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John, GM FACTORY CERTIFIED TECHNICIAN
Category: Pontiac
Satisfied Customers: 9176
Experience:  ASE A1-A8 w/L1 GM master technician.Factory certified/40 years experience
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2001 Pontiac Bonneville SE: cyl..acceleration..rough idling..EGR valve

Resolved Question:

I have a 2001 Pontiac Bonneville SE - 3.8 liter - 6 cyl with 132,000 miles. I started getting a P0300 code and then had a problem with poor acceleration and rough idling - basically the car was not drivable. I have replaced the plugs, wires, fuel injectors, coil packs, EGR valve and now the catalytic converter because it was plugged. The car is running better but it still has a misfire that will intermittently throw a P0300 code. My mechanic scoped it and showed me that it was misfiring on cylinder 1 when it was cold and then on cylinder 6 as it warmed up. He believes that I have a flat spot on the cam lobes but I am skeptical and I think he is guessing because we are almost out of things to replace. Could I be having a problem with the camshaft position sensor magnet or the mass air flow sensor. If not any other ideas?
Submitted: 4 years ago.
Category: Pontiac
Expert:  John replied 4 years ago.

HelloCustomer

Were all 6 fuel injectors replaced with new ones ?

Customer: replied 4 years ago.
Yes they were
Expert:  John replied 4 years ago.
I have had a problem like this before ,by that I mean a missfire only when cold & it was injector problem.I know you have done a lot of work on this vehicle & you most likely just want it to be right.I suggest removing the fuel rail (injectors will come out with it).This particular engine it is not a big job to do this.Clean out the fuel (flush with fuel mixed with to GM top engine cleaner.Remove #1 & #^ fuel injector,lay on bench.Remove any 2 of the other 4 injectors & install #1 & # XXXXX in their place,then install other 2 injectors& reinstall fuel rail.Clear codes & drive for a couple of days.I suggest a highway drive to clean out exhaust.This eliminate the possibility of an injector failure.Inspect all injector wiring harnesses & terminals for proper contact.
Customer: replied 4 years ago.
I don't want to mislead you. After all of the work was done, the car ran much better, but the misfire ws still happening when the engine was cold and when it was warmed up as well. The P0300 code didn't show up today until I had been driving about 15 minutes but it idles rough and accleration is OK but not what it had been before this problem showed up. I agree, pulling the fuel rail off is not a big deal and I can try that but I won't be able to get to it until next weekend. Any other thoughts on the position sensor or the mass air flow sensor. Also, do you put any credibility to the camshaft lob flat spot?
Expert:  John replied 4 years ago.

The cam sensor is used by the computer for injection control on all cylinders.The MAF is used for fuel delivery for all cylinders.i do not believe either of these 2 parts are your problem.

If the cam lobe was flat it would be flat on a cold or hot motor.& when this happens a cylinder power goes down & does not come back no matter what.I have seen a broken valve spring cause a intermitten missfire ,but usually only on one cylinder.

John, GM FACTORY CERTIFIED TECHNICIAN
Category: Pontiac
Satisfied Customers: 9176
Experience: ASE A1-A8 w/L1 GM master technician.Factory certified/40 years experience
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