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2000 Forester Manual
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Discussion Starter · #1 ·
Hey everyone, great to be here. Hoping to get some advice on an issue.

I have a 2000 Subaru Forester with a manual transmission. Shortly after purchasing it a year ago, I had a subtle misfire issue in cylinder 4. I bought it used so I was expecting these drawbacks. I bought it from a mechanics place that buy Subarus with gasket issues, fix them up and then resell them at normal prices. So I've ruled out the head gaskets since they've allegedly just been replaced. Still after many attempts I can't figure out what is causing the misfire. It only happens during above-idle engine speeds (above 700rpm). This means when I have my AC on, the idle kicks up a bit, and the misfire subsides almost completely. Over the summer my CEL never came on. However now that the weather has cooled, I see this code every 50-150 miles to the point where I feel I need to address it. Usually I just ignore it since its not noticeable at higher speeds or under load.
I have 150k on the engine, and I'd like it to last a while longer as I love this forester.

Parts I've replace:
All 4 spark plugs (NGK 7090)
Spark plug wires (NGK 8691)
Catalytic Converter (Walker 54573)
Front O2 sensor (Bosch 17018)
Ignition Coil (Import Direct 23-0403 from Oreilly's)

Tests I've ran:
Compression Test* (results shown later)
"Dollar Bill" Test (holding bill up to exhaust sometimes sucked the bill in, pointing to exhaust valve issue?)
Code Reader (P0304 every few hundred miles, VERY occasionally (twice) a P0302 code)
Swapping Fuel Injectors (Swapped cylinder 2 and 4 injectors to see if the misfire code would change. It didn't)

Compression Test Results:
As a note, I've never done a compression test. I did my best to find a tube or tool that would allow me to squirt oil sideways into the cylinder. The results were not what I was expecting for Dry, and the Wet tests just made things more confusing. But as I've mentioned, this may be due to rookie error.

3- 158

Please let me know if I'm missing any pertinent information. I'm open to suggestions. I've called some mechanics to get an idea of what they'd do differently if I took it in to them, but they pretty much told me they'd re-run the tests with their own equipment.
I should note that 5 months prior to posting this, I did have a severe issue with the ignition coil where I was getting a flashing CEL on cylinders 1 and 2 misfiring. I've since replaced them. However the issue in cylinder 4 was a problem before and after this event.
Thanks so much for everyone for any help you can offer.

2004 Forester XT 4EAT
1,367 Posts
I'd do a Leak Down test to rule out valve issues. #4 has a history of getting 'burned' due to it getting fuel(ed) last.

Be glad it's a SOHC and not the DOHC, as it's much easier. Read up on how it's done - may be w/in your skill set. Otherwise, take it to a trusted shop.
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