Intermittent Misfire After Throttle?

SVT232V6

Member
Asking for help because I can’t seem to understand what I believe is an intermittent misfire.

2004 3.8L V6 176K. I have 2 codes:

P0316 Misfire Detected On Startup(First 1000 Revolutions)

P0304 Cylinder 4 Misfire Detected

I have a spare donor parts car, so I’ve changed out the:
-spark plug
-spark plug wire
-ignition coil
-fuel injector

No change. I replaced the Y-pipe and crank sensor and the car ran perfectly for several days on short trips around town. Then it started missing again after a longer trip to the city. I experimented a little to recreate the misfire circumstance. If I start up the car cold and let it be, it will idle fine. If I give it throttle, it will rev up, then the idle will go very low(~500rpms) and nearly stall, then start missing consistently at idle. If I pull the number 4 spark plug wire from the coil, the miss gets worse. The idle improves after putting the plug wire back on and the miss will get better. If I then shut off the car and immediately restart it, there’s still a misfire but it’s no longer as bad. I’m confused and lost. Open to suggestions and further testing! I don’t know if anything that will cause or worsen a misfire after getting on the gas. What else am I missing?
 
Last edited:

6 Shooter

Well-Known Member
have you checked the wiring harness on fuel injector #4 to make sure it is fully plugged in? And, sometimes faulty/sticking EGRs cause misfires.
 

fasterthanyou

Active Member
It may not be #4 that is misfiring even though the code is for #4. Check the rest the same way you checked 4. Pull the wire off of each cyl while its running until you find the one that has little to no change.
 

SVT232V6

Member
have you checked the wiring harness on fuel injector #4 to make sure it is fully plugged in? And, sometimes faulty/sticking EGRs cause misfires.

I unplugged the connector and checked for voltage at the pin, Key On Engine Off and had 12V. My problem turned out to be the coil(so far). Computer read misfire of cylinder 4 but it was actually cylinder 2 that had no spark..

It may not be #4 that is misfiring even though the code is for #4. Check the rest the same way you checked 4. Pull the wire off of each cyl while its running until you find the one that has little to no change.

You were right! ECU was reading Cylinder 4 was misfiring, but I waited until dark yesterday and started pulling the plug wires at the coil and the coil for cylinder 2 was not firing. The coil is brand new. Replaced the coil with a used one and it’s better now. Now onto other issues lol
 
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