Volvo V70 random misfires

Pull 1 and for plugs and look at them. Also look at the coil boots. Inspect for carbon tracking. This is lines etched into the coil or plug were electricity has found a new path to ground therefore causing a misfire. The coil may just be dead and there may not be c/t. Let me know what you find.

It warmed up to 20F today, so I swapped the coils on cyl #4 & #5.

The ODBII misfire code changed from P0304 changed to P0305. Replaced the bad coil, no more misfires. This is the 3rd coil replaced in the past 4 years. In fact the coil for cyl #4 was replaced one year ago. The one year old coil failed.

While conducting the coil position switch test, I was able to localize the source of the hollow popping noise. It was definitely originating from the exhaust pipe/cat converter area, near the left rear wheel well. My guess is that due to the low temps, unburned fuel mixture must have been igniting in the exhaust pipe or cat converter; hence, rear location of the popping sound source.

When previous bad coil induced misfires occurred, the engine ran rough with the expected loss of power; however, the hollow popping sound was not present. Previous coil failures occurred during warmer months. There were no carbon tracks on the bad coils.

So far, two of the original, failed coils and the 3rd coil were Volvo/Bosch coils, made in Germany. Today's replacement is Borg Warner, made in China. We'll see how it holds up.

The plugs are year old platinum plugs. They look clean, except for the misfiring cyl.

Thx,

Ed Terry