Hello, I own a 1998 Grand Prix GTP. I've owned this car since new and have taken the best care possible with this car. The car has not given me any issues except for now. About a week ago it became hard to start when cold. This car typically starts right on ignition. Now, when it's cold, it cranks over for at least 2-3 seconds. What I've done so far is replaced the wires and spark plugs, thinking that maybe the wires (original) were the culprit. No go. Same issue. The car runs perfectly fine otherwise, however I've noticed quite higher fuel consumption. I'm slightly at a loss. I've done some researching on these forums but haven't really acquired a sense of what it could be. If anyone can provide some direction regarding what to check, that would be great. I'm suspecting a fuel related issue, however I'm unclear. Thanks in advance for any help.

How about the fuel filter? How old is it or when was it last replaced?

You can check fuel pressure at the front fuel rail Schrader valve located towards the supercharger snout. 48-55 psi. Low fuel pressure may cause a lean trim mode so the PCM will compensate by adding more fuel to the fuel injection system to compensate.

Also, remove the vacuum line at the fuel pressure regulator and check for raw fuel indicating a ruptured diaphragm. A flaky fuel pressure regulator may cause longer than normal starting but the fuel pressure check will test it. Check at fuel pump prime, at idle and with the vacuum line at the fuel pressure regulator on and off. Readings will vary as you do this.

I'll assume since you didn't mention it, that your check engine light is not on. If it's not, try unhooking the MAF and see if it starts easier. IF the CEL is on, pull the codes and post them.

If it's not, try unhooking the MAF and see if it starts easier. IF the CEL is on, pull the codes and post them.

Doesn't look like a MAF sensor issue to me. :grinno:

Cold, wet, road-salt laden winter air (op is in Canada) wreaks havoc on MAF sensors, that's why I suggested it as symptoms were kinda vague other than harder starting and higher fuel consumption. A fuel pressure issue usually causes drivability issues.

I'm betting your fuel pump is going out. Before you start the car, just turn the key to the "on" position. You should hear the fuel pump prime. After you do that for a few seconds try to start the car. My guess is that it will start up right away.

Cold, wet, road-salt laden winter air (op is in Canada) wreaks havoc on MAF sensors, that's why I suggested it as symptoms were kinda vague other than harder starting and higher fuel consumption. A fuel pressure issue usually causes drivability issues.

It could be possible of a bad MAF but unlikely based on the OP's symptoms as posted in which there appears to be no further driveability issues other than hard starting (2-3 seconds) not indicative of a bad MAF. Usually you will get excessively long over 5 second crank times and accompanying symptoms such as backfire, misfire, stallout and in many cases black smoke out the exhaust. Once started if it starts the idle will be very bad or erratic too.

I would concentrate on checking fuel pressure to make sure it is in specs and fuel filter as suggested and/or try to rule out the fuel pressure regulator which may cause the OP's symptoms.

Guys, thanks alot for the quick responses to this problem. First of all, to answer one poster's questions, the CEL is not on and has never come on. The car drives perfectly fine after started, but appears to be consuming considerably more fuel than it has in the past. Just changed the plugs and wires last night and it doesn't appear to have made a difference. The fuel filter was replaced about 40K Kms ago...or about 2 years ago, so I'm thinking it should be ok. However if required I will change it again. Not a big deal. Any further feedback would be very much appreciated. Thanks again.

Guys, I haven't received any further feedback on this. I haven't really tried anything else since my last post (i.e. disconnecting MAF sensor). However, I have purchased an OBD II PC based scan system and I'm wondering what I should be looking for. I'm not sure what the specs are on all the sensors in this car, such as MAF, CAT, etc. Therefore, I'm wondering whether anybody has some sort of list or maybe some specific sensors and values to look for in attempting to diagnose this problem. To recap, the car is starting hard (cold or 10 mins after turning off), turning the key to on, I hear the fuel pump, but it doesn't help the starting situation. Fuel consumption is very high, and the car does appear to not be as "peppy" after warmed up. During cold operation it starts hard but appears to drive normally, with the expected power. I've read in other forums, the potential for the catalytic to be a culprit, but I'm not sure how it would impact the hard starting issue, or whether the high fuel consumption and hard starting is even related. Any help on this would be very much appreciated. Thanks.

Welp, I unplugged the MAFS today and attempted to start and got the same result. Did a fuel pressure check and when I turn the key to on the fuel pressure jumps to about 50 psi and once the fuel pump cuts off the pressure drops down to about 5-10psi very quickly. I'm suspecting I'm dealing with a fuel pressure issue. Not sure what to do next...should I be investigating leaking injector or messed up FPR? Any help would be very much appreciated. Thanks.

What does the fuel pressure read at idle? Check with vacuum line disconnected and connected at the fuel pressure regulator. You will get two different readings in addition to the reading at fuel pump prime which you posted. FPR is a possibility depending on the readings. Post the results if possible.

Thanks for the reply....at key on only the reading is approximately 51 psi. But after fuel pump priming is complete, the pressure drops to about 5-10psi within about 4s. On startup, the fuel pressure runs about 43 psi with the FPR connected to the vacuum line, with the vacuum line off, fuel pressure jumps to about 51 psi. At this point, I've deducted that I have either a faulty fuel pump (I've done the fuel resistor bypass method by bending one of the pins on the fuel pump speed control relay), a leaking injector (haven't done a resistance check), or a faulty FPR. Any help on this would be much appreciated and all help provided thus far is very much appreciated. I'm boggled by this one. Thanks again.

Based on GM specs your fuel pressure regulator is borderline but I hate saying it is bad because it is expensive without being sure. The vacuum on and off FPR readings is too much.

The fuel pressure bleed down at prime in that time is abnormal. One thing you can do is remove it. Located at the front fuel rail towards the supercharger snout. One c-clip fastener and pull. Inspect it for overall condition, o-ring seals and clean. You did check the vacuum line for fuel contamination?

http://i5.photobucket.com/albums/y186/lizzywiz/fpr.jpg
FPR for L36 and L67 SII 3800 Engine

Thanks again BNaylor. I did check the vacuum line for fuel contamination and there was nothing there...not even the smell of it. So maybe I will take the FPR apart tonight and just check to see if a seal is gone or anything. I agree that the FP bleed off that quick after key on is not normal at all. Could this at all be a leaking Fuel Injector? Or even a bad fuel pump? Any tests I can do on either of those to rule them out? Thanks again for your help.

Based on what I see I would rule out the fuel pump to include control circuits and concentrate on the FPR first and fuel injectors next. Try running a bottle of Chevron Techron with a full tank of gas or you may need to have it done professionally or even DIY in which we have a DIY tech procedure posted someplace here for cleaning the injectors. The FPR is tied into the front and rear fuel rails and helps control the return line or return of fuel back to the gas tank at the fuel pump pod.

When it does start up do you notice any black smoke out the exhaust tailpipes or does it run rough initially?

Thanks again Bnaylor. I appreciate the help with this. First of all i would agree with ruling out the fuel pump, although the reason I'm focusing on it is because it is one of the pressure relief paths. Really I'm seeing only three paths here either the cylinder through fuel injector or fuel tank through FPR or fuel pump. When the car finally starts after the hard start it runs beautifully. I've had time where it started, then for about 1s or so it seems to want to stall but then immediately stabilizes and runs perfect. Fuel consumption is about 40% higher than normal which may or may not be related to this fuel pressure problem. Not sure. I will try and get some of the Chevron stuff or something comparable (I'm in Canada). I will also look at the DIY fuel injector cleaning procedure. The car has 135,000 kms on it so having the fuel injectors cleaned wouldn't be a bad thing to do just as PM. One thing to note too is that I have run 87 octane in this car for quite some time. Maybe that has something to do with it. Tonight I will also try cleaning the IAT and MAFS with some contact cleaner just as precautionary as well. Thanks again.

P.S. is the fuel pump on these vehicles accessible through the trunk or does the tank need to be dropped for that?

I can only recommend using 91 or better premium gas but I don't think the lower octane fuel is related to your problem.

For fuel pump pod access there is a cover with 7 nuts holding the plate right behind the rear passenger seat in the trunk. Easier if you have the rear passenger seat pass-through door. Set aside the trunk carpeting to see it. Good luck and let us know how it turns out.

It might be your Intake Manifold Gasket. I had mine replaced just resently and now it funs great get it checked before its too late

Well, everybody it definitely wasn't the FPR. Swapped it out and same thing with same rate of fuel pressure drop. I've just spent the hefty $400 and purchased a fuel module assembly. Will be swapping that out tonight and will post back the results. My first suspicion was fuel injectors, however once the car starts it runs perfectly fine. No stumbling or hesitation during the first few seconds of starting. Therefore I'm ruling out the fuel injector leak. The only other thing I can see here is fuel pump. There's nowhere else for fuel to go. Either back to the tank through the pump or FPR or into the cylinders through the fuel injector. I'm suspecting the check valve in the fuel sender module. Thanks guys.

Yes, I sort of suspected the check valve in the pump also.

I don't recall seeing it posted but what were the fuel pressure readings at ignition to ON only which is fuel pump prime? And after about 10 minutes to see if adequate fuel pressure is maintained for starting. The fuel pump is too expensive just to shotgun replace but hopefully it resolves your issue since you already purchased it.

Bob if i remember right, his readings at key on ongine off were 51, but dropped to 0 within a couple seconds after the fuel pump shut off.

I guess he shouldnt rule out a sticky injector, this would jive with the bad gas milage.

A problem like this is hard to diagnose without a very expensive fuel pressure guage.

Thanks for the heads up Tim. Too many posts to look at with the limited time I have. The way I look at it is if you are going to do DIY and do it right then diagnostics tool are a must such as an automotive fuel pressure tester and possibly fuel injection system service kits. My Actron gauge wasn't that expensive. I recall around $40 but invaluable especially when I have to adjust my Casper fuel pressure regulator and perform maintenance checks. Also, Actron tech support sent me new hoses and other fittings for free.

Now there are fuel pressure and return line adapters/fittings with turn off valves that you can get to properly troubleshoot fuel system supply problems. I believe the GM dealerships and other specialized auto shops have them where you can determine which direction to head. Simple test with the right tools. For example see below.


Testing for fuel injector or fuel rail leakage: Clamp or turn off the return line. If pressure falls below last known good psi reading, a fuel injector or the fuel rail is leaking. If pressure holds, it is most likely a bad fuel pump check valve.

Hey guys, just wanted to close the loop on this one. It was definitely the fuel pump. Popped it in tonight and all is good. Fuel pressure hits 51 psi and holds when priming is done. Sits at about 43 psi when running with FPR connected to vacuum and about 51 psi with FPR disconnected from vacuum. FPR is brand new as well. Thanks for all the help guys.

alright good. Glad to hear you got her running. How hard was the pump to change? Not so bad was it? The easy access to the pump was a selling point of the GP to me.

Thanks TBlake. It was not bad at all replacing the fuel module. The access cover just behind the middle swing out armrest made it a snap. The hardest part was putting the new module in because of the new o-ring, but touch of dish soap sure did help that out. Once I did that it went on very nicely. The car is mint now, back to the way it was supposed to be. Fuel mileage is back to normal, so I'm very happy. An expensive fix but i have my GTP back. Thanks to all for the suggestions and help. Very much appreciated.

Well, I think the fuel economy stabilization was definitely a mirage in the distance. Fuel economy is back to normal.... shitty. This car always driven around 12.0L/km (average between city and highway driving). It's burning 16.0 L/100 km right now. It's unreal. No SES light or anything indicating a problem. Not too sure what to look for. O2 sensors? PCV? Both? If anyone can just let me know what they think, that would be great. I'm planning on attaching a PC based OBD II scanner to it and logging vehicle data on a drive to work, either tomorrow or the next day and determine whether anything is acting screwy. When I hooked up a few weeks ago, I was getting readings but I don't know what the ideal specs are for all the sensors. Again, some further assistance would be much appreciated. Thanks again guys and sorry for the confusion.

Best thing to do is monitor the 02 sensor in real time with a scanner capable of doing that. Alternative with a DMM at the purple wire which is output see if the voltage varies from .1 volt to 1.0 volts.

Usual suspects for unexplained loss of gas mileage is the front 02 sensor, CAT convertor and even the thermostat just to name a few. Other factors are weather and type fuel being used. TCC lock/unlock in 4th - OD.

Thanks BNaylor...here's my plan : a) Scan car using PC based OBD II system and determine whether anything is out of the ordinary (MAFS, IAT, Coolant Temp, etc.). b) Clean IAT and MAFS using electrical contact cleaner. c) Replace PCV valve and Thermostat (these have never been done before). If required replace O2 sensors (would it be worth just replacing them both?). What is a good brand of O2 sensor? I've seen Walker, Bosch and Delphi online. Thanks again for the quick responses.

For 02 sensor I recommend staying with the AC Delco/Delphi AFS 109 (pre-cat) and AFS 123 (post CAT) for a '98 GTP. Replace both due to the age.

Hello, I own a 1998 Grand Prix GTP. I've owned this car since new and have taken the best care possible with this car. The car has not given me any issues except for now. About a week ago it became hard to start when cold. This car typically starts right on ignition. Now, when it's cold, it cranks over for at least 2-3 seconds. What I've done so far is replaced the wires and spark plugs, thinking that maybe the wires (original) were the culprit. No go. Same issue. The car runs perfectly fine otherwise, however I've noticed quite higher fuel consumption. I'm slightly at a loss. I've done some researching on these forums but haven't really acquired a sense of what it could be. If anyone can provide some direction regarding what to check, that would be great. I'm suspecting a fuel related issue, however I'm unclear. Thanks in advance for any help.
from previous problems wit my GTP i figured it was the check valve in the fuel pump assembly on mine. starts great now, basicly its a one way valve and its letting gas go back in the tank when it sits and when u start it cold it has 2 prime the fuel system, hit ur shrader valve after it sits awhile it should spray alittle if it bearly trickles that would be my guess

Having seen your issues, hate to mention yet another thing to check, but I have just overcome such issues with my lesabre and riviera. Turns out both had pinhole air leaks in the fuel lines. The holes were not big enough to leak much fuel or even cause a smell... I would check those next.