'04 Comp G, 95K, stock except for very minor suspension upgrades.


I just replaced my LIM a few weeks back, no problem. I drove the car for a couple days, and all was well. On about the fifth day of driving it after the LIM job, it wouldn't start well from sitting overnight (very long start....needed a little pedal action). After it started, it ran fine and restarted fine the rest of the day. On the way home at night (same day), the car ran a little rough (slight hesitation) at light to moderate throttle from a stop (i.e. in 1st gear).

The next day, it didn't start well again, and it only had about a quarter tank of gas, so I filled it up. No rough running at this point. Again, it's only the first cold start of the day that is problematic....all subsequent starts are fine.

After reading about starting issues on here, I decided that I would turn the key to ON twice before starting, to see if maybe it was a fuel pressue issue. Since doing this (several days now), it has always started up OK.

Today, on the way home from work, it again started the hesitating at light to medium throttle, especially from a stop in 1st gear. Looking at the gas gauge, again it has about 1/4 of a tank. So I stopped, filled it up, and the problem is gone.



Although there are, I'm sure, many possibilities here, I'm thinking that it seems like a fuel pressure issue. Mind you, I don't have gauge, so I've never measured the fuel pressure. However, these two issues (long start, hesitation with a low gas tank) seem to occur during some sort of low fuel pressure moment (starting after sitting for 12+ hours, low fuel in tank).

What things could cause this? Failing fuel pump, clogged fuel filter (it probably has never been changes, at least not since I've owned it), some sort of bad relay? Just a bad tank of gas that is still lingering? Bad fuel level sensor.....i.e. I'm almost out of gas and don't know it?

Your thoughts?

Thanks in advance.

i would do change the fuel filter sense you dont know if its ever been changed and if its still acts the same do a fuel pressure test good luck

Having similar issues myself turns out to be the fuel pump. Try this when its having a hard time starting have someone spray starter fluid into the intake and while they're doing that try to start the car if it almost sounds like uts turning over its a fuel issue and more then likely the fuel pump. Change the fuel filter to.

Sent from my Samsung Infuse

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Thanks for the advice. I'll do these simple things first before going after the fuel pump, although I tend to believe it is probably going bad.

Has anyone replaced the fuel pump on these 04+ GPs? How long of a job is it? Do you need a special tool to get the lock ring off the remove the pump, or can you do it with normal tools?

J 45722 Fuel Sender Lock Ring Wrench

This screams fuel pump. I had been having these issues for a long time and just replaced the fuel pump with a 255lph pump car runs great now.

Do you sometimes notice that when you go wide open the car will start off normal and then instantly drop 800 or so rpms and run like shit until you let off?

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2004 Grand Prix GTP
FWI | HP Tuner | 1.9 Rockers | Headers | 3.5 Pulley | 97-03 Control Arms w/GMPP sway bar|

No, when it is running OK at light throttle, it runs fine all around. Admittedly, I never floor it completely, but I'll take it up toward 5000 rpm pretty quickly without seeing any issues.

The only issues are long starts (which haven't happened since I've been "double-ON-ing" the ignition before cranking) and then the hesitation when the fuel tank is low, near 1/4 tank left.

I have a new fuel filter, and I bought a new fuel pump relay. I'm pretty sure neither of these are the problem, but the filter should be changed anyway and the relay was a few bucks, so why not?

Fuel pressure leak down when sitting for extended periods of time. Not really familiar with the fuel system on the returnless system's on the 04+ but it could be a check valve (which might be part of the pump, again, not sure) which is causing the system to completely depressurize when sitting and letting fuel run back into the tank and not stay in the line/rail. This also makes sense when you have low fuel in the tank. The little fuel isn't keeping enough pressure in the lines just by gravity as it does when the tank is more full.

Just spitballing ideas here.

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Dubs:00 VW GTI VR6, Low and Slow 91 VW GTI 8v, Shave the Bay!! 91 VW Cabriolet 8v, bitch Basket
GP's:04 GP GT, Past now G-Ma's Girlfriend's 97 GP GT, "Project Pink Power"

Admittedly, I don't know much about the fuel system workings, either. Apparently, the 97-03 has a pressure regulator under the hood that can go bad, but it is part of the pump on the 04+ (at least, that's what I gather from reading).

My best guess is that the pump is still working, but not really as well as it should. Hence, low pressure after sitting for a while, and low pressure when the tank is low (no added pressure from the weight of the fuel). Again, I haven't measured it, but I should (I'm slow moving on this, since keeping gas in the tank is giving me a temporary break from caring that much).

Well, this morning, the car exhibited different symptoms.

With only 1 turn of the key, the car started fine (and it's 29F outside). In fact, I haven't had a long start since I orginally posted this. Also, it essentially has a fuel tank of gas. I drove it for about 4-5 miles, and there were not any signs of any abnormal running behavior.

As I go to pull away from a lilght, the hestiation at light/medium throttle suddenly appears. At the next light, I put the car in N, then back to D. Pulling away from that light, the hesitation remains. I then proceeded toward work for about 10 miles on the interstate, and decided to get off at exit to check how the car responds to accelation from a full stop (having been driven and had a chance to warm up). From a stop at the exit ramp, the hesitation remains.

So I pulled into a gas station, shut the car down, and the restarted it less than 5 seconds later........hesitation gone. The car drives prfectly the remaining 20 miles to work.

What the he11 ? This is the first time the car has had the hesitation with a fuel tank of gas, and it's the first time that it has appeared in the middle of driving. All other times, it was there from first pulling away.


I'm less sure that it is a fuel pressure issue now, although I don't think it's ruled out either. When it had done this at other times, the fuel tank was on the low side, so I stopped and filled up, and the problem disappeared. Apparently, it was the stopping and restarting that made the problem go away, not the adding of gas.

To me, it just doesn't seem like it could be anything mechanical. I thought maybe that the hesitation could be the beginnings of a transmission failure, but it doesn't make any sense to me that shutting down and restarting the car would make any difference.

It fact, nothing mechanical or vacuum related would be cured by simply shutting the car off and on (would it?). The only thing that comes to mind is maybe the supercharger by-pass flap thingy that modulates boost. I suppose if it were somehow not functioning properly, you'd get weird acceleration. But again, what does stopping and restarting have to do with curing that?

My main fear is that the "hesitation" is really some transmission slippage, but in my mind I just don't see how turning the car off and on would in any way make that problem go away if it were a transmission mechanical problem.

It seems to me that it is likely to be something electrical. Maybe a sensor, or maybe still a fuel pressure issue (since the fuel system is electrical). Besides the fuel issue (which I still haven't investigated well enough), what typical sensors fail? The MAF is the only one I'm really familiar with. The car has thrown no codes, so what ever it is, it isn't speaking up.

I don't know if any of this brings up any other ideas (or just confirms the original idea of fuel pressure), but your opinions are all greatly appreciated, even if it you just say "it's still the #@$@ fuel pump".

-- Fri Nov 18, 2011 6:48 pm --

I got around to getting a fuel pressure gauge. I'm getting 50 psi in the ON,pre-ignition state and about 58-60 psi running. I did replace the fuel pump relay before I tested the pressure (I bought the relay because it was cheap and I was ordering parts anyway). I probably should put the old relay back in an re-test.....that'll have to wait until tomorrow (it's dark and I'm hungry), when I'll also change the fuel filter.

Is it possible that the pressure could read OK on an occasion, and then be way off on a different occasion?????

I did notice something that I've never noticed before. When you move the key to ON, you can hear a faint, high pitched buzz from the throttle body, followed by a "clack" when it opens slightly. I thought it was a little weird (never) having heard the noise before, so I checked my wife's 04 GT.....sure enough, same noise. I can't believe I've never noticed that before, it's actually very conspicuous. I thought I was maybe onto something, like the TB malfunctioning, so hearing the noise on the 2nd car actually was a bit of a bummer.

Well, I was unsucessful at changing the fuel filter. The old one's threading is rusted on so badly to the fuel line that I couldn't break it lose. Suffice to say, I'm sure it hasn't been changed, seeing as how corroded on it is.

I've been measuring the fuel pressure here and there, both with the old relay and new relay installed, and it seems to be OK: ~ 50-52 psi with the key in ON and about 58-60 psi running. That being said, the car has been acting normally during these measurements, so I'm not sure that it is very informative. I'm going to leave the gauge attached to the fuel rail. Take it out intermittently, and in the event that the hesitation returns, I'll pull over and check the pressure to see if there's a change.

Just to clarify this for future reference, the check valve for the returnless is in the fuel pump. Derek and I are working on a check valve for my car now that I have the 255lph pump from the ford gt since it's not in the pump. I'll probably do a writeup on it if I get the chance.

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2004 Grand Prix GTP
FWI | HP Tuner | 1.9 Rockers | Headers | 3.5 Pulley | 97-03 Control Arms w/GMPP sway bar|

Nice, so I did guess right.

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Dubs:00 VW GTI VR6, Low and Slow 91 VW GTI 8v, Shave the Bay!! 91 VW Cabriolet 8v, bitch Basket
GP's:04 GP GT, Past now G-Ma's Girlfriend's 97 GP GT, "Project Pink Power"

An update on this:


Since I last posted (about a week), I've not had any troubles. Neither the long start or the hesitation have reappeared, and the fuel pressure has been normal at every start up and during running.

I talked with my brother-in-law this weekend, who is an electrical engineer for a car manufacturer. He didn't think that the relay had anything to do with it, because it wouldn't intermittently work according to him. He suggested that since I had the battery disconnected while replacing the LIM weeks ago, the the ECM might not have properly "re-learned". Other than that, he said it sounded like a bad sensor somewhere.



Update to the update: It's been two weeks now, and the problem still hasn't resurfaced. I'm guessing it was some ECM wackiness since I had the battery unplugged for the LIM job. Either that, or the fuel pump relay.

For the first time in nearly three weeks, the hesitation returned. I immediately pulled over, left the car running, and checked the fuel pressure (gauge left attached to fuel rail). The fuel pressure checked out OK, 58-60 psi.

So, that rules out the fuel pump relay that I replaced.

Like before, I shut the car down, fired it back up immediately, and the problem was gone. It has to be a computer/sensor glitch.

does it happen only on cold as balls days or just in general? sorry if this has been asked already

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BRAP BRAP BRAP nuff said

I seems to be independent of outside temperature. It has happened on mild days and cold days, but there are plenty of cold mornings when it has been just fine.

when was the last time you changed your plugs

^^I see spark plugs are your "topic o'the week." This doesn't sound like a spark issue IMO.

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Dubs:00 VW GTI VR6, Low and Slow 91 VW GTI 8v, Shave the Bay!! 91 VW Cabriolet 8v, bitch Basket
GP's:04 GP GT, Past now G-Ma's Girlfriend's 97 GP GT, "Project Pink Power"

well seeing as how i had the same issue before i did a tune up, and now its gone, all im saying is how much would it be to throw copper core in to rule it out like i did $2 a pop not bad, isn't that what you post over the forums matt to start from the cheapest and work your way up

Plugs were changed about 5K miles ago with OEM ACDelco plugs.

Coming from the guy who wanted (or did I can't remember) to buy all new injectors becuase you thought your's were noisy Just busting your balls by the way. Nothing personal.
The main time that spark issues are intermittent (since the problem is intermittent in this case) is when's its raining out or high humidity.

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Dubs:00 VW GTI VR6, Low and Slow 91 VW GTI 8v, Shave the Bay!! 91 VW Cabriolet 8v, bitch Basket
GP's:04 GP GT, Past now G-Ma's Girlfriend's 97 GP GT, "Project Pink Power"

I recall hearing about a certain STi driver doing the same thing. haha and i believe you were in on that

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DIY intake-HV3-3" catless dp-180 tsat-DIY shift kit-murphy custom tune

Too soon too soon

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Dubs:00 VW GTI VR6, Low and Slow 91 VW GTI 8v, Shave the Bay!! 91 VW Cabriolet 8v, bitch Basket
GP's:04 GP GT, Past now G-Ma's Girlfriend's 97 GP GT, "Project Pink Power"

I do what i can

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DIY intake-HV3-3" catless dp-180 tsat-DIY shift kit-murphy custom tune