My engine continues to progressively run worse. I tried cleaning the IAC when I had the surge at idle per Vader but to no avail. I added a BBK AFPR last Sunday, bumped pressure to 48 PSI and fouled the plugs. With the pressure set at 42 PSI the car runs great off idle but idle is rough, it shakes the whole car and I get a stumble, pulling away from a light. Here's what I've recently replaced: Bosch O2 Sensor, Accel Module, Accel Cap & Rotor, AC Plugs and Mag Plus Wires. No matter how bad the car is running, I get no trouble codes. Could it be the Coil? Fuel Injectors? Sensor? Thanks

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1991 5.7L Z28
14.456 @ 92.78 MPH

 

J's Z,

Pardon me if I can't remember, but what other modifications have been done? If the rest of the engien is essentially stock, the higher fuel pressure might not net you any gains.

The oxygen sensor is a fairly tolerant device, and the ECM will accept a wide range of signals before setting an error code. You might be operating lean overall or have one extra lean cylinder.

I would suggest that since the ignition system is apparently functioning, and your problems are not only at high ROMs but at idle and above, you likely have a fuel problem.

To eliminate the sensor option, scan for error codes. Some codes might not always set the MIL lamp on, so you should scan. You can also use the Field Service Mode feature of the ECM to help determine if the engine is running lean or rich.

If you have only one or two offending cylinders, you need to perform a power balance test, which should be preceded by a compression check or cylinder leakage test.

Personally, I'd lean toward the possibility of a lean cylinder or two, but do the diagnosis to find which one(s).

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Later,
Vader
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"Fear is how I fall, Confusing what is real..."
Adobe Acrobat Reader

 

Also, a little off-topic...

Did I recently hear of an Ohio circuit judge declaring that it is "Just as legal for a woman to appear topless in public as it would be for a man" ????

Does that mean that your town will soon change it's name to "Cleavageland"? I'm bookin' a flight to corporate headquarters right now...

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Later,
Vader
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"Fear is how I fall, Confusing what is real..."
Adobe Acrobat Reader

 

yes Vader Ohio is a great state to live in

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ICON Motorsports

1st & 3rd
MM Black Diamond 538 F&AM

 

we have the topless law up here in toronto 2. its great at the beach

[This message has been edited by Paul_Hughes_87 T/A (edited May 27, 2001).]

 

Thanks Vader,
The only mods are: Airfoil, Gutted Cats, Gutted Air Box, Hooker Cat back, Lakewood Pan Hard Rod and Lakewood LCA's.
The engine has 140,000 miles but doesn't burn oil or smoke and up until about 3 weeks ago, ran fine. That's when the idle started to deteriorate.
I'll check everything out and let you know.
I hadn't heard about the topless thing but that sounds very interesting.

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1991 5.7L Z28
14.456 @ 92.78 MPH