Need help with a P0300 code

**derpyimp** · 05-27-2018

I just got done swapping over my coil packs and ICM from the Pontiac to the Impala. It's still misfiring, and I know those parts are good. Any other ideas? Anyone know if the computer would throw a code if the crank position sensor was bad?

**derpyimp** · 05-28-2018

Also, here is a scan of it misfiring at WOT. You can see where the engine RPM starts to struggle and the MAF readings match it.

http://i346.photobucket.com/albums/p...psgkpl64zm.png

**derpyimp** · 05-28-2018

Just pulled all the spark plugs, regapped them from 0.060 to 0.045 and reinstalled them. Still misfiring badly, now even at idle.

**derpyimp** · 05-28-2018

Tried taking off the oil fill neck while the car was running to see if the engine reacted at all. It didn't do anything. Also no noticeable coolant loss, so I don't think it's the LIM gasket. Tried unplugging PCV while it was idling, then driving around to see if the valve was opening too much. Still missed. I'm running out of ideas lol

**SgtMarshal** · 05-28-2018

I'd go smell the exhaust, if the catalytic converter is bad it will smell like rotten eggs.

**derpyimp** · 05-28-2018

Just tried it, smells okay to me. The car also doesn't feel sluggish like a clogged cat would do to it. It just starts missing really bad.

**Scottydoggs** · 05-28-2018

pull the o2 sensor out the manifold, then drive it, if the misfires stop or are reduced, its a cat.

**BillBoost37** · 05-28-2018

good test for a cat there.

**derpyimp** · 05-28-2018

Just tried it. Still missing really bad. The car actually died when I was pulling it back into my apartment's parking lot, though that may have been because it was missing the sensor lol

**derpyimp** · 05-29-2018

I found a new clue. When I start the car, it will idle normally at first. Then, after a minute or so, the idle increases to around 1300 RPM and it starts misfiring. Is this the EGR turning on or something else the computer does shortly after starting the car?

**derpyimp** · 06-04-2018

I think I figured it out. When I swapped the transmission, there was one ground on the transmission toward the front of the car under the front manifold/crossover pipe connection that I apparently did not tighten down enough. I guess the connection was flaky enough to cause electrical issues, which would explain why my misfire was intermittent. Once I got the nut holding the grounding wires tightened down properly, I had zero misfiring. Stupid simple fix.