2011 LT MPG dropped majorly

2056 Views 7 Replies 3 Participants Last post by repairman54, Oct 25, 2020

StephSD

Discussion Starter · Oct 14, 2020

2011 LT 4cyl 2.4L I posted earlier about this and since then have tried some different things. Currently I’m at 14.9 mpg city and when I hit the highway it’ll go up to 15.1. I’m just burning through gas and I work up the road; it’s ridiculous. Air filter is new, spark plugs changed. MAP sensor changed, professional fuel injector cleaning service performed. No change ... actually it dropped after the service. What else could this possibly be ?!? No codes. Runs a little rough when idle; doesn’t purr like when I first got it. ANY suggestions I’d appreciate it!

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repairman54

· #5 · Oct 16, 2020

#1 O2 sensor, the one in the exhaust manifold. That is what monitors fuel mixtures, it may be on the edge of failure or getting weak but not bad enough to set a code.
When I changed the O2 sensors in my Tahoe I got back 2 mpg highway on it, no codes, scanned fine and it ran fine on the old one.
2 mpg is a big deal on something that only gets 18 mpg highway normally.
Use only a AC sensor also, aftermarket ones known not to be reliable.

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repairman54

· #8 · Oct 25, 2020 (Edited by Moderator)

Downstream is only there to verify catalytic convertor is working, no other purpose or effect on engine running.
Did you use a ACDelco sensor up front ? Hopefully yes as other brands are not dependable and erratic.

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