2001 S60 non turbo had a misfire on cylinder 3 a couple of weeks ago. Replaced the coil pack (after market) and problem solved. Figured a good idea to replace the other 4 and the plugs. Install 4 more coil packs, and 5 plugs and the car runs rough and misfires and gives code p0300 random misfire. Several iterations of new and old parts, even back to the old coil packs and plugs and it still ran rough and throws the p0300 code. Now the car won't start. Ideas???

 

Check the wire connections on all of the coils. I use a dollop of Di-Electric grease on all of the electric connectors. The connectors to the plugs can also use some.

 

Also don't rule out getting a bad coil right out of the box. I've seen that kind of stuff happen, especially if you go cheap on the aftermarket parts.

 

And covering that, try a swap position of two different coils and see if there is a change in running or the code.


Troubleshooting the coils is difficult, but a swap will sometimes tell different story.