Bad gas mileage

[JiP]

I used to get like 20mpg back in june, but I cant give you an exact date but the past few months my gas mileage has been horrible, like 15mpg on highways like 12 on streets. on a 4g64 group I went through an entire checklist of crap and I'm out of reasons

New spark plugs,
distributer cap and rotor checked and are in good condition
Air filter is clean
Recent Compression test yielded great results
No CATs on the car so its not a clogged they were removed to try and solve this problem
Car runs at around 195 degrees so its not running cold caussing power loss

Tranny does have a little too much fluid in it, could that drop 5mpg on the car?

Everything I've been told to check is in spec so what else could it be its driving me crazy!!

[BEAST]

When did you take your cats off and when did you do all this exhaust work? That may be the reason, you have very little backpressure now so it really runs through gas. I have heard of people losing mpg with just a new straight through muffler so image what happens in your case.

[JiP]

No the cats were removed as I said to try and SOLVE the problem. I had 15mpg still with both Cats, and after going through the usual checklist of crap everything checking out fine, a clogged CAT was next on the list, So I removed only the center one and replaced with a testpipe...still 15mpg...then I made my own elbow section for the downpipe so that I could remove the cat that is the elbow of the downpipe from manifold to flex section...and STILL only get 15mpg.

I'm out of ideas for things to check that cause bad gas mileage throw some out to me...

[BEAST]

Check

Fuel Filter
Injectors
Try cleaning your throttle body

Thats all the more I can think of right now.

[JiP]

injectors cleaned, tb removed and cleaned wasnt even dirty I have no EGR from why I duno but my intake stays amazingly clean.

Fuel filter I have a new one, havnt put it on yet, but it doesnt make sense that a clogged fuel filter would be cuasing lower mpg. clogged filter would make your car run leaner using less gas according to my a/f ratio im running normal.

[manybrews]

how much modification has been done? is your check engine light illuminating?

[JiP]

When I first noticed that I wasnt getting as many miles out of the car, the only mod was a CAI. Everything else on the car was just "rice". And I have a datalogger there are no problems. The car isnt lacking power either or hesitating in anyway, it just uses more gas then it used to.

[JiP]

Hey Many,

You think it could be my thermistat? How can I tell if its functoining properly my ECT gauge is installed in the upper radiator tube reads about 190 when the car is warmed up, datalogger says that the ECU is reading 195 or so from the cars stock ECT sensor.

Sounds about right to me?

[manybrews]

if your car is running at 195, the CTS is fine.

the most likely componant to fail when getting bad milage is an o2 sensor, but it would likely throw a code.
timing would be the second thing i would check.

[cantbeatmy97]

most likely yur losing more gas is cause yur defroster runs on the a/c which wastes gas big time and also its winter so they switch gas over to more oxygen so yur car runs better in the cold they change this around oct in the spring time u get better gas cause they use more ethyl gas i lost bout 40 miles to the gallon due to the fact of them switching gas

[Oli97GalantES]

cantbeatmy97
That is a good explanation and answers what I have always been wondering. In the spring/summer, I used to get 360-370 miles before the gas light went on but lately it has been turning on at 325-335 miles. I thought it was my filters but all of those were cleaned or replaced right before winter, never occured to me it could be the gas.

[JiP]

If those are your numbers then My car has a serious problem. A full tank of gas gets me only about 220 miles. A year ago, in winter, drove 200 miles to boston, and got there with a little more then a quater of a tank left over. So its not the fuel its something with the car, im sure the fuel is making my problem even worse though.

And for defroster...basically I never use it. used it once this winter. It only snowed twice over here.

[laxattack2001]

i get about 280 at the most and thats when im lucky most of the time i get about 260 for a full tank so i guess something is up w/ me too

[JiP]

Id kill for 260 right now! I have to put gas in like every other day..and I only drive like to the store and to my gfs house..its killin me

[laxattack2001]

that sucks man but gas prices are starting piss me off real bad i cant wait till they go down again

[Kain]

Egads! 15 MPG!?! I get 45! I'd take a serious look at your O2 sensors. When fiddeling around with my Colt one day I accidentally forgot to plug the O2 sensor back in before starting it and it ran like crap and actually had gas coming out of the tail pipe. But, if your O2 sensor were that bad you'd have a CEL. Umm, could be a computer problem, but I've not heard of that often on the Galant. Hmm... you could do a test on the spark strength to make sure each cylinder is completely combusting (but that would cause very rough running) Umm, I've never heard of a car having that low of gas milage and still run decently. Phew, I just don't know what to tell you on this one. Maybe your brakes are draging very badly? Towing a trailer? 4 flat tires? Seriously, when I think of bad gas milage I think 20 or so, but 12-15 is near '74 Mercury Cougar levels of milage.

[JiP]

Thats what im saying. Its baffeling everyone Ive spoken to. The car runs great. Like I said I have a datalogger, and gauges everywhere, o2 readings are normal. Spark strength..well like you said there would be lack of power in the engine, which I do not have.

I have too much tranny fluid. I know that much. Aside from tranny fluid, everything else that I have been told to check is 100% fine and its starting to piss me off that there is no cause to this problem..it just is.

A dragging break would have to be REALLY dragging to drop mpg that low, and if it was I would feel it, or feel lack of power, or quick slow downs when I release the gas, and I feel non of that.

Someone suggested that maybe my gas gauge is screwed up and giving incorrect reading and so it appears that im using a lot of gas when im not. But i highly doubt thats the problem, it appears to work fine. It is slow to move up when I throw gas in, but my berretta was like that too so I assume thats normal.

[Kain]

Ok, the last thing I can think of may sound a bit strange, but I did see it once. Perhaps you suddenly have a smaller gas tank. I had a slightly similar case where this dude brought his Dodge pickup truck into the shop complaining his truck was gettin really crappy milage all of a sudden (like 5 mpg) and he thought his ex had done something to his truck when they broke up. All tests turned up nothing until we decided to look in his gas tank. We found all kinds of crap down there just about anything she could drop through the fuel filler hole. So, it seemed like the truck was gettin bad millage when it really just was suffering from a partially filled gas tank. Look at how much gas goes in next time you fill up. As a frame of referance (if you don't already have one) I always refill when I get down to 1/4 of a tank and I take in right at 10-12 gallons. It's a stretch, but that's really all I can come up with.

[Nick VR4]

You might want to check that you have no leaks in tank or piping

[JiP]

If there was a leak wouldnt I smell it? Plus in warmer weather im under the car a lot, I would have noticed a leak. the lines are under pressure arent they? Any small leak would shoot streams of gas out. (?)

Happend on my berretta AAA wouldnt tow me until I called the firedepartment first lol

I am almost competely out of gas, so after a lil driving today I will fill the tank and tell you what I fill, our tanks are about 16 gallans right?

[JiP]

When the gas warning light how much gas is left in the tank? I drove about 14 miles with the gas light lit up bright, and the car was still going..Anyway I filled up only 13.5 gallons. So unless the light comes on with 3 gallons still left in the tank, then I have been calculating things wrong.

But we'll see the new calculation when I empty this tank.

[cantbeatmy97]

also depends on what u use for gas i use 89 and push 320 i was usin 87 and pushin 390 citythe better octane the less miles u get

[JiP]

I use 87 mostly. again, Does anyone have any idea at what point does the warning light come on, how many gallons are left in the tank?

[cantbeatmy97]

i believe when it comes on u have 2 gallons i filled mine on E but not idiot light came on i had bout 4 gallons left we have a 16 sumthing gallon tank