Misfire on Cyl #3, 2008 outback 2.5i

[sanjeevv1]

Hi guys, hoping someone can shed some light on next steps for me on this issue.

I have a 2008 Outback 2.5i with 112k on it. Done nothing to the car except change clutch at 96k and replaced spark plugs at 96k. So I'm driving down the freeway and all of a sudden there's a short squeak from under the hood and I notice a drop in compression. Compression drop is more noticeable at lower revs that at higher revs (can still feel it at higher revs too, but more noticeable at lower revs) 

Limp home, get the scanner out and there's a P0303, misfire on #3. Took out the spark plugs and there was oil on the boot, and like a thin black thread on the plug gap (like a carbon/oil thread). So I changed the valve cover gasket and plug seals, cleaned out the plug. Run the car for a bit but code stays on #3. Take out the #3 plug and now I smell (and can touch) gasoline on it. For some reason its not getting hot enough. Swapped the plug and plug wires between cylinders #1 and #3, code stays on #3. Thought maybe its the ignition coil (the primary coil resistance didnt appear to be right) and I was getting a good deal on Amazon so I changed the coil. Code stays on #3. 

Checked out the injectors, seemed to be firing OK when listening with a long screwdriver. But I swapped the #1 and #3 injectors just to see if the code moved. Code stays at #3. Looked around, visually and by touch for leaks in the hoses etc. and didnt find anything. Now, I was officially out of ideas, since the only code it was throwing was P0303. 

Then I took it to a shop and the guy does a wet dry compression and leakdown test. He tells me that I need a valve job. He says carbon deposits on the valves are not allowing it to seat itself properly, which is creating a loss in compression (he says the pressure in #3 is about 50 psi compared to 130 psi for #1). He also says that at higher revs the valve is able to open and close better because things are happening at a faster rate, but at lower revs they valves are not able to open and close properly so its more noticeable. The overall tab for his labor is $1500, plus the machine shop will need $400-500 and then the head gasket set and whatever else. This is northern California in San Jose. He has charged me $400 to replace my clutch which I thought was a very fair price. The questions I have are 1) Can something else be done before a valve job is attempted to fix this issue. e.g. the valve lash/clearance adjustments etc. should that be attempted first (I am a not an experienced mechanic even though I did change the valve cover gasket, I could have checked the clearances and adjusted then, but I didnt since I thought the oil leak was the problem) 2) If the valve springs are worn, can that be fixed without taking the head off 3) If its the carbon deposits that are the issue then the Motor Medic Motor Flush product claims it can fix sticky valves and generally the reviews on Amazon are pretty positive. Can this be a potential fix? Or am I gonna make things worse 4) The napaonline website says that pouring a 1/3 can of SeaFoam down the brake booster vacuum inlet is something to be tried. What do you guys think should be my next step..? Really appreciate any input as I'm not able to fork down over $2k for a valve job, but I do need a smog test which wont happen until this issue is fixed. Thanks a bunch.

[Caboobaroo]

Not something I see happen with this era. I have seen them drop an exhaust valve guide which then holds one exhaust valve open, but never a "carbon build up".

 

These are also not known for injector issues either. If you had a tracer on the porcelain of the plug (the side where the wire attaches), you need to start with a new set of plugs and wires. Also inspect the coil pack terminals for ANY corrosion build up and replace with an OEM coil pack if it's bad enough. I will only use NGK plugs and wires on this model. I've had issues even with OEM Subaru wires in the past but only for this specific era.

[idosubaru]

Your mechanic sounds like a very thorough and competent place with great prices.  That's great. 

 

 

Not something I see happen with this era. I have seen them drop an exhaust valve guide which then holds one exhaust valve open, but never a "carbon build up"..

 

I've always wondered this, not being well informed on machinist stuff - I've poured fluids into heads and sometimes the valves will seep.  

Why do they do that and what symptoms will it show if it gets "bad enough"?  and what is "bad enough" ?   Or is this pretty normal for higher mileage/aged heads?  

I've only done it to a few and use it to lap my valves clean and tight.  

[86 Wonder Wedge]

A 60 psi difference is quite large. And 130 psi doesn't sound too great either (I thought spec was between 130-180, but can't confirm at the moment). I assume he heard the leaking air during the leak down and discovered is was coming from the valves rather than the cylinder/piston?

 

A sudden change in compression like that is normally not "fixable" by adjusting the valve lash. However, if this was out of spec for a while, it could have burned a valve.

 

Either way, that head is coming off for more inspection. Hopefully it's just head work.

[1 Lucky Texan]

maybe borescope inspection would reveal scored cylinder wall? might help you decide whether to tear into it or just swap.

[GreaseMonkey03]

I also rarely see valve issues with these. If you have a compression tester or can rent one, do a base compression test on cylinder 3. Then spray some penetrant into the cylinder and run the test again. If compression goes up, its the rings. If it doesn't, its the valves, but they usually make noise when they're shot. make sure you disconnect the coil pack when you run the compression test.

 

If you run the test and compression is normal, change the wires and then the coil in that order. Compression can be as low as around 100 without causing a misfire.

 

I would definitely do your own compression test first before you make that call just to make sure your mechanic is on the level.