Question'01 Pontiac Grand Prix, 3.8 engine, 6 cyl Front Wheel Drive Automatic 125000 miles (This car has a remote starter and a car alarm).
Car was always being taken care of - preventive maintenance and etc. At about the 3rd year I owned this car, I began having the following issue: when accelerating uphill and/or with a heavier load, at about 50-60MPH the car would vibrate heavily (the RPM gauge would follow the vibrations). It was still under warranty I took it to the dealership - they produced the problem but they could not find anything wrong that would cause it. I took it to another independent repair shop, they produced the problem, but told me that I could just push the gas pedal down even more and I would (pick-up speed and) lose the vibration altogether... My father has a '00 Impala LS (very similar to my Pontiac GrandPrix GT) and he has the very "same" issue. I spoke to a technician at GM headquarters about it, he claims that they have no knowledge of something like this - and could not help me in any way...
Recently I was driving the car full of people (heavy load) and a steep uphill highway, when I tried to push the gas pedal it sort of gave me an empty roar - as if I was driving in neutral... I drove it in to a local mechanic they ran it thru a computerized check and it came back with the following codes: P0131, P0300 & P0404. They diagnosed it and reported that they found a hole in the upper plenum. They replaced the "Upper Intake Manifold", did a complete tune-up (spark plugs & wires, fuel filter & air filter), they also claimed that the fuel pump is bad which is plugging the Catalytic Converter, they replaced both (the Catalytic converter used is not a Delphi part).
It ran fine but I had difficult starting it in the morning or when not used for long period of time (sometimes so bad, that I lost power as soon as I stopped pushing the gas pedal - in park, drive and neutral), I took it back to them - they claimed that the Fuel Pump is defective and they changed it for me.
Now... The starting issue is better than it was, but I still have a problem starting it in the morning and when not used a period of time - I have to raise the engine (pushing the gas pedal) at the time of starting or it will just not start.
When I left the mechanic the last time they told me that if this will not do it, it might be the fuel injectors...
I was told any of the following: Fuel Pressure Regulator problem, to check the crank sensor, check and clean the throttle body, check clean idle air control valve and check for vacuum leaks, change the distributor (or coil packs). Another one I got was: I'd be lookin' at the fuel pressure... if it hangs steady at shutdown we'll look in a different direction for the problem.
I just put in about $2,200, and I hate to throw good money after bad money. Is there anything else you can suggest?
AnswerHi Dave:
I would look at a fuel pressure regulator or a leaking injector. If it starts hard 1 of 2 things is happening. The engine is loosing it's fule pressure prime. And if the pressure is leaking down into the engine then that would cause the hard start. If the injetor are leaking or the regulator is leakin it will run RICH and start hard. You need to have a fule pressure gauge put on the enegein and let it sit to see if the pressure drops off fast. If so it's either leaking into the engine or back into the gas tank. either way that will cause a hard start especially if it's a hot soak meaning you drive it till hot then say go into a store and come back out in 20 minutes it will start really hard. Once you find out where the pressure prime is leaking it' just a matter of finding wich component is causing the problem. Good luck :)
