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Pontiac Repair/1998 pontiac gran prix supercharged

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Question
the car runs rough and misses especially under load. Scan tool codes were 0171 & 0306.(lean mixture & #6 cyl. misfire). I replaced#6 plug and coil.I also replaced the fuel pump, filter ,and pressure regulater.Static fuel pressure is 42# when I cycle the fuel pump without running the engine.According to the shop manual it should be between 48 & 55 psi. The pressure was the same with the old fuel pump. The pressure will go to 50# when I cycle the pump but drops down to 42# in a few seconds and stays there.What could be the problem ?

Answer
Hi jerry:

That pressure drop is normalonce the engine is running the vacuum on the pressure regulator drop the line pressure down. if you fixed the misfire and your just chasing the 171 code I would look for a vacuum leak there is a plasti hose that runs under the nose of the super charger the port then splits the line off usually that port cracks and there is a vacuum leak there or the gasket between the super charger and the intake manifold is sucked in and cuaing a lean condition there. with the engine running spray some carb cleaner under the nose of the super charger and see if the engine idle changes if it does you found the issue and then it's one or the other for the vacuum leak. good luck and happy holidays. :-)

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Todd Puccio

Expertise

General auto repair,electrical issues,driveability issues,anti-lock brakes,SIR systems,HVAC,engine performance,Gm specific. I have worked at my current dealership since the 1990 model year anything much older than that I have limited exposure to. I do not have very much transmission experience so those question you may want to ask of another expert. When you send me a question let me know the exact make/model/engine and year for the car or suv you have it makes it easier to answer the questions that way. If your happy with the answer I gave you please feel free to Donate. This is a free service to you and I am not compensated at all by this web site. I have 22 years of experience to share with you and my knowledge wasn't free to me. I had to pay for my education.

Experience

Experience in the area: I have been a technician in GM dealerships for over 22 years and I am a ASE master technician. I work at a Buick and GMC truck store Previously I worked at a Pontiac GMC store for 18 years. I Served a a lead technician when dealership was on a team system. I just recently moved to a Buick,Hummer,Saab Store when my franchise was purchased by this dealership. Organizations: ASE master technician

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ASE

Education/Credentials
Education/Credentials:High school diploma,2 year vocational school degree 2 year college degree. Associates degree in applied sciences (auto technology)Awards and Honors: GMC master technician

Awards and Honors
Master GMC truck technician Master ASE technician in 9 categories

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