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Thread: 260z stalls at idle after warm up. Carbs?

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    Default 260z stalls at idle after warm up. Carbs?

    Hello, kind folks of CZC, long time lurker here! Normally I can figure out my issues through the vast information already here but this is the first problem I came across that I feel the need to post and get some more direct answers.

    The car cold starts every single time and runs from anywhere to 30 seconds to 2 minutes. The RPMs bounce from around 750 to 1,000 until it puts up a fight to stay alive and then stalls out. Very occasionally white vapors will pour out the carbs trying to crank her right back up. After that I will have to wait about 5 minutes for it to crank back up. Now the problem first arose with some bucking on the highway, normally around in the 2,000 to 3,000 RPM range. Then it slowly came to the state that it is in now.

    Little bit about the car.
    1974 260z. Stock 2.6L with Ztherapy carbs. Electric fuel pump. 77,xxx miles. Daily Driver. Owned about a year.

    I started the search for engine harmony in the ignition. Pulled plug wires until I came across #1 to see the tip of the plug and plug wire was rusted completely. I then replaced with NGK plugs and wires along with cap and rotor thinking that had to be the problem. Same symptoms afterwards.

    I then started to believe I became victim of the timing chain jump myth but after checking TDC with marks on the rotor, cam, and piston everything seemed to be in line. Timing set to 8 degrees at 750 RPM's the few times I had it running well enough to do so.

    Valves were adjusted tight a couple months ago. Moved on to a dry compression test and the results seemed consistent enough to rule out any issues there.
    1. 160
    2. 160
    3. 165
    4. 175
    5. 170
    6. 170

    I then moved over to carbs and disassembled the majority of the body and cleaned out what I could do the best of my ability. I came across a crack in the top portion of one of the floats. Would that possibly cause flooding issues after a certain period of time of running and cause the white vapors from the carbs?

    I redone the fuel tank and cleaned out the lines when I first bought the car so I believe all is good there. Clear fuel filter installed so I do see clean amounts of fuel flow going through it. Been running the same fuel delivery setup for months. Brake master vac always had a leak in it but spraying carb cleaner around other lines had no effect on RPMs.

    I grew a terrible stubble of facial hair to profusely scratch while trying to think of a solution to no avail. I feel like the problem is so minuscule and I may feel like a dummy afterwards but better a dummy that has a running car than none. I'm losing days at work, patience, and money at parts to trying to get it going again. Sorry for all the reading material. Any input appreciated guys!

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    Probably could have been put in a more appropriate thread category..

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    Things I forgot to mention before and a little more information.

    The engine does experience dieseling after cutting off the ignition with the key every now and then. The fan spins in a counterclockwise direction and white smoke emits from the carbs.

    In my first post I was worried about the carbs maybe overflowing due to a crack in the float but forgot to mention that no fuel is coming out the carbs mouth. A friend mentioned the idea of one of the needle and seats maybe not sealing and fuel being let into the intake manifold. I checked for fouled plugs and smelled for any fuel on them without finding any problem there. It's being ran and has been ran on 89 octane since I've had it.

    After some stalling I checked the fuel bowl levels on each, both even, but they seem to only fill about a 1/4 of the bowl up no matter how I adjust the float levels. Levels are same after ran and after stalling.

    I measured a consistent 5 p.s.i right before the fuel rail with a fuel pressure gauge.
    I will do a better measurement of vacuum readings tomorrow. Still can't find any hints of leaks with starter fluid.

    A picture of the distributor rotor, of what I assume is right for TDC, for ghits and siggles.
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    Ignition coil was replaced with no change in performance because I like wasting money.

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    You measured 5 PSI? I think you need to dial that down a bit. By the way, do you need to use the choke to start the car?
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    I never had to use the choke since she starts up right away when left alone for a bit. The choke doesn't seem to help at all when trying to start her back up after she stalls out.

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    The stock mechanical pump is designed to have about 3.4 to 4.3 PSI (values rounded). (See 1972 FSM, EF-3.) Can you dial your pump down some or install a fuel pressure regulator?
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    Man, forgetting my FSM has been the biggest mistake of this whole entire situation. Don't rub it in haha.

    It's worth a shot. I might not be able to get my hands on a regulator today but I'll dig around for the stock pumps and try that. It's tough to think that too much fuel pressure could be the issue.

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    It is impossible to forget the FSM as long as you have an internet connection available. It will ALWAYS be with you. If you don't understand what I'm saying, read my signature.

    By the way, even if the fuel pressure isn't the direct cause of the problem, it is best to minimize the number of variables at play by having as many conditions as possible set at the factory specifications.
    Last edited by SteveJ; 09-16-2013 at 10:31 AM.
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    You're absolutely right. I should have stated before that it's hard for be to believe that fuel pressure could be AN issue, instead of THE issue. I wasn't able to get my hands on a regulator today but I will try for tomorrow.

    I've seen the FSM on XenonS30 before and this is the first time it actually opened in WinRar for me so thank you for that.

    Any other variables to maybe look into while I'm out wrenching on it tonight?

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    Check to make sure the oil doesn't smell like gas. Also, I can't remember, what does the FSM say about the symptoms of a plugged PCV valve?
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    No smells of gas in oil. I couldn't locate anything in the FSM about symptoms of a plugged PCV valve, just some information on how to diagnose if it is working properly. Which does seem like it is working fine.

    Tonight I blocked off the fuel line, popped open the float bowl lids and just spoon fed the bowls with fuel just to see what it would do. Same symptoms, runs fine until it warms up.

    Steady 17 in Hg through the intake manifold where it would normally connect to the brake booster line.
    About 12-13 in Hg through the PCV valve.

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    Could your chokes/choke be stuck open?

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    What ignition system are you using?
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    Rob, chokes open and close fine and do not stick.

    Steve, I'm using the stock ignition points system that came with the vehicle.

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    Set your timing and jet heights after the car is good and hot. Besure to balance the air and fuel into each carb at idle and at 2,500 rpm.


    For cold starting, be sure to use the choke.

    Also make sure your TDC mark on the pulley is correct (get cylinder 1 at the top of its compression stroke then check the pulley marks). Some times the pulley separates and the timing marks creep.
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    Keep in mind that the stock 260Z system did NOT have points. It has a transistor ignition system. See the EE section of the FSM starting on page EE-27.

    Okay, we may need to move our focus. Verify you're getting a good spark when the car is warmed up. I'm thinking that the stock ignition system may be the issue. Look for an erratic spark with your timing light as the car warms up or any drift in the timing. Check the transistor ignition box in the passenger footwell to see if it's heating up. If so, turn a can of air upside down and spray the box so the liquid hits the box and cools it off rapidly. See if the car restarts easily. Unfortunately Nissan only provided directions to test using a testing box. There is this thread (http://www.classiczcars.com/forums/e...ce-manual.html) that says there is another testing method. You could PM DRBall to see if you can get a copy of it.

    Was the car initially an automatic? If so, try unplugging the temperature switch. It's a Yellow/White wire that should be around the thermostat housing.

    I've never played with the stock system. A PO installed a ZX distributor/ignition in my 260Z. I think that's what a lot of people have done.
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    Air and fuel has been balanced at 2,000 RPMs whenever I did it last. After I bring it down to idle speed I never get a consistent idle. Sometimes I get an idle of 900, sometimes it'll find itself around 750. Seems to depends on how close to death she is.

    I've been checking timing with a light every day for the course of this week. Only time the timing changes is whenever I do so.

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    Steve, those sound like some very interesting things to check out later on today. I go out there everyday to work on it and find myself pretty much fiddling with the same thing expecting something to change. So anything new is appreciated. That link you posted also lead me to some other information that I could try to narrow out some issues.

    I seem to be getting good sparks from the spark plug wires and no erratic light flashes with the timing light, but I only checked #1 spark plug wire with the light for timing issues. I'll check through all of them today.

    The car was born and raised a manual. I've read a lot about people changing the ignition system in their Z's and the benefits but I always believed "Don't fix what isn't broke." Except, you know, it might be broke.

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    As I was running the car I started checking electrical wires until I ran into a loose connection on the ballast resistor. As I shook the wire the car died out and I got excited thinking this could definitely be an issue. I flipped the resistor over to tighten the connection and with the slightest turn this happened.

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    So all connections cleaned and tightened on the resistor and still having the same issues. I'm not sure how hot the resistor is supposed to get but I didn't think it would get THAT hot, to the point of burning my finger. Anyways, at least it's nice to fix these little things that can arise in the future.

    I did what I could with the transistor ignition box. I took the cap off of the box and after she stalled out again I took air from an air compressor and blew air all over it. I'm sure it wouldn't cool it off as much as using the upside aerosol can so it didn't help with any quicker of a start up. I even tried putting a blower on the box while it was running to see if it would prolong the idle time, which it didn't.

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    Well, that ballast resistor has seen better days. I'm running out of ideas to supply you. However, you may want to read through the troubleshooting guides in the FSM to see if we have been overlooking something. I just can't help but think there is something electrical involved since it dies and will run 5 minutes later. It's like something is cooling down after overheating. It would be great to monitor the coil voltage with an oscilloscope to see if anything shows up then.
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    So the car started it's life as a 260 with a manual trans, right?

    Who swapped out the original flat tops for the current round tops? Did you do that swap, or was it like that when you got it? Also, how much of the original 260 stuff remains now that you're running round tops? Did they swap to 240 intake manifolds and balance tubes too, or are you running the original 260 stuff there?

    I'm just trying to get my bearings... Got any engine bay pics?

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    Quote Originally Posted by SteveJ View Post
    Check the transistor ignition box in the passenger footwell to see if it's heating up. If so, turn a can of air upside down and spray the box so the liquid hits the box and cools it off rapidly. See if the car restarts easily. Unfortunately Nissan only provided directions to test using a testing box. There is this thread (http://www.classiczcars.com/forums/e...ce-manual.html) that says there is another testing method. You could PM DRBall to see if you can get a copy of it.
    You may have been right on the money after all. I decided not to give up on the electrical side of it just yet. I pulled out the transistor box completely, removed the back side this time and started running the vehicle. It stalled out as normal but when I would try to crank it over, it would actually start and die right back down. It did that every time now. So I repeated the process but this time blew air on it after it wouldn't start. Started right up. So I put a blower on the box and it idled for over ten minutes until it stalled out but it started right back up at the turn of a key. I even took a video of the process because I couldn't believe it haha. Of course, the idle is still a little jumpy but it runs, still running as I type this.

    I just have no idea how this transistor box is supposed to function. I'll definitely dig into some research tonight. This is where I have no idea what I'm doing. Could that mean the box's internals may be bad or something external causing the overheating? I really have no idea what I'm talking about. I need to get my hands on a multimeter.
    Last edited by Rill Cosby; 09-17-2013 at 06:39 PM.

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    If it's on its way out, I think you might be able to use an HEI as a replacement.
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    Quote Originally Posted by Captain Obvious View Post
    So the car started it's life as a 260 with a manual trans, right?

    Who swapped out the original flat tops for the current round tops? Did you do that swap, or was it like that when you got it? Also, how much of the original 260 stuff remains now that you're running round tops? Did they swap to 240 intake manifolds and balance tubes too, or are you running the original 260 stuff there?

    I'm just trying to get my bearings... Got any engine bay pics?
    I believe so.

    The previous owner switched to the Ztherapy round tops. Everything else seems to be original. N36 intake manifold and balance tubes. Some emission deletes. The previous owner was amazing with including just about every single part he did remove and include it with the vehicle along with some spare parts.

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    Quote Originally Posted by SteveJ View Post
    If it's on its way out, I think you might be able to use an HEI as a replacement.
    Pardon my ignorance on this. I did some research and I'm still at a loss on what I exactly need or could use in a replacement for that part. The unit number on the transistor box is E12-05. I've only found one site that may have that part.

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    The HEI would replace the transistor box. You would wire it near the distributor, going to the pickup at the reluctor and to the coil. It's at least an order of magnitude cheaper than the transistor box, too.

    You would use a writeup for a 280Z, like this one: hei. Here's another one: GM HEI retrofit

    Here's another: Turbo Ignitor Swap / Upgrade - Chevy HEI - ZDriver.com. Log in at ZDriver.com to see the pictures.
    Last edited by SteveJ; 09-18-2013 at 01:45 PM.
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    I hate to have everything spelled out for me but I'm going to need it. So what you are saying is the quickest and cheapest method would be the HEI 4-pin module way? I should be able to go to the local auto parts store and pick up a HEI 4-pin ignition module, like the one in the Chevy HEI link you posted, pull out the old transistor module and wire in the new ignition module? What I'm gathering from the other links is that I would also need a different type of distributor than what I have now to run the new module.

    By the way, thanks for the patience and all of your help, and everyone else's input. I definitely owe you a beer or two!

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    Quote Originally Posted by Rill Cosby View Post
    I hate to have everything spelled out for me but I'm going to need it. So what you are saying is the quickest and cheapest method would be the HEI 4-pin module way? I should be able to go to the local auto parts store and pick up a HEI 4-pin ignition module, like the one in the Chevy HEI link you posted, pull out the old transistor module and wire in the new ignition module?
    It would be quicker than to find a working 260Z box.

    Quote Originally Posted by Rill Cosby View Post
    What I'm gathering from the other links is that I would also need a different type of distributor than what I have now to run the new module.
    That's not the way I understand it. The 260Z distributor is similar to the 280Z distributor in that it has the reluctor and pickup. Some of the old writeups on 280Zs and 240Zs do not always accurately capture what aspects of the 260Z are similar to which car. I selected the 280Z links on purpose. The HEI is a cheaper route than the 280ZX distributor. For the ZX conversion, you need the distributor and the mount. For this one, I believe you only need the HEI. Even if you do need the 280Z distributor, you could swap that in and not have to change the mount.
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    Good pics. I don't see anything that screams obvious problem. Two things catch my eye. First is a couple missing clamps on things like the brake booster and PCV vacuum lines. Not the cause of your problem, but might be providing a little vacuum leak. Second thing is what's with the hole in the middle of the EGR mounting casting. It's not sucking air through that little hole in the center, is it?

    As for potential heat related ignition issues, before you drop time or $$ on a different system, you could shoot a hot hair dryer at your existing module to try to recreate the problem. And buy a $5 can of circuit cooler at Radio shack to cool it off and see if the problem goes away.

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    Quote Originally Posted by Captain Obvious View Post
    Good pics. I don't see anything that screams obvious problem. Two things catch my eye. First is a couple missing clamps on things like the brake booster and PCV vacuum lines. Not the cause of your problem, but might be providing a little vacuum leak. Second thing is what's with the hole in the middle of the EGR mounting casting. It's not sucking air through that little hole in the center, is it?.
    I plan on going through new hoses and clamps, hopefully sooner rather than later. The hole in the middle of the EGR mounting casting isn't pulling in any air.

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    It has clearly became a overheating issue in the ignition module. Now the only problem I have is identifying is if the ignition module itself is bad or something external is causing it to overheat. I found a "never been used" ignition module with the same serial number and plug so I decided to go that route first. The cost was about double the HEI replacement but I would don't mind paying a little extra for a direct plug in and ease of mind of proper installation. That way if I experience any overheating afterwards I can narrow it down to the problem hopefully being something external.

    I'll definitely report back once the part comes in after a couple of days.

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    Glad that you were able to narrow the problem. That makes things much easier.

    Thinking out loud, the only "external" thing I got that would put extra heat into the ignition module would be the lack of a ballast resistor where one is required. Maybe the PO didn't get it hooked up right and/or shorted it out somehow? Without the ballast resistor, you run the risk of pulling too much current through the ignition coil, and that might be enough to mess with the ignition module. I've not seen it, but I guess it's possible.

    Just to be prudent, you should check your coil and ballast connections carefully and make sure everything is done correctly.

  33. #33
    No more body roll! SteveJ's Avatar
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    Corrosion in the box could cause hot spots.
    73 240Z
    74 260Z

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    Registered User Rill Cosby's Avatar
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    Sorry for getting back so late to this topic, I've been so busy lately since the car has been running and haven't really had access to another computer. I just want to clarify some things, just for future reference, if someone stumbles upon this thread. The problem did seem to be the ignition module. The car has been running fine since the new one was installed.

    I wanted to post some picture of the old, stock ignition module and the new one that I picked up.

    This is a picture of the old, stock ignition module. Almost like a soft aluminum casing that has a heat sink style to it. The number on it reading E12-05.
    Click image for larger version. 

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    Then a picture of the new one. I was aware the numbers didn't match up exactly, or I should say the extra letter didn't, on this one but the plug matched up and I was that desperate. Crossed my fingers and hoped for the best. The new one reading E12-05K. It's been installed and running fine since. The outer casing is completely different and so are the internals but I just figured they might all do the same job in the end. Hopefully it performs well in the long term. Sorry for the blurry picture.
    Click image for larger version. 

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    All in all, thanks for all the help guys. It would have been a long road trying to figure it out without you guys. I'll definitely be back again haha.

  35. #35
    No more body roll! SteveJ's Avatar
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    It would be interesting to crack open the case and identify the transistors and circuitry in it, too.
    73 240Z
    74 260Z

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  36. #36
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    I believe they switched from the finned aluminum cover to the black painted steel case on the 260 to 280 changeover. The 260 used the finned aluminum and the 280 used the black painted modules.

    So, you were thinking that your original module was getting way to hot... Does the new replacement get hot too, or has swapping the module taken care of that issue?

    Quote Originally Posted by SteveJ View Post
    It would be interesting to crack open the case and identify the transistors and circuitry in it, too.
    I popped the cover off the 280 style a while back. Exactly what you would expect... Lots of mid-seventies discrete electronics. With the easily obtainable alternatives (like ZX or GM HEI) I wasn't interested enough to do any reverse engineering. Interested enough just to peek around, but didn't trace anything.

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