Hi everyone. I recently purchased a 2003 Tahoe 1500 with the 5.3L. I'm getting horrible mileage. I just drove 140 miles and it used over a half of a tank. The instant mpg on the dash says 11-12 mpg this is on the highway at 75mph. It's even worse in town. I have a Hypertech tune in it and it runs very strong, just really poor gas mileage. The computer has not thrown a code, but is it possible the O2 sensors are too carboned up to read the air/fuel ratio correctly? Or if anyone has any other suggestions/thoughts, please respond. Thanks.

 

What kind of mpg did it get before the Hypertech?

If your O2 sensors are carboned up, then you have a mixture control problem.

Remember that to get more power, you have to burn more fuel or burn it more efficiently. Since the mfgs are under the gun for more mpgs, I doubt that you are going to burn fuel more efficiently w/ a chip. So that leaves poorer mpgs. There is no free lunch.

 

Is this dual exhaust? I just went through this type issue with my tribute. MPG went down to about 14 before it quit. It has two precats, and a single exhaust cat, well not anymore. Turned out the back cat finally plugged to the point it quit.

 

It was the same. I already had the programmer so I thought I would try it. It worked on my 99 Tahoe with a bigger older style motor. That, went from 15 to about 17mph.

 

Might consider having the fuel injectors serviced, if you are getting some leaking from any of the injectors, over a period of time that will add up.. that also plays into your concern about carbon and to 73shark's statement about running too rich....

 

Norvaracer1, you should not get worse gas mileage with the Hypertech programmer. We optimize the spark and fuel all the way through the rpm range. Usually you will pick up around 1 to 2 mpg on the hwy.I agree with in2pro, get the injectors checked and cleaned.