2005 s40 P0300
 

two weeks ago had to replace a coil pack on #2. All worked fine, but yesterday check engine light started blinking. checked the code and it was a P0300. Since this is a random misfire any suggestion on where at start trouble shooting.

did you also replace the plugs? try clearing the code again but I'd be looking at the connections to the coil pack - look for any cracks on the connectors, feel if its securely connected etc.

Thanks, It is probably time to change the plugs anyway.

I changed out the plugs and still have the random misfire. Do these engines only like a certain brand of plug? I installed AC Delco double platinum.

as long as you have the right plug temperature range and gap, there shouldn't be an issue. As a next step, I'd look at the intake - did you install a new stock air filter? is the MAF clean? throttle body clean? Next I'd look into the fuel delivery system - fuel filter, relay, pump, check pressure at the rail. Anything about the randomness? ie at cold start up vs after a long drive? does it happen when the gas tank is on E vs F? How many miles on the car?

air cleaner is good . Acts the same cold or to operation temp. Did throw a fuel rail sensor code a few months ago but has not showed up since. 237000 miles.

I have heard and read that some misfire issues do come down to not using volvo oem plugs on this particular car. I have my personal doubts about this but there are a lot of threads out there that suggest this.

Generally I like AC Delco products, they tend to be OEM quality.

There is one review for these plugs on Amazon that says new AC Delco double platinum plugs had cracked insulators causing a misfire, so there's that.