Intermittent Cylinder Misfire Subaru Valve Guide Problem

Whenever you remove a Subaru cylinder head you should always look at the valve guides to see if there is any evidence of them moving, particularly the exhaust valve guides. I have seen these guides moves causing misfires or even worse completely drop causing valve to piston interference. The problem seems more prevalent in the 2.5L engines but I have seen it with all 2.0L, 2.2L and 2.5L SOHC and DOHC cylinder heads. Below are some pictures so you can get an idea of what it looks like when the valve guide moves or drops. Sometime it will be just enough to knock of the valve seal and that’s it, still runs okay but starting to consume more oil than it did before.

 

ValveGuideSideView1

Side view of the dropped exhaust valve guide with valve installed

 

They seem to be causing these random intermittent misfires that with OBDII becomes a problem. The misfire will be detected and the code stored. Well now (here in Oregon) your car will not pass a DEQ emissions test. Not to mention it’s annoying to have a check engine lite on. You could have other problems setting codes and wouldn’t know because you think it’s just from the intermittent misfire codes that set randomly. I have seen this problem as intermittent as once a month to a continuous misfire (valve guide dropped holding valve partially open). Check the guides for excessive clearance; if the engine overheated I have seen them shrink also. If the guide to valve clearance is okay then just knock the guide back in place and knurl it. It will never move again if you do it correctly. Over the years I have worked for shops that insist on replacing the guides, but that’s expensive and like I said they’re usually okay. Just make sure the valves are good and replace the seals.

 

This post was written by: Martin Hand

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Martin Hand

About Martin Hand

ASE Certified L1 Advanced Mastertech. Martin Hand has over 15 years experience in Asian and European Import Auto Repair. Specializing in electrical diagnosis, engine performance, AT/MT transmission repair/rebuild. Martin is also pursuing a degree in Computers Science & Information Systems starting at Portland Community College while he plans to transfer to OIT. Certified in Java application level programming, experienced with other languages such as PHP, Ruby, JavaScript and Swift. Martin has future plans of automotive diagnostic software development.

10 Comments

  • Irv Hurd says:

    I just had to have all of my exhaust valves replaced on my 2012 Outback 2.5L engine. It died on the NJ Turnpike. I had taken the car back to Miller Subaru in Mt Holly several times because the check engine light kept coming on. Technicians at Subaru dealership couldn’t pin point the problem Currently in the process of having one of the coils replaced. While my car was being repaired another 2012 Outback was towed from the NJ Turnpike for the same problem

    • Martin Hand Martin Hand says:

      Yes it’s a common problem on the early model Subaru 2.5L SOHC engines. The valves can be refaced and guides pressed and knurled in place and will not move again. Later model 2.5SOHC engines (2008 and up I think) seem to have this problem taken care of, the guides don’t seem to move on these engines.

  • Carlo says:

    I have a subaru impreza.the intake valve is jammed and i dont know why.i do the top over haul and still the problem is there.any idea sir

  • Rich says:

    How does knurling the guides keep then in place? Kurl is inside diameter of guide. Or does it get removed from cylinder head and the Outside get knurlled?

    • Martin Hand Martin Hand says:

      You can see an example of the repair here: Subaru headgasket replacement tips The guide does not get removed, the aluminum cylinder head is knurled on the edge of where the guide comes up for the valve spring. Use a special hollow punch with sharp edge(ID of punch is same as guide OD). The aluminum will pinch the guide in place and it will not move anymore.

  • Bryan Bueckert says:

    I think I may have this issue

    Got an 01 Legacy GT that started misfiring. My wife didn’t tell me for almost a year and thus it burnt out the catalytic converter. Once I replaced it, I noticed it was still misfiring on only cylinder 2. After swapping coil packs, wires, plugs, and ECU with my 00 Forester and no change, I brought it to my buddy’s shop.

    He checked timing, vacuum leaks, injectors (in and out of the car) and no change. Ran compression tests on it and it’s got perfect numbers. It’ll run smoothly for a minute or 2 then just a quick misfire then go back to normal. It’s especially apparent when you’re driving under heavy load.

    My question is, my buddy’s boss suggested to get a used set of heads to replace them. I don’t want to do this cause then I’d be into HG replacement (which it doesn’t really need since it’s got awesome compression). If we confirm the guide has dropped, can it be fixed for cheaper?

    Thanks!!

    Bryan

    • Martin Hand Martin Hand says:

      Most likely from what your explaining there’s a problem in the valve train. Broken valve spring or loose valve guide but regardless the cylinder head(s) need removed. They most definitely don’t need replaced though. We fix all our valve guide problems here in house. Just press the guide in place and knurl it so it will stay. Sometimes the guides need replaced if they’re too loose but I rarely see that.

  • lee hagen says:

    my 2011 Subaru is an “oiler.” New short block put in by dealer last October. Then in January after about 1,000 miles from short block repair, oil escaped and covered the engine. Most of the oil was lost. The DPSM said it was a “defective” oil filter that caused the oil loss. (I think the tech did not remove the first O ring and so there were two in the filter, causing the leak.)
    So, dealer redid the repair. New short block plus heads, cam shafts and related parts. Also found the A/C compressor had “internal open causing issue.” Dealer replaced compressor. Only 33,960 miles on car at this time.
    After 1,000 more miles, accelerated rapidly to pass and CIL came on, so did abs system light and the cruise control light flashed. Cruise stopped working.
    Diagnostic tool shows misfires in cylinders 3 and 4. Going back to dealer this Thursday.
    The diagnostic tool listed 11 possible causes, and they mostly are poor connections.
    1. Why did my compressor quit? Were engine misfires going on before that damaged the unit?
    2. Can this car be fixed? What should be done and what should the tech check out?
    Many thanks. Lee Hagen

    • Martin Hand Martin Hand says:

      The AC compressor is completely unrelated and coincidental. The obvious preliminary things should be checked for the misfire. I doubt the valve guides are dropping at this point. You can easily find out by removing the exhaust, I have never seen intake valve guides have problems and it’s always the exhaust valve guides that move causing a misfire.

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