MY 454 IS LOSING POWER ON ACCELERATION.

  • Tiny
  • justfixit
  • 1992 GMC Truck
  • 195,000 miles

I've changed many parts, including engine. No power and engine backfires if you hold pedal down.I changed original engine due to broken pistons. The same problem occurred right before engine failure. I have changed, fuel pump, fuel filter, exhaust system, O2 sensor, distributor assy, coil.

No codes either. Idles nicely, just won't pull anymore or go up hills.

Thursday, September 22nd, 2011 AT 2:37 PM

13 Answers

  • Tiny
  • justfixit
  • Member

PS: the truck is a K2500 automatic.

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Thursday, September 22nd, 2011 AT 2:39 PM
  • Tiny
  • Jacobandnickolas
  • Expert
  • 68,305 posts

Do you have TBI or multi port injection? Have you done anything with the injectors? Have you checked compression in the new engine? Is timing correct?

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Thursday, September 22nd, 2011 AT 3:55 PM
  • Tiny
  • justfixit
  • Member

Thanks for responding! I do have TBI, original and changed the accelerator diaphram too. Timing is set properly, runs good when cold or flat ground. Just changed my MAP today, no avail?

Help

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Thursday, September 22nd, 2011 AT 6:00 PM
  • Tiny
  • justfixit
  • Member

PS compression is really good! Only 85K on new engine.

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Thursday, September 22nd, 2011 AT 6:01 PM
  • Tiny
  • Jacobandnickolas
  • Expert
  • 68,305 posts

Have you checked the catalytic converter? It could be plugging.

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Sunday, September 25th, 2011 AT 6:02 AM
  • Tiny
  • justfixit
  • Member

I'll find a temp lazer somewhere and check it out. However, not sure how it could be "plugging".

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Sunday, September 25th, 2011 AT 2:42 PM
  • Tiny
  • racefan966
  • Expert
  • 5,127 posts

Todays ethenal fuel leaves lots of deposits. Heat gun won't do much to answer this however. Remove the O2 sensor and see if the power comes back if so the cat is pluged. It will be loud when you test drive it because of the O2 being removed just so you know.

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Tuesday, September 27th, 2011 AT 4:41 AM
  • Tiny
  • justfixit
  • Member

Thanks again for the tips. The heat gun said 425 and 420 out. New o2 sensor last week. Vacum lock maybe? But how do I prove it? Any suggestion are helpful.

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Tuesday, September 27th, 2011 AT 1:37 PM
  • Tiny
  • racefan966
  • Expert
  • 5,127 posts

Tell me what all you have checked so I know what to go over or not. Thanks

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Wednesday, September 28th, 2011 AT 4:45 PM
  • Tiny
  • justfixit
  • Member

OK, this is great. Replaced engine, Map sensor, O2 sensor, complete exhaust sys, new ignition coil, replaced pick up coil inside distributor, new wires/plugs, new fuel pump and filters, and replaced the press regulator inside TBI assy. Ignition timing has been triple checked many times again and again. To include retiming the engine with distributor. Still loss of power after engine warms up only, runs great when cold or at slow in town speeds. Thanks again for your time.

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Thursday, September 29th, 2011 AT 1:08 AM

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