Fuel pump

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Schurkey

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My 88 was a little different, it had a ball joint with no gaskets. My headers are the same. The Y pipe is 2-1/4" to 3".
As I said, it's been ~20 years...but I don't remember that at all.

Might it be that a 2 1/4" pipe would be flared-out to take a 2 1/2" donut? I'll have to break out the tape measure and verify. Yes, I'm fairly sure the catalyst-end of the Y-pipe I have is 3", because that's what I bought for a catalyst, and muffler--3" inlet, 3" outlet.
It runs but cold idle is bad it goes up and down almost stalls. When warm seems good. Any idea? Map or iac?
Connect a scan tool, look at the data stream.

What is the actual fuel pressure under load?

How long has it been since the vehicle got new plugs/wires/cap/rotor/PCV valve/ignition timing verification, air filter, and throttle-body cleaning?
 

Dylan88

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Has a code 42 and its been awhile since changed anything. Just slowly getting it going
 

Dylan88

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What could that be? Has hard time revving up also backfires etc
 

Schurkey

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Has a code 42 and its been awhile since changed anything. Just slowly getting it going

What could that be? Has hard time revving up also backfires etc

Find a REAL service manual, follow the procedure for that code. Remember that the fault could be in the ECM, the ignition module, or the wire harness in between.
 

Schurkey

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Would a bad icm cause it to run like crap?
Yes. Might make the engine not run at all.

So would fifty other things, like a failed wire harness, a failed pickup coil, a failed ECM, a failed injector, failed intake gaskets, failed valve or seat, on and on and on and on.

There is NO SUBSTITUTE for proper diagnosis. Replacing parts at random can work out OK, but there's no guarantees; and if the part you replace failed due to a problem somewhere else, the "new" part will soon fail, too.
 

Schurkey

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Find a REAL service manual, follow the procedure for that code. Remember that the fault could be in the ECM, the ignition module, or the wire harness in between.

So what's the best way?
See quote above. You need the Genuine GM service manual, you need to follow the "official" procedure for diagnosing Code 42. You'll be testing each component as they describe, or you're just guessing.

Some folks like to guess. Sometimes they get lucky. Often, they end up posting on forums like this, they they've replaced a bunch of parts and none of it fixed the problem; or it fixed the problem for a week or three but then whatever issue came back.
 
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