Well, I just replaced the optispark and I am getting a misfire in ONLY cylinders 5 and 7. I am also throwing code P0300 for a random misfire. Since 5 & 7 are right next to each other, I was thinking that I might have a blown head gasket. Does the PCM on these cars pick up ANY misfire (such as a misfire with a blown head gasket) or does the misfire have to be electronic??

Also, before the install, I never threw any codes for a misfire. It was missing all over the place via Tech 2 (missing in all 8 cylinders), but it never once threw a code. I have checked and double checked to make sure that the wires are headed to the correct location.

You can move this to 'LT1 Tech' if you think it belongs there, but since it was a computer issue, I thought that I would start here.

Just checking before I get too worked up!!!

 

The PCM detects "misfires" by looking for tiny irregularities in the crankshaft speed. This is accomplished by looking at the pulses from the crank position sensor, and is the only purpose that sensor serves. Hence, anything that causes the crank to have an irregular velocity will cause a "misfire" report, and that would include both electrical and mechanical caused misfires. It will also pick up irregularities caused by a radical cam, or even rough roads.

Since you have adjacent cylinders misfiring, look for a cross-fire on the plug wires for those cylinders, assuming you have verified the wires are attached to the correct plugs.

 

Well, I have checked them one time, but since it is beautiful out today, I am getting ready to check them for a second time.

That helps out a lot...Thanks!!!

 

could running lean cause this code?

 

Anything that causes a cylinder to misfire can set the "misfire" code, including running way too rich, running way too lean, bad spark plug or wire, bad injector, burned valves, etc.