Help Troubleshooting Subaru 3.6L
 

Hi All, figured I'd ask the Subaru junkies-ahem-enthusiasts for advice.

My wife's car is a 08 Subaru Tribeca with a 3.6 H6 (EZ36D). Driving down the road, it started lurching as though it were misfiring. Surely enough CEL showed up. Stopped it, checked to make sure there was nothing visibly wrong, got it to a gas station to fill up because it was pretty low, then got it home. Pulled codes and sure enough, two codes for misfiring on cylinders 5 and 6. I believe these are the back cylinder on both banks.

So some history. This car doesn't get driven much, just had an oil change and has a new catback because the old one had a hole that failed inspection. I didn't have time to do it myself, so I let the inspecting shop do the recent work. I had driven the car 2 days before and there were no problems. It had about 1/8 tank of gas when this happened. The Tribeca is stored outside if that matters. I doubt any ignition components have ever been replaced.

An interesting note is that above ~2500-3000 rpm it drives fine. No lurching at all. It's a sudden change like hitting that rpm (don't know which rpm value precisely) flips a switch.

My troubleshooting so far:
I didn't see any leaks, oil level looks fine, and I filled the gas tank with 93 (it'll take 87 but I wanted to see if bad gas was the problem) and ran the engine for a bit in neutral to see if it got better. I do not think it's a matter of resetting codes because the physical symptoms are still there. Easy next step is spark plugs/coil packs, but it's a bit odd that two different cylinders would go out at exactly the same time? Another possibility a friend pointed out is fuel pressure problems.

Any thoughts?

Fuel filter.
Lower rpms not getting enough flow starving cylinders and getting misfires. Higher rpms create enough flow to run fine.
Sounds counter intuitive but I have had it with other cars.

Yeah, that was a possibility I talked about with my friend. I suppose I should start there. In the fuel tank... that's now full of fuel... :bonk:

Not sure where the filter is on those. Maybe get lucky and it is an in-line?

The internet says any Subaru after 2004 is in the tank.

Well that sucks.

Is there an access panel in the trunk or passenger area to do this through without having to drop the tank?

i had an 06 but it was just the 3.0 with variable lift and timing on the intake. no issues ever besides speed sensor wires to 140k.



move the coils around and see if the codes move to those cylinders. a ratcheting gear wrench or a 1/4" drive fits.

There is theoretically an access panel under the 2nd row seats. But it seems that I am going to have to drain the full 17 gallon tank first or capillary action is going to spray gasoline all over my interior... 17 gallons is a lot of gas to store... I don't have any tanks that large, and I probably shouldn't be driving it around to burn it.

Apparently the pump is inserted into the filter, so I have to disassemble that assembly then reassemble it with the new filter so it's not exactly a quick pull and replace. I suppose I can probably just buy the whole assembly.

That sucks!

i have the PDFs of the 06 service manual if you need a section.

I think I will be alright. Youtube is a wonderful place.

Were you speaking off the cuff, or did you really mean capillary action because, unless I am misunderstanding the situation, I am failing to see how that phenomenon applies in your situation. If you are referring to the tank being filled and overflowing when you access the port then that will happen. I'm pretty sure all you have to do is syphon off a quarter tank, so the fuel is at or below the height of the access port. There should be no need to drain the tank completely. If you are referring to fuel vapor pressure causing fuel to spray everywhere then that seems less likely if you have a functioning EVAP system. Regardless, siphoning the tank should purge the vapor.

If you disconnect the fuel lines before removing the pump assembly from the tank, the fuel will run up the narrow pipes connected to the pump assembly. I don't think you can remove the pump assembly before removing the fuel lines, but I could be mistaken.

Also, I'm pretty sure I saw this happen before, but I could be mistaken as to the physical cause if it.