“The problem here is that I don’t have specific knowledge of this vehicle, other than it has a V6…”
Nope!
It has an H-6.
;-))
@the same mountainbike -
I’ve always appreciated the mechanics who know their limits, and in particular the few that are highly specialized and team up among their shops to refer problems to each other… for example, my regular mechanic will refer a lot of suspension work directly to a specialist friend (who in turn refers engine work to him). Neither charges premiums for their work, but they don’t guess at all when it isn’t their expertise.
However, I’m a little stunned that the OP’s mechanic wouldn’t have invested in a real-time scanner of some sort by now. Thanks to the fact that OBD systems are pretty darned standard and the standard is in the public domain, you can now buy hardware and software for around $100 that, while not being the easiest stuff to use, will allow you to monitor sensor signals in real time… so you can strap a laptop (or in some cases even an OBDuino) to the computer, ride around for awhile, and when the misfire happens, you can see which, if any, sensor(s) seem to be off. Almost as good as professional equipment, and well within the range of affordability for a mechanic’s shop…
I assume that the H6 engine uses the the same design for the crank position sensor that the H4 engine does and if so there can be a problem with that sensor possibly. The crank sensor picks up the signal from small reluctor tabs that are mounted on a ring on the crankshaft. As the magnetic tabs pass by the sensor it produces a pulse in the signal. The H4 engine uses three tabs for each side of the engine operation. If one of those tabs gets broken off somehow then the ignition for that side of the engine will not work. I assume that the H6 engine just adds another tab for each side of the engine. It would take a scope to see if the pulses are being picked up correctly. If one of the tabs were to get broken off I don’t think a error code would be set in the ECU. This isn’t a common problem but it has been an issue for some Soob owners.
Eraser, I guess it takes a lot to surprize me anymore. The difference between a basic wrencher and a diagnostician is the ability to use the diagnostic tools, to check thins slike the pulses from a crank position sensor or the waveforms from the coils. But there are also some very good and honest wrenchers out there that aren’t good diagnosticians when it comes to modern systems. They consider lots of what goes on to be “black magic”. Since the OP’s guy referred him elsewhere, I suspect he’s in this category.
Personally, I’m the opposite. I’m driven to understand how stuff works. I can’t even try a new wiper blade without thinking about how the pressure will be distributed and how the crossection is likely to affect the aerodynamics of the blade at highway speeds. Most people would just put the blade on and see if it clears the windshield. It’s a curse, but I live with it.
@Cougar -
Fascinating… so you may be right, mountainbike!
I’m stunned that they would bother with such complexity rather than a simple hall effect sensor…
@eraser1998
Unless something has changed with the newer vehicles, which I doubt, they do use Hall Effect sensors to pick up the magnetic pulses generated by the reluctor tabs.
I did end up taking this to a Subaru service center. They diagnosed the problem as “massive carbon build-up on one side of the head” and said they’d need to re-build the head to guarantee the check-engine light will go away.
So now the question is: who wants to buy a H6 Outback for cheap?
I can’t afford to pay the Subaru service center for these repairs, and I don’t have a place to do the repairs myself.
It’s a 2001 LL Bean edition with no rust anywhere, 9/10 leather interior, 8/10 exterior (a few dings). 122k miles. Needs the check engine light addressed and front CV axles. Engine actually runs smooth. Transmission is smooth and shifts without problems. No fluid leaks anywhere. KBB private party value in fair condition is $6120. Asking $3500. Please PM me if interested.
Or if anyone wants to direct me to a more proper place to post this (since it’s now basically an ad), please let me know.
Thanks again everyone for your input.
No, I’m not interested in buying it. Sorry.
However, I have some advice for your next venture into used car buying, namely–never buy a car that has a CEL (or any other warning lights lit up). This car was abused and/or not maintained by its previous owner(s), and unfortunately you are paying the price–literally–for that previous lack of care.
The 3.0 six-cylinder engine on this car is essentially bullet-proof, but my best guess is that failure to maintain it over the long term led to the alleged carbon build-up. Next time, make sure that any car you are considering comes with full maintenance records that you can compare (at your leisure) to the mfr’s maintenance schedule, and that it be inspected by a competent mechanic prior to purchase.
I wish you the best of luck in selling this car and in locating a replacement.
Where’s the car located?
http://www.ultimatesubaru.org/forum/ is a good Subaru forum. They have a for sale forum as well.
Thanks RemcoW, I’ll post at ultimatesubaru.org. The car is located in NYC. I bought the car from the original owner and I do have a stack of service records.
I would try an upper engine cleaner before removing the cylinder head(s).
Lexus uses GM upper engine cleaner to remove heavy carbon build up from the intake valves and combustion chambers on its direct injection engines.
I can’t say that I’m buying into that massive carbon buildup scenario that you were given unless it’s related to oil consumption, fouled plugs, etc. and if that’s the case then the engine has a serious issue. If a compression test has not been performed then it makes any diagnosis like this even more suspect.
The ad you posted makes no mention of misfires, massive carbon buildup, etc and only refers to a CEL issue that needs to be addressed.
The ad links to a thread 2 pages long describing the mis-fire symptoms. But I’ll edit it to make sure that it stands out more.
The Subaru tech said the diagnosis came from seeing erratic readings on a vacuum gauge. The gauge leveled out when injector cleaner was sprayed in, then returned to “erratic” after a few minutes, presumably when the cleaner burnt off. I don’t understand it all myself, but that’s what I was told.
I forgot to add that the Subaru tech said the carbon build-up is likely due to using a low octane gas. He said only high octane should be used.
I think ok4450 is right. Have a compression test done. If the compression is good, then their diagnosis is wrong.
If they sprayed injector cleaner into the intake and the vacuum readings smoothed out, it may be because if a fuel problem, not a compression problem…if the injectors on that side of the engine are sticking, then not enough fuel is reaching the cylinders, causing the misfires. When they sprayed the injector cleaner into the intake, the injector cleaner burned like gasoline, making up for the gas that the injectors weren’t supplying, and the vacuum readings smoothed out.
Not saying that’s definitely what happened, but I believe that’s a more likely explanatiion than theirs. If the injector cleaner smoothed the vacuum readings by magically removing carbon buildup, why did the vacuum readings go rough again as soon as the spray stopped? The carbon that disappeared momentarily suddenly came right back? I’m not buying it.
I would do two things:
- Have the compression checked.
- If compression on those 3 cyls is bad, have the valves adjusted, then recheck compression.
“the Subaru tech said the carbon build-up is likely due to using a low octane gas. He said only high octane should be used.”
That statement is plausible, as the 3.0 H-6 engine does require premium gas. Of course, that leads to the inevitable question of…why would gas of too low an octane cause carbon deposits only in one bank of cylinders…?
But, as OK4450 recommended, only a compression test will tell the real story, which likely has to do with some genuine abuse of this car by the previous owner.
Could this possibly be a problem with some common ground for these three cylinders? I know nothing about COP systems so I’m asking, thinking maybe some of the experienced mechanics can follow up with an answer.
Maybe this has been mentioned previously, but has a qualified mechanic inspected the camshaft timing on the cylinder head in question?