Ok, this just happened to me today. I changed my plugs a little over a week ago to Pulstar Iridiums. I got a #4 misfire code (P0304). Called a local Subaru shop and they confirmed the misfire from the symptoms I was describing. So i bought a new coil pack thinking that would fix the problem, but it did not. Any ideas/help please!!
04 Engine Misfire
- Thread starter tonyhaymond
- Start date
HolyCrapItsFast
Drinks beer!
I would start with the easy stuff first. Pull the plug and inspect it. Check that the gap on all of your plugs are .028". I know you replaced the coil pack already but to rule it out anyway you should swap out the coil pack with another cylinder. If the misfire follows the coil pack then it is the coil pack. If not then you have ruled out the coil pack. Next would be to swap injectors. If the misfire follows the injector then replace the injector. If not then you ruled out the injector and now need to look at wiring and connectors. Else do a compression test to rule out ring landing.
I was only able to get up to the part about switching the coils around. the #4 is still pulling the code, even after i changed around the coils. The plugs came pre-gapped at .028. I dont have the means to do the injectors or anything like that. Would changing back to the NGK Iriduims possibly solve the problem?
If you have the old plugs it would help the trouble shooting process by reinstalling and see if it relieves the miss fire. Do not trust pre-gapped spark plugs check the gap with feeler gauges (do not use the round wire/wedge type gauges)
Could you give us a little more information on what the car is doing when the miss fire happens. No detail is too small.
Could you give us a little more information on what the car is doing when the miss fire happens. No detail is too small.
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well shouldnt all of them misfire if they were gapped wrong to begin with?
Im not saying that all are gapped wrong but one might be 0.030, You never know. I had the same problem when Holy was doing a tune on my car. I took someones word that my spark plugs where good to go but when it came to WOT it would miss fire and stumble all over its self with a miss fire on cyl 3. I went though all the steps of trouble shooting believing my spark plugs were good. Got to the point were I was checking everything from spark plug on back and, what do you know, cyl 3 spark plug was gapped at 0.038, all others where 0.030. Moral of the story is dont believe the box check it yourself before you install it in your STi
HolyCrapItsFast
Drinks beer!
I'm just laying out the process of elimination but the how to is up to you. The injectors are not simple to remove and install but it can be done at home on your driveway if you know what to do.
So why all of a sudden would this happen after over a week changing the plugs? wouldnt there have been a misfire right away?
A great deal of these misfires come in coincidence with changes you do. #4 misfire is common for many reasons, usually do to an exhaust leak, injrctor o ring seal, sparkplug gap, injector running a bit lean or worst case a ringland. Swap injectors to the number 1 cyl. If no dice then check all gaskets for vacuum or exhaust leaks. If the injector swap doesn't do it try taking a portable propane torch and obviously don't light it but run the engine and point the propane nozzle at all the vacuum lines and around the injector etc. If the engine raises in rpm then you found your problem area. Fix it then try one more time until no change.
