Lean(?) Condition on cylinder #1.

Hi gents!

I have a 2008 Subaru forester 2.0 L variable valve timing 158 hp.

I'm trying to diagnose a lean condition.
Around 7% at idle going to around 4% at higher rpm and under load. At idle I can feel a slight misfire and also in acceleration, in the low to medium rpm range mostly. Especially when it is hot outside.
Cylinder 1 spark plug looks clean like in the picture below (left). From my understanding it's lean afr and it's burning hot.
Checked for vacuum leaks for ages and I can't find any. Replaced spark plugs and coil.

I have 2 sets of injectors because the car is converted to run on lpg. Same behaviour on lpg. So the injector is ruled out.
Also when I unplug one of the healthy cylinder's injector the fuel trim goes to 29%. When I unplug the cylinder 1 injector the fuel trim goes to 26%.

I have pulled the valve cover on that head to find the valve lash almost in specs. 0.2 mm for intake and 0.35 for exhaust valves. Only one exhaust valve on the cylinder 1 is slightly out of specs. It's around 0.27mm when it should be 0.35mm. Can this make such a big difference?
Compression it's in specs for all cylinders.
I have checked and reseated the timing belt.
I have pulled and moved around the wiring harness for the injector and coil pack, nothing.

It's too consistent. It's a permanent condition. Like a vacuum leak, leaking valve or ecu fault.
One more clue - it seems that the misfire is better when the engine is cold. And gets worse when it's in closed loop. But I think it's not that relevant, because when the engine is cold the fuel is dumped and not really metered. So it tends to run better because it's a rich afr.

I didn't find a cylinder leak down tester here (i asked some shops and they didn't even hear about it) but i did put some (2 Bar) pressure in the cylinder at top dead center through the spark plug hole. And apart from a bit of hissing in the oil filler neck I could not hear anything in intake or exhaust. I had a healthy cylinder to compare to.
Also I put some pressure with my mouth in the tube to feel the air escaping. And it felt the same.
But with the engine cold.

Vacuum gauge connected to intake is steady.

Please give me some advice!

1 - Valve lash? - it's closing a fraction of a second too late and some of the mix is escaping in to exhaust.
2 - Leaking valve when engine hot?
3 - Fantom vacuum leak? - this little. should not be felt under load
4 - Ecu fault?

Thank you!

forester08 wrote: I'm trying to diagnose a lean condition.
Around 7% at idle going to around 4% at higher rpm and under load.

Fuel trims of +/- 10% are considered normal. I, personally, wouldn't go chasing a 7% fuel trim issue.

At idle I can feel a slight misfire and also in acceleration, in the low to medium rpm range mostly...I have pulled the valve cover on that head to find the valve lash almost in specs. 0.2 mm for intake and 0.35 for exhaust valves. Only one exhaust valve on the cylinder 1 is slightly out of specs. It's around 0.27mm when it should be 0.35mm. Can this make such a big difference?

I don't see a 2.0L for the 2008 Forester. But for the 2.5L, it shows an acceptable valve lash deviation of only (+/-) .04mm. Your deviation of .08mm is 2X that. Tight valves will open sooner and close later, increasing valve overlap. It would be my guess that this is a more likely cause of your slight misfire.

Thank you for your reply.

Fuel trims don't bother me.

I'm after the misfire. It will generate knock from time to time and the timing gets pulled and learned for that rpm/load. And after that driving is not that enjoyable.
Also it's smelling like unburnt fuel and i can't pass emissions.

I forgot to mention that i'm in europe. And the car is made in japan.

This is a shimless solid bucket system. I will have to modify the existing buckets to obtain the desired thickness.

The manual says +-.02 mm. So 0.08 mm it's 4 times that.

Thank you for confirming my suspicion. I will go that route and post updates.
But man is a hassle to do a valve lash job on this boxer engines.

I'm with Chad on this. The only other thing that comes to mind is a head gasket, which these are famous for. A leak down test would be nice here. You did a compression test, but I've seen them not sure up there, but show up on a LD test, especially if not done on a warmed up engine. I can't see the plug pic you posted to see if it looks clean.

Paul has some good videos on testing if you want to cross that one of your list. Since you already have a rig made up, you could warm up the engine and put air pressure in the cylinder with the radiator cap off and look for bubbles.

Chad's reasoning is sound though and clearly out of spec there,but those buckets probably do suck! I hate that style.

Nissan Technician

Update (maybe is of use for someone):

Like I said the valve lash adjustment on boxer engine is a hassle.

So it took 3 attempts.

You have to take cam sprockets out and they are held in place with this stupid design and weak metal bolt.
First attempt:
I got stuck at the stupid bolt. (this implies to take out fans and timing belt off)


Second:
After I saw on the internet that it's a common issue and the solution is to use a striped bold extractor. So i bought this set

And of course it didn't help. Because the only size i needed was 18 mm and the set doesn't have it. Only chewed the bolt a bit.

So i took the timing belt again for nothing. But this time i striped the thread of 2 timing pulleys. Fun time.

Third time was the charm. I bought the 18 mm striped bolt extractor. Took out timing belt, cam sprockets, cams and the valve buckets.
I used a drill bit type of grinder on a drilling machine to thin out a bit of every bucket interior.

It seems that on that cylinder both exhaust valves were out of specs.

Tip - put something over the exhaust pipe under the valve cover. It will drip oil and it will smell for 2 months. And still does.

The engine works more smoothly. But i guess it needs a little valve lash adjustment on the other head too. Which i will do when the warm weather returns.

"Don't be a parts changer"