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May have found my misfire problem...probablly not, help?


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30 replies to this topic

#26 Fairtax4me

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Posted 08 October 2012 - 12:04 AM

I would at least check the knock sensor (since it's free to look at it, only costs you a few minutes). Any signs of cracks in the housing or corrosion on the metal base means it needs to be replaced.

Compression issues don't typically come and go, though timing issues can cause misfires at low RPM that go away at higher rpm.

The loose valve guide is a good suggestion, but I would expect the valve to burn in a short time and cause a constant dead misfire afterwards. Not something that will come and go randomly. :confused:

#27 upDUHcreek

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Posted 09 October 2012 - 03:38 AM

Ok, thanks again for the help guys, I have a little knowlage about how engines work, but I'm not a mechanic, so I have no practical experience. I don't think it's a timing issue, because the other night when the light wasn't on, and it ran perfectly, I let it idle for 30 to 45 seconds to warm up, before I put it into gear to leave. Any timing issue should have shown up then. Is this correct?

I don't think it's a burnt valve, because that would be consistant, and it wouldn't have passed the "dollar bill over the tail pipe" test. Is that correct?

I'll keep the valve guide thing in mind, and I'll check that if I don't see obvious issues when I check the knock sensor, and swap injectors. Those sound much easier to deal with than pulling the header, so I'll check them first.

I had hoped to check the knock sensor earlier today/yesterday aka Monday, but I had some stuff that came up. By the time I got everything taken care of, it was dark, and I had a wild hair crawling up my ***, so I decided to go to the bar. Hopefully I won't sleep off my buzz all day, and I'll check it tomorrow/today aka Tuesday.

I've never messed with any fuel injectors, are there any tricks I need to know, threads I should read, and should I have extra O-rings on hand when I do this?

Sorry for all the questions. I am just smart enough to know how stupid I am when it comes to working on cars. That's why I usually take my cars to a shop. Unfortunantly, there aren't any shops here that specialize in Subaru repairs. Even the Subaru dealerships here sell multiple brands, so even their mechanics spend most of their time working on non-subaru cars.

Thanks a bunch guys. I am truely gratfull for all the help.
Charlie.

#28 upDUHcreek

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Posted 09 October 2012 - 01:32 PM

I tried to remove and inspect the knock sensor, but it was so tight I decided I didn't want to break my cheep tools. It wouldn't come off, even though I used at least 50ft/lbs of torque worth of force trying to remove it. From what I've read, that's WAY too much torque on the sensor, and probablly broke it when they (last owner) torqued it down that tight. I'm going to use some penetrating oil on it in an effort to make removal easier. I'll get a new one, and run by my buddy's house so I can use his high quality tools. I should take some time to brouse sears website for some decent tools. They're having a tool sale right now.

#29 Fairtax4me

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Posted 09 October 2012 - 02:48 PM

Use a breaker bar on the knock sensor bolt. If the bolt breaks you can relocate the sensor. Those have a tendency to corrode and can stick. Penetrating oil will/may help.

I don't think it's a burnt valve, because that would be consistant, and it wouldn't have passed the "dollar bill over the tail pipe" test. Is that correct?

I've never heard of that one, and I'm not sure of it's accuracy. But yes, a burned valve would create a pretty much constant misfire due to low compression. If the burn is minor it can cause misfire issues at low rpm that go away at high rpm. This won't last long before more of the valve burns away and turns into a constant misfire.


Knock sensors are known to cause many issues from pinging, to occasional small power loss, to multiple misfires, and can result in the ECU going into Limp mode which prevents ignition timing advance beyond a certain point. Depending on the failure mode the sensor may not set a code. Limp mode will be accompanied by a CEL for the knock sensor, the other symptoms may not.
Over-tightening can damage the sensor. Corrosion can damage the sensor. Either way, I'd try to get that replaced before chasing other possibilities.

#30 lumpycam

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Posted 10 October 2012 - 01:49 PM

All of these smart people and no one suggested you start with a compression test?missing and engine smoking suggests bad or broken rings. I have seen several engines with bad knock sensor have number four piston broken from detonation.

#31 torxxx

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Posted 10 October 2012 - 08:52 PM

Have u put a vacumn tester on it? burnt valves will.register on odb2 as a misfire. 2.5s are common valve burners




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