1998 Gd Prix sputters and stalls when engine warm

**jmickevi** · 08-31-2009

Hello all!

I have a 1998 Grand Prix GT with 3.8L non-supercharged engine. 270,000 miles on the car and 160,000 miles on the engine. I replaced the engine 2 or 3 years ago and have had no problems with it until now.

I was driving down the road when the car just quit. Could not get it to start so had it towed home.

Almost seemed like a fuel supply problem. I tested fuel pressure and when I turn on the key, pressure jumps right up to 50 psi. However, after two seconds, the pressure drops.

When the car sits for a while (a day or two) I can start it up and it runs for about 10 minutes. Then, the engine starts sputtering for a few seconds (5 seconds or less) then dies. Then, attempts to start the car are unsuccessful. If I hold the pedal to the floor, it helps, but only for a couple of seconds before it stalls again. Fuel pressure is good (42 or 43 psi) while the engine is running until it stalls, and actually for a couple of seconds after the engine stalls. After the engine is stalled for a couple of seconds, the pressure drops again.

Initial codes indicated a bad throttle position sensor. I replaced that and it made no difference.

I tried to determine what is causing the fuel pressure drop after the key is on for two seconds. I replaced the fuel injector pressure regulator, no help. I pulled the fuel injectors our while still attached to the fuel rail to see if I had a fuel injector which was leaking, but did not see any leeks.

Also, after replacing the throttle position sensor, there have been no codes.

Also, when the engine stumbles after 10 minutes or so, when I get the engine to run, there is a heck of a nasty smell coming from the exhaust. Definitely not burning the gas properly.

The way it runs OK for 10 minutes or so then starts sputtering for only a few seconds… it almost seems like some sort of a sensor which has gone bad, but no codes are presented. However, the OBD reader does show 4 monitors in a status of READY and 4 monitors in a status of INC. I don’t know what the monitor status of INC means, but the 4 monitors in the INC status are: MISFIRE, FUEL, COMP, and 02 HTR.

I was going to replace the fuel filter because it is such an inexpensive piece but have not done it yet. Having problems loosening the nut on the “non-quick-disconnect” end of the fuel filter – it seems to be rusted on and I am afraid of twisting and breaking the fuel line if I apply too much pressure. I have been hosing it down with WD-40 for a couple of days but it still has not broken lose yet.

Anybody have any ideas where I should look next to figure out what is going on?

Thanks!

John.

**Liquifire** · 09-01-2009

did you check your fuel pump relay? the real question is why does the fuel supply stop?-Is it some other sensor telling the pcm to cut it off or is it the pump and/or relay? Could also be MAF, IAC or others.......hopefully this gives you somewhat of a place to start.

**BillBoost37** · 09-01-2009

You say the fuel pressure tests good and then stays constant while running, right? Ok, not a fuel supply issue.

Is the smoke coming out your tailpipe white and have you checked the coolant level lately? If not, please do so. Doubt it's your issue, let's get it out of the way though.

**jmickevi** · 09-06-2009

Thanks for the replys Liquifire and BillBoost37. Was not ignoring you, I only have time to work on this on the weekends. When the car sputters and stalls, the smoke out the tailpipe is black rather than white, so I don't think it is coolant leaking into the combustion chamber. I did not check the fuel pump relay - I will do that today.

Anybody think it could be a valve problem which is causing it to sputter and stop after it is warmed up? I would not think so because if it was a valve problem, I don't think it would run fine for 5 or 10 minutes and then just stop so abruptly if it was a valve problem. As long as I have time today, I will probably run a compression test on it to see what that looks like.

Thanks again for your replies!

John.

**Liquifire** · 09-06-2009

From the way you describe it, I would guess that it is not a valve issue. If you had a bad valve, it should happen at all times when the motor is running. It could also be the MAF or the IAC as well....please check oil and coolant for looking normal and proper levels(this should be normal, but dont want to overlook anything before digging deeper.

**jmickevi** · 09-23-2009

Hi all. Finally got this one figured out and decided to post what I found.

There were two major problems.

First, I replaced the MAF sensor, but that in and of itself did not take care of the problem.

Second, I found that a mouse (I assume it was a mouse) had chewed on some wires and stripped the insulation off the bundle of wires which are located below the air cleaner housing on the driver side of the car. Sorry but I am not sure what this "bundle of wires" is called. Some of the wires were bare and touching one another.

The combination of repairing the wires and replacing the MAF sensor seems to have taken care of the problem. I let the car run for about an hour on two different occasions. Decided to take it down the road. Have only put about 10 miles on it, but things appear to be working correctly.

The fuel system still does not hold pressure when the fuel pump is not running, but while the car is running, all appears to be OK. I will need to address this next because there are 270,000 miles on the care and the fuel pump has never been replaced.

Let me ask another quick question or two if I may.

Is this model of Grand Prix (1998 GT, four door, 3.8L non-superchared engine) one of the "lucky models" which allows access to the fuel pump thru the trunk, or will I need to remove the gas tank to replace the fuel pump?

Thanks again for all of your replies. You have all been very helpful and I will keep an eye on this forum and offer assistance whenever I can.

John.

**tylerbinski** · 09-23-2009

fixed yet?

Take a look here.. I had same issue: (i hope its gone as of last night)

ClubGP Message Forum troubleshooting

--- um... test your crank sensor by letting your car heat up and sputter, then spray freeze spray (air duster upsideown) onto your crank sensor through the passenger side fender of the car (right by the oil filter) - open the flap..

if your car starts and runs good.. you know its the sensor..

Can also test the cam sensor this way, i heard it cause a similar issue.

..... does your tach bounce when its cutting out under load?

**David F** · 03-14-2010

My car is the exact opposite!!! When I go to start it up, it stalls! If I have had it running for a while, it will start right up. A person at an auto parts store told me it could be the fuel pressure regulator. He told me to test it by turning the key on....wait 5 sec.....turn the key off.....turn back on....wait 5 sec. Then turn over the ignition. Well that worked a few times and now I have to sit and give it some gas. Once it warms up its fine, idles fine runs fine and it goes! Anyone have a clue?

**Liquifire** · 03-15-2010

check your IAC ....see if it is working properly

**David F** · 03-16-2010

IAC?

**David F** · 03-16-2010

Idls Air Control Valave? Where is it? Is it something that I replace myself? Or is it something that needs to be cleaned? Don't know too much about this?

**icolex1** · 03-16-2010

IAC can be cleaned, in my "02 it sits on top of the intake manifold has one plug with 2 wires on top should be 2-3 bolts to remove it -can't remember. once off you'll see carbon deposits on the bottom -you can spray carb cleaner in it -be careful -I think it's expensive! Don't stick a screw driver in it to remove the carbon deposits (if they're heavy) I think it works like a thermostat for exhaust
good luck

**Liquifire** · 03-17-2010

yes, the idle air control.....if when idling, you can have your car stay running by keeping your foot on the gas, but when you remove it, the car dies there is a very good chance it is the IAC....in your case I don't know how likely it is that the IAC is functioning properly but it never hurts to clean it out and see. On my vehicle it is located on the throttle body, directly behind the MAF sensor and directly above another sensor. It is located more on the side of the TB, but the upper of the two sensors. Well, first clean it...they can break, but more likely get dirty or gummed up and the spring/pintle setup don't work properly. Clean it and see if it helps(replace it if you see something broken obviously)

**03GPScottyd** · 03-17-2010

My wifes' car would start and run but then as she was driving down the street the damn thing would die on her. Then she would start it up again and could drive for a while till it did the same thing. Our problem was the crankshaft posisiton sensor. It tells the system that the engine is running and that controls your RPMs. When it starts to go bad it stops sending this info so the car thinks that the engine is off so it shuts off the fuel pump.
So even though we were doing 65 on the expressway the car thought the engine was off and shut down the fuel pump on us. Kindof a pain to put in neutral and restart on the expressway but it would start back up instantly. It cost me $25 for the sensor, 18 for the shop lift at Ft Knox and 2 hours trying to put together a working puller set because you can't use a universal puller on our cars.

Crankshaft-position-sensor-replacement

**David F** · 03-17-2010

The strangest thing happen yesterday! Of course my car wouldn't stay running when I left work yesterday (unless I held the gas pedal down). But on my way home (I commute 30 mi. each way) I really opened it up and upon my arrival home my car was running good. I opened the hood and started to look around for loose wires or anything out of the ordinary (meanwhile the car was idling fine). I did however notice that my coolant overflow was low. I added a little bit of H2O to it and closed the hood. This morning I started up my car and had no problems. I let it sit for a few hours and went and tried to start it and it fired up no problem again!!! Do you think by me just nailing it on the way home cleaned something out of there or did the water have something to do with it?

**Liquifire** · 03-18-2010

I don't see how the water would have had anything to do with it. Maybe you had some buildup that you cleaned out with running it hotter, but I wouldnt be surprised to see your issue come back at any time either.

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