TEST 5: Common Causes Of A P0300

What really sucks (when diagnosing a misfire condition) is when the check engine light is being illuminated by a P0300 Random Cylinder Misfire trouble code.

This is because the PCM can not pin-point a specific engine cylinder as the cause of the misfire... and that whatever is causing the problem, is affecting the majority (or all) of the cylinders.

In this section, I'm gonna' offer you a few suggestions to get to the bottom of such a dilemma:

  1. Visually inspect spark plugs and COP coil boots.
    1. What you're looking for is extreme wear and tear on the spark plugs and COP coil boots.
    2. This also includes checking for:
      1. Cracks on the spark plugs porcelain insulator.
      2. Carbon closing the spark plug's center electrode gap due to the engine burning oil.
      3. carbon tracks on the spark plug and COP coil boot.
      4. Oil leaking and soaking the spark plugs and/or COP coil boots.
      5. Water soaking the spark plugs and/or COP coil boots from power washing the engine.
  2. Check for leaking intake manifold gaskets.
    1. The intake manifold gaskets are made out of rubber and over time, this rubber gets compressed to the point that it looses its sealing ability.
    2. This can be done by spraying Carb. Cleaner around the intake manifold while the engine is running.
    3. IMPORTANT: You should never spray carburetor cleaner on a hot engine, or you run the risk of a fire. This test should be done with an engine that has not reached normal operating temperature.
    4. Whenever the carb spray is sucked into the spot that's BAD (on the intake gasket), the engine's RPM's will rev up.
  3. Fuel injector resistance test.
    1. There's a good chance that the miss (rough idle condition, misfire condition) is being caused by a BAD fuel injector.
  1. Check fuel pressure.
    1. Low fuel pressure will cause the air/fuel mixture to go Lean and will cause a rough idle condition.
  2. Engine compression test.
    1. This is a pretty simple, yet overlooked test, in finding the cause of a rough idle condition.

Where To Buy The COP Ignition Coil

You could run down to your local auto parts store and shell out a few bucks for a chinese knock-off ignition coil (you know which auto parts store I'm talking about)... or, you could buy the original MOPAR COP coil online.

You can find out more by clicking on the links on the boxes on the right (of the COP coils).

COP Ignition Coil Test Summary

Troubleshooting a BAD COP coil is not that hard to do. I know that this article doesn't cover all of the possible failures associated with a rough idle/misfire condition... so if you would like to add your two cents and/or want to share your own diagnostic and repair experience with the rest of us, you can use the contact form below: