Turns out I got a BIG issue. Here's the background as it all started yesterday

Car (01 XC70, 120k on the clock) was running fine. Suddenly started running rough and lacked power. Check engine light came on. I pulled the codes for the Check Engine light and the computer had set codes P1355 and P0303. These codes translate to a misfire on cylinder 3.

I pulled the plastic engine cover cover to access the plugs and coil packs. I found that the coil pack on cylinder 3 had almost melted! The housing was bulged and cracked and was obviously bad. It was an original coil pack so I figured it just gave up the ghost. I had a new spare plug boot/coil pack so I installed it. Car started fine, idled smoothly and no Check Engine light. Thought the problem was fixed.

Today, after running about 6 miles, the same thing occurred, bad running, check engine light, etc. Pulled codes again, and got P1355 and P0303 again. Swapped the coil packs on cylinder #2 and #3 to confirm the new coil pack installed just the day before was actually bad now. Started car and it ran really bad. Codes this time were P0300 (Multiple Cylinder misfire detected) P0302 (Cylinder 2 misfire) and P0303 (Cylinder 3 misfire). The good coil pack from Cylinder #2 that was put on #3 is now also bad. It also got VERY hot after running the engine for only about 30 seconds. So hot I could only touch it with gloves on!

Something in the circuit for Cylinder #3 is taking out coil packs. It took out the original coil, a good replacement, and a known good one from Cylinder #2.

Any ideas before I trailer it to the dealer!!

 

Update:

I've looked at the wiring schematic for the coil packs and I will trace wires tomorrow afternoon. I'm thinking it is either a bad/shorted wire, or a bad ECM. According to the schematic, wires going to the coil pack are: Ground, a common voltage wire that is tied to all the coil packs from a central point, and the signal wire coming directly from the ECM.

Side question: Can you buy replacement ECM's for these cars, or is it a dealer only item? Just trying to find my options!

 

Did a wire to the coils get pinched?

The ECU's are Dealer only.

 

Bingo, it took the dealer two days to diagnose it, but it turned out to be the ECU, just like I figured. Total bill is $2200 out the door......OUCH!!!

 

Ouch Sorry!