02 GMC Envoy horrible gas mileage

Asked by WeaverJ55 Dec 08, 2019 at 10:39 AM about the 2002 GMC Envoy 4 Dr SLT 4WD SUV

Question type: Maintenance & Repair

I drive a 2002 Gmc envoy slt, 4.2l 6 cylinder, recently its gas
mileage has dropped to 6mpg, instead of around 16-20
where it used it be. It has stock sized tires, no warning
lights on the dash, and the live read of the o2 sensors are
fine. Any idea on what's causing this and how to fix it?

2 Answers
11,625

FJ4072 answered 5 years ago

Several things can cause this, from a lazy upstream 02 sensor to thermostat, to fan clutch, to the cat. If your 02 sensor has more than 80k on it, replace it (don't use Bosch). This engine loves the AC Delco sparkplugs, 41-103 to be exact. Have your cat back pressure tested to rule that out. Also, check your fan clutch, if it doesn't disengage, engine will run cooler, which is another mpg robber.

1 people found this helpful.
Mark helpful

Shannon answered 4 years ago

had the same problem with mine... Removed the catylitic converter.... Gas mileage went from 10 mpg to 16..

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