1999 Grand AM Code P0300 | Replaced Many Parts

1999 Pontiac Grand AM GT 3.4L V6.

Computer codes- P0300.Repairs- Replaced spark plugs, catalytic converter, battery, all filters, all electronics.I'm having multiple cylinder misfires and am wondering what in the world to do. I've come across one cylinder misfire and fixed it no prob but I'm having multiple and I'm not used to working on Pontiacs. What can i do?

Answer: You could possibly have one or more fuel injector that are sticking or going bad. If you have a scanner, or can tell what cylinders are misfiring, it will help in diagnosing the problem. Since obviously the plugs are new, those should be alright if you're sure the gap isn't closed on one or more plugs or they aren't cracked at all. You might want to check the wires and replace them if they are original. Coils can also cause multiple misfires and be checked for spark to see if they are operational. Usually ignition modules don't fail on your vehicle, so that is the least likely cause. I'd go for an injector first, although not an easy repair. You could try cleaning the fuel injectors, but you would probably need to visit a shop to have it done properly. One other thing to check, if the car has ever had the rocker arms off, such as while replacing the intake gasket, it is possible the threads have come out causing that particular valve not to open resulting in a misfire. Usually it's a bit noisy if that's the problem, but something to check.

1996 Pontiac Grand Am 2.4.

Question: car shuts down when hot or damp ,i wait up to 1 hour and it starts right up again,but runs rough for a few seconds then it's OK for a time.

Answer: Sounds like you have a faulty crankshaft sensor. Those are problematic on the Quad 4 engines in your vehicle type. A scanner would help in diagnosis if you have one. When the car is acting up or dies out, you can watch cranking rpm on the scanner, and if the reading stays at zero, you know that you aren't getting a crank signal. Also, you might want to check the coil pack and ignition module. They can act weird at times depending on the circumstances. Any trouble codes that are stored would help in leading you in the right direction as well. Usually dampness or heat affects ignition, and sensor function if they are bad, so I would definitely start in that area.

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