2004 Volvo V70 2.5T FWD Misfiring engine

[atemelon]

It is a bit of a story but it all started on my drive up from Texas to New Jersey pulling a loaded 5x8 Uhaul trailer using my V70. I was driving at 55-60 mph for 7 hours a day taking long breaks every 3-4 hours. Everything was going well until at some point in West Virginia going up the hill the car started losing power and the CEL started blinking until it lit up solid. I pulled over immediately and the code reader announced the P0300 and P0303. At the idle the engine was working rough and rocking the car slightly. To test, I swapped the 3rd and 4th coils and the problem shifted to the fourth cylinder, which to me was an indication of a failed coil #3.

After a short search a local auto parts store happened to have an after-market ignition coil in stock and I was back on the road. The problem seemed to be gone, but as soon as I hit the first uphill the problem came back with CEL flashing. I pulled over the codes now were similar but the problem had shifted to the 2nd cylinder (P0302). Swapping coils around just kept the problem shifting from a cylinder to cylinder. Pulling out and swapping injectors did not seem to transfer the problem from one cylinder to the other. It couldn't have been the fuel, because it took a half tank of gas since my last fill up for the problem to first appear.

I replaced PEM module with another unit and that did not eliminate the misfire problem. Swapping for new spark plugs was the first time that the car came back to life and the problem seemed to be solved, the car ran and idled grate with no loss of power whatsoever. But the next morning after driving it for ten minutes the problem came back and now giving out the P0302 code again. It idles rough with engine clearly misfiring and there is a slight loss of power but not as notice.able as it was when the problem first occurred. The VIDA revealed no problem with MAF sensor. My next step is to try replacing all of the coils, but how far do I continue the process of elimination. Any thoughts? Could it be that driving it with (a) bad coil(s) I have done damage to my catalytic converter?

[chrism]

"...I pulled over the codes now were similar but the problem had shifted to the 2nd cylinder (P0302). Swapping coils around just kept the problem shifting from a cylinder to cylinder..."

Sounds like you have another bad coil.

[abscate]

How many miles are on this?

My 2005 had 2 bad coils at 80k, I replaced all 5

My 1999 coils lasted to about 120k, I replaced all 5