1994 Silverado 5.7- 1) runs rough 2) AC compressor

BretB · May 10, 2005

1) I have a 5.7/350 with 165k that after starting, runs very rough. When initially idling, it almost seems to be occuring rhythmically on the same cylinders firing, maybe 3-4 of them? When I accelerate, it will buck a little bit unless I really step into it. Then as I accelerate, it will all of a sudden "catch on" and accelerate fine. These symptoms happen both when cold and after running a while. I received a "lean mixture" code on the engine light.

I took it to the shop to diagnose, they said my fuel pump (which at the time was 2 wks old), was only putting out 9 psi instead of 10-13 spec. So I returned the fuel pump and changed it, but that did not alleviate the problem.

It still has original O2 sensor and MAFS and TPS. Shop said wires were okay.

Any ideas?

2) also, I may need to replace the AC compressor, does anyone know the range of Silverado years that the compressor on my 94 fits, as I may try to find one at the salvage yard.

Thank you.

Friz · May 10, 2005

Your rough running problem sounds a little similar to mine.

My '95 TBI 350 needs a new distributor cap and rotor about once a year. it gets corroded inside and will intemittently start running rough, then smooth out for a while, then run rough again.

After I change the cap and rotor, it runs fine for about 8 months to a year. I have 120k on mine.

I would guess that the a/c compressors would be the same for any tbi 305 or 350. That's just a guess, though.

btmaster · May 12, 2005

My 1994 C2500 350 runs the same way. It has 71K miles. I have changed the O2 sensor, with no difference. I have not messed with a MAF or TPS sensor either. Plugs, wires, Cap, and rotor are new. I thought about changing out the ignition. My problem is primarily when it's cold (idle's rough), and even warmed up, it still has somewhat of an offbeat rough idle in gear at stops. I wish I knew where to start next to eliminate this simple problem. Would an engine diagnostic find the problem? Might be cheaper then throwing parts at it. btw- My compressor is worn out too.