78' 280z running rich

[Pochie45566]

Hey, My z has lately been running rich. It smells okay but when I pull the plugs they have a decent amount of carbon buildup. I have gone through every component check in the EFI manual and can assure that all EFI components are working as they should. So I leaned out the car by tensioning the spring in the AFM, a lot. And it did get leaner but the plugs are still sooty. So I leaned it out more, and the car wants to die at idle. I then turned the AFM idle control screw clockwise to richen up the idle and it does nothing. It seems that the fix of my problems would be to just richen the idle but I can't seem to control that via the idle screw on the AFM. 

 

Any ideas what I could check? 

[mbz]

I just had a similar problem, I hope this can help:

The issue for me was there was a bad (worn out/old) connector cable going to the water temperature sensor. DaveWM was super helpful in walking me through a logical step by step process of troubleshooting the problem. Maybe reach out to him for some guidance.

First started with checking fuel pressure, both BEFORE the return line (could be fuel pressure regulator), and AFTER the return line to see if there is blockage in the return lines to the tank. Be sure you have a good fuel pressure gauge made for Bosch fuel injection systems. I had a bad gauge that caused a lot of problems.



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[mbz]

Oh... forgot to mention, one quick test that helped confirm running rich (besides pulling spark plugs), when the engine is running, take off the oil filler cap on the valve cover.... see if that makes the engine run better or worse.


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[Pochie45566]

1 hour ago, mbz said:

I just had a similar problem, I hope this can help:

The issue for me was there was a bad (worn out/old) connector cable going to the water temperature sensor. DaveWM was super helpful in walking me through a logical step by step process of troubleshooting the problem. Maybe reach out to him for some guidance.

First started with checking fuel pressure, both BEFORE the return line (could be fuel pressure regulator), and AFTER the return line to see if there is blockage in the return lines to the tank. Be sure you have a good fuel pressure gauge made for Bosch fuel injection systems. I had a bad gauge that caused a lot of problems.



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I tested the water temp sensor via the ecu and it checks out so I think I am good there. It’s just odd my AFM idle screw seems to not do anything  

Also at idle I have 28 psi of fuel pressure with 19 psi of vacuum which I read somewhere else of the forum that those are good numbers.  Should I do further fuel pressure testing?

Edited May 11, 2019 by Pochie45566

[Zed Head]

Did you check the FPR vacuum line for fuel?  It's the hidden cause for rich running.  A small leak can add a lot of extra fuel but still control pressure correctly.

[Pochie45566]

22 minutes ago, Zed Head said:

Did you check the FPR vacuum line for fuel?  It's the hidden cause for rich running.  A small leak can add a lot of extra fuel but still control pressure correctly.

Yes, I just did and there is no fuel coming out of that line. 

 

2 hours ago, mbz said:

Oh... forgot to mention, one quick test that helped confirm running rich (besides pulling spark plugs), when the engine is running, take off the oil filler cap on the valve cover.... see if that makes the engine run better or worse.


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When I take off the oil cap, there is no change in how the engine runs. 

[Zed Head]

56 minutes ago, Pochie45566 said:

I tested the water temp sensor via the ecu and it checks out so I think I am good there.

Did you actually compare the resistance readings to the chart?  The G. or N.G. tests don't show much.

The other fuel source is the CSV.  The idle air bypass screw under the rubber plug on the AFM is only good for very fine adjustments, and only at idle.  It won't affect much above that.

I just went through a similar situation, trying to pass emissions.  My engine ran fine and I could take the oil filler cap off at idle.  It turned out that my AFM was "tuned" rich.  I had to put an old stock Nissan AFM back on.

You really should reset your AFM to the original settings.  Adjusting the spring never works right, from what I've seen.  It just makes a messy problem messier.

[Dave WM]

how about the cold start valve. leaking or stuck on?

ZH beat me to the CSV. To be sure you could just plug the line, not really needed unless its cold as in less than 65f, above that is really should not fire.

 

Edited May 11, 2019 by Dave WM

[Dave WM]

Ditto, on not messing with the AFM. If the problem suddenly occurred with out any changes being made, then you want to look for a part that has failed, not adjusting something that was working fine before.

I fought a long battle with fouled plugs, in my case it was a faulty ignition, my fault since it was a cobbled together system that was not OE. Point being foul plugs don't always mean rich mix. So were there any changes done to the car at the same time as the onset of the problem?

Edited May 11, 2019 by Dave WM

[Pochie45566]

30 minutes ago, Zed Head said:

Did you actually compare the resistance readings to the chart?  The G. or N.G. tests don't show much.

The other fuel source is the CSV.  The idle air bypass screw under the rubber plug on the AFM is only good for very fine adjustments, and only at idle.  It won't affect much above that.

I just went through a similar situation, trying to pass emissions.  My engine ran fine and I could take the oil filler cap off at idle.  It turned out that my AFM was "tuned" rich.  I had to put an old stock Nissan AFM back on.

You really should reset your AFM to the original settings.  Adjusting the spring never works right, from what I've seen.  It just makes a messy problem messier.

yes i compared them to the chart and they are all within spec, the CSV does not leak. i pulled it out and started the car and let it run, no gas came out. I have a working afm with the factory setting mark and when I set it to that it just runs even more rich. 

 

What steps should i take to check to determine why my plugs are getting carbon fouled if it may not be the mix? 

 

I should add that I leaned out the AFM a lot. It does not idle correctly now so I set it back. And this was not an all of a sudden issue, it’s always run pretty rich. 

Edited May 11, 2019 by Pochie45566

[Dave WM]

Well what I did, and this may not apply to you, try unplugging the water temp sending unit, yes this SHOULD send the mix super rich, for me it made the car run better but was still fouling the plugs.

If for some reason unplugging the sensor does not result in near instant super rich (and engine dies), then there maybe something else going on, causing the fouling not related to the mix.

 

Edited May 11, 2019 by Dave WM

[Dave WM]

also I have to ask, I presume the air filter is in good shape.