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Discussion Starter #1
Well, I'm entering the stumped zone and looking for thoughts on what to check next...

It's a '99 Outback, manual trans, with 188k (motor rebuilt at 150k so the story goes). I've owned it now for 5 months or so. Right off the bat, the CEL was throwing a P304 cylinder 4 misfire; it was very intermittent and would clear itself after the 5 start/run cycles of not repeating. This went on for months where the same p304 would throw every few weeks and then reset itself. Recently it began happening more and more often and the idle began suffering, alternating between low and normal, getting rougher as well. Last week, the CEL got really pissed and started flashing every few minutes while the idle and low speed stumbling grew worse.

I started searching through all the old threads I could find and it seemed the first step was plugs/wires. I replaced all four plugs and wires last night with NGKs and cleared the codes when done. Two miles down the road, the p304 misfire threw again. I picked up a new ignition control module today and popped it on at lunch and cleared the codes again; the idle still seemed rough and within 5-6 miles, back came the light. I haven't been able to read it yet, but I'm betting it's the same p304 cylinder 4 misfire (the only code that keeps tripping).

So, where's my next logical step? Injector? Fuel rail? Some simple test to try first? The idle now spends a lot of time at 500ish and the whole car has a good shake. It seems to stumble below 2000rpm and, for the most part, smooths out completely at 2500 and beyond. I've seen some of the suggestions in other threads, but many of them complain of multiple codes being thrown together, i.e. multiple cylinders misfiring at random; not sure if the fact that it's constantly the same one plays any specific role here.


Thoughts? :confused:

I appreciate it! :cool:
 

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I picked up a new ignition control module
Not sure what you mean. Is it the coil (the device with small towers that the spark plug wires plug into), or the igniter (mounted on the firewall), or something else? If the coil, then the igniter could still be faulty, and if the igniter, then the coil could still be faulty. (Poor answer but have to cover all bases.)

Yes, the injector at cylinder 4 could also cause a misfire.

Unfortunately codes don't always identify the specific cause.
 

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03 H6 OBW & 06 WRX Sportwagon
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have the code read.

compression check might be in order, could be a valve isn't closing.

was there any oil in the plug holes?

might try some seafoam or Techron through a tank or 2 - might clear out a dirty injector.

maybe fuel filter? (another longshot)
 

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Discussion Starter #4
Not sure what you mean. Is it the coil (the device with small towers that the spark plug wires plug into), or the igniter (mounted on the firewall), or something else? If the coil, then the igniter could still be faulty, and if the igniter, then the coil could still be faulty. (Poor answer but have to cover all bases.)

Sorry, I replaced the coil that the plug wires plug to. Haven't touched anything on the firewall yet.


have the code read.

compression check might be in order, could be a valve isn't closing.

was there any oil in the plug holes?

might try some seafoam or Techron through a tank or 2 - might clear out a dirty injector.

maybe fuel filter? (another longshot)

There didn't seem to be any oil in the plug holes, and FWIW the old wire connections didn't look bad. One oddity was that the spark plug in that fourth cylinder was definitely a different style plug than the other three, and looked more burnt and discolored.

I ran Seafoam through when I first got the car, but not since; I'll go ahead and run another can through this weekend.

Would a fuel filter account for only the one cylinder misfire? Or would that be assuming the code is not being completely honest with me...?
 

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03 H6 OBW & 06 WRX Sportwagon
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meh - just dreaming up someway restricted fuel flow might trigger a problem in the 'weakest link'.

swapping injectors to see if the problem follows might be diagnostic.
 

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I doubt the fuel filter, but swapping the injectors is a good idea.

looked more burnt and discolored.
Plug condition -- color, wear, deposits -- can be valuable in diagnosing a misfire. Many shop manuals and repair manuals will have color photos of 6 - 10 plugs, each different, with the "diagnosis" for each. It's not 100%, but can help narrow things down.

Do you still have the original plugs? There's probably a page on the Internet with the same type of photos to compare to; or, post some close-up pics of the plugs and especially the one from cylinder 4 and perhaps someone will be able to identify a possible issue.

In the meantime, what plugs were in there before?
 

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Discussion Starter #7
Here's the plugs that came out. All are NGKs, but the one (from the 4th cylinder) is a different style.






I have an injector that should be showing up tomorrow so I can replace. What about the likelihood of the wiring to the injector being bad?
 

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03 H6 OBW & 06 WRX Sportwagon
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looks like an Iridium or ????


makes me wonder if that cylinder has been having an issue and a PO put in a 'better' plug expecting to solve the problem.

still think a compression check is in order.
 

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Discussion Starter #9
Swapped in the new injector I'd previously purchased; cleared the p0304 code again; went for test drive; threw the code again a mile down the road. So, once the engine cooled down, I pulled the plug and threaded in the compression tester; pulled the other 3 wires and cranked it over with the starter for 8-10 seconds or so. 25 psi is about all I got on both attempts.

I called up All Wheel Drive Auto in Kirkland, WA (saw someone recommend them on the forum) and listed off what I'd done thus far. I also asked about likelihood of a burnt exhaust valve since I've seen that repeatedly come up while searching. They said it could be, but another very possible scenario is a dropped valve seat requiring head off, machining, rebuilding, etc. Said roughly $2300ish if that was the case. Does that sound reasonably in line?
 
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