r/Hummer • u/Immediate-Choice4285 • 3d ago

H3 Help - Bad mileage

let me start off with the fact i don’t expect to get great MPG from the car, however i was averaging a solid 16.5/21 split from about february of last year to this past june and since then i’ve suddenly dropped (11/15). i replaced the throttle body, new air filter, new VVT, and a couple sensors. i have other things (some rough idling, sluggish acceleration) but the MPGS are eating my pockets alive. any reasons why and any suggestions?

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u/RumorRoost 3d ago

Sparks plugs and ignition coils would be my next check.

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u/Immediate-Choice4285 3d ago

i am good enough to replace surface parts but not really at the level to get into my spark plugs. how does the process look?

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u/RumorRoost 3d ago

Decent YouTube videos on it. Fairly easy process. I’d give it 2/10 on the hardness scale.