[justaguy93]

I'm driving a 2001 Outback wagon with the 2.5 motor and I seem to be getting a random CEL that decodes as a P0304 cyl #4 misfire. I am in the process of clearing it and letting it pop back up to try and identify a pattern but at this point I am kind of stumped. I don't notice an actual misfire while driving, the light just sort of shows up from time to time. I have new plugs and wires and I tried testing the resistance on the coil, secondary was 13.6k on both, I wasn't able to get any reading on any of the pins where the 4-pin wire plugs in.

Last time I cleared the code I drove probably 30 miles, mix of highway and in town before it came on.

I've done some research on this but the causes seem to be all over the board. Since I don't actually feel anything happen to the engine when the code shows up I'm hoping you good people here may have a suggestion or two for things I can look into. In the meanwhile I'll be trying to log when and where the code shows up and I have purchased Torque for my Android and a BT adapter for monitoring the engine while I drive.

Thanks for your time,

-justaguy93

 

[cardoc]

A misfire can be caused by lack of fuel or a vacuum leak also. When was the last time you replaced the fuel filter? Checked for vacuum leaks? Crack in the intake tube after the MAF?

If fuel and vacuum check out, try a new PCV valve and recheck your wires. It is possible for a coil to lose one cylinder sporadically. If you have or can get a spark tester and install it inline between the wire and #4 plug, it will give you an indication of fire from the coil.

 

[justaguy93]

Thanks for the reply. I will check those things out. Do you have any tips for testing vacuum lines? That's not something I have any experience with yet.

 

[cardoc]

Easy way to do it in your driveway is to use something like "brake cleaner" that is flamable and start spraying the intake tube, vacuum hoses, base of the intake manifold, etc.. Otherwise, you would need a $1000 smoke machine to force air and smoke into the intake system.

 

[justaguy93]

Well still waiting for the WI weather to turn so I can check for leaks. In the meantime I have been able to isolate a pattern in that my car only throws the code if I drive it right after starting. If I let it idle for a few minutes before driving it never seems to throw the code.

So at least this is something I have some control over in the meantime.