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Pontiac Grand Prix Fuel System

dribs15dribs15 Posts: 6
edited March 19 in Pontiac
well my heavy foot city mpg is up to 13.2 at 1100miles-would love to end up getting 15+...maybe in time.

also, i travel on rte 295 in s. jersey same stretch every day when i go to work and few times i've tried cruise control at 80mph (b/c of the posts seen here), sometimes DOD has definitely kicked in b/c i'm getting at least the upper 20's and maybe higher (can't remember) mpg, while other times it's lower, but i've noticed more wind resistance.

chats1 sorry about your hum, but mine is not loud and goes off as soon as you turn the car on too...maybe it is onstar.


  • rayainswrayainsw Posts: 2,496
    “also, i travel on rte 295 in s. jersey same stretch every day when i go to work and few times i've tried cruise control at 80mph (b/c of the posts seen here), sometimes DOD has definitely kicked in b/c i'm getting at least the upper 20's and maybe higher (can't remember) mpg, while other times it's lower, but i've noticed more wind resistance.”

    In the interest of science (ahem) I tried an experiment this AM on the way in to work.

    Since the traffic was (much) lighter than usual, I was able to set the cruise at 80 for a few minutes. Twice.

    Although there is no “DoD On” indication like there is in the Impala SS, my observations are that even the slightest incline \ upslope (Interstate upslope on I85 just north of I285 and just south is likely less than 1%) will dramatically reduce the instant MPG – from 28 – 30 on level or (very) slight downslope to below 20 MPG.

    As always, YMMV.
    - Ray
    Wishing my every commute could be this light, traffic-wise . .
  • tjrgxptjrgxp Posts: 2
    Also drive 295. New GXP 2006. Have gotten 25 mpg on 295. Have averaged near 23 in a week with mixed hwy/city driving. Have gotten as low as 18 mpg also. Car is black and is very hot looking. Two problems so far - 1) Thermostat bypass hose on top of engine was gashed open by the pulley (maybe a poor factory installation). Dealer fixed and repositioned. Hose was hard to get. Came from lansing Michigan. Was without car for three days with onlt 1000 miles on engine. 2) No automatic dimming rearview mirror is a disappointment and a downgrade from my 1999 GTP. Owners manual says it is an option. Well, what model do they put it on, if not the GXP? No mention of that option in the book. Nevertheless, my GXP is all that they say it would be. Love it. Too bad GM is cheaping out without telling the buyer. Watch out for your bypass hose.
    Tjr GXP :shades:
  • bob97bob97 Posts: 16
    I also miss the auto-dimming feature – my guess is that it interfered with the microphone pickup for Onstar. But my biggest problem with the rearview mirror is how much of the front view it blocks.
  • The good news about the rear view mirror is that it takes up so much of the view that when I mount my GPS (Garmin Nuvi 350) under it, I hardly notice the difference. ;)
  • smallegansmallegan Posts: 10
    Does anyone know if there is a way to verify that your DOD is activating? I drive the GXP pretty hard and I am just wondering at what point it activates?

  • dblducedblduce Posts: 58

    I read that a good way to verify when the DOD turns on is to put your information display on 'Instant MPG'. That way, you can watch your actual miles per gallon usage as you drive. I have tried this on the highway. Normally it is around 19-24, but after a few minutes if the road stays level you can tell it has turned on because the MPG starts going up to around 30 or more. I think it has to be running at a constant speed for a set amount of time before it kicks on.
  • rmozolrmozol Posts: 124
    That's good to know. I always watch that screen, but probably not for long enough.
  • gxpjoeypgxpjoeyp Posts: 38
    I would like to know too,on the Impala ss and the monte carlo ss there is a dummy light that comes on the dash when it is running 4 or 8 cyl. why did gm put that light on those 2 models and not the gp gxp,after all they are the same engines.
  • rmozolrmozol Posts: 124
    I'm guessing because they made the GXP in 2005, and not the others, and didn't want to change the GXP's design.
  • I have a 2000 Grand Prix GT and have noticed a high pitched whining noise that increases at low speed accelerations. I've also noticed that when accelerating at low speeds, the engine drags/shutters.

    Not sure if these two are related or separate problems.
  • I had a similar problem with a high-pitched whining noise when accelerating and worse when turning. My power steering fluid was low. I had the dealer add fluid and the noise has stopped. Good luck.
  • my car is choking really bad when i floor it my car sounds like its dieing out and the rpms are jumping up and down and it kind of shakes a little its a 98 pontiac grand prix sc
  • I need a new MAF sensor. I was thinking with going with a Granatelli. Does anyone know any other performance brands that are good for a GTP?
  • I recently have been having a problem with my grand prix that no one can figure out. about a month ago i started up my grand prix and it stalled out after about 7 seconds, it kept doing this so I had it towed to a local service center. I was told it was my fuel injector and regulator. Both were replaced and the car started. I took my car home and about an hour later I started it up and it again stalled out after a couple of seconds. At this time I now had the car towed to a dealer who had it for two weeks. They told me that my fuse box was bad and they replaced it. They guaranteed me that this was the problem. $1400.00 dollars later I got my car back. I was able to drive it for two days with no issues. Again I got in my car to go to work and it started up for a couple of seconds and stalled. I was thinking there was an issue w/ my security system but the dealer said that was not it. Does anyone know what could be wrong with my car. I have had no problems with this car until now. My pocket book is getting slimmer everytime it is at the dealer. Any suggestions on what is wrong with it would be greatly appreciated.

    thanks !
  • I need desperate help!!! 12.2MPG (yea some people think they got it bad with (20MPG) It was at 11.0 MPG before everything I'ved replaced, heres the list.
    1.Rebuilt SuperCharger
    2.ACDelco SparkPlugs
    3.Wire Set (spark plug)
    4.oil change every 3K (oil filter too)
    5.New PCV Valve
    6.New O2 sensor (before catylic)
    7.New Fuel Filter
    8.K&N filter and intake

    Anyone out that can really help. with any Idea Please EMAIL ME at as you can see there has been alot of money invested and im not seeing any progress. 12.2mpg city / and 12.5mpg hwy. HELP!!! HELP!!! HELP!!!
  • Any ideas what the problem was? My 98 Grand Prix is in the shop at this very moment and the mechanics are stumped.
  • toolnuttoolnut Posts: 1
    Check the fuel pump resistor, a common issue on supercharged engines. Most likely it will run if you hold it floored, but a common issue.
  • jeff65jeff65 Posts: 1
    I just got my 200 GP GT back from the dealer after the same issue. It turned out to be the Theft Deterrent Module $560. They said their is no way around it. GM had a bulletin out that said the wires were prone to chafing. I hope this helps.
  • hey bud, well i dont know if this is much help but my buddie was having the same problem. next time this happens to you un hook your battery for about ten miutes then put back together and see if it still happens if this works them it has something to do with your security system . thats what happend to my buddy grand prix ( i know it sounds stupid buy hey its worth a try )
  • i just replaced the fuel pump and fuel filter in my 00 Grand Prix GT and it still sputters every once in a while when i drive it even does it when i drive down the highway it sputters any idea whats up? :cry:
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