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Battery may be 2 years old. Discounting bad gas. Only recent repair involved replacing the exhaust middle pipe last week. Just the misfire codes.

 

May be a contributing factor. Returning from a late Thanksgiving dinner last year the engine developed a serious misfire. #6 cylinder was the failure. Problem solved itself the next day.

 

Wondering now if the #6 cylinder misfire could somehow now be causing the other 3 misfires. 

 

Can't believe 4 of the 6 COP failed.

 

Plan tomorrow is to replace the #6 COP and see if anything changes.

 

Just cleared the codes, ran engine for a few minutes and now have codes for only cylinders 5 and 6. 

 

Can't recall ever replacing the fuel filter. Could it be causing this problem?

Edited by john in KY
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coil failures are rare and you're right , multiple simultaneous coil failures approaching impossible.

 

look for oil on the coil boots, maybe leaking VC gaskets ?

 

check battery and changing system health.  If it misfires or runs rough at idle and squirting some starting fluid in the intake smooths it out - that would indicate a fueling problem I think.

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Someone had one in New York with multiple misfires and someone figured it out but i can’t recall what it was LT?

 

Swap injectors?

 

A buddy had multiple misfires on his 03 H6 and swapped a coil around with no change. He took it to a shop and they said they replaced multiple COPs years ago and the car has been fine since. I figure Either he incorrectly swapped around or something was miscmunciated but who knows, it always seemed odd to me.

 

I’ve seen one tight exhaust valve on a perfectly running EZ 220,000 miles I pulled to reseal the timing covers.

Edited by idosubaru
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Are you getting ANY O2 codes at the moment? Is the loom for the down O2 damaged?

 

I had a 99' Saab 9-3 that I bought with heating element code (IIRC, the downstream then eventually the up had it as well) for the down O2. I ignored it for over a year w/o any real issues. Then, the engine eventually developed a random misfire, randomly. Though the times it did misfire, it would usually do it during the 1st 5-8 minutes after starting, then run fine w/o issues. Other times free revving briefly would clear it. No codes other than a rare random misfire and the O2 heating element. Towards the worst of it, the downpipe was cat-less, and during a rough bout, I free-revved and it backfired, blowing the actual muffler apart at the seams :D (thankfully it wasn't a welded muffler case and the cat was absent, or it could have been worse).

 

1st replaced up O2 due to a code for it, and it still happened. After more observations, discovered the down O2 casing (it had a metal sleeve on top) was noticeably cracked, almost top to bottom. The internal failure was causing a short, and it was creating havoc with the ecm. After replacing, the problem stopped. IIRC, the down O2 was way off and I think it showed a short.

 

Do NOT run the engine until you figure it out, as it can quickly kill your cats.

 

My 99' Continental had a random misfire, and it was from rodent chew on the wiring loom for the coils on the back of the engine. I bought it like this, and repaired the chew, but still ended up having 2 bad coils on top of that for the same side as the affected wire damage. And not long after the repair, at least one of my cats is damaged, hence why you shouldn't drive with a random misfire ;)

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john i have a 2006 H6 do you want me to send you the injectors? i ran that engine 1,000+ miles before I pulled it and never had any misfires and ran perfect minus headgasket. 130,000 miles and it's been stored in my garage.

 

fuel injectors caused 1,3, 5 here. might want to try getting a set cleaned or swapping in my set:

http://www.ultimatesubaru.org/forum/topic/102192-exhaust-manifold-bolt-thread-size/

 

That might seem the most likely if we consider the 6 misfire as well on yours?

 

Mis-aligned cam sprockets caused 1-3-5 misfires in these two:

http://www.ultimatesubaru.org/forum/topic/162145-mystery-misfire-on-ez30-cyls-1-3-5-noticed-on-idle/

http://www.ultimatesubaru.org/forum/topic/101119-h6-30-dead-bank-135/

 

How do you check cam sprocket alignment without pulling the timing covers? I guess you can only pull the valve covers and check valve clearances and compare?

Edited by idosubaru
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Really appreciate the offer but going to wait on tomorrow to see if the new plug does anything. The more I think about the problem the more fixated I get on a lean condition causing the problem. Today the weather sucked, snowing in KY in April WTH? Tomorrow and the rest of the week forecast to be nice again.  

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Great, glad you found an easy fix. Those engines love the stock plugs.

 

Every 100,000 mile H6 EZ plug I’ve pulled still looks awesome and I’ve never seen a misfire caused by stock plugs in H6s, they’re great plugs for simple reliability and low maintenance.

 

The plugs are easy to replace with the valve covers removed so I usually try to time VCGs and plugs at the same time on H6s which means I only ever do that labor job once. I guess if I can make 300k before rust gets it I’ll consider another change.

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Great that you found the issue.  Interestingly I have had two vehicles both poorly running that ended up being a coil in both cases.  The 03 was getting constant misfires and check engine lights.  The 99 misfiring but no check engine light.  After doing all of the usual things ended up putting in a used coil and problem solved!

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