Pontiac Repair: Surging Engine, chevron techron fuel system, ac delco spark plugs

Question
QUESTION: Hey Todd,
My 2002 Grand Prix GT 3.8L has developed a pulsating surge that occurs when under a steady heavy load (when climbing a long hill in high gear, for example).  It's not severe surge.  The tach fluctuates about 150 RPM.  If you kick the tranmission down a gear the pulsation stops.  Don't know if it's ignition or fuel delivery.  I replaced the plugs and wires with no improvement.  Any idea what else to check before I bring it in?   Thanks agian.

ANSWER: Hi Colin:

I would look at possbaly a dirty mass air flow sensor or a plugged fuel filter.use only a good brand of 87 octane fuel. You can try a couple of can of a product called Chevron Techron fuel system treatment if you have a dirty or restricted injetor(s) that product works great. I would dobt it is an ignition issue if it were it would do it under a heavy load. Did you replace the spark plugs with AC Delco spark plugs only. That is where I would start looking at a fuel deliuvery issue first and foremost.

Good luck :)


---------- FOLLOW-UP ----------

QUESTION: Hey Todd,
No luck with your suggestions.  The MAF looks clean and the injector cleaner did not help.  Fuel pressure is good and constant during a test drive.  I suppose the MAF may still be at fault.  Will unplugging the unit during a test drive be a definitive test for the MAF.  A OEM unit is $590 and a Delco remanufactured unit is $430 with exchange, so there's alot riding on a proper diagnosis.  ALSO, is there anything else that could cause this surging or pulsation under a heavy and steady load.  It occurs when climbing a long hill in low gear at 1800 to 2100 RPM.

Answer
Here is a nother thing to try when it doing it hold the gas pedal steady while gently applying the brake pedal just enough so it would turn on the brake lampp but not enoughto really slow down the car that will disengauge the torque converter cluth in the tranmisssion If that is slipping that COULD cause a stange sensation like you have stated here. If that makes no difference and I would look back at the engine running issue. There really is no good way to test a MAF sesnor BUT if you drive it unplugged the engine computer runs off calsulation called speed density and it usses other input like the tp/map and coolant temp along with engine speed to "calculate" fuel delivery. The MAF sensor fine tunes the fuel delivery that speed density does anyways. The MAF can actaully calculate the exact amount of air entering the engine and then the fuel delivery is bassed off that. It's a critical input to say the least. drive it and see what happens. It will hesitate from a stop but see how it runs at the same sppeds and loads you experince the issue at. If it run fine then It's a real good call that the MAF sensor is bad. If you go that route go with ONLY A AC DELCO sensor go with the reman unit. OR try a junk yard and get one off an engine from the same year and engine. Good luck :)