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2002 Subaru Forester automatic 200k popping sounds from exhaust


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I just bought a 2002 forester S with 200k.  Drives ok, but at idle the motor is shaking a little and the exhaust is sputtering.  I ran the codes and they were initially po301, po302, po420 and po442.  Previous owner couldn't pass emissions he says and gave up on her.

 

I cleared and drove it some more and got back a pending po301 and a po302 and that is it.

 

I was thinking of switching the wires from side to side and putting on a spare coil I have to start.  I figure it could be injectors or valves after that.  Anyone else have an opinion?

 

 

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Cylinders 1 and 2 share the wasted spark coil, so a coil, terminal, wire, or plug problem could affect both cylinders. Usually this means the coil pack is the issue but it could be coincidence. If a spare coil doesn't solve it, then run a compression test across all 4. If 1 and 2 come up low then the problem is internal because they don't share a camshaft so timing is ruled out. In that case most likely would be burnt exhaust valves which will be a re-ring and new valve situation.

 

GD

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so I swapped a working coil and 2 known good wires and same behavior.  I am going to pull the plugs on that side next but my gut is telling me it is the exhaust valves.  there was a little bit of oil on the plug wire of #3, but not dripping.

Edited by 3Pin
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put in new plugs and replaced the knock sensor after getting a code for it.  Still getting misfire in 1 and 3.  I also put in some premium fuel and some fuel injector cleaner as a last ditch.  Seems to run better than it did before, but still is send me a pending code and eventual code for miss on 1 and 3.

Edited by 3Pin
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It's faster to do a compression test as the next test. But injectors may be indicated if it's got good comp. numbers.

 

GD

Provided he has, or has access to a tester. Yeah that would be a lot quicker as the next step. Completely forgot about compression testing in this scenario.

 

Love being able to turn around, open my toolbox, and have everything i need right there.

Edited by golucky66
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Well I usually have to walk over to the diagnostic tool shelf for the compression tester. It's a little farther than turning around to my box. I keep that stuff more centrally located so all the guys know where to find it. Expensive diag tools are community use at my shop. I don't expect the techs to buy that stuff.

 

GD

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