2007 Pontiac Grand Prix Problems

I own a 2007 Pontiac Grand Prix Gt. It has a 3800 III motor and it is super charged. I have noticed lately that when i drive it is has lost its power. My girlfriend has a 2002 bonneville with the same engine and it is supercharged also. When you step on the gas you can tell the super charger is there. My car seams like the motor works really hard for the super charger to be kicked in. I have also noticed that when i am at a complete stop it kind of shimmys and shakes. Is this normal? I know that this car is supercharged but i can only seam to get 250 miles a tank. I just want some pointers before i go to the mechanic. I am starting to think that i got a lemon but i am not sure. It also shifts hard for a car. But i always thought it was because of the super charger. Not sure. It slams into second when you get on it and when you are idling you can feel it shift.

Doesnt sound good. Slam shifting is never normal

With mine I'm usually able to get 250ish miles give or take out of 3/4's of a tank of gas. I never let it get lower than that.

How many miles are on your car?

There is 40000 miles on it. It doesn't slam slam. But you know its rougher than normal. I have taken it to a dealership they have told me that its because of the super charger. Another said that its normal shifting. But i have had a lot of cars and when you are at a stop light and you get on the gas it shifts hard. So 250 miles a tank is good then?

4000 is all? wow.

250 per tank is about right especially in the colder months. Your a packer fan, so I assume your in WI? Its a reletively large car with a decent motor and a supercharger.

Also the final drive gear ratios between your GTP and g/f's ssei might be different.

Yes i live in Wisconsin, so i wonder why it feels like its losing power. I should just take it in i still have the 5 year 100,000 mile warranty but i just like to know what might be wrong before i take it in because they will screw you yea know...

4000 is all? wow.
I think he indicated 40000 miles Tim. :lol: Anyway, do you have any DTC's? Do you have access to a scanner that will monitor sensor readings, especially STFT & LTFT 02 & misfire readings. Do you have a boost gage, if so, what is it boosting? Any vacuum leaks? Have you checked the boost solenoid & valve operation? In addition, it may be time for a full trans service (fluid & filter). BTW, contrary to what the dealer said, firm shifts has nothing to do with the SC, that is BS!

I do not know much about cars haha i know the basics like oil change and some things inside the engine i could change my own alternator or fuel pump or steering pump. But that stuff i do not know anything about. I just know that it seams like it doesn't have the power it should have. I believe this car should have 286 hp. My girlfriends car is a bonneville and the power is right there as soon as you step on the gas. Same engine and its super charged also. I always put premium gas in it also. at least 92 octane.

Is your car still under warranty?

Hay man i seen this prob many times... Check fuel pressure. Had alot of problems with fuel pressure regulators in past causing same problems. Check it out sorry do not have specs at hand though.

what does the boost gauge say when you get on it? is it holding boost and running at the right PSI?

also...with 40K, has the car had a tune up just yet? fuel filter??

Lefty, yes he has warranty.

packerfanjc says, I should just take it in i still have the 5 year 100,000 mile warranty.

My mileage goes down in the winter, I usually get around 30 Mpg in the summer and in the winter it drops down to around 26 Mpg.

No, i have not changed the fuel filter, i think i was told that it does not have one? Doctorhardware, is your car a grandprix and is is super charged that you get 30 mpg? Yes my car still is under the 5 year 100,000 mile warranty. But i do not want to just take it in. I would like to know what might be going on before i take it in there. Dealerships i have found seam to be lazy. If they have to look into something in depth they won't they will just say they do not see anything wrong with it. I took this same car in for a rear shock making noise. My dealer told me the shock has nothing wrong with it. i went to a different dealer they told me that its probobly the stablizer bar, and that you would have to change it to notice its bad. It was already past the 3 year 36,000 warranty so i havent done it yet. The boost gauge always goes up, and you can feel it. But seriously the motor sounds like its working as hard as a car without a super charger.

you cant realyy tell how hard a car is working by sound alone. 3800SC motors are always going to be a little more noisy than 3800NA motors deu to the supercharger.

Guys just some advice but I would be careful comparing apples to oranges. The 2004 and up GPs with the Series III 3800 engine whether supercharged or not do not typically get as good fuel economy as the previous generation '97-'03. And the EPA ratings don't mean anything. There are too many variables on getting good fuel economy.

We have plenty of anecdotal data right on this forum if you check the old/archived posts on the issue about later generation GPs getting less than desirable fuel economy. :wink:

As suggested I would check the short and long terms fuel trims with a full function scan tool in addition to all the other basics like how you drive, tire pressure, quality of tires, grade/brand of gasoline, etc.

I know there is going to be some noise there as it is a 3800 motor..plus super charged. I can hear the super charger running as that. But i do not think the power is 280 some HP.....the tires i have on there are all terrain KUMHO tires.. they are kinda expensive but i think i need then rotated. Thanks for all the help...i will try to see if there is a fuel filter. Maybe change the air filter and tranny fluid. I have also heard the the break pads wear out fast. As mine are starting to get bad at 40000 WOW. As GM makes cheaper products..then they used to

I recall HP for the SIII 3800 SC engine was 260 engine hp stock. What brand Kumho tires and did you mean all season versus all terrain?

I don't think you will find a user replaceable external fuel filter. It has been incorporated into the gas tank at the fuel pump assembly. Not like the '97 - '03 GP models.

I don't think you will find a user replaceable external fuel filter. It has been incorporated into the gas tank at the fuel pump assembly. Not like the '97 - '03 GP models.

wow, didnt know that. to tell you the truth...I've never really worked on an '04+ GP. done brakes on an '06 but thats about it. kind of a sh*tty design huh?

wow, didnt know that. to tell you the truth...I've never really worked on an '04+ GP. done brakes on an '06 but thats about it. kind of a sh*tty design huh?

No big deal. Your advice is always good otherwise. :wink:

GM did the same to the GTO and G8. :twak: I'd rather have a fuel filter that I can replace. :grinyes:

260 is still a lot tho and i do not think i am getting that to be honest. Is there any way at the dealership they can check that? Yea all season haha all terrain i don't have an atv :D Anyways yea i thought that the fuel filter was in the gas tank. Well i will just change the air filter and maybe spark plugs. Does anyone know a good site to buy brake rotors from? For cheap i do not want the factory ones i want better quality.

No big deal. Your advice is always good otherwise. :wink:

GM did the same to the GTO and G8. :twak: I'd rather have a fuel filter that I can replace. :grinyes:

Can the fuel pump at least be replaced from the trunk in the 2004+ GP's? Or does the tank need to be dropped?

Can the fuel pump at least be replaced from the trunk in the 2004+ GP's? Or does the tank need to be dropped?

Still the same as far as I know Tim. The only major difference is there is no fuel return line going back to the gas tank and fuel pump assembly like on ours. The '04 and up have a pressure fuel supply system only.