tbolt1003 Posted January 9, 2015 Share Posted January 9, 2015 Our '99 Forester will throw code P0304 every now and then, Misfire Cylinder 4. We had the head gaskets, timing belt, water pump, etc. done over the summer. Subaru head gaskets, Gates timing belt kit through Amazon. Prior to the job, car was running horribly, as would be expected with coolant flowing into cylinder 4. At the time, we were getting the P0304 code. Since the job was completed, car runs well again, however, over the last 2 months, the CEL has started coming on about every 1-2 weeks with the wonderful P0304 code. The car still runs well, although I did notice the other night, at idle, the engine was shaking a bit, but once RPMs rise, the roughness goes away and the engine feels strong through the power band. Is it possible the code is somehow locked in the computer and won't completely clear without some fancy-dancy code reader? I'm running NGK V-Power plugs and Standard brand wires. I have a set of Subaru wires on standby if I need to change over. Any thoughts on the recurring code? Thanks!! Link to comment Share on other sites More sharing options...
johnceggleston Posted January 9, 2015 Share Posted January 9, 2015 first, do a compression test on #4. and then check the valve clearance on all 4 valves, especially the exhaust valves on #4. Link to comment Share on other sites More sharing options...
Fairtax4me Posted January 9, 2015 Share Posted January 9, 2015 The 2.5s are picky about plugs and wires. Pull the plug on cylinder 4 and see how it looks. Link to comment Share on other sites More sharing options...
tbolt1003 Posted January 9, 2015 Author Share Posted January 9, 2015 Thanks, I'll start with those suggestions. Link to comment Share on other sites More sharing options...
golucky66 Posted January 9, 2015 Share Posted January 9, 2015 Had a similar problem on my 97' Outback. Ended up being ignition coil. But I would definitely check plugs and wires as well as that coil. Link to comment Share on other sites More sharing options...
tbolt1003 Posted January 10, 2015 Author Share Posted January 10, 2015 Is there any particular brand of coil pack I should go with should this pack be bad? Are the 2.5 engines picky about them? Link to comment Share on other sites More sharing options...
heartless Posted January 10, 2015 Share Posted January 10, 2015 before messing with the coilpak itself, do as suggested and check the plug on #4. if it looks ok - white-ish to light tan color, no buildup of gunk - then try swapping in the Subaru plug wires (these cars are very fussy about wires) if you do need to replace the coilpak, try getting a used one from a junkyard - not a real common failure, so odds of getting a good one are pretty high and cost is a lot less than new would be. try car-part.com to find one locally, or if needed, many yards will now ship to your door. I was getting a misfire on my '95 Legacy that turned out to be the coilpak - swapped in a used one from my retired '90 (that had more miles on it) and no more problems. Link to comment Share on other sites More sharing options...
keith3267 Posted January 10, 2015 Share Posted January 10, 2015 Cheap trick for the coil pack, if it is the issue. Pack some dielectric grease around the coil tower where the spark plug wire goes. Coat the outside of the plug wire, boot and right down the tower to the edge of the coil itself. A lotof time, there is a hairline crack in the tower and the grease will contain the spark. You can buy a little pack of this grease, enough for one coil, for about a buck at most parts stores. Link to comment Share on other sites More sharing options...
tbolt1003 Posted January 11, 2015 Author Share Posted January 11, 2015 All great suggestions! Thanks for the input. Probably taking her car to work with me Tuesday and dig into it after hours. Link to comment Share on other sites More sharing options...
tbolt1003 Posted February 3, 2015 Author Share Posted February 3, 2015 Update: I went to Harry's U-Pull-It in Pennsburg and found a 99 Forester with a great looking coil pack. I put the "new" pack on our Forester and it seemed to be running better, idles smoother. That was about (2) weeks ago. Last night, she tells me the CEL is back on. When I scan the codes, not only am I getting the P0304 code, but now P0303 has shown up. If memory serves me, cylinder 3 is passenger side rear, correct? Opposite side of cylinder 4? I have a set of new NGK plugs and Subaru plug wires ready to go. I still have the old coil pack. I'm going to put the old pack back on and replace the plugs and wires. Am I approaching this in the proper way? I've never seen both cylinders 3 & 4 misfiring at the same time. At idle, I can definitely hear that the idle is rough, however from about 1000rpm up, the engine smooths out. Advice? Thanks. We are trying to make the car last another year before she gets a new Impreza. Link to comment Share on other sites More sharing options...
tbolt1003 Posted February 3, 2015 Author Share Posted February 3, 2015 Update: I went to Harry's U-Pull-It in Pennsburg and found a 99 Forester with a great looking coil pack. I put the "new" pack on our Forester and it seemed to be running better, idles smoother. That was about (2) weeks ago. Last night, she tells me the CEL is back on. When I scan the codes, not only am I getting the P0304 code, but now P0303 has shown up. If memory serves me, cylinder 3 is passenger side rear, correct? Opposite side of cylinder 4? I have a set of new NGK plugs and Subaru plug wires ready to go. I still have the old coil pack. I'm going to put the old pack back on and replace the plugs and wires. Am I approaching this in the proper way? I've never seen both cylinders 3 & 4 misfiring at the same time. At idle, I can definitely hear that the idle is rough, however from about 1000rpm up, the engine smooths out. Advice? Thanks. We are trying to make the car last another year before she gets a new Impreza. Link to comment Share on other sites More sharing options...
heartless Posted February 3, 2015 Share Posted February 3, 2015 make sure your plugs are gapped properly - do not just assume they are - take the time to check them and adjust as necessary. Owners manual should give you a gap range - I know for my 95 Legacy EJ22 it is something like .039 to .044 (your Forester EJ25 may/may not be the same) - I generally try to get all 4 around .040 - just slightly above the lowest number in the range. This allows for normal wear of the plugs and still staying within the gap range. Link to comment Share on other sites More sharing options...
tbolt1003 Posted February 3, 2015 Author Share Posted February 3, 2015 Thanks, will do Link to comment Share on other sites More sharing options...
tbolt1003 Posted February 6, 2015 Author Share Posted February 6, 2015 Ok, swapped on a known good coil pack, new NGK BKR5E-11 plugs gapped to .44 and new Subaru plug wires. The engine is still missing, although the CEL light hasn't come back on yet. Cylinder 3 misfire not showing up anymore, only cylinder 4. I'm pulling my hair out. What else am I missing? Link to comment Share on other sites More sharing options...
keith3267 Posted February 6, 2015 Share Posted February 6, 2015 Look at the old plug from the #4 cylinder. If it was unusually clean, almost new looking, you may have a coolant leak in that cylinder. A small leak will steam clean the plug tip. Link to comment Share on other sites More sharing options...
tbolt1003 Posted February 9, 2015 Author Share Posted February 9, 2015 The center of the plug was a light tan. Around the area of the threads, it had a crusty carbon material. I showed it to a coworker well versed in cars, and he said it's not bad looking, but definitely not as clean as the other (3) I took out. He's thinking a compression test is in order. Link to comment Share on other sites More sharing options...
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