2001 Dodge Ram How can low compession, valve problem through

Hi:
Yes compression can cause the problem. Once it starts to get below 120 problems may begin. Have you checked the compression both dry and wet? What is the compression in that cylender? Also, I can't identify the code you listed. When you checked it, did you press and hold the odometer reset button while turning the ignition on?

Let me know.

Compression can throw a code. Doesnt have to be comp controlled to set misfire codes. Sorry the other mod should have assumed P0 at the front. Since you have a scanner, drive it and watch the injector waveform, this could be a bad injector, overfueling at part throttle. The PCM may have only thrown a code for cyl 8 too, pull other plugs to see if there is a problem with any others.

A misfire in a specific cylinder should lead you to check the spark plug, fuel injector and compression.

Misfires can be caused by worn or fouled spark plugs, a weak spark (weak coil, bad spark plug wire), loss of compression, vacuum leaks, anything that causes an unusually lean fuel mixture (lean misfire), an EGR valve that is stuck open, dirty fuel injectors, low fuel pressure, or even bad fuel

To diagnose a P0308 trouble code we begin by checking for proper fuel and ignition system operation, and then follow up with the less likely causes listed above, such as EGR and EVAP system problems. New style coil on plug applications have a high failure rate, and can be concluded faulty by swapping to another cylinder and checking to see if the misfire moves to that cylinder. This is a quick check

Ok this is back the others as it is possible to get a code that is not sensor related here is how it works. The computer monitors the engine while runnig after running a crankshaft postion learn procedure. A missfire code will be stored when more then a 2% missfire rate is measured during 2 trips (one on Cal models), or a 10 to 30% rate with one trip. Some of the possible caused are as follows cam or crank sensor, bad timing, ignition system fault, mechanical problems, fuel contamination or fuel pressure. This is what the computer is set to read so with that if it has low compression that is allowing it to see either a 2% or 10 to 30% missfire rate it will pic it up and send a code for the cylinder that is causing the problem. I hope this is more of the answer that you are looking for I can't explain it any better.