Mechanics

CHEVROLET CHEYENNE COMPRESSION PROBLEM

1998 Chevrolet Cheyenne

I have a 1998 5.7 vortec, came out of a 1998 Tahoe with approx 145,000 miles, it ran good 4 years ago. I pulled it out of the Tahoe and put it in a K2500 Cheyenne automatic. I have replaced the fuel pump (ac delco) it misses. When on the scanning tool (when it's cold) it misses on # 1 - #5 - & #7, then when it's warm it misses on #2 - #3 -& #4. It seems like it just jumps all over the place. The following is what I have already replaced/changed: the ECM - new spark plugs, wires, distributor cap - rotor, coil and ignition driver, fuel injectors, map sensor, the TPS - crankshaft position sensor,
I've done a compression test and every cylender has 190 to 195 psi. If any of you can help me I'll be glad to send you a check for $100.00 asap as I need to get this truck up and going for work!
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Scott Pemberton
December 28, 2012.



I wonder with it sitting over time that the valve springs may be weak or broken from valves being open.

It you replaced all those parts, then you need to look out of the box right now.

Roy

ASEMaster6371
Dec 28, 2012.
Nope, it wouldn't have the amount of compression if the springs were whacked. Any other ideas?

Tiny
Scott Pemberton
Dec 28, 2012.
I dis agree. Weak valve springs can have good cranking compression but when it is running will not seat the valves. Use a vacuum gauge to check for fluxuating vacuum

Roy

ASEMaster6371
Dec 28, 2012.
Hi Roy,
I've already done that and there is no fluncuation. This engine is really trying me! Any other thoughts - suggestions?

Tiny
Scott Pemberton
Dec 28, 2012.