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Replacement engine runs rough

Tiny
MUMZY
  • MEMBER
  • 1993 GMC C1500
  • 5.7L
  • V8
  • 2WD
  • AUTOMATIC
  • 120,000 MILES
Truck had bad knock, changed motor, set timing but ran really bad. Code 43 registered. New knock sensor, replaced distributor, new ignition module but still running bad tries to stall and revs up and down), wires to knock are good, distributor wires checked out. Noticed if unplug A/C compressor runs a little better but not much. Plug compressor back in and back to running real rough. Need advice as he is driving my truck until this is fixed.
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Wednesday, November 28th, 2018 AT 9:57 AM

1 Reply

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,513 POSTS
If the new engine has extended clearances it will make noise for the knock sensor causing the issue. How does the engine sounds when running? Can you please shoot a quick video with your phone so we can hear the noise, that would be great. You can upload it here with your response.

If the engine is quiet I have seen a bad ECM cause this problem as well. I would try a used/rebuilt unit.

Check out the diagrams (below). Please let us know what happens.

Cheers, Ken
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Thursday, November 29th, 2018 AT 12:15 PM

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