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Old 09-25-2009, 05:59 PM   #1 (permalink)
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Default fluffy / misfire especially when cold

Hi - I'm in Auckland, NZ and have a 1998 Forester S/20. I've had it about 3 months and cannot get rid of the fluffy / misfire that is especially bad when cold. It had a low compression in 1 cyl that was diagnosed as the problem, so that head was refurbished. No improvement!! Winger Subaru can't work it out but suggest using higher octane fuel. Local mechanic is not a specialist but sensible, has conceded defeat. I have been guilty of putting 91ron in the tank and the fluffiness is def worse on low octane - so I am sticking to 95+ and that helps but its just masking the problem. Auto-sparkie has checked everything he can, and mechanic has now had injectors checked. We love the car but can't live with its misfire. The symptoms are reasonably subtle when tootling about but very obvious with four up, up a hill or under load, when cold. Can anyone help as I don't want to start buying parts in order to try and eliminate problems without knowing what it is. Help!!
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Old 09-25-2009, 06:57 PM   #2 (permalink)
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Misfiring can be a tricky issue to accurately diagnose. An engine misfires when there is a problem with the compression, spark or air/fuel mixture. If you have had diagnosed compression problems in the past, it would be a good idea to have the mechanic check the compression again in all 4 cyl. including the one which was previously faulty if you haven't done so already. Subies run better on higher RON fuel, but this should not cause it to misfire as you describe. Sometimes it's wise to get a 2nd opinion on the car through another mechanic. Fault finding and troubleshooting are skills some are better at than others. It may be a very simple problem that has just been overlooked.
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Old 09-25-2009, 07:27 PM   #3 (permalink)
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I had a cylinder 2 & 4 misfire, but the problem was cylinder 4. Had low compression. Wasn't the heads, it was the cylinder itself (piston rings to be exact). A "leak down" test will test the heads for holding pressure, the compression test failing is usually the piston. When you pulled the heads, did you notice cylinder 1 having any score marks in the bore?
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Old 09-25-2009, 07:36 PM   #4 (permalink)
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I see this is your first post, so welcome to the forum from Oregon!

Before I add my .02 cents worth, some questions. Is your CEL on? Is your exhaust tip overy sooty. How's the engine performance, any hesitation?

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Old 09-27-2009, 12:25 AM   #5 (permalink)
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Default misefire / hesitation

Quote:
Originally Posted by Blue Fox View Post
I had a cylinder 2 & 4 misfire, but the problem was cylinder 4. Had low compression. Wasn't the heads, it was the cylinder itself (piston rings to be exact). A "leak down" test will test the heads for holding pressure, the compression test failing is usually the piston. When you pulled the heads, did you notice cylinder 1 having any score marks in the bore?
I used a local mechanic after initially taking it to Subaru who couldn't find a fault. I'll relay your comment (and the leak down suggestion) to the mechanic. I agree about getting additional opinions - I guess the next stop is a tuning specialist as they tend to be more detail orientated than generalist mechanics. Thank you all for your comments so far. Please do keep them coming.

For what its worth, I feel this is likely to be electrical or electronic. I notice another thread about "hesitation" which is similar symptoms to me. The car has new plugs so perhaps I should just pop some new HT leads on too.
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