Replacement engine runs rough

1993 GMC C1500
120,000 MILES • 5.7L • V8 • 2WD • AUTOMATIC
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MUMZY
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  • 1 POST
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.
Nov 28, 2018 at 9:57 AM
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STRAILER
  • ✓ASE Certified Mechanic
  • 54,832 POSTS
  • ASE Certified Mechanic
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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Nov 29, 2018 at 12:15 PM
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