engine runs fine until warmed up then it backfires

1990 CHEVROLET SILVERADO
85,000 MILES • 5.7L • V8 • 4WD • AUTOMATIC
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RANDALL1961
  • MEMBER
  • 2 POSTS
engine runs fine until warmed up, about three miles, then it backfires on passenger back exhaust and slows down cannot accelerate, but will idle. I have replaced plugs cap and rotor, MAP, TPS, water temperature sending unit no positive result.
Jan 14, 2017 at 1:23 AM
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HMAC300
  • ✓Experienced Mechanic
  • 48,601 POSTS
check for a vacuum leak under TBI unit may be the problem. then scan for codes by crossing A and B b on ALDL. also, check plug wires 5000 ohms per foot.
Jan 14, 2017 at 1:42 AM
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RANDALL1961
  • MEMBER
  • 2 POSTS
have not replaced wires. trying to avoid, but will and send you a reply as to results.
Jan 14, 2017 at 1:46 AM
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STRAILER
  • ✓Experienced Mechanic
  • 55,694 POSTS
Please let us know what happens so it will help others.

Best, Ken
Jan 17, 2017 at 10:17 PM
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