Broken AFM...expensive part

[Funky-P]

Hey all, I just picked up a 77 280z a couple of weeks back which doesn't start. In trying to determine why I've found that the AFM failed almost all of the testing specs. I'm not sure whether this is due to tester error or not, but its an expensive part so I'd rather be sure that its the problem before trying to replace it. I was wondering if anyone had any advice or a functioning one that we could borrow to make sure that it is the issue.

Thanks, hopefully we can get this thing running soon.

[conedodger]

Find another and swap it out or send the existing one to Brett Industries in Orange, CA and have it rebuilt.

[webdawg1]

conedodger,


You have the contact info for Brett Industries (I.E. - website url, address, phone number...etc...etc) Have not been able to locate anything on them thus far using Google or other search engines...unless I just can't see the forest for the trees...


webdawg1

[Zed Head]

Hey all, I just picked up a 77 280z a couple of weeks back which doesn't start. In trying to determine why I've found that the AFM failed almost all of the testing specs. I'm not sure whether this is due to tester error or not, but its an expensive part so I'd rather be sure that its the problem before trying to replace it. I was wondering if anyone had any advice or a functioning one that we could borrow to make sure that it is the issue.

Thanks, hopefully we can get this thing running soon.

You might put your test numbers out here to be looked at. Some one could probably help you decide if they're terrible or not bad.

Your car should start and idle with a bad AFM anyway, as long as the fuel pump contact is working. Your 77 still has the contact in the AFM if it is stock. I would get it started and idling first, then you'll have a better idea of how bad the AFM might be.

[conedodger]

Mr. Head is correct. Are sure it isn't the Throttle Position Sensor? It has a setting for idle and WOT. Have you also checked the Cylinder Head Temperture sensor? If the wire is broken or the sensor is bad it sends an infinity resistance signal and the engine if it will run would be full rich. Lots of variables in EFI...

You just have to call directory assistance for Brett. The last time I was there was a decade ago and they were under the original owner. I had a website called PlanetZ and I used to make Turbo AFM for NA cars. Frankly it doesn't work very well, and I quit doing it.

[MikeO]

In response to the numbers... when we tested it it was getting 0 continuity through the ECU and 0 continuity at any point after we pulled it. As far as resistance we're getting between 11 and 13 on any of the pins, 6, 9, 8, 7 in any combination. The flap is the only thing working properly and displaying standard readings.

[Funky-P]

I'll have to check the tps and temp sensor, I just was checking in the order the fsm has to check and stopped at the afm as it was giving bad readings.

One thing is the engine will crank fine, but not start and it smells real strongly of gas almost as if it were flooded even though that doesn't seem like the issue.

[conedodger]

You should be able to put the AFM model number found on the side of it in an ad in the classified section here. If a guy named Daniel Parsignault contacts you, I have never gotten anything from him that didn't turn out to be near perfect so trust him. I (and Mr. Zed Head) are not saying the AFM isn't bad, it could well be. It's just that it really doesn't have a function during start and idle. Enough air bypasses it to start and idle.

A couple things that could make it rich and not able to start, one is if that wire from the cylinder head temp sensor found on the thermostat housing is disconnected or internally broken or if the sensor itself has gone bad. This tells the 'brain' that the engine is overheated and it calls for a 'full rich' path on the algorithm. A second would be if the injectors themselves are leaking or stuck in the open position. It doesn't take more than say one or two of them sticking to have a car that doesn't start as it just pours fuel in.
What does your fuel pressure do after you turn your key off? It should stay constant. If it drops you would have problems with hot start even if you could get it started and running.
It sounds like you have gotten a hold of a manual which is good. The problem is that although you find one problem, it doesn't mean you fix that and the car runs. EFI adds many levels of variables which can complicate figuring out what is wrong. The benefit to doing the more complicated job of figuring it out is that EFI cars are very drivable. This means they start easily, get good mileage, are happy no matter what altitude you drive to.
As for Brett industries, try calling 411 from your cell phone and when they ask for city and state say Orange, CA. That should get you the number. These are the guys that supply rebuilt AFM to Motorsport Auto and many others.
For injector cleaning and balancing I recommend RC Engineering or Marren (sp?). Check the back of Grassroots Motorsports for their contact info as they are both longtime advertisers. I have some spare injectors you can have, in case some of yours are bad. You send them your injectors and they rebuild them and clean them. Then they balance the flow. Makes for a very smooth running engine when you get them back and in. Cost the last time I did it was about $30/ injector so not dirt cheap.

[Zed Head]

In response to the numbers... when we tested it it was getting 0 continuity through the ECU and 0 continuity at any point after we pulled it. As far as resistance we're getting between 11 and 13 on any of the pins, 6, 9, 8, 7 in any combination. The flap is the only thing working properly and displaying standard readings.

Well, thanks for following up on the response. I'm not sure which test procedure you're using though. The procedure I've used is on Page EF-52.

You should get 180 ohms between 6 and 8, and 100 ohms between 9 and 8. Those are the two limits of the potentiometer and determine the feedback to the ECU from the flap position. If you're getting 11 - 13 ohms then you must be shorted somewhere. But then you shouldn't get proper readings from the flap. So we have conflicting results. Are you using a decent ohm-meter? 100 and 180 ohms are on the low side and may be out the range of your meter.

Between pins 36 and 39 you should get continuity when the flap is open. That powers the relay that powers your fuel pump.

Pins 6,7,8 and 9 should be tested to ground and should not show continuity. No shorts.

Are you connecting 12 volts and measuring volts out for your flapper test?

Have you confirmed that the fuel pump works and that you're getting spark?

It's good that you're digging in but you might be jumping too far ahead.

Edit - forgot to mention that you can take these measurements at the connector inside the car, with the AFM plugged in a grounded (or installed). The hardest part is figuring out the pin numbering at the connector but there's a picture in the manual, plus some of the pins are missing (not used). This way you test the harness and the component together.

[Funky-P]

Thanks for the info guys.
We went in and plugged it back in and checked the flap action which was good, but didn't recheck the resistance. It sounds like you are saying that it has to be plugged in to be getting the right resistance readings then? When I measured it originally I had it disconnected, which is how it is shown on EF-52.

I went through though and checked the water temp sensor, the fuel pump contact points, the EFI relay, the ground circuit. The fuel pump contact points were okay, but everything else was showing an open circuit. We noticed something that seems to be wrong, the negative terminal of the battery looks to just be connected to the starter and then to the body. Two grounds and no harness connection, which struck me as odd and clearly is not what the wiring diagram shows. So I guess tomorrow hopefully with some daylight we can try to figure out whats going on, there is a lot of rewiring done by the PO which may be the root of the problems.

I haven't had to deal with this sort of electrical issue before so I definitely appreciate the help.

[Zed Head]

You can do it either way. Still not clear on how you could be using page EF-52 but report "between 11 and 13 on any of the pins, 6, 9, 8, 7 in any combination." You didn't give any of your test values... 6 to 8, 9 to 8, 36 to 39.

Sounds like you're checking things, but you're not telling the values you're getting. Or whether you have power to the fuel pump, spark, etc. Are you looking for the magic loose wire? Most people confirm fuel pump power, then fuel flow, check fuel pressure if you can, turn the engine over, check for spark, etc.

Good luck, keep going, then come back later and re-read these ideas.

[Funky-P]

OK, I'm going to start over with the testing from the beginning and taking notes as to what all the readings are and try to check everything you've suggested. Then I'll post up my findings.

[Funky-P]

Today we went back over and tested all of the connections listed in the engine fuel section of the fsm. While I don't it still seems like the afm is not showing the right resistances I don't think it is preventing the car from starting as all the pins to the ECU (6&8,7&8,8&9) all show continuity as well as those to the fuel pump contact points (10&20). All the circuits checked out for continuity for the Fuel pump relay, the air regulator and fuel pump, the ground circuit and the throttle valve switch.

The problem appears to be the water temperature sensor whose circuit does not have continuity. I guess we will try to replace that and hope it is the sensor itself rather than a wiring issue. The troubling thing is that after further investigation it still appears the negative terminal of the battery goes solely to the body to ground without connecting to the harness at all. There has been some rewiring of the harness and connections in various places, likely having to do with the alternate ignition wired in.

[conedodger]

The Water Temperature sensor or Cylinder head temperature sensor as I said before richens the mixture when it senses the head is hot. Since it is a resistance signal, full resistance means the head is hot and the ECU is responding accordingly. Probably a bad connection or a brake in the wire.

[Zed Head]

Conedodger, this car uses the water temp sensor with the attached temperature vs resistance curve. I'm not sure what the CHTS sensor uses. But no continuity or high resistance would be "very cold" to the 77 ECU.

Funky-P, from your answer, I'm guessing that you're looking at the wiring diagram also? Measuring 10 to 20 instead of 36 to 39. Still no numbers though, and no reports of fuel pump working (you can test it separately from the relays, just run 12 volts to it and listen) or fuel flowing. Don't forget that 0, 100, 180 and 1,000 ohm will all show "continuity." You really need the numbers.

Read this thread from the past. Lots of good measurements and a positive outcome - http://www.classiczcars.com/forums/s...ad.php?t=37299 .

The major difference to your situation is that her car was running at the time. Still not clear why you're focused on the AFM. Confirm fuel flow, fuel pressure and spark first.

[Funky-P]

I'm checking the continuity based on the continuity check setting on the multimeter, so it doesn't give number values. What I figured today was that the afm may be bad, but not likely to be the main problem. I did not recheck the connectors directly on the afm, but the various connectors on the harness to the ECU. Yes I've been referencing the wiring diagram as well. It smells very strongly of fuel in the components. Could not check the spark yet, I needed to get a tool first, so its next up. I'm not sure what the process is for checking the actual fuel pressure is, but I will check as to whether the pump itself works.

I've been going over the issues in the order specified in the FSM, hence checking the continuity circuits before the pump itself, which was my original thought to do.

I probably wont have time to do any more checks over the next few days.

[MikeO]

Hey all,
Perry grabbed the tools we needed to check the spark plugs but is going to be busy this week with work on top of school. I am going to try and get some other things checked out while he is doing his thing.

if someone could inform me on the procedure to check fuel pressure and what is needed to do that? I've done a search on the forum as well as google and couldn't find anything.

Thanks,
Mike

[conedodger]

Hey all,
Perry grabbed the tools we needed to check the spark plugs but is going to be busy this week with work on top of school. I am going to try and get some other things checked out while he is doing his thing.

if someone could inform me on the procedure to check fuel pressure and what is needed to do that? I've done a search on the forum as well as google and couldn't find anything.

Thanks,
Mike

You have to break the fuel line at some point and put a gauge in-line. I think if memory serves the FSM also calls for a check of the quantity pumped in a minute as well...

[sblake01]

The gauge goes inline between the outlet of the fuel filter and the fuel rail. If you have the 1977 FSM the test procedure is on page EF-58. I tried to scan it but since my 77 manual is a copy of a copy of a copy (etc.), it doesn't come out too clear.

[Funky-P]

Okay so we finally had some time to get some more work done today.

We found that the spark plugs were no good so we replaced and now we are getting spark.

We replaced the water temperature sensor and the continuity check for that circuit is now good.

We did the sound check for the fuel pump, didn't get any sound. We removed the fuel pump and checked it by just running it directly off the battery and it worked. So it seems the circuit to the fuel pump is disrupted, tomorrow we are going to try to trace the circuit and hopefully find out what the problem is.

I think the cold start valve may be no good as well, when I ran it off the battery before disconnecting the fuel pump I didn't notice any sound or anything. I'll look into that further as well I guess.

I think we're getting closer to getting this thing started, or at least I hope so.

[Funky-P]

The continuity for to the fuel pump checked out, so we went to check the ECU. Using the lamp to injector harness method it appears that the ECU is not functioning properly as we got no pulse. The car came with two ECU's, both of which gave the same result. Is there any other situation that would prevent the injectors from getting pulsed? It seems a little unlikely that both ECU's are bad, but I wouldn't be all that surprised.

[Zed Head]

What is the "lamp to injector harness method". A test light in series with an injector? Watching for flashes?

I think the injectors should have twelve volts to them at all times. Testing is described on page EF-23. They fire when current flows and activates the solenoid. Current flows when the ECU grounds the circuit. That is my current understanding of how the EFI works. I could be wrong.

[sblake01]

Not true. The dropping resistors bring the voltage at the injector down to roughly 9 volts from what I have observed. Top of page EF-15 mentions this though it doesn't state the actual voltage.

[cozye]

The ECU doesn't control when the fuel pump comes on.

There is a 5 blade relay in the relay bracket. When you turn ignition on, it should turn the fuel pump on. Look for a white/black wire with 12v going to that relay. Test the relay.

The ECU gets power from the 6 blade FI relay right next to it. So you might as well test that relay while you are there. Test procedure for the relays is in the FSM under the EF section.

[Zed Head]

Darn! I wrote a nice long post and this thing timed out on me. Hit Go Advanced and everything is gone. Any way for the admins to add a little time to that function? Do I set that somewhere?

SBlake, I thought about that, and I have read the same, but I have measured mine according to the procedure and the wires going to the injector all measured line voltage (12.6 V).

I think that dropping resistors actually drop current. This is what the manual states - "The dropping resistor is provided to drop electric current flowing through the injector and control unit."

(Edit - Not sure of my reasoning so removed it. Tests still worth doing)
(2nd Edit - My reasoning was wrong. Apparently both voltage and current drop when the injector is fired. Apparently to nine volts. But at zero current flow, voltage measured is line voltage.)

Funky-P, my comments are from the 1976 FSM. Your 1977 might have a different pinout but the test is still worth doing. If you have power, then you can focus on why the ECU doesn't fire.

[Zed Head]

The ECU doesn't control when the fuel pump comes on.

There is a 5 blade relay in the relay bracket. When you turn ignition on, it should turn the fuel pump on. Look for a white/black wire with 12v going to that relay. Test the relay.

The ECU gets power from the 6 blade FI relay right next to it. So you might as well test that relay while you are there. Test procedure for the relays is in the FSM under the EF section.

Cozye, just noticed your post. The fuel pump only runs when the motor is running (opening the Air Flow Meter flapper valve) or when the key is at Start. When the key is at On, you can make the fuel pump run, on 75, 76 and 77 cars, by opening the AFM flapper, which makes the contact for the fuel pump. Otherwise the fuel pump should not run when the key is at On.

This stuff is addictive.

Good luck Funky-P (I hope that's like a Married with Children ref or something and not an attribute...).

[Funky-P]

So some more information on what I've been doing/how I've been testing:

Based on page EF-22 I checked the Electronic Fuel Injection Relay: Fuel Pump Relay, by checking continuity between ECU pin 20 and grounded body metal. This checked out fine.

From the same page I checked the Air Regulator and Fuel Pump circuit by checking continuity between pin 34 and body metal. Again this was fine.

Based off of page EF-46 I checked the continuity of the circuit from fuel pump to air regulator to the ECU harness, connector 34. This circuit also checked out fine.

The fuel pump itself works when connected straight to voltage, so I'm at a bit of a loss as to why it doesn't come on at the START position. Unless the relay is bad, but the only test I see for that in the FSM is the ecu harness point test. Is there a good way to actually test this relay on its own?

I tested the injector pulse using the steps outlined on EF-52, where it describes connecting a small lamp to the harness of injectors 1 & 4 (not simultaneously) and cranking the engine to see if the light pulses. The light did not come on at all, and I tested to make sure the light functioned. Is there any other reason than a bad ECU for this issue?

A previous owner has messed with the wiring, there's a new ignition wired in and the connectors to the battery are rewired as well as some various other things, so its a bit more convoluted than it should be to try to get things tested individually.

I think it would be a bit more of addictive car if I could get it started, thanks for the suggestions though guys.

[FricFrac]

Yes the current limiting resistors limit the current. They do of course act as a voltage divider as well since your injectors have a resistance that is in series with the resistors so you will get a voltage drop across the resistor and across the injector.

Problems with AFM's (and current limiting resistors for the injectors) are often bad contacts. Make sure you have a good clean contact between the two and that the clip for securing the AFM is in place and you aren't just relying on the friction from the pins to hold the AFM connector on. The resistor pack can have the same issues as well will bad or broken connections.

Current won't drop when the injector is fired. It's the only time it will actually flow. Without the injector firing there is no completed circuit and without a completed circuit there is no current flow.

For the ECU there is an LED that lights up to give various fault codes as well IIRC. Check with the FSM at www.xenonS30.com or www.xenons130.com

You should typically be able to start the engine for a bit but it will sputter and stall if the AFM is completely disconnected. Poor running, stuttering, stalling, etc are AFM issues - not starting is likely an issue elsewhere. Got Spark?

[Zed Head]

Coincidentally, just saw this on Hybridz from a guy who had an ECU that wasn't firing the injectors. Said he had his coil wired backwards. Post #72. Also said his fuel pump wouldn't run because he had a bad EFI relay.

http://forums.hybridz.org/index.php/...60#entry904721

[Funky-P]

Hmm I'll take a look its definitely possible with all the rewiring that has been done. Probably wont have time though until Friday.

[Funky-P]

Today was the first day I had to get to check out the relay due to school, work and the weather.

We tested the relay based off of the 280z fuel injection book. What we found was that the relay did not click when ignition is turned to start, so we checked the circuit between ECU pin 4 and ground for battery voltage when the starter solenoid and cold start valve were disconnected, and ignition was turned to start. We did not get the twelve volts, more like .7 to .01 volts. The fusible links appear to be okay.

So it looks like the power relay/fuel injector relay is not working, this relay is surprisingly expensive as well, I'm wondering if there is anything else we should be checking before buying one esp as it looks like it has been replaced before. The relay has 78 fuel pump relay written in sharpe on it is why I assume it has been changed before.

[Bruce Palmer]

I'm starting to get a better understanding for why guys are opting for the carb swap. BRrrrrr!

[Funky-P]

It looks like the relay has been replaced before (written on it in sharpe is '78 fuel pump relay) making me more skeptical that it is the problem.

[Zed Head]

I lam lovin' my EFI! It is smooth and clean running, and starts right up in the cold.

Funky-P, I was talking to a guy doing a V-8 swap the other day and he mentioned that he is using an inexpensive relay he picked up at the auto parts store to get 12 volts to his fuel pump.

Since you are deep in to your wiring diagrams, it might be a simple, cheap solution for you. I don't think that there is anything extraordinary about the Datsun relays. You could probably put together something that works for under $20.

[Funky-P]

I was wondering if that might be a possibility, I had to do that for my rx7 to get the wipers running. I'm going to check to see if I'm even getting power to the relay first, I don't think I did that yet for some reason.

[cozye]

Cozye, just noticed your post. The fuel pump only runs when the motor is running (opening the Air Flow Meter flapper valve) or when the key is at Start. When the key is at On, you can make the fuel pump run, on 75, 76 and 77 cars, by opening the AFM flapper, which makes the contact for the fuel pump. Otherwise the fuel pump should not run when the key is at On.

This stuff is addictive.

Good luck Funky-P (I hope that's like a Married with Children ref or something and not an attribute...).

I thought the 77 was the same as the 78 and they deleted the fuel pump cut off switch in the AFM ? If not, yeah my bad. There is that switch in the AFM on the older models. In any case he could jumper it on the AFM connector just as a test.