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Discussion Starter #1
Hi all,

I was referred over here from the sb9t forums for more knowledge on the h6 engines.

I have a 2006 Subaru B9 Tribeca Base 3.0 model.

It has been misfiring with a P0301 code & occasional (but more steady) P0306 code. It is possible the P0306 code could be a bad injector o-ring from pulling fuel rails, so I am not too concerned about that one. The initial problem is the P0301.

Here is a list of symptoms and what I have done currently...

First started misfiring while driving 40mph after about 10 minutes of driving.
RPM's at cold start are about 1500
RPM's will fluctuate upward when switching gears to drive or reverse
Misfire feels like it steadys out when increasing RPM's to 2000-3000
Bank 1 passenger side is running extremely lean. Typically around 30-35%
Drivers Side Bank has been running rich, -5-(-10%)
Intakes on cylinder 1 side are significantly hotter to the touch than other side
Old spark plugs had no abnormalities on them
Coolant has been running on the lower end
No oil in the coolant
No coolant in the oil
No bubbles in coolant resevoir
Air/Fuel Ratio fluctuates when misfiring, sometimes 15+
Misfires occasionally disappeared upon cold start up in the beginning
Misfires also occasionally disappeared after running vehicle for 20+ minutes
Have noticed that the exhaust does smell of extra fuel upon startup


What I have done
Replaced all Spark Plugs
Switched Ignition Coils
Checked power to coils from the wires
Switched Fuel Injectors and checked power to injectors
Cleaned MAF Sensor
Cleaned Throttle Body
Replaced Throttle Body Gasket
Replaced Intake Manifold Gaskets
Cleaned top of head around injectors
Checked for Vacuum Leaks (Don't have a unit to do smoke test, so could have missed)
Swapped 02 Sensors
Checked 02 sensor wiring
Checked ECM Signals from ECM
Compression Test was great in cylinder 1 at 207




After all of this, still at a loss. If anyone has any insight it would be greatly appreciated. Otherwise, I may have to bite it and spend some money on a mechanic.

Thanks!
 

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On the Super Mod Squad
2002 3.0 VDC Wag + 2018 2.5 Leg Ltd
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26,305 Posts
Hi all,

I was referred over here from the sb9t forums for more knowledge on the h6 engines.

...After all of this, still at a loss. If anyone has any insight it would be greatly appreciated. Otherwise, I may have to bite it and spend some money on a mechanic.

Thanks!



moved thread and updated title. the firing order may suggest something.

that other H6 people have typed of in the 2005-2009 section.


and what I hope it is not,...a need to source a new ECU/ECM. the outbacks that have had issues needing one were about 2008s,
but Tribeca EZ30 were on different production schedules with their early switch to the EZ36.

 

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Discussion Starter #3
moved thread and updated title. the firing order may suggest something.

that other H6 people have typed of in the 2005-2009 section.


and what I hope it is not,...a need to source a new ECU/ECM. the outbacks that have had issues needing one were about 2008s,
but Tribeca EZ30 were on different production schedules with their early switch to the EZ36.
Thank you eagleeye. I hadn't found anything on a firing order so I appreciate the picture. The firing order definitely sticks out as a sore thumb with 1 and 6 being the first two cylinders to fire.

I have had a couple people suggest the ecm. I hope it is not, as it is an expensive fix. But on the brighter side, still a much easier fix than head gaskets or valve issues. The ecm was carrying a current when running it to the sparkplug wires. But that isn't to say something else isn't amiss within it. As well as, it was only a multimeter that I used to read it, and I know nothing of ecms and hadn't ever pulled one before this.




Also, thanks for the move and update!
 

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2001 VDC/SC One of a Kind
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Have you looked closely at the wire harness for cracked insulation, varment niblings, etc.? Is there any corrosion in the main harness connection?

Car-Part.com--Used Auto Parts Market I looked and see several available ECMs across the country. Just look at what's close to you by your zip. From one Tribeca to another, no programming needed, plug and play.
 

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03 H6 OBW & 06 WRX Sportwagon
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any chance the fuel lines have been misrouted?

checked the vacuum line from the fuel pressure regulator for fuel wetness?

does the car run the same or better immediately after an ECU reset?
 

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2009 3.0R Outback
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Do you live in the rust belt? I had a cylinder 3 and 6 misfire right after I bought my used OB. The coil pack laminates had rusted enough to expand and crack the cylinder 3 coil and the clip for the electrical plug on cylinder 6 was broken causing intermittent spark.
 

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Discussion Starter #7
Have you looked closely at the wire harness for cracked insulation, varment niblings, etc.? Is there any corrosion in the main harness connection?
There is some cracking in the plastic housing surrounding the wiring, but no corrosion that I can see.
 

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Discussion Starter #8
any chance the fuel lines have been misrouted?

checked the vacuum line from the fuel pressure regulator for fuel wetness?

does the car run the same or better immediately after an ECU reset?
No, the lines shouldn't be misrouted. I haven't checked that vacuum line though, I will have to locate it.
I haven't done a reset of the ECU, is there anything besides loosening the negative terminal that needs to be done? Because I haven't driven it for a while my battery keeps dying after jumping it. Would the battery being dead create the same result?
 

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Discussion Starter #9
Do you live in the rust belt? I had a cylinder 3 and 6 misfire right after I bought my used OB. The coil pack laminates had rusted enough to expand and crack the cylinder 3 coil and the clip for the electrical plug on cylinder 6 was broken causing intermittent spark.

Kansas. Upon the initial misfire in cylinder 1, none of the clips were broken. But, after having to remove them, a couple coil packs wires were almost impossible to remove, one of them being cylinder 1's. So the clip on cylinder 1's wire attachment is broken. I really jammed it in there after that, I haven't noticed it coming off. Without the plastic clip, would it be enough for it to be intermittent? Cylinder 3 hasn't had a problem yet .
 

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Master Caster
2005 XT, Mildly Modified...2006 XT Limited, Highly Modifed
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What is the voltage when the car is running and misfiring?

Bad battery and/or bad grounds are not going to be helping any electrical issue.
 

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Master Caster
2005 XT, Mildly Modified...2006 XT Limited, Highly Modifed
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16,141 Posts
Kansas. Upon the initial misfire in cylinder 1, none of the clips were broken. But, after having to remove them, a couple coil packs wires were almost impossible to remove, one of them being cylinder 1's. So the clip on cylinder 1's wire attachment is broken. I really jammed it in there after that, I haven't noticed it coming off. Without the plastic clip, would it be enough for it to be intermittent? Cylinder 3 hasn't had a problem yet .
Yes, it could be. You can actually get a zip tie around the connection. It's rectangular and there is enough meat on the coil side to get a good tie on it cinched down. I have done it several times. The clips are easy to replace as well, you only need to source the clips.
 

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Without the plastic clip, would it be enough for it to be intermittent?

It was for me at least. I think I broke the clip when I took all the coils out to check their condition when dealing with the cylinder 3 misfire. The connector housing is fairly easy to replace and not too costly. You can either buy them here...


Subaru, Honda, Suzuki - Coil on Plug - COP Ignition Coil Connectors


... or search "FW 090 connector" on ebay, but they go for twice the price there. If you want to replace the terminals it requires a special type of crimping tool. You can pick one up on Amazon for around $20.


When dealing with electrical connectors I also like to give everything a generous spray of CAIG DeoxIT. You can find it at Guitar Center if there's one in your area.
 

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Discussion Starter #14
What is the voltage when the car is running and misfiring?

Bad battery and/or bad grounds are not going to be helping any electrical issue.
The battery, before it started dying after no use, was at 12.97V. But I did not run it under load, I will do that today.
 

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Master Caster
2005 XT, Mildly Modified...2006 XT Limited, Highly Modifed
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The battery, before it started dying after no use, was at 12.97V. But I did not run it under load, I will do that today.
Both of my cars will pump out 14-14.3 volts when the car is running, rarely drops below 13.5

I wonder what logs would tell. Battery voltage at the time of miss-fire.
 

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Discussion Starter #16
I pulled the battery and ran it up to O'Reilly's where it was purchased, to have it tested. They charged it and it came back as having a bad cell. I took the old battery to costco and got a new one with more cranking power. After putting it in I had some hope it would fix the problem, but there is still a misfire. It seems more intermittent now than it did before though, as in, the misfire will come on and then fade out for 10-15 seconds, then come back again. So on and so forth. At this point I'm at a loss. Would a bad valve or gasket be intermittent like that? The RPMS are at about 2000 upon start up, and after revving up the engine they will drop to about 1000.
 

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Discussion Starter #17
Alternator Voltage

Does anyone know what alternator voltage should register if it is working well?
 

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On the H6s, the alternator output is controlled, in part, by the ECM. (Not so for the H4 engines). This is to reduce alternator load on the engine when full charging capability isn't needed. Consequently, in a properly-operating system, the voltage can measure in the low 14s at times (e.g. just after starting the engine), but as low as the high 12s at other times (when the battery is approaching full charge and full alternator output isn't needed). The readings in the high 12s have caused concern and have been the subject of discussion here in a number of threads dealing with alternator/battery problems.
 
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