98 Grand Prix - Hard Starting and Higher Than Normal Fuel Consumption

[FCPorto]

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.

[BNaylor]

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.

[richtazz]

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.

[BNaylor]

Originally Posted by richtazz

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.

[richtazz]

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.

[GTPpower]

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.

[BNaylor]

Originally Posted by richtazz

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.

[FCPorto]

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.

[FCPorto]

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.

[FCPorto]

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.

[BNaylor]

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.

[FCPorto]

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.

[BNaylor]

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?


FPR for L36 and L67 SII 3800 Engine

[FCPorto]

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.

[BNaylor]

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?