Whats with GP's mileage

[troy1]

huh new look around here I like it


Whats with the crap mileage that my GP seems to get? I can never get over 24.5mpg no mods dont drive like a wild man out on the highway. most of the time going 80 its only like 23.2. All tuned up dont use 10% ethonal blend no SES light & the car seems to run good its only got 81K this thing is really pissing me off.

[Biggben]

What year do you have? I know personally that ive always gotten bad gas mileage with my gp. Who said that they did have good gas mileage?

[andylikespez]

i have a 2000 SE with the 3.1 liter and i average about 19 city and 33 highway going 75 or so on cruise. in the summer i average 25 mpg total average and about 22 in the winter.

[SNKPWR]

i'm getting about 24 mpg w/ mixed driving in mine

[jimmyv-21]

there are many causes for bad gas mileage. have you had any other probs with the car and how long has the bad gas mileage persisted? i have the 01 gt and i get 19 city and 32 highway. here is a list of just a few of the possible culprits;

bad air filter
dirty injecters
cheap gas
malfunctioning 02 sensors
low air pressure in tires (believe it or not)
dirty spark plugs

[JonJon68]

97 GP GT 110,000 still getting 32-33 highway and 19-21 city.

[troy1]

Mileage issue when I fist got to car was good been declining lately Its got a new Air filter plugs wires coil packs (terminals rusted) fuel filter new tires as of yesterday (plus one rim) new upstream Borg O2 sensor. PCM update. The only thing this car does on take off when say about 170/180*F you can feel the engine hold back slightly barely notice jerky acceleration. TCC locks up good and so on. Dang thing just should get better gas mileage than what it does. Even going 65 I can't hit 28MPG when I first got the car it was 30mpg. The only thing I can think of is maybe the cat is getting plugged. Gas I get it from a couple different stations so that shouldnt be an issue. Were is Merlin when you need him

[JonJon68]

Keep us posted once you find out what's going on.

[bearinns08]

i would be happy to get this good of gas mileage in my 97 gtp. maybe i should stop driving so fast. but its so hard not to "have a lil fun in the gtp" every now and then. ...i get like 20 mpg

[troy1]

Yea i can get 18-20 intown but out on the road only 23/24 should be able to get more than juat a couple MPG more on the intersate

[04GTP-WhatLAG?]

i'm getting 19-24mpg(mixed driving), of course my lead foot doesn't help matters any...

oddly I actually seemed to have gained a mpg since the mods... don't know what happened there, i checked it around X-mas and got 22mpg, checked it again last week and got 23mpg...

So apparently it pretty much stayed the same...

[KX2000GTP]

2000 GTP 105K, i average 25.1 with mixed driving, 93 octane, and a lead foot at red lights

Before I modded I was running with about 22 mixed...

[BNaylor]

I posted a reply in the Regal forum but noticed your post in the GP forum. Just a suggestion but you might consider trying AC Delco OEM 02 sensors both front (AFS109) and rear (AFS141). If you have access to a scanner run some tests of the 02 sensors even if the engine vacuum test shows the CAT appears to be good. Both 02 sensors still have a major impact in fuel economy especially in PCM closed loop mode operation such as highway cruising speeds. From what I understand an 02 sensor can degrade to 60% before tripping a MIL light and do degrade over a period of time due to carbon, etc. The response time slows. The rear 02 sensor not only monitors CAT efficiency but will allow the PCM to fine tune the air/fuel mixture to the fuel injectors so I would not rule that out either. Interesting article below:

http://www.asashop.org/autoinc/july97/techtotech.htm

Your highway mileage should be a lot better on a L36 Grand Prix.

My L36 '99 Regal LS gets 22 - 23 city and 28 highway. Of course it has 3.05:1 gearing versus your 3.29:1. Even at 75 mph taching 2100 rpms I get 28 mpg highway.

[richtazz]

My 99 GT gets around 20 in town, and better than 32 on a trip (cruise set at 75'ish. I'm not a lead foot, but it makes a HUGE difference around town. If I drive like a grandma (what torture even for a short time experiment... ), I can squeeze 22.5-23 around town. I'll give up a couple MPG to have a little fun at the lights. I agree with bnaylor that replacing both oxygen sensors (preferably with AC-Delco ones) should help you regain your lost mileage.

[92grandprixx]

My 92 sucks also for mileage.3.1.maybe 20 if i am lucky!!I havent changed the 02 sensor yet... everything else tho I have.plugs.wires,fuel filter,how do u clean injectors ?I have tried the bottle stuff...Also do you guys experience you gas guage moving alot...mine will move like a 1/8 usually never know where the hell its at! ..Ithinking about just going and let it run out and see where my mileage is then! maybe guage is off?