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


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.


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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