Running rich, slight misfire at all times when at idle. Help!

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Running rich, slight misfire at all times when at idle. Help!

Postby JacksonKlatt » Tue Aug 02, 2022 8:16 am

I'm at my wits end here fellas. I purchased a 96 Z from a guy who basically rebuilt the thing, and I've been going about refining it since June. One issue is how much fuel I'm consuming while driving like a grandma, and the misfire I have at idle. The car also only gets up to the first notch of the temp Guage when operating. New parts are as follows:
Coils and wires
Coolant Sender Sensor
Cam and Crank Sensors

O2 sensors going in today

Other than checking every single connector for power, is there anything i could be missing here? The only other thing I can ad is the previous owner put a block on the EGR.

I've spent more time waiting on parts mid-job and returning incorrect parts than I have spent driving it! I just want it to run right so I can actually enjoy the damn car.

Any help is appreciated!

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Re: Running rich, slight misfire at all times when at idle. Help!

Postby Rettax3 » Wed Aug 03, 2022 12:23 am

New doesn't mean good. '96 is true OBD-2, so a functional scan-tool is easy and cheap to find. For the low temp, make sure it is actually running that cold, not just an inaccurate gauge. What temp thermostat did you give it?

You are probably going to find something very basic as your problem -a low-compression cylinder or more likely bad fuel injectors. A weak or leaking FPR is also a likely cause.

A fuel-pressure test-gauge will point you to the FPR, and can show if the injectors are leaking-down, but for a true injector test, you will want to have a fire-extinguisher handy... ;) I have in the past removed the intake upper plenum, fuel injectors and rail assembly, placed baby-food jars with holes in the lids for the injectors (and a tiny vent-hole is recommended too). Have someone crank the engine for you a few seconds at a time and watch the spray-pattern through the jars. You can also see after enough tests if the injectors are flowing the same amount of fuel.

Compression-tests are just basic on these engines, nothing special about the procedure.

Finally, a plugged catalytic converter could be a problem, unlikely if you aren't losing power or performance at higher RPMs or throttle-settings, but one concern with blocked-off EGRs is they CAN lead to converter fouling -very worth it IMO considering the crap recycled back into your engine otherwise, but to each their own...

1989 SuperCharged 3800 Srs-II (First)Six-Speed GTU
1990 Turbo 3.4 5-Speed T-Type
1990 4.0L 4-Cam 32-Valve V-8 5-Speed Indy GTi (Project)
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Re: Running rich, slight misfire at all times when at idle. Help!

Postby woody90gtz » Fri Aug 05, 2022 10:51 pm

Being 96 this should have the 3-pin coolant sensor in the intake manifold that runs to the PCM and gauge. When I first used the same style gauge for my 3400 swap I got two bad brand new ones. And a bad CTS will cause what you're explaining. Log the car and see what the coolant temp reads on the scan tool to check.

Does it run better dead cold and get worse when it gets up to temp?

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