2004 Grand Prix getting 7 to 13 mpg in city?? HELP PLEASE

[cindyhh]

As i said, i get 7 o 13 mpg in the city, and up to 18 on the highway >> WOW.. This is a 2004 with the 3.8 Grand Prix GT. I am driving it normally, I assure you. I have had it in the shop and they can find NOTHING wrong with it at all. No codes of any sort. I was just hoping somebody had some idea. MY mother is looking at an Impala to buy but it has the 3.8 also and she is afraid of it. I know i have heard so many good things about this motor, it has 75,00o miles in case you are wondering, regular maintenace. I just bought it 2 months ago so i dont know how long it has been this bad. It was a lease car to a pharmaceutical company. No repair work ever when they ran the VIN.. Any help appreciated and also, what is your experience with mileage with the 3.8? I admit when i say city i mean it, stoplight to stoplight, but it should be better than it is in town and even on the highway. thanks

[jessep28]

How many miles?

When I bought my 00' with the Series II 3800 NA it only got about 18mpg. I changed the fuel filter and now I am getting about 20-22. Although I only got 19 on this trip after running it a little hard . (these cars are fun to drive)

I would change the fuel filter as the easiest option. You will not get the nice 22+ mpg since you are primarily in the city.

Tell your mother to not be afraid of the 3800. The engine is very reliable and MANY people swear by it.

Let us know how things turn out.

[Rally Sport]

With that many miles.. i'd suspect your air filter way clogged up by now.. so go ahead and replace that too while you're at it.. you'll be suprised how dirty the thing is if it hasnt ever been replaced. This will also help out in gas mileage.. I would say replace spark plugs and wires but they are suppost to last up to 100K miles so not yet, but soon.

[GTP Dad]

Don't bet on the wires and plugs lasting 100K. If your mileage is that bad then you may want to change them as well. Fresh plugs and wires will produce a better spark that will burn the fuel more efficiently and increase mileage. You may also want to go ahead and spend the money for new O2 sensors. Expensive to change but they may be failing and have not gotten bad enough to give you a code but are causing the engine to run too rich. At the price of gas today, even a 3 mpg increase can mean a lot.

Welcome to the forum!!

[BNaylor]

That's as bad as a SUV or pickup truck. I don't know if GM has improved the CAT convertor on 2004 and up GPs but with that mileage have the CAT convertor tested for efficiency and possible clogging if all the basic tune up items mentioned earlier by others don't significantly improve the terrrible gas mileage. Good luck!







Thrasher CAI, DHP v1.0 PCM, SLP Headers,
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u-bend delete, 160 TS, ZZP Stage 1 72mm TB,
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Goodyear Gatorback Serp. & SC Belt,
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1/4 ET: 13.210 sec. @ 104.490 mph
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[richtazz]

I agree with GTPDad, it's time for plugs and wires, fuel and air filter also. Try those first and see what happens. If those only help mariginally, then I'd also change the oxygen sensors as he said. Being a company car, it was probably city driven most of its life prior to you buying it.

[regalfriend]

Try what was suggested(complete tune up)...check tire pressure make sure they read 32 PSI.Im not sure but i think your car is supposed to get 18 MPG local and 28 HWY from the brand new....dont wait until 100k to tune up...do it now at 75k...also when you run the vin, through carfax it wont show any repairs...it will show thefts, accidents, inspections, title info, etc...if after a tune-up you get 15-16 MPG local and 25-26 HWY , thats probobly the best yo will get....good luck.

[cindyhh]

the new air filter, although the other appeared clean, the mileage on the sticker says 20 city, 30 highway. I did ask about the fuel filter, they said if it was bad enough to cause mileage like this it wouldnt idle right driving it? Also, asked about the tune up, and 02 sensors. I was told by the service manager, if anything is that wrong it will definitely throw a code?
Just for my own sanity, how much difference can a tune up and these other changes make? I cant spend a fortune just for nothing. Hope this makes sense, i feel like i am on a hopeless mission here.

[cindyhh]

Oh, I meant to tell you, I know running the vin on carfax wont give me this info, but at the dealership they can tell any repairs while under warranty and there were none ever. Never brought in. It belonged to Pfizer Labs and they do mostly highway miles to each town then to the docs offices.

[corning_d3]

An OBDII vehicle will only throw a code if the PCM thinks that there enough of an emissions problem to cause concern. They can run on the threshold of "bad enough to cause the car to perform poorly, but not enough to set the check engine light"

[regalfriend]

I think the dealer was not 100% honest...i think...by law they have to tell you if it was a fleet vehicle...Brand new your car is supposed to get 20 city 30 hwy....thats if you drive like a grandma.....13 mpg's local does not surprise me.....18 mpg's does surprise me.... maybe your tranny

[Ninjo]

i may be new an all... but i must say...13mpg? jebus.... i drive my GP harder than my ex-gf and i still get about 25mph average.. there must be something serious..................

[04GTP-WhatLAG?]

I have a 04 gtp, drive it like hell, and still get 19mpg(on average), the tank of gas I tested my mpg in town(didn't get on it much), I got 22mph, got 27mpg driving to Atlanta and back...

Something is definitely not right with your car...

[cindyhh]

Something is definitely not right with your car...[/quote]

I SURELY agree with this I didn't buy the car from a dealership, i bought it knowing it came from Pfizer so this was no surprise from me, but did not expect mileage problems like this. I wondered if the tranny could be bad also. I will call the dealer and see how much the 02 sensors would cost to replace, I just cant afford 13 mpg at best in the city when most of my driving is city.. I would never have expected this.
Also, have a friend who is looking for an impala, same motor, 3800, and she is a little concerned given all my bad luck, but my thinking is this is just a fluke and not all are going to get between 7 and 13 in town... At least i hope not.
thanks again

[romeguy1]

Are you trusting the computer to tell you the mileage or are you doing the math yourself?
If you're trusting the computer maybe this is really the problem...? Just a thought....