Valve lash question

[ten2doyle102]

Alright, so I have a 2008 Legacy gt and I really do love driving the car, makes good power, The handling is great for a car this size and it has awd for the winters. Perfect family sedan! However, I have been having an issue with intermittent misfires on all cylinders at idle and a hard starting situation. When you're driving, it's great. No hesitation with a small exception of when it comes off idle quickly. I have replaced injectors, coil packs, did leak downs and compression tests both of which have come back good. I also check fuel pressure which was good.

Which leads me to my thread title. My buddy who is a Subaru nut is insistent that a tight valve lash is the cause. I did pull one valve cover and check it and confirmed that they were indeed under the spec, but only by .002-.004, and never so tight that the valves would constantly be open. The tightest lash I saw was 0.005".

Since the car has a hard start cold or hot, wouldn't the lash only be able to affect its starting ability if the valves had nearly 0 clearance leaving a valve essentially open? Or honestly can the valve opening a tiny split second early or late cause this much of an issue? I could see it developing a miss once it's up to temp since the valvetrain components may expand and close the gap to not allow the valve to fully close, but it misfires immediately. This leads me to believe something else is at play. Normally I would just adjust the valves, but you have to replace each lifter, and at a cost of $30/ea, plus the fact that the motor has to come out to do it makes me want to exhaust all the other options first as this would be costly to do and then to find out later that it wasn't the cause would be greatly annoying...

So essentially I just want to try to get a better understanding from you guys if you can help me with how a slightly off valve lash can give this many head aches. I could totally understand if there was 0 clearance.... But that's not the case. And the addition of the hard start makes me think something else is at play here. My buddy told me the hard start is likely from the lash as well.

Sorry for the long post.... Lol.

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[Yoshi]

I don't know subaru motors but that makes no sense to me. hard starts are caused by lots of things. But if your valves aren't too tight, that shouldn't be an issue.

The injectors you swapped out were flow tested and remanned or just some other injectors? How about plug wires and spark plugs?

Car needs three things to run, air/fuel/spark. If any of them are a little off, it'll case your problem. So it could be a very tiny air leak. Fuel seems ok. Could be shitty spark plugs.

[M20_fever]

I agree, no way valve lash will cause that kind of a symptom. Is it a belt or chain driven timing system? How many miles on the car? Any codes? Since you have good fuel pressure (I assume you checked at the rail) I would lean towards and ignition system fault. Did you gap the plugs? Have you tried hotter or cooler plugs?

Does it leak any oil from the top of the engine? I know when I got the Passat the valve covers were leaking and oil was filling the plug holes causing the bad wires to arc, which created a stumble at idle. Full tuneup and new VC gaskets fixed it.

[ten2doyle102]

Yoshi, the injectors I swapped out were brand new. Also, it uses coil packs, but we did replace the one that initially popped up with a misfire. The symptoms began with cylinder #4 and eventually made its way to the remaining cylinders.

Tony, I did check the pressure right at the rail with an inline pressure gauge to verify it was firing properly. Usually when it does the hard start, once it fires over you can smell a bunch of unburnt fuel, probably from loading up during the starting cycle. The only codes it throws are random misfires on all cylinders. It is a belt driven system. I'll be doing the belt this weekend just for peace of mind. The car has 92k on it. Also, no I have not tried hotter or colder plugs. Might be worth a shot. Also, it uses iridiums which are technically not supposed to be gasped as the tips are pretty fragile. I should pull them though just to see what they look like.

Thanks for the help though. Just wanted to make sure I am not losing it.

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[Ryki]

You're correct, they are pregapped depending on the number at the end so a -10 is 1.0mm and -11 is 1.1mm and so on. It is a belt driven system and a flat four motor. Rough idles are typically electrical related but checking the fuel pressure is never a bad thing to do. I'd suggest asking a buddy for a spare coil pack and put it in cylinder #4 and seeing if that helps, I just have an inkling that the new coil pack could have a different resistance since it is new and now your engine is having issues as the coil pack could be getting to voltage quicker than your other three and it's constantly trying to adjust for that.
-caveat to this, I've only owned three subarus and rebuilt one so my level of knowledge is limited.

[ten2doyle102]

Lol! Yeah, I have had a number of subies, most older ones. This is my first boosted one. The shop we bought the car at did replace the suspect coil initially, but it hasn't helped. Though what you're thinking is the new one messed with the others some how? That was about, 15k ago, and since then all the cylinders are misfiring. Might take it to our trusty advanced auto to have them scan it again just to see if anything new cropped up and might tell me more. I am also going to inspect every ground on this thing as I being to work on it tomorrow just in case one is loose or not connected.

I'll probably still go through the trouble of resetting the lash on the motor though. These motors have issues with burning valves which is commonly associated with a tight lash. Don't want that happening.





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[Ryki]

Yeah, that was my idea but bad grounding can cause some funky things on cars... Good luck with everything!

[ten2doyle102]

Alright... So I got the whole motor just about ready to come out when I noticed something... I think I may have found the possible issue.... Both grounding straps from the valve covers on both sides were essentially non existent. They crumbled apart in my hand into dust... No joke.

I still pulled the motor just because I do know the lash is too tight and I don't need any burned valves from it. I'll test out the theory of grounding issues when I re install the motor with and without them. If it still misfires with the lash corrected, hopefully those straps fix it.

Wish I would have seen that earlier... Lol

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[Yoshi]

That's possible. the car should slow crank to start up then as well.

[M20_fever]

I've been amazed what kind of issues poor grounding can cause.