10 mpg with new Jasper engine & transmission

Asked by May 02, 2016 at 06:15 PM about the 2001 GMC Sierra 2500HD 2 Dr SL 4WD Standard Cab LB HD

Question type: Maintenance & Repair

1993 GMC Sierra runs rich.  ALL components new and I mean everything, Jasper 5.7 engine and transmission.  I have talked to several full time mechanics and nobody has an answer?????

3 Answers

35,185

Did the O2 sensors get plugged back in during engine replacement? Is the check engine light on?

Bob, I've been dealing with this problem for some time and swapped 3 sensors... I wish an engine light would come on so I could get a little closer to finding the answer. Expecting to keep the truck till the end of time I went all out with engine, transmission and ALL components, again everything! Six other mechanics have had their hands on this thing without success.

35,185

I know the spark plugs are new, but have you pulled them to see what the coloring looks like? Does the engine feel like it is running at full power?

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