Chronic Misfiring - Subaru Forester Owners Forum
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post #1 of 9 (permalink) Old 02-13-2009, 03:41 PM Thread Starter
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Car Year: 1999
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Chronic Misfiring

My Forester (1999, 125,500 miles) started acting strange last night. On my way home, it felt like it was losing power, then felt like a cylinder or two were misfiring, then started sputtering and stalling. Luckily, I was able to make it home. Diagnostics told me that three of my four cylinders were misfiring, so I purchased plugs & wires, hoping the problem wasn't with my fuel injectors. After replacing the four plugs, everything was working fine. It started right up, the engine ran smoothly, the code was gone, and acceleration was great. I drove it to the auto parts store to return the wires that I obviously didn't need, and when I was nearly back home (~10 mile round trip), the symptoms started again while climbing a very small hill. Loss of power, some engine lurching, check engine light flashing, and wanting to stall.

I haven't checked anything since I arrived because I wanted to consult the Subie crew first. If the new plugs have failed already, could a major engine problem be causing this? The plugs that I replaced only had 17,000 miles on them. Also to note, when I first pulled the boots, I noticed some oil near the top of the rubber in cylinders 2 & 4. Please let me know if you have any suggestions. I hope my baby isn't dying!
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post #2 of 9 (permalink) Old 02-13-2009, 03:45 PM
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Were the codes for misfires? It sounds like an arcing coil pack ( better to see the arcing at night ) OR a dirty MAF sensor. Search for ways to clean the MAF.

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post #3 of 9 (permalink) Old 02-13-2009, 04:36 PM Thread Starter
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Were the codes for misfires? It sounds like an arcing coil pack ( better to see the arcing at night ) OR a dirty MAF sensor. Search for ways to clean the MAF.
Ferret - Thanks for your quick reply! Before I changed the spark plugs, the codes were for misfires on 3 cylinders. I haven't checked for the new code(s), since I don't have my own OBD2 scanner. I will carefully clean the MAF tonight and see if that helps. I will also check the coil pack for arcing. What is the best way to do this? Mist it with water while running with the lights out? Also, if there is arcing, could the problem be the wires and not the coil pack? Dang, I'm kicking myself for returning them so quickly...
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post #4 of 9 (permalink) Old 02-13-2009, 04:40 PM
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Yes to mist it in the dark. Then you must look and determine, wires or coilpack IF you see arcing.

Misfires can also ( rare ) be a fuel delivery problem. Anything from a clogged filter, to a flaky fuel pump or relay. Or even the injectors as you have already mentioned.

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post #5 of 9 (permalink) Old 02-13-2009, 05:00 PM Thread Starter
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Originally Posted by ferret View Post
Yes to mist it in the dark. Then you must look and determine, wires or coilpack IF you see arcing.

Misfires can also ( rare ) be a fuel delivery problem. Anything from a clogged filter, to a flaky fuel pump or relay. Or even the injectors as you have already mentioned.
Thanks again, I'll take a look. What concerns me is that everything was fine after I replaced the plugs. I would think that a bad coil pack, wires, injectors, MAF sensor, etc would not have let the car run like new for 10 miles. Why would the problem be delayed? Am I just being crazy & pessimistic?
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post #6 of 9 (permalink) Old 02-14-2009, 05:14 AM
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Misfire on 2 (paired) cyls would be one side of the dual double-ended resonant coil, seeing it on three cyls points to either the coil primary feeed harness or fuel delivery. Fuel Filter done recently? line pressure OK? I would go with fuel. Good luck on this.
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post #7 of 9 (permalink) Old 02-14-2009, 09:29 PM Thread Starter
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If I had been born after 1996, maybe I would have come pre-installed with OBDII. Then at least I would throw a code that says I'm an idiot! After looking under the hood today, I noticed that one plug wire was loose, causing the latest misfire. Either something caused it to loosen, or I didn't push it in far enough. After reattaching it, I drove the car over 30 miles today, up a mountain, under several different conditions, and it's working fine again. I'm leaving the coil pack alone, but I will replace the wires just for normal maintenance. Thanks again for the suggestions!
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post #8 of 9 (permalink) Old 02-14-2009, 09:42 PM
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Hey, check out this thread, if you haven't already.

Cylinder 3 and 4 misfire

I had a similar thing happen to a car I had, changed all the seal, valve, head gasket, etc and my problem went away.

09 Forester MT Touring
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post #9 of 9 (permalink) Old 12-15-2011, 05:24 PM
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I need help.

I have a subaru forester 2002 147 k miles. couple months ago started to misfire. It was getting worse. But no engine light. I change spark plugs and wires. The problem continuous. I bring it to the mechanic . Who spend three days in they car. Change a new coil . And the problem still there. Usually the car start fine until warm up. I cleaned the fuel injectors. Still have the problem.buy no light engine. Tomorrow I will replace the computer with my friend computer. I don't know if that will help but I'm running out of ideas. I'll appreciated any suggestion.
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