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1990 GMC Sierra no power

Tiny
KEVINKEFFER
  • MEMBER
  • 1990 GMC SIERRA
  • V8
  • 4WD
  • AUTOMATIC
  • 13,500 MILES
Truck is a big block 454, with throttle body injection and a 400 turbo transmission
just did full tuneup, checked for vac. Leaks and has good fuel pressure and no codes
idles fine except for occasional surging but when I try to move trucks it begins to stumble and miss even backfires a little if you push it. How can I check my t.P.S. Or what else could it be.
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Saturday, January 31st, 2009 AT 7:26 PM

1 Reply

Tiny
MASTERTECHTIM
  • MECHANIC
  • 4,749 POSTS
Check igniion timing. These trucks are known for the shaft in the distributor to spin causing timing to advance or retard. Timing will not change if you dont move the distributor so if you ckeck it and its off then you knkow the shaft spun. Also check vacuum source to map sensor, I have seen a lot of these plug the vacuum port under the throttle body to the map sensor causing slow response and thus leaning it out. Removing throttle body and cleaning out ports on bottom would be a pretty good idea just based on mileage and its simple to do.
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Sunday, February 1st, 2009 AT 7:06 AM

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