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1999 GMC Suburban misses under load, trouble light comes on

Tiny
DMLFRAZIER
  • MEMBER
  • 1999 GMC SUBURBAN
Engine Performance problem
1999 GMC Suburban V8 Automatic 178000 miles

The car starts fine and idles well, but when pulling up a long upgrade the car misses, loses speed and the check engine light comes on. This often happens on the bridge going to work which has a fairly steep climb to the top. The light stays on, but the miss goes away after I clear the top of the climb. It seems a bit sluggish for a while, but usually on the way home the light goes out and the cars seem sfine again until the next time. This some times happens at highway speeds on a fairly level stretch, but the long upgrade really brings it on.
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Wednesday, June 10th, 2009 AT 3:06 PM

5 Replies

Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
You need to get the computer scanned for OBD2 code/s and comeback with it this is where we start. Autozone provides this service free of charge.
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Wednesday, June 10th, 2009 AT 4:19 PM
Tiny
DMLFRAZIER
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  • 4 POSTS
When auto zone scanned the code was random misfires. This has happened soon after a tune up which was supposed to cure it.
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Wednesday, June 10th, 2009 AT 4:30 PM
Tiny
RASMATAZ
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P0300 Random misfires normally points to vacuum leaks and bad fuel

Misfires can be caused by worn or fouled spark plugs, a weak spark (weak coil, bad spark plug wire), loss of compression, vacuum leaks, anything that causes an unusually lean fuel mixture (lean misfire), an EGR valve that is stuck open, dirty fuel injectors, low fuel pressure, or even bad fuel
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Wednesday, June 10th, 2009 AT 4:33 PM
Tiny
DMLFRAZIER
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Can the EGR valve stick and then unstick. This problem has been going on for some time.
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Wednesday, June 10th, 2009 AT 4:48 PM
Tiny
RASMATAZ
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You need to open it up and investigate could be carbon preventing it from closing completely
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Wednesday, June 10th, 2009 AT 5:26 PM

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