impreza wrx misfire P0302

[paybillg707]

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.

 

[Tony Hwang]

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.

 

[Carl 1 Lucky Texan]

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.

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
- if so they may be overdue for a change.

Carl

 

[BD]

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.

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.

 

[mulder]

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
- if so they may be overdue for a change.

Carl

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.

 

[john]

I was driving my 2002 wrx on freeway and suddenly the engine became
I replaced spark plugs #2 and #4. The old plugs look ok to me. I also
swapped the coils to see if the problem would migrate from #2 to #4.

To my surprise the problem is gone. I still don't know why or what caused
the problem, but I'm not complaining.

It could be a bad contact, or maybe the plug was bad, just not visibly. Or
perhaps rebooting the ECU (side effect of removing the battery to get at the
plugs).

It was hard to torque the #4 plug with a torque wrench.