This one really stumps me.
I have ALWAYS gotten 320 miles per tank of gas. had my 2002 Z24 (with GMPP SC) for years now. lowest i ever got was 290 miles per tank, if i didnt break 300 i was pissed off. typically i could get 320 with my leadfoot driving style.... if i drove like a normal person, i could easily get 350.
Well i was getting ready for a road trip, so decided to freshen my engine up a bit. I sea-foamed the engine (via brake booster line) I washed and re-oiled my K&N air filter, i did a "engine flush" and then changed oil and filter (bosch filter, and castrol full sythetic oil), slapped in some brand new NGK plugs, filled all my tires up to the proper pressure, washed the car and heaed out on my trip.
first tank was 100% freeway... and i only got 230 miles out of the tank.
return trip, another full tank.... and i hardly broke 250.
now even a week later, i am still seeing CRAPPY milage. this current tank, i am at 3/4 full and only drove 60 miles since filling up. (normally i am close to 80 at this point)
I have even been driving slower and trying to save MPG... and STILL getting the worse MPG the car has ever seen.
i have plenty of power, no engine light, cars runs grerat, A/F ratio all normal.... only thing wrong is the 50-70 miles less i am able to drive.
why the hell does my engine run like POOP now that i cleaned it up?
i am tempted to dump dirt in my crank case just to soil things up so i get my MPG back.
what the heck could be going on here????
only thing that rings a bell are the spark plugs. put the old ones in, see what happens.
-----------------------------------------------------------------------
-----------------------------------------------------------------------
- Sold my beloved J in April 2010 -
^^ yup try going back to the stocker plugs or going to some ac delco's...ive heard certain brands cause bad gas milage..
or depending on where you live, that winter oxygenated gas tends to kill gas mph, was it windy on your trip? The trip i just took the one that i cracked the head i got 290 miles on a half tank
and the plugs may not agree with your engine like the other guys siad
well on my trip, the way back was aweful windy.... (but i got more MPG on the windy ride home than the not windy drive down.)
Before i was using the bosch platinum +4 plugs... they were the ones you cant "gap" you just use them as the come. I had those in forever... but recently ready that you dont want to use those kind in a supercharged engine, and the best plugs are the plain old single electrode plugs... and was told by several people that the NGK's were the best plug for my needs.
So that is what i went with.
The car RUNS alot better since my tune up. more power, better acceleration, and all that.... i was thrilled about how well everything was working right up until i went to fill up and saw i was empty like 80 miles too soon.
did you check your tire pressure?
when mine was just a few pounds low it was throwing my mileage off.
Yup,
actually overfilled them a touch.... i had like 45 all around.
(i have 18" low profiles on the car, the car pictures in my sig below is the one in question.)
Sounds like you overfilled the tires a BUNCH. Seeings how our car is rated around 33 psi. Now I'm not sure that overfilling them would actually decrease the mileage, but drop them back down to 33-35 and see how things go.
and cold weather wont affect your a/f ratio at all. but it will hurt your mileage when its TOO cold. there is cold, and there is too cold.
just a thought would the over inflatting the tires change the diameter of the tire, which changing revolutions and milage just a thought could be way off
