I HAVE A 1998 5

  • Tiny
  • Scott Pemberton
  • 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!

Friday, December 28th, 2012 AT 2:25 AM

4 Answers

  • Tiny
  • ASEMaster6371
  • Expert
  • 25,549 posts

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

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Friday, December 28th, 2012 AT 2:32 AM
  • Tiny
  • Scott Pemberton
  • Member

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

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Friday, December 28th, 2012 AT 2:37 AM
  • Tiny
  • ASEMaster6371
  • Expert
  • 25,549 posts

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

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Friday, December 28th, 2012 AT 2:39 AM
  • Tiny
  • Scott Pemberton
  • Member

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

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Friday, December 28th, 2012 AT 3:09 AM

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