Poor gas milage

[troy5190]

hey all,

IM getting about 20 percent worse gas milage than I used to. here is what im dealing with.

3800 GM series 2 engine
LTFT 16.4 at idle about 11 on the highway

Topic

[troy5190]

if there are exhaust leaks well past the O2 sensor will this matter?

[EricTheCarGuy]

Depends on where they are. If you have known exhaust leaks they could be masking others that COULD effect the O2 sensor readings.

[troy5190]

Problem fixed! The MAF was on its way out must have been reporting too slow or incorrectly. The GM service manuel had it listed to unplug the MAF and see it LTFT corrects if it does the MAF is bad. I did this and sure enough it corrected without the MAF. Looks like on this vehicle when the MAF is off it defaults to a preset number but the O2 sensors still keep alternating between rich and lean to keep the cat happy.

Anyway my LTFT is about 1-4 while driving and about 9-10 at idle Im happy with that. I was at 16.4 but that value is maxed out for this vehicle. The 16.4 was also paired with about a 4-7 STFT. Now both trims look pretty good.

Thanks for all the suggestions. It was very difficult to determine it was actually the MAF because you have to basically prove there are no vacuum leaks before the MAF test is valid. I tested for leak by blowing cigar smoke into my throttle body, maybe not the most reliable method but i think it worked, had no leaks visible so i went ahead and replaced the MAF.

[John B Kobberstad]

Another maybe overlooked cause may be one of the brakes dragging on a disc or drum. I assume there are no CEL /MIL on.

[EricTheCarGuy]

Those readings seem high. They should be as close to 0 as possible at idle on a good running engine. Positive numbers indicate it’s adding fuel to compensate for too much air. Give it some time though because it will take a bit for the LTFT numbers to ‘normal out’ so you get an accurate reading.

[Author]

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