QuestionQUESTION: 1998 Pontiac Grand Prix GT. 195,000 original miles. Several months ago, engine started idling rough but service engine light never came on. Last week service engine light came on. Shortly after, engine would stall at lower RPM's and tried stalling between gear shifts. After engine stalled (shut off), traction control switch would also light up indicating traction control has been turned off. After re-starting engine the traction control switch is not lit up, assuming traction control is turned back on. I had Autozone read engine code. Code is P0171. Trying the cheapest route first, I tested and cleaned MAF sensor. Sensor tested good and cleaning did not fix problem. During testing of MAF sensor, I noticed engine sputtering or misfiring when RPM's reached 4,000. I also noticed it at around 1,500 RPM's when I slowly increased RPM's. I can also hear a rattling/vibrating noise coming from top of motor near alternator at around 1,500 RPM's. At first I thought it was coming from alternator, but it seems to be coming from around the pressure sensor. I have not checked fuel pressure yet or checked vacuum hose from pressure regulator for any gas leaks. I am not sure where regulator is and don't know how to check fuel pressure. Any advice would be much appreciated on what the problem may be and what I should do next. I'm trying to avoid wasting any money by just throwing parts at the car.
ANSWER: Hi Rob:
what V6 is in this a super charged engine or non super charged? the most likley cause would be a fuel pressure issue or a restricted fuel filter or dirty injectors. you will need to check for fuel pressure. as far as injetors dirty you can try a product called Chevron Techron fuel system cleaner it worsk better then any injector cleaner I have seen. If this is a super charged engine there is Vacuum leak issues ubder the super charger and there is a vacuum line uner the nose of the super charger that leaks as well. Although usually a vacumm leak will give you an elevated engine spped at idle. That is where I would start looking.
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QUESTION: At this point, I have not checked fuel pressure yet. I am answering your question about which engine I have. It's the 3.8L "k" (non-supercharged). Just letting you know, in case you may have anything else to tell me. I will let you know what I find as soon as I can get back to the car.
ANSWER: No not much more to add with that engine. With that kind of milage on it though it can be just about anything. Another thing to check is all the engine grounds for the computer. they are on the engine to transmission mounting bolts towards the front of the car and I belive one on the back side of the engine by the power steering pump. With out the aid of a true scan tool it's a guessing game other then what I mentioned to you already.
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QUESTION: I check vacuum hose connected to fuel pressure regulator and saw no gas or smelled any gas after running engine. I replaced fuel filter just to be sure. I tested fuel pump fuse and relay, they tested good. As far as I can tell, I have good ground connections. Then I checked the fuel pressure. KOEO I get about 52 psi at first, then after couple of seconds I hear a click sound (I assume its the fuel pump relay) then psi drops to 47/48 psi. It will hold at 47/48 psi for a little while then very slowly starts to drop. With engine running I get about 43 psi at idle and under acceleration I get about 48 psi. At this point, I am fighting the temptation to buy a new fuel pump and fuel pressure regulator, because I am not 100% sure they are the problem yet. Based on this information, do you have any other thoughts or conclusive answers?
AnswerI think your at a dead end here. With out the aid of a scan tool you hands are tied. You need to see what the engine data sensors are doing when this goes lean and sets the code. I would not thrown an more parts at this! the fule pressures you noted are right on the money. one more thing to check here is is this ever had a PCV valve changed make sure #1 it's a factory valve and that the O=ring is still in place under the valve. Other then that there is not much more you can do.
