here's the deal... for the past year or so i've noticed my gas mileage getting worse and worse. so everytime i get some extra money... i do some maintanance work. here's what i've done in the last 8k... tranny fluid change @ 68k... fuel filter @ 71k... ngk plat. plugs @ 73k... cleaned my TB @ 73k... and i change my oil with mobil syn. 5w-30 every 4k. my mileage isn't realy horrible or anything... it went from about 23-24 city and 29-31 hwy to 18-19 city to (as of last weekend) 24 hwy. i've checked my ecu, 05-05. there are a couple of things i can think of... my pop charger... i've had it about a year... there is this hissing sound from under my car... near the rear axle... maybe an exhaust leak?? and i've got this whistling noise from under the hood while under light throttle... sounds like my girlfriends 1.8t... i have no idea what it is.
but is is possible that i have a o2 sensor prob. or KS prob. and the ecu isn't picking it up? i'm kinda lost in this one. my next step is to put my factory intake back on and have those noises checked out. but does anyone have any suggestions?? anything is appreciated.

 

did you put a breather on your car? thats what causes the slight whistle at light throttle....also, if you put a breather on, im guessing you may have done the DIY custom upper....that sucks away gas, same thing happened to when i first installed it.....if you didnt do it, then im puzzled

 

what is DIY ?

 

Do It Yourself

 

I have a Hybrid/JWT and my gas mileage is still 25+mpg average.

 

i guess im just a really hard driver

 

Possibly, but I do tend to drive hard occasiaonally. My MPG also went up slightly because I put on my stock wheels instead of my 17's.

 

I just got back from a 2100 mile trip and averaged about 27mpg with four people and a truck literally full of luggage. Florida to West Virginia with a stop in the North Carolina mountains. I had a best of 30mpg and a worst of 23mpg.

All I have for engine mods is a CAI. I have 17's with 235's so I'm sure this would have been quite a bit better on stock wheels. If I do this trip again I will put new tires on the stockers and put them back on.

 

You could have a seized piston in one of your brake calipers. To test the front rotors raise the front end or just a corner if you don't have a big enough jack, put your max in neutral and spin the wheels. They should rotate freely. Do the same thing for the rear and make sure the parking brake is released. If your wheels don't move or there is heavy resistance then you have found a seized piston.

I had deteriorating gas mileage for the past six months and the cause was a seized pistion in my rear passenger caliper. If you are hearing noises from the rear I would check the rear brakes first. The sound you hear could be the brake pads dragging. Since I replaced my rear caliper I have gained back 50+ miles per tank.

 

What type of gas are you using and octane number. I started experience poor gas mileage when I started using gas at 711's with an octane of 91. I then decided to go back to Hess and use their 93 octance (same price by the way) and my gas mileage is much better now! I don't know if it was the change of gas, higher octane or a combination of the both. Give it a try.

 

How do you all get such good gas mileage? I usually get 20-22mpg and I drive pretty economically, shifting at 3K in all gears and such....what's going on? I usually use regular unleaded but I just filled up with 93 a few days ago and I think my mileage is already improving. I don't even think this has anything to do with my car, because I got pretty poor mileage on my old '95 GLE before I wrecked it. Maybe I've just got bad karma

-Jon

 

yea, my gas mileage is horrible. I get around 220 miles per tank! What I've noticed on my 95 GXE is that whenever it's switching from 2nd to 3rd gear, it seems like it's struggling. It's hell weird. It goes from 3k RPM, goes down to 2k, then finally back to 1.5k. I think that's my problem right there... any suggestions?

 

i use and always use 93 octane... from either BP or Mobile... i recently changed my brakes... front and rear... but i'll check on those since i did have some trouble adjusting my rear side. and that whistling noise... thats my breather? is that the flat round black thing near my TB? i'm gonna try to do a TBI through my work... supposedly that can help quite a bit. but thanks for the help everyone... much appreciated.