MY 95 gs has been getting horseS**^ mileage ever since i got it.(15 mpg) I did all things that i could to improve it. (cap, rotor, sparkplugs, fuel treatment, oil treatment, K&N intake, tranny fluid exchange and i drive nice) Seems like if i drive a lot harsher compared to grandma driving. Also, my car slows down really fast from 80 to 40. Seems like either the tranny or even Rear slip could be slowin it down. (Draggin)

I went 80mph getting off the highway on a ramp, and put it in neutral and the car kept rollin until i had to brake (80-65). But if i was to do the same with my car in gear, i would have slowed down to 45 mph. I know the higher the rpms, the faster the car will slow down, but not this fast!!!

I don't know when the rear diff fluid was changed.

Any ideas guys?

 

15mpg for a lead foot isn't bad. I noticed you did a bunch of maintenance but didn't replace the O2 sensors. When they get old they are slow to respond and can be the cause of bad gas mileage. The symptom of bad O2 sensors is theyy have bad idle after driving at part throttle. Driving along at 45mph, then come to a light, slop, the engine idles rough for a time (can be 10-20 seconds), then recovers. Having said all of that, I'd just replace the O2s if they original, can't be bad on a 94.

BTW, I doubt your rear diff isn't the cause of bad mileage. OTOH, can't hurt to change it.

 

I'm not a lead foot...I accelerate 25-3500 rmps daily which is fairly going light on the car. I don't ever put the pedal down, maybe once in a while.

What do you mean by rough idle?? If i'd be going 45 and come to a stop, the rmps would be at 1000 and slowly drop to 750-800.

About the rear diff. fluid, I got the car 3000 miles ago, and by the way the car was mainained, i wouldn't be suprised if it wasn't changed for 5 years. The last owner was a moron and did a poor job maintaining it.

 

Sounds like you should do the O2 sensors too, that symptom with bad gas mileage is usually caused by old O2 sensors with slow reaction time. It can't hurt, esp if they haven't been channged since the car left the factory.

 

Hey Xeeeem, I was curious as to how wide your tires are and whether you have rims or not. It's just to help paint the total picture of rolling resistance for your car.

You may have heard this before, but, even though you have the 6 cylinder, your gas mileage isn't actually that much greater than the V8 GS400 assuming both are driven normally. Part of this is because the 6 cylinder has a higher stall speed torque convertor in it, and I believe lower gears also (higher numerically) compared to the GS400.
I've noticed that my gas mileage recently (winter) has gone to crap.
My trips are usually short, as in, the car doesn't even fully warm up in the winter time. This means that I'm usually in the richer mode with it being cold outside, and the engine being 'cold' as well. On a trip to KY this weekend, I did knock down 22mpg at about 80mph there AND back. On short trips though, when it's cold, my gas mileage is SUCKY.

If you put up some coasting times for a FLAT road, maybe some of us can post up our findings for comparison. I'd do it, but the GS400 wouldn't be a good comparison because our RPM's / speed are not the same as yours.

I recall your recent postings about the brakes dragging, and now hearing this about the tranny and rear end has me scratching my head. I mean, brakes, yeah, they go bad, rust a little, lines swell up, water in the lines, etc. This is all very noticeable.

The rear-end and tranny are pretty much going to give you trouble free performance if they have fresh fluid in there. There's nothing there that would cause you to "slow down faster" if you've got all stock parts, which it would seem that you do.

 

i got winter yokohama iceguard tires...really heavy duty soft tires....205-60-16 which could maybe contribute to the crappy mileage. I filled up today 16 mpg and 60% was highway.

My brakes aren't that big of an issue, sure they smell once in a while and my car will vibrate a short distance but will go away within 2 3 mins. (Car roles fairy freely in neutral on hills)

I have no idea when the last time rear diff fluid was changed out and have no way of finding out.... I'm still shootin blanks!!

Could it have anything to do with engine compression, or engine wear?? I raced my buddy today and got smoked....you'll get a good laugh out of this. 1991 oldsmobile ninety eight. I took him from 40-70 but he killed me 10-60, and not to mention a 04 alero coupe....which would be a more respectful loss BUT NOT A OLDSMABOAT!!!!! MAybe that helps??

 

0-60

weather: 32 F

First run 1 month ago: 8.6 with traction slippage

Second run today: 10.03 Traction slippage

Third run today: 9.76

What is going on?!?! Why did i lose so much time?? If anything it should be better, i started putting synthetic mobil one, K&N filter, new iridium plugs, changed oil with restore can (supposed it restore compression etc) and just did a fuel injection clean.

 

Don't forget the fuel filter! Made a difference on my car, and reset the ECU as well

 

How do you check if your fuel filter is clean or dirty

I heard fuel filter, o2 sensor, MAF sensors don't need to get replaced until a check engine light goes on.

Like my dad and grandpa say...."If its not broken, don't fix it!!" I've learned many lessons the hard way.

 

Try getting some electrical sensor cleaner and clean the mass air sensor and how about a dirty throttle body??? Just throwing some things out there. I would think if you had a rear end problem...you'd be hearing some strange noises.

 

Go synthetic all throughout.

 

How do you clean the MAF correctly. What parts do you spray, what don't you spray??

I already cleaned my throttle body...or atleast tried. I got this thing from firestone, it says open up the intake tube, spray half can. start up car, spray the other half while working the butterfly (rev up engine). Problem is, the car won't stay on with the intake tube off no matter how much gas you give.

Is there a way for me to check my fuel filter to know if it needs to be replaced?

 

tried to send you an email, IMHO, it's time to consider new O2s, esp with your symptoms

 

FIGURED IT OUT!!!!!!!

Just got my brakes done...just as i suspected it. My rear right inner pad was completely stuck on the disc. MOST of my pads except the front right were worn down 3/4s way down from clipping!! From 8000 miles of drivin on em. It was TERRIBLE!!! I switched out all 4 calipers, pads, and rotors and now my car drives like silk and a lexus. IT stays in the 2500 rpm range easy with plenty of power but before i had to always go in the 3000 3500 rpm range.
But now that i got all my tune up done and brakes done, i should be gettin pretty good mileage. So far, i drove 115 miles on the tank and the arrow is just below the 3/4 line....never had that before. I'll post my mpg when i fill up in a few days.

IF you guys are having problems with gas mileage and have done your tuneup and maintance....CHECK YOUR BRAKES!!!!!!!

 

19.1 MPG