Reman 1997 Chevy 5.0 bad gas mileage

Johnathan Payne

Asked by May 20, 2014 at 12:17 PM about the 1997 Chevrolet C/K 1500 Cheyenne Extended Cab SB 4WD

Question type: General

I just had my mechanic install a Jasper remanufactured Engine in my 97 Silverado 2wd. I
just did a direct changeout (same size engine) 5.0 to 5.0. While this was being done I sent
my ECU out to be "tuned". With my old engine I was able to achieve 15 mpg average and
at its worst at the end we were looking at 13mpg. I now have about 5000 miles on the
reman engine and I havent got any better than 11.5 mpg since the changeout. Any ideas?
Could the tune be my culprit?  I also have a K&N intake, 3" catback exhaust, and a 3
chamber flowmaster. All of these I had for 5 years before I changed the engine. I also had
a new cat installed after the engine changeout too. Any help would be awesome! At this
point I can't afford to keep my truck or to get rid of it.

7 Answers

Tom Demyan

What did you do to the ECU? Tuned as in more performance? If so, you will use more fuel. Also a new engine will get worse gas mileage due to it being new and tighter internal tolerances. Once you get over 5K, you should see some improvement once the engine is broken in.

1 out of 1 people think this is helpful.
Johnathan Payne

No, I wanted good fuel economy. I put a lot of miles on my truck.

Tom Demyan

OK, are the tires at the right pressure? Try cleaning the MAF, I see you put a K&N filter in, and if the oil from the filter gets on the MAF element , it could effect the MPG. Go to to see how. If so that checks out, then I'd wait a couple more thousand miles to see if the MPG improves before you get rid of it.

1 out of 1 people think this is helpful.
Johnathan Payne

Yea everything is good. Having ac problems all of a sudden now. Could my ecu be bad?

Andrew Olsen

check your fuel pressure/leakdown rate. Its a vortec engine with the spider injectors. The fuel pressure regulator is a known problem to fail and start leaking a little. Early sign is poor fuel economy. Just a thought, do you know what year 5.0 you swapped to? I'm wondering the cam it has

1 out of 1 people think this is helpful.
Johnathan Payne

I have no idea what year they changed it out with. I will ask my mechanic to check the fuel pressure stuff as I do not have a Guage or knowledge to do so. Thank you for your help!

Eddie Toro

check your ecu the ac system works thru the ecu if your ac is malfunctioning is probably a good sign that theres an internal ecu issue I work on this models all the time goodluck godbless

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