P0300 - Random Cylinder Misfire

My venture started missing pretty badly activating the SES light and giving code P0302, #2 cylinder misfire, so to start, I changed all the plugs and wires as they were past due anyway. However, the misfire continued and was getting worse and under a load, the SES light would blink. I got the codes read again and it showed P0300. I removed the plug wires from the coil pack feeding the #2 and #5 cylinders and noticed the terminal for the #5 was corroded pretty badly. The guy at the parts store had printed out a table that showed the primary and secondary resistance values for the pack, so using a multimeter, I checked them. The primary was good but the secondary was virtually open instead of the 6k-11k shown in the table. I checked another of the coil packs and the resistance readings were good. So, $27 and some change later for a new coil pack and it runs like new again.

The primary reading is taken from the bottom where it snaps onto the Ignition Control Module. There should be .2-.7 ohms resistance across the input terminals and then the secondary is taken across the output terminals for the plug wires, there should be 6k-11kohms resistance.

I hope this helps someone.

What's all in common with all cylinders?

Air - New air filter, replaced MAF/IACT sensors, new upstream HO2 sensor, and clean the throttle body.

Fuel - New fuel filter, fuel pressure test.

Exhaust - A plugged catalytic converter, can cause random misfires.

Keep all replacement parts for spare parts, except for the filters.


Also, see Similar Threads at the bottom of yours.

He was having issue with 2 cylinders (common component was the coil, it was bad, he replaced, and posted procedure to test so someone else can benefit.)