Misfire Cylinder 4

[cheapo]

A few weeks ago, the car went into limp mode on startup. Engine chugged violently and I turned it off and left it for a day.

Next time I started it, it ran smoothly, but the CEL was on. I drove the car home. (About a mile.)

I made an appointment to have it looked at. Drove it a couple of miles to the shop. It ran smoothly and the CEL was off.

Mechanic checked it out and read the codes with VIDA/DICE. The electronic throttle was acting up.

He put in a good used one.

Car ran fine for a few weeks, but at the end of the second of two 5-hour highway drives, it started misfiring.

Since then, my mechanic has read the codes again, and replaced all coils and plugs. The misfires continued, so he swapped in a good used injector rail and injectors.

The misfires went away for a day, then reappeared, but were much more gentle than before. However, they got stronger and stronger.

Now he suspects that either the wiring harness is bad or the Engine Control Module. (No codes to this effect of course, just "Misfire 4".)

The car has over 360,000 km.

Any suggestions greatly appreciated.

[AutosDirectFlorida]

http://forums.swedespeed.com/showthr...lugs-and-Coils

Honestly, I just googled Volvo XC70 random misfire - there are several existing threads with suggestions.

Edited - since I asked a dumb question -

Since we know its always cylinder 4 and everything else has been replaced - do a leak down and compression test

[AutosDirectFlorida]

Injector and coil plugs/connectors would be something to check - ensure nothing is corroded or wires pinched under the plastic cover and shorted
Mechanic should be to check that stuff easily while prepping for the compression and leak down

[AKAMick]

The mechanic needs to replace more stuff, as you still have money left, it needs analyzing, before throwing parts at it, move the #4 coil to another position and see if it moves with the coil? compression problems are not random, low compression stays, it does not come and go,