Mystery Misfire on EZ30 Cyls 1 3 5 Noticed on Idle

[tryanbaseball]

2001 Subaru Outback H6 3.0 150k miles

The issue is that cylinders 1, 3 and 5 (the same side) are throwing a misfire code. I can notice the misfire at idle and the check engine light will flash when it's occurring. There's also was a code 0491 in the freeze-frame, using my cheapo OBDII scanner. If I clear the codes I will still experience the missfiring at idle but when the MIL starts blinking , as in the case of a misfire, I can give it 200-300 RPMs or more and hold it there (or simply drive away) and the MIL will go away. The traction control "VDC OFF" indicator comes on and off simultaneously with the MIL during these instances. I notice no issues with acceleration,cruising or shifting, nothing indicates a loss of power.

I have owned two of the EXACT same vehicle (only difference was color) that had a new chain and related componants and hg job so I know how the EZ30 should feel like. I have referenced the following links but there seemed to be an unclear closure on the two issues:

 

http://www.ultimatesubaru.org/forum/topic/82331-check-engine-light-blinking-after-timing-chain-tensioner-replacemen-fixed-now-p0420/

http://www.ultimatesubaru.org/forum/topic/129688-misfiring-3-of-6-cylinders-in-a-2001-outback-h6/
 

Swapped around coils and O2 sensors and replaced plugs but no change was noticed. Took vehicle to Subaru Dealership and they were stumped. They suggested tearing down the head/removing timing cover and inspecting from there. The vehicle isn't worth that much so I was wondering if I could get your help. Have you guys ever come across anything like this ended up being another reason than the dreaded decision I face?

 

Not generally a fan of additives but I will probably try seafoam in case it is a carbon buildup issue. Subaru performed various tests and everything checked out good. They also did compression test that isn't on their report and they said everything looked good around 150psi. I intend on doing a leakdown test as soon as I am able.

 

This is Subaru's word (not much news really):

 

 

Anyway, I understand I am in effect resurrecting old posts with this post but it has me and Subaru stumped. Thank you to anyone who cares to comment!

 

[1 Lucky Texan]

sure it was P0491 ?

 

any work done or wrecks before this began?

 

how old is the battery? spark plugs? are they NGK?

 

do you run high octane?

 

maybe try refreshing some ground connections. maybe pull and compare plugs. (I know, it's a hassle)

 

I think some folks have had fuel regulator problems. I think they can be swapped side-to-side.

 

any other electrical or operating problems?

[idosubaru]

check valve clearance.  if they're tight you can slip the shim out and ground it down (the side facing away from the cam lobes). 

 

carbon build up in the heads.

[tryanbaseball]

Thank you grossgary and 1 Lucky Texan for your replies!    Here is an update on the whole deal:

 

Yes, I changed the plugs and put OE plugs. Battery is new and OE. All the plugs in there were basically new and they all looked similar, maybe a little more buildup on the misfiring side. Since I've owned it I run 93 as the manual requires. No idea on the history really. No known accidents. There are some minor electrical issues, for example one of the dash lights (the one that illuminates the clock LED) is sometimes on but most of the time off. It is not a bad bulb and the problem is not with the circuit board. Perhaps a wiring issue. It is strange though because the light is on the same circuit as the other led illuminating bulb and it works fine all the time. There is evidence of some sort of after market something electronic. Perhaps running lights, as there is a deleted LED indicator drilled and mounted through the dash trim. The MIL light also "surges" in brightness whenever it's on simultaneously with the blinker light. . . this is all probably unrelated but you did ask.

 

Anyway, the update is that I took it to an independent shop (that I distrust less than most) and they did all of the same tests as the dealership but added a leakdown test to the mix. . .they found everything to be in normal ranges. They noticed as well that the hg on the misfiring side is externally seeping oil. . . but get this--- they concluded that the misfiring is a result of a bad air fuel ratio sensor on that side. I am not a certified mechanic but I thought it was strange they reached that conclusion because there is no code for lean, rich, or no signal from either sensors. Further, wouldn't switching them to the other bank switch what side was misfiring? I can't tell if they are OE except that that have the same blue wire cover as the OE one the dealership sells. I would like to find another 01 EZ30 with known good sensors to swap it with before draining $280 into new OE sensors. Have you guys ever heard of sensors getting bad to the point that they are causing a misfire--with new plugs, mind you--but without throwing a code specifically related to the sensors?

 

Also, do you think 3-4 years (60k mi) of life on the hg is reasonable with an external hg leak? In my experience I would say yes, but I'm not quite to my 30s and may lack the experience. 

 

Thanks again everyone!

[1 Lucky Texan]

has the car had a rebuilt alternator installed? Did the shop mention anything about the surging light or any other electrical problems?

[idosubaru]

swap the O2 sensors from side to side.  free and if they're the cause, the symptoms should move as well. 

 

HG just keep an eye on how much it's loosing and keep the fluids topped off and you'll be fine.  they usually force a repair once they're leaking enough to drip on the exhaust and smoke like crazy. 

[tryanbaseball]

Hi again,

 

Thanks for the replies.

The alternator is aftermarket, I can tell that from looking at it. Beyond that I do not know. . .

 

Replaced both A/F sensors just for fun and no change. Cleaned out IAC valve and its ports on the TB just for fun, which wasn't a bad idea being that they were very dirty, and no change. What else have I done? ...Oh yes, I cleaned every ground connection I could see and access. I noticed that the shifting was actually a little bit smoother after doing this, but still the mystery issue.

 

I do not want to give up here. The next "easy" thing I might try is to switch the knock sensors.

[1 Lucky Texan]

in addition to the poor reliability of rebuilt alternators, there have been reports of H6 owners receiving the wrong one. The alt for the 4 cyl. will NOT work for the 6 cyl.

[tryanbaseball]

Following up here. An internal vac leak was found leaning me to believe the timing was slightly off. Decided to take the plunge and save the car. So I pulled the engine, took off tc and found RH exaust cam was off by one tooth. Performed repair (did head gasket, valves, etc. while I had motor out) and put it all back. Definately resolved the issue. Thank you for your inputs.

Edited August 13, 2017 by tryanbaseball

[idosubaru]

Woah the cam was off, are you absolutely sure? Good catch finding that, thanks for letting others know.

 

That's nuts, that doesn't just randomly happen, what do you think cause it?

 

did you take any other repair precautions - replace the timing tenaioners?

[Subaru Scott]

I think your mechanic was mistaken, or telling you a story. Unless someone put it together like that, which would be nearly impossible as well as the chain and sprockets are marked, it would have to have catastrophic damage/wear in the chain, guides, tensioner for it to actually skip a tooth. 

[1 Lucky Texan]

any indication the timing system had been opened-up before?

[idosubaru]

any indication the timing system had been opened-up before?

 

2001's were subject to timing chain noise sometimes, being related either symptomatically or to previous work wouldn't be weird.