I was driving my 2002 wrx on freeway and suddenly the engine became rough and the check engine light came on. The car was still drivable but shaking all the way. Using a code scanner I got "P0302" which means cylinder #2 misfire.
The car has only 43K miles, still on original plugs.
Are there simple ways to narrow down the cause of the misfire without opening the hood? Perhaps the code scanner could be of use??
Otherwise, my next plan of action is to replace the fuel filter, then the spark plugs. If that still doesn't help, I'd probably take it to a shop.
Hi, Which cylinder? One thing you can try is in the dark(after sunset) open the hood and look to see if you can see spark jumps around. My bet is coil, wire, plug in tat order for a particular cylinder. Fuel filter has nothing to do with it, remotely maybe injector.
If this happened a mile or 2 after a fill-up , or the next morning after filling up and parking, suspect water in the fuel. a bottle of HEET or similar gas 'dryer' and 3-4-5 start/drive cycles will likely clear the code and the problem will be resolved. I would also suggest accelerating the schedule for a fuel filter change if not doing it immediately.
43K may be a little eraly for bad wires - though high voltage stuff can be stressed and go downhill quickly. I dunno if the 02s had copper plugs
I had 2 cylinders start to misfire on me at the same time. The dealer dialed the problem in to the coils, and rather than just replacing them reactively, decided to swap the coils between the cylinders - the idea being that if the problem recurred and followed the coils, then there's the problem.
That was about 5000k ago, and I haven't had a CEL since.
The turbo Subarus don't have plug wires, they are all coil-on-plug design, so there are no wires to go bad. Since this is a single-cylinder misfire, it's unlikely to be caused by something like bad fuel which would be expected to affect all cylinders. The cause will likely be something confined to that cylinder, either a bad plug, coil or injector or an internal engine problem. You are going to have to open the hood to troubleshoot this, there is no hands-off solution. The first thing to do would be to check the wiring to the coil and make sure it's still plugged in. Sometimes they come off and that will of course set a misfire code. If it's ok, remove and inspect the coil and plug for that cylinder. If the plug is fouled that is a visual indication of the problem, it should be clean with minimal deposits. At 43K the plugs should not be worn out on a healthy engine, the service interval for the OEM platinum plugs is
60K. The coil should be checked for visible signs of failure, such as carbon tracking or cracks/bulges in the housing. If these are seen the coil should be replaced. If it looks ok, it can be swapped with another coil to see if the problem then moves to that cylinder. If it does move then you've confirmed a bad coil. If the coil is ok and you've replaced the plug (if necessary) and the problem still persists, it could be a bad injector. This is a bit more difficult to troubleshoot on your own but you can at least use a long rod or screwdriver to confirm that the injector is clicking on and off as the engine runs. Next would be a compression and leakdown test to check for loss of compression due to bad rings or valves. This is unlikely though due to the sudden onset of the problem.
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.