Strange misfire issue - have googled myself silly

aewoodhouse · Post by **aewoodhouse** » 22 May 2021, 07:07

Please forgive me for adding yet another misfire post to the collective millions but I am at my wits end trying to sort this out.

Cutting right to the chase: Recurring codes PO351 and PO352 on my 2009 C30. Started when I changed the plugs for new NGK Iridium IX doing routine maintenance. Plastic tabs broke on the coil connectors in the process so i replaced the connectors on coils 1 & 2 / A & B with new OEM connectors from FCP

Cleared codes. Problem returned after about 30 miles.

Swapped coils around. Problem returned after about 30 non-continuous miles.Same codes same coils

Replaced connectors AGAIN for ones from junk yard. Problem returned after about 30 miles. Same codes same coils.

Swapped new plugs around. Problem returned after about 30 miles. Same codes same coils.

Replaced plugs for Volvo plugs. You guessed it - problem was back after 30 miles.

With every attempt to isolate the problem, the car runs flawlessly for about 30 miles and only then does the problem return. Again - the miles are never continuous - so whether the car is hot or cold is not a factor.

I should also add that the 30 miles to recurrence pattern happens whether or not I clear the codes. Merely disconnecting as few as one coil wire will "reset" the problem.

Any sound advice would be greatly appreciated - this is starting to tax my sanity!!

Post by **theWIFES_S70** » 22 May 2021, 09:48

Are you using original coils? When I picked up our S40. I decided to replace plugs. When I put everything back together again, I got three misfires. Removing reseated, dialectic grease, etc. And still had misfires. As soon as I replaced all coils, the misfires went away. I know we're not supposed to throw parts at our cars, but replacing coils every 100K miles makes sense to me. I would check air intake first though. Those gaskets can get pretty compressed. I replaced those, too. Good luck troubleshooting this.

Post by **RickHaleParker** » 22 May 2021, 19:59

aewoodhouse wrote: ↑22 May 2021, 07:07 Cutting right to the chase: Recurring codes 351 and 352 on my 2009 C30.

No text code, It is P0351 & P0352. Cylinder 1 & cylinder 2.

Misfiring on two adjective cylinder is a symptom of a leaking head gasket. Do a compression check.
Check for damaged voltage supply wire between cylinder 3 & 2.

aewoodhouse · Post by **aewoodhouse** » 22 May 2021, 20:35

@RickHaleParker - In my haste I omitted the text from the code. Thanks for pointing that out.

Of course the day I post after chasing this for longer than I will ever admit, I figured out the issue: Loose ground wire to coils A/B. Hope this saves someone else some time.