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Need tuning help/diagnosis '78 280Z Factory EFI


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So this is a long story and I will answer any questions as I go but I am stuck. My car is running super rich and wont pass SMOG. I figured it would be time to go through and do the factory tune-up procedure (well most of it) in the FSM. Started with adjusting the valve lash. All but one needed some adjustment. Ran a lot smoother afterward, but didn't check AFRs as I was still waiting on my air/fuel gauge. Next I adjusted the cam timing. It was on setting 1 and was out of spec, moved it to setting 3 and it is better but still out of spec so I need a new timing chain. I then adjusted the ignition timing, it was off and I changed it to 10deg BTDC. Last thing I did was check the contacts on the TPS and that should be functioning properly.

 

My air/fuel gauge showed up today so I put it in to get some readings and see if anything I did helped. Hooked it up and it is rich at idle (about 12.9-13.0) and super rich at WOT (below 10). Stumbles at the top end of the RPM range, etc but otherwise idles and cruises part-throttle fine.

 

I have replaced the AFM with a rebuilt unit so I thought if everything else was in spec (except valve timing), I will start with the idle air mixture at the bypass screw in the AFM. No matter what I did with that screw, all the way in, all the way out, anything in between, the air/fuel ratio didn't change at idle. Still running really rich.

 

Went and checked the electrical at the ECU per the EFI section of the FSM. Everything checks out except the electrical connection for the air regulator but I don't see how this would be my problem.

 

Cold start valve is deleted, water temp sensor is new and has conductivity from ECU and good ground, injectors are all new and it runs great except at WOT so I don't think it's a single cylinder problem anyway.

 

The really confusing part is the lack of change in AFRs at idle no matter what I do with the bypass screw. What else can I check before cracking open the AFM and adjusting the spring tension?

 

 

Edited by TheWeekendWagon
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14 minutes ago, TheWeekendWagon said:

I have replaced the AFM with a rebuilt unit so I thought if everything else was in spec (except valve timing), I will start with the idle air mixture at the bypass screw in the AFM. No matter what I did with that screw, all the way in, all the way out, anything in between, the air/fuel ratio didn't change at idle. Still running really rich.

 

 

Where did you buy the AFM?  I bought a new one and it was rich.  I had to go back to an old factory unit to pass emissions.

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4 minutes ago, NewZed said:

 

Where did you buy the AFM?  I bought a new one and it was rich.  I had to go back to an old factory unit to pass emissions.

 

ZCarSource.com

 

I just want to make sure that everything else is as it should be before I start messing with it. I am more puzzled with the fact that the bypass screw doesn't seem to do anything for my AFRs at idle.

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Most AFM's are rebuilt by FuelInjectionCorp.  I could run the idle air screw all the way out and it would still run rich.  Other people have reported the same problem.  I had to install an adjustable FPR to lower the fuel pressure to get it to pass if I did not swap an old Nissan AFM in.  I think that FuelInjectionCorp just didn't do a good job of matching specs. to Nissan's AFM.

 

https://fuelinjectioncorp.com/

 

 

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