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240DL?

Runs rich, wont rev past 2-3k

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My 1976 280z won't rev past 3500 when not in gear, and about 2000 when in gear. When in neutral it will blow clouds of black smoke at higher rpm. It has run way to rich like this since I bought it. I have checked the wiring and sensors and rectified the issues I found to no avail. The water temp sensor was the first place I looked, I replaced it when I first got the car. It is giving the correct reading all the way to the ECU and has a noticeable effect when I unplug it. My only guess would be a AFM, I have two but don't know the condition of either. They both passed the ohm tests, could there still be an issue with them? If not what else could be causing such a rich condition, especially at higher rpm.

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The whipper moves free, if I hold it closed a little it doesn't really get better. The fuel pressure is correct and I have a gauge in place of the cold start valve as I live in a warm climate. 

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Tps has the cover removed but does work, I have it adjusted correctly and it has passed both tests. I believe the injectors are this set, except for one that was dead when I got it so I replaced it. They all have the correct resistance and don't show a huge difference when I pull and inspect the plugs. 

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try another AFM if that does nothing I think the FSM calls for a new ECU once everything else has checked out.

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I would think it has too, did you try testing the AFM to see if the resistance varies with movement? compare all three if they do the same thing its likely they are all ok.

Edited by Dave WM

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Sure would be upsetting to find that ground wire to be the issue. One AFM has a ground wire while the other does not? I will try the one with the wire grounded well but I doubt that is the issue as I recall checking that a while ago

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this is what I did, best to use analog meter, I setup a simple voltage divider using some 9v batteries. Hopes its just a ground wire, but if you are still getting no where after checking that, you could get all 3  out on the bench and do a test like this.

 

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If the EFI system checks OK and fuel pressure is OK  then it is possible the injectors may have been swapped with larger ones from a turbo for example.

 

Please try to read any numbers on the injectors and report back.

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For rev limiting, I have witnessed three causes:

 

1. The EFI system has a false Idle signal from the TVS due to a short.  The ECU thinks that the foot is off the pedal and will not flow gas above ~2800rpm

2. The ignition system has a fault. I'm my case, a points distributor was the cause.  The power died under load at high rpms as if there was a fuel cut-off.

3. Weak fuel pressure.  Weak fuel pressure is not an issue with no load (revving in neutral) but under load on the road, there will not be sufficient fuel to power the car beyond a certain rpm X load point.

 

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3 minutes ago, 240260280 said:

3. Weak fuel pressure.  Weak fuel pressure is not an issue with no load (revving in neutral) but under load on the road, there will not be sufficient fuel to power the car beyond a certain rpm X load point.

 

And to check that put your fuel gauge on a hose and zip tie it to the driver's wiper arm.  Go for a drive and watch it fall or hopefully stay the same. 

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I wouldn't think it would be the first or third as it is running rich and blowing black smoke when I get to the limit. Would a 76 have a similar distributor issue? I'm getting plenty hot spark when cracking but haven't tried testing it at higher rpm.

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1 hour ago, 240DL? said:

 Is it possible to check simply with resistance if it is functioning correctly?

I see a lot of "correct"s and "good"s and questions that should be clear if you were in the right place of the FSM or Guide for testing.  The only numbers you've shown are a couple of RPM values. The AFM resistance values are in the FSM.  Easy to measure, even from the ECU connector.  The way the FSM is set up is that if the continuity/no continuity super-quick tests don't find a problem then you go to the more time-consuming tests of actually getting resistance numbers.  This thread is starting just like about 20 others over the last few years.  No offense, everybody tries to find the quick "bad part" solution.  Post as many numbers as you can measure, and include the AFM and ECU part numbers.

Two kind of hidden ways to run really rich are a hole in the FPR diaphragm or a bad ECU.  A bad ignition module can also send too many pulses to the ECU while failing.  Usually that will also show up on the tachometer with funky needle movement.  And, to make things possibly worse, if it ran bad when you got it then the PO probably messed with things to try to fix it.  A common mistake is to adjust the AFM vane position.  You might have to go through and reset almost everything.

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My apologies for being unclear about the situation, I just got back to the car, I have spent a lot of time on it a while ago but not recently. I will go threw all the continuity and resistance checks here and post all the numbers before guessing again. 

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No need to apologize.  I'm just pointing out that many people do what you're doing and it almost never gets them where they want to be.  Just trying to help you down the path...

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