1997 Chevrolet Cavalier

It's a performance problem.
The code p0300 means :cylinder misfire detected (random).
Begin with the easy checks first.
Check base ignition timing;a timing that is retarded by 8 1/2 degrees indicate the valve timing belt has jumped one teeth.
Next, check fuel pressure, low pressure can indicate a worn regulator, faulty fuel pump, you did replace fuel filter allready, or damage fuel line.
Now you can do the compression test.
Start with the dry compression, if that fail then proceed with the wet compression test.
Come back here with the result so we can find out what is wrong with it.

The code p0300 means :cylinder MISFIRE detected (random).
You said your engine runs rough.
If the rings or valves are not seated and allow compression to leak pass them. Power to push the piston down is loss. In addition, the ability to compress the air/fuel mixture properly is also lost. If one cylinder has loss of compression, there will be a complain of a " MISS".
The result will be loss of power, poor fuel economy.
__________________

Correct valve timing is importance for engine performance, and I have explained that allready. If the timing jumped only one tooth.
Check also for plugged or restricted exhaust system, faulty coil,
if you fail to see the relevance, you can do what you feel if good to get your car running.

Good luck

Hi Steve,
If you are not familiar with the location of the powertrain control module (computer), it is in the passenger wheel well area in front of the wheel. When you find it, you need to first get a good look at the connector before touching it so you know how it is positioned. Then see if it is tight. Also get a good look at the computer itself, especially the seam around it. These were a problem for water intrusion and especially problematic in the "road salt regions".

GM offers a protector that should be installed for future problems ( I'll send you the list of cars that qualify). The bad part is, they don't cover the computer. I don't know that this is your particular problem, but I v'e seen this happen on others like yours.

There is one other suggestion that may help. The intake valves can get a carbon build up, doing a variety of mis-deeds. If there is a significant build up, it can impede air flow and reduce effiecient fuel burning. I "think" the various air intake sensors adjust for the air flow, but the fuel problem is different. The build up on the valves:

and on the piston head will get dry from the heat of combustion. When this carbon dries it will act like a sponge, sucking the fuel into it as it enters the combustion chamber. Anyways, try this as good maintenance:
Try what I call an air induction service.
I like to use castle hydroblast. You spray it into a vacuum line such as the brake booster line if nothing else is accessible. Full spray for 3 minutes, stall the engine with it or have someone kill it while your spraying. Let it set for a few hours then take for a short drive in low gear, revving the rpms to help break it up. First use Castle cleansrite to clean the throttle bore. Try to get the throttle plates scrubbed good with a brush, while your spraying. Use a rag to wipe the carbon out between brushings. Seafoam is another good product, but smokes a lot.

http://www.seafoamsales.com/motorTuneUpTechGas.htm

http://www.castlepackspower.com/Pages/training/hitech.html

IF you can't find Castle, here is my rep's email:
robw@castlepackspower.com

Thank you again paul.

Did I mention PCM?
If you are not familiar with the location of the powertrain control module (computer), it is in the passenger wheel well area in front of the wheel. When you find it, you need to first get a good look at the connector before touching it so you know how it is positioned. Then see if it is tight. Also get a good look at the computer itself, especially the seam around it. These were a problem for water intrusion and especially problematic in the "road salt regions".

You don't have to go to the dealer. An independent can be located by contacting the local snap-on tool rep, if you are unsure where to go. Www. Snapon. Com.
It may very well be the pump, but wouldn't jump to that conclusion. You could see if power gets to the pump to verify or eliminate it. You can swap the relay with one of the same to see if it starts.

You can half-assed test the pump by rapping on the bottom of the tank while someone cranks the motor to see if it starts. That usually indicates a pump is bad.

You're welcome :)