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2006 Wagon 2.5i M/T
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Discussion Starter #1
I took my used 2006 Outback 2.5i 5-speed on it first significant stretch of highway driving. Some things I'm happy about - like achieving 32 mpg in cool (35F) weather - although I was using some tricks like coasting in neutral down hills and slowing down uphill. Power is ample, and the engine runs smoothly under low loads and/or rpms.

But, under hard acceleration, the engine note is fairly loud, moderately shaky "rrrda-rda-rda-rda" like the old V-8's of my 60's muscle car days - very different from the steady "yaaaaaaowwwl" of the inline 4 engines (mostly Toyotas) I've owned or worked on since.

Is what I'm experience a normal condition for these H4 "boxer" engines or is something not right?

I should note that the previous owner, fairly recently, had a new head installed on the right side, but the original head is still on the left side. The reason for the head replacement was reportedly due to a clogged oil passge ruining the camshaft/bearing. It seems all but a couple valves were re-used on the new head (presumably re-ground?) - might this be producing a it of a power imbalance betwen the right and left sides?

I appreciate any advice in advance. Thanks.
 

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2006 Outback 2.5i Limited 5MT, 1984 Porsche 944
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Look under the hood. Are both driveshafts the connect to the transmission green? My car did the same thing when I (stupidly) replaced one of the axles with a rebuilt axle. A used axle off ebay fixed the problem.

The alternative would be bad motor mounts or transmission mount.
 

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03 H6 OBW & 06 WRX Sportwagon
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maybe look for exhaust leaks too. Check that the air filter box is installed correctly. easy to miss the tabs at the bottom.

do you have a CEL on?
 

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2006 Wagon 2.5i M/T
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Discussion Starter #4
Thanks for the advice, but the driveaxles and exhaust and intake is fine. No check-engine light.

My impression is that of a possibly normal, but maybe not, asymmetry (not to be confused with a misfire) in cylinder firing order. Something like a V-8 - their "bda-bda-bda" rather than a "bwaaaaaa" of in-line engines being one of their appeals to traditional hot-rodders. So, I thought maybe the "bda-bda-bda" is normal for boxer engines too - due to their similar to a V-8 - but fewer cyinders - exhaust arrangement. But I can feel it as well as hear it - maybe the variable intake valve lift is not actuating in one of the heads?

I'll probably have to take it to mechanic faimilar with Subarus and see what he thinks. I hate dealing with car dealerships.
 

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03 H6 OBW & 06 WRX Sportwagon
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well, the turbo cars definitely have a rumble from unequal length exhaust. But the NA cars can sound just like a Honda. some people do put UE headers on NA cars to create that sound.

not impossible to have a valvetrain problem causing some odd exhaust sound and vibration - but I'd expect a cylinder misfire code I think.

Do you 'feel' a vibration or only hear an odd exhaust note? Is the experience the same revving the engine while parked?
 

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2006 Wagon 2.5i M/T
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Discussion Starter #6
I was feeling it - a bit of pulsation rather than a steady engine vibration and maybe in the engine torque too (hard to tell). I'll check again, but it seems to be only noticable when the engine is under a good load. With the 2006-onward variable lift, the cylinders in which the variable valve is not switching to "high" would still fire normally, but the would produce a bit less power under higher load/RPM's than the normally operating cylinders. And if it is a sticking mechanical part rather than the oil-pressure actuator not working I don't think it would produce a trouble code.
 

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03 H6 OBW & 06 WRX Sportwagon
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well, I was thinking exhaust valves, but point taken on something like a sticking intake valve or valve actuation. seems like that would be less likely to affect the exhaust note.
maybe investigate whether the oil banjo bolt needs cleaning replacement?

I wonder if you could visit another seller/dealership and 'test drive' a similar car to confirm you're not hearing something normal?
 

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2006 Wagon 2.5i M/T
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Discussion Starter #8
I assume you are referring to an oil line connection to the Turbo? This is the naturally aspirated engine.

I think I am just experiencing the engines natural vibration and noise from the engine's right-right-left-left firing order which is aggravated by having a brand new head and camshaft on one side and a 146,000 mile old head and camshaft on the other side. It is probably purely an aesthetic annoyance. I've been listening to other Subarus when they go by, and for quasi-luxury cars, they are noisy. There are a couple people at work with later-model Outbacks and Legacys, maybe I'll see if I can get a check ride from one of them.
 

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03 H6 OBW & 06 WRX Sportwagon
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oil pressure operates the variable valve system.

just a thought.
 

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Lawn ornament XT
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oil pressure operates the variable valve system.

just a thought.
Yeah, but at low pressure (below 3500 RPM) it shuts down one intake valve per cylinder.

I've always understood this system to fail by not triggering the 2nd intake valves when going over 3500 RPM rather than failing to disengage the secondaries when dropping below threshold.

Have I got it backwards?
 

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03 H6 OBW & 06 WRX Sportwagon
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just pointing out that there may still be an oil screen that could be partially clogged, robbing the variable lift system of flow/pressure.

I'm not convinced that's the problem, but since he brought up a concern, that banjo is one area that could be examined.

I suppose some issue with a stuck pin/control piece, or odd stuck intake valve could be an issue...seems unlikely

but yeah, low lift at low rpms I guess gives better 'mixing' in the cylinder; high lift at high rpms breathes better? http://drive2.subaru.com/Spring07_whatmakes.htm

these systems are almost too complex even for OBDII to help much at times. I'm fighting an odd intermittent miss myself on my wrx - no codes.
 

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Car: 2008 Tribeca, 2010 LGT, Sold: 2005 XT Limited
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There is a code that the VVS throws when it isn't working (like from low oil pressure).
 

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2006 Wagon 2.5i M/T
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Discussion Starter #14
The VVS

The oil to actuate the VVS is gets there via an oil passage in the head. There are no external oil tubes, hoses or banjo bolts.
 

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2006 Outback 2.5i Limited 5MT, 1984 Porsche 944
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Maybe whatever is wrong with yours is for the better. I'd love to get 32mpg...
 

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03 H6 OBW & 06 WRX Sportwagon
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The oil to actuate the VVS is gets there via an oil passage in the head. There are no external oil tubes, hoses or banjo bolts.
ah, OK. I guess I'm thinking of the AVCS .
 

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Car: 2008 Tribeca, 2010 LGT, Sold: 2005 XT Limited
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I was also thinking of the code which is for AVCS.
 

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There's two codes with the AVLS that are seen quite (too) often -- P0026 and P0028. These occur when the ECM is commanding a low, or high, lift on the second intake valve, but the corresponding oil pressure sensor switch is indicating the other. (These codes are more often seen when the oil pressure sensor switch fails, and less often, if the solenoid fails.)

The control system is based on duty cycle signals sent to the left and right side oil solenoids. When the duty cycle is low, oil pressure to the mechanical cam switch is low, and the lift remains low. When the duty cycle is high, the pressure is high and the mechanism locks the second valve cam to the high lift cam.

The OBD checks to see if the oil pressure sensor switch is indicating whether the pressure is low, or high when that's what the ECM is commanding. As has already been noted, it doesn't detect if the mechanical cam switch actually reacts properly. So when the duty cycle is low, the oil pressure could be low, and the oil pressure sensor switch would be sending the right signal to the OBD, but the mechanism could, theoretically, be mechanically stuck in the locked high position.

But if the duty cycle is low, and the oil pressure switch is indicating high, or vice-versa, that can trigger a DTC and the CEL.

The duty cycle signals to the right and left side solenoids (among many other parameters) can be monitored and logged using a compatible scanner connected to the OBD port. Programs such as FreeSSM and Romraider Logger (both free but require an interface cable) should work. (See http://www.subaruoutback.org/forums/65-parts-accessories-performance/39426-freessm-complete-access-your-ecm-tcu.html?highlight=freessm)

If Romraider Logger is used, the data can be recorded and analyzed afterwards.

Here's an sample from a log of all engine parameters parameters for my 07:



The right side scale is engine speed in rpm. The left side scale is vehicle speed (kmh) and OSV duty cycle (%). In this sample only the left side OSV duty cycle is charted, because the right side is identical. But a comparison of the two could be done, against throttle position, and engine and vehicle speed, to see if there's any apparent difference. Throttle, and other parameters also affect whether the duty cycle is low or high; in other words, it isn't only engine speed, so these could be added to the chart to see what happens when the throttle advances and drops off.
 

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2005 Legacy 2.5i Wagon 4EAT; 2005 Forester XS 4EAT
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...although I was using some tricks like coasting in neutral down hills...
Just an FYI: it will actually use MORE gas by doing this. When you're going downhill in gear, fuel is shut off while coasting. The momentum of the car rolling is keeping the engine "running" without using gas. With it in neutral, it must supply gas to keep the engine running at idle. The Outbacks have done this at least since Gen 2 ('00 - '04).

Awesome mileage, btw.
 

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2007 Outback 2.5XT Limited; 2012 Outback 3.5R Limited. Is is just noisy or is it a true vibration, like the car shaking? My 2007 had a LOT of engine noise when accelerating (and with the Turbo it seemed like I was ALWAYS accelerating), but it wasn't actually vibrating--it just seemed like the engine was about ready to fly apart.
 
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