
    Kelly R. Johnson
    1978 280Z...yes it's automatic...but I'm fat.

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    No problem, Zed! Yes, it's a very easy test. I've never had occasion to use it, but it seems a great way to confirm that the ECU is awake, is being triggered, and is sending out injector pulses.

    Kelly, if the injectors don't click, then it's either a triggering problem (e.g. wiring to the #1, weak ignition), a problem with the power (which you say you have), the drop resistors and/or injector wiring, or a dead ECU. You can rule out the drop resistors and injector wiring by grounding the individual injectors at the ECU plug. You should be able to make them click.

    If the injectors do click, then your EFI is functioning, and you have some sort of fuel or fuel/air ratio issue -- bad fuel, clogged injectors, clogged rail, wrong fuel pressure, massive vacuum leaks, or whatever.
    My last three sports cars while I still owned all three:

    2001 BMW Z3 Roadster 3.0i soft/hard top (sold)
    1966 Ford Mustang Coupe (sold)
    1978 Datsun 280Z (enjoying very much )

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    That's a good point on the vacuum leak. An old-timey mechanic might have the oil filler cap off to listen for noise or something, not realizing that that would be a massive vacuum leak. Everything needs to be buttoned up tight. Too bad the garage owner's not on the forum.
    1976 280Z, with some minor modifications

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    lol, I can say for sure that the oil filler cap is on tightly.

    I went over the vacuum lines yesterday, since I've had some vacuum leaks in the past. It would have to be fairly major to prevent it from starting. Even when I had a large enough leak that the transmission wouldn't shift, it would turn over and start very easily.

    The real issue is that he's got a lot of needy customers that take priority over the guy with the old rustbucket that doesn't need it to live day to day. There's a possibility that he won't have time to get to it until the weekend, at which point I'll try to spend an hour or so at the garage working on it at the same time, like yesterday.

    Wonder if it might be worth pulling an injector and seeing if there's any flow through it at all. If it was home in my garage I could run out there more frequently, but because of the layout of my driveway, I probably can't even have it towed. If it comes down it to, I'll see what I can do.
    Kelly R. Johnson
    1978 280Z...yes it's automatic...but I'm fat.

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    Listen for the clicks first. With no sounds but the tap of that jumper wire, either grounding the injectors directly, or grounding the coil you'll hear if the injectors are even opening. I would do both tests, first ground the pins at the ECU as FW originally suggested to verify that the injectors have power and will work, then ground the coil - to see if the ECU can do the same job.

    A jumper wire, the key, a charged battery (don't forget that), and you'll know much more.
    1976 280Z, with some minor modifications

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    I agree. And don't go pulling injectors! Pulling injectors can open you up to having to do other stuff -- replacing O rings and insulators, replacing fuel lines, or even mucking with screws rusted in place (like on my engine). There's a much easier way to verify flow if your system holds fuel pressure: Put a fuel pressure gauge somewhere on the fuel rail (or between the filter and the rail). Briefly run the fuel pump to pressurize, stop the fuel pump, and then ground an injector to depressurize. If you don't see the pressure drop when you ground an injector, then you have no flow. Easy.
    My last three sports cars while I still owned all three:

    2001 BMW Z3 Roadster 3.0i soft/hard top (sold)
    1966 Ford Mustang Coupe (sold)
    1978 Datsun 280Z (enjoying very much )

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    Here's a cheap ECU that might be worth a shot, for testing. Should work even if the numbers aren't a perfect match. The differences are minor among the variations.

    280z parts/ FREE L24 / Price drop - Parts for Sale - HybridZ


    And superlen has been known to loan an ECU I believe. He has collected a bunch for his project.

    http://www.classiczcars.com/forums/f...tml#post463189
    Last edited by Zed Head; 09-03-2014 at 12:36 PM.
    1976 280Z, with some minor modifications

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    I thought the ECU was different for 77-78 versus 75-76...am I mistaken?
    Kelly R. Johnson
    1978 280Z...yes it's automatic...but I'm fat.

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    They are different, sometimes, in ways that I'm not clear on. But the injector grounding circuit is the same. It might give you enough to get the engine started and get the car home.

    I had a 76 and 78 280Z with exactly the same ECU's, but the number on that 1975 ECU is different. I only suggest it because it's cheap, $25, and might tell you something, if you get to the point where the ECU is the only possible source.

    The weird thing about your situation is that the engine ran when you drove it over there and then it just sat. The ECU is in a fairly dry spot and I think that they probably go bad from usage not sittage. Odds are something strange happened like your gas tank filled of water. It happened to EuroDat and he was using his car.

    If your guy decides to really go for it with some time, he might run a hose from a gas can to the inlet of the fuel pump with fresh gas. Especially if the injectors click.
    1976 280Z, with some minor modifications

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    I'm tempted to just have it towed home, but I'm going to see if I can get some more garage time this weekend. I'm also going to see if I can pick up that ECU - I'll let you know how it goes.

    Edit: Went ahead and bought that ECU. Even if it's only a pseudo-spare, it'll be nice to have on-hand just in case.
    Last edited by Virto; 09-04-2014 at 08:47 AM.
    Kelly R. Johnson
    1978 280Z...yes it's automatic...but I'm fat.

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    ECU will be here Monday - swinging by the shop tomorrow morning to ground the injectors and see if we can get a click. I should have an update around lunchtime and I'll come back to beg for help after that.
    Kelly R. Johnson
    1978 280Z...yes it's automatic...but I'm fat.

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    I don't know whether to hope you need the ECU or not. If you do get clicks from directly grounding the connectors, then find on Monday that the 75 ECU gets the car home, there's somebody selling a 1978 ECU on Hybridz.

    Good luck.
    1976 280Z, with some minor modifications

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    OK, wow - what a weekend.

    Friday afternoon a big storm cell moved across the Elgin area, 70MPH winds and quarter-sized hail. There was one funnel cloud reported about halfway between here and the office in Arlington Heights.

    I lost the fence and all power until literally 10 minutes ago. The first thing to do was restart all the fish tanks - looks like I may end up with some dead loss in one of them, but we'll find out in the morning.

    Now, the storm essentially passed right by the Z and the garage it's at, which is less than 2 miles from the house. I ran over there this morning (errand day, what with no power at home, and all). Grounded the injectors out via the ecu harness and got clicky clacks from each and every one. Drained some of the gas and found it clear, free of water and with no varnish smell.

    The ECU will be here Monday afternoon - I plan to jet over there Tuesday morning just to see what happens. I also told him to go ahead and hang the rest of the exhaust and push come to shove, I'll tow it home if need be.
    Kelly R. Johnson
    1978 280Z...yes it's automatic...but I'm fat.

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    Well, you've got...

    1. Power to the injectors, which operate when grounded. (Therefore working drop resistors, etc.)
    2. Power to the ECU. (Therefore both EFI fusible links and the fusible link relay are good.)
    3. Good ECU ground.
    4. Likely good connection between ignition coil (-) and pin 1, because tach bounces when cranking, and you have +12 at pin 1 with key on.
    5. Fuel pressure
    6. Typically pathological priorities at a time when your power is out, your fence has blown down, and your fish are suffocating.

    Assuming your mechanic was correct that you have no injector pulse (and I'm not totally convinced yet), then it does seem likely the ECU is bad. It will be interesting to see what that '75 ECU does for you.
    My last three sports cars while I still owned all three:

    2001 BMW Z3 Roadster 3.0i soft/hard top (sold)
    1966 Ford Mustang Coupe (sold)
    1978 Datsun 280Z (enjoying very much )

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    Bummer that you were short on time. Good though, that you got injector operation. Narrows things down a little more. I wish that you had run the other coil grounding test (three taps and a click). That would have shown if the ECU could work with the proper Pin 1 signal. Grounding the coil is like the best on-off ignition module signal the ECU will see. If you're going to have it towed if the 75 ECU doesn't work it doesn't really matter right now anyway.

    The 1975 and 1976 EFI diagrams are identical as are the the engine parts. Operation should be identical, it's probably just a different set of electrical components in the ECU box to do the same functions.
    1976 280Z, with some minor modifications

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    I would have done the coil grounding test, but I forgot exactly what to do - and no power meant I couldn't jump on and check.

    If I was smart, I'd have brought a charger to the garage with me and charged my phone and then looked - but I was a bit preoccupied. Hopefully I can avoid the tow, as it would just be 100 bucks down the drain, but we shall see. Tomorrow is fence repair day, but I'll be taking a nice long break for the Bears home opener.
    Kelly R. Johnson
    1978 280Z...yes it's automatic...but I'm fat.

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    OK, it arrived today - he was closed, but I couldn't wait, so I zipped over there, plugged it in and turned the car over.

    Same sputter as before, then dead. Flat battery. So no real verdict as of yet. I did notice a code enforcement officer in the next parking lot over ticketing a boat that was being stored - probably expired trailer plates - so I locked the car down and got out of there before I drew any attention to myself.

    So anyway, further updates as events warrant, I guess.
    Kelly R. Johnson
    1978 280Z...yes it's automatic...but I'm fat.

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    Another bummer. A weak battery can cause many problems, some not so obvious. I've seen it said that the Z's EFI system gets flaky if voltage gets under 10 volts. Plus the weak spark from the ignition module. It can only pass the current it's given. And, the load on the alternator if it does start, charging a dead battery, can cause regulator failure (the solid state internal ones like your 78 has), as I understand things. The system is not designed for long-term high current. You really need a fully charged, good battery to make progress. I wouldn't even try to jump it, I'd swap the dead one for a known charged, good one. One less unknown to worry about.
    1976 280Z, with some minor modifications

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    Hoping to get it buttoned up and home this weekend, regardless of running state. If it's in the garage at home, I can at least run out and mess with it when there's a suggestion versus waiting for a chance to get over to the shop.

    Just a random question, though - does the oil pressure sender kill the engine somehow if it has no reading? I only ask because I knocked the plug off while poking around and it seems to fit not all that snugly, and the plug is a bit corroded inside.
    Kelly R. Johnson
    1978 280Z...yes it's automatic...but I'm fat.

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    I would clean up that connector and re-install it and see what you get. I think the 78 will not run if there is no oil pressure, just not sure if it affects "starting". Hopefully someone will correct me if Im wrong. My 77 has the fuel cut off built into the AFM. IIRC the 78 fuel cut off is in the oil pressure circuit. Again I'm not 100% certain of this.

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    I think they changed over to the Oil pressure sender around August 77. Mine is May 77 and has it in the AFM. If the treminals on the sender are damaged, they could be causing problems with fuel delivery or lack of it.
    It must be frustrating not being able to dash out and try things. Good luck getting her back home.
    Chas
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    Thats right Chas, you and I have the same manufacture date. Yes things did change as of August 77. Hope that is the issue, would be an easy fix.

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    If I recall correctly, you get about 5 sec of fuel pump operation when you turn the key to "start." Thereafter, you don't get more fuel until the engine actually runs. For the '78, a running state is detected when you have EITHER alternator output OR oil pressure (or both). Your oil sender being unplugged would eliminate the oil pressure detection. That leaves the alternator, which wouldn't be putting out much while you're cranking. So I bet you have no fuel.
    My last three sports cars while I still owned all three:

    2001 BMW Z3 Roadster 3.0i soft/hard top (sold)
    1966 Ford Mustang Coupe (sold)
    1978 Datsun 280Z (enjoying very much )

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    FastWoman described the pressure switch and alternator pump control. Those are both bypassed during starting though, powering the pump directly. On my 76 when the AFM contact stopped working, the engine would start, run for about three seconds, then die. It would do that over and over.

    With a low battery the alternator powered relay may not be getting enough juice to keep the fuel pump operating. And a dry engine may not be generating pressure right away even with the switch intact.

    Collecting all of the facts, if it were mine, I would get a good, charged battery in there, pull the small vacuum line that feeds the AC control bottle (the tiny nipple on top of the intake manifold), and squirt some starting fluid in to the manifold. Ideally, you would have a friend either running the can of fluid or the key, and just keep the engine running long enough to get things moving.

    If that didn't work, I would probably short the fuel pump relay to keep the fuel pump on. Actually I would probably do that first, just to take the fuel pump control out of the picture. That's a little more involved though.

    This leaving and coming back to the problem really kills the flow, just on the internet. Must be way worse trying to do it on the car.
    1976 280Z, with some minor modifications

  68. #68
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    i'm no electrical savant, but i'm pretty sure the oil pressure sensor works opposite to the previous posts... unless mine is somehow wonky. unplugged would be infinite resistance, right?

    on my 78 pulling the oil pressure sender plug when the key is on and the engine is NOT running is a quick way to run the fuel pump. it's how i used to prime my fuel rail when dealing with hot start issues. just turn the key to "on", pull the plug on the oil pressure sender and the pump would run until it was plugged back in. at one point i was going to put a momentary disconnect push-button inside so i could run the pump without getting out of the car.

    quite handy, actually...
    '78 280z - Daily driver/work in progress...

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    That's a good catch. So take the plug off, clean it up so it's an open circuit, then leave the plug off and try to start the engine. Much easier than shorting the relay. You've uncomplicated things.

    I've actually cut the FSM section out on that before but forgot about it.
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    1976 280Z, with some minor modifications

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