My 96 2.5DOHC started missing and the engine light come on, checked the code and it said #3, so checked the compression on #3 and it was very low 60psi. I assumed it was a burned valve because of the fact it has a hundred and ninety thousand on it, But two times now the check engine light has gone off for a while and the comes back on, would it do this if the valve was burned? It has a miss more noticeable at idle but runs great going down the road, and starts good even in the cold. I think I read somewhere on usmb that the HLA`s can actually cause a valve to stay partly open after the valve seat has become worn? But also read that these HLA`s can be shimmed? My 2.5 has had the head gaskets redone and like I said it runs great. If it is adjustment how hard is it to adjust them in the car? I don`t want to junk an engine that`s still running. I am planning on doing a 2.2 swap but would sure like to wait until it`s warmer or really needed!!  Thank you all who willing to help me learn about subaru`s

HLA = Hydraulic Lash Adjuster

HLAs do Not typically cause valves to stay open. HLAs automatically adjust for valve seat wear.

Regardless, your 2.5 does NOT have HLAs. Lash adjustment on your engine is done by shims on top of the valve. These are much more prone to burning valves because the valve seat wears, and adjustment has to be done manually by removing the lifter bucket and changing the shims.

 

A burned valve will act exactly as you describe. The engine may run fine when cold, and at rpms higher than idle. But will misfire at idle. But more often than not, the cause of a misfire is old spark plugs and wires.

 

When you did the compression check, did you check compression on all 4 cylinders?

Did you remove the spark plugs from all 4 cylinders before the test?

Did you have the throttle all the way open for the test?

If you can say No to any of these, your test result is inconclusive and really doesn't tell you anything about the health of the engine.

The 96 2.5s have hydraulic lifters. The 97-99 2.5s are solid with the shim over bucket setup. I'd definitely say you've got a burned valve. not all that uncommon

 

edit:  Lash adjusters.  sorry.  Need to quit thinking of push rod engines.  lol

Edited February 22, 201412 yr by soobie_newbie67

I only checked the #3 cylinder because that`s where the computer said the code was coming from, plugs and wires are not very old at all, What does holding the throttle open do? I have never heard of this. Subie-newbie67 says the 2.5`s with HLA`s don`t use shims, is this correct? if this is the case then the valve is most likely to be burned? Right?

Newbie is correct, 96 is the only year the 25d had hlas, they are hidden on the inside of the valve bucket. There are no shims on this particular ej25d. Burnt valve is a fairly safe assumption.

Have 20 heads for that engine sounds like valve clearance was not set right if valve cover says twin cam on it hydro lifters if not no hydro buckets.

So should I put a different head on it? and what would a used head cost? Can it be done in the car? or is it faster to pull the engine? or just can the whole idea of fixing this one and continue with the 2.2 swap?  I know everybody says do the swap and I am going to, but if I can fix this one, then maybe I can get a few bucks out of it to help pay for the swap? If it is running good and in the car so they can drive it then maybe I will get more for it? I have seen several 96 to 99 Subarus for sale with bad engines so I would think someone could use it!  Thoughts please!!!

I only checked the #3 cylinder because that`s where the computer said the code was coming from, plugs and wires are not very old at all, What does holding the throttle open do? I have never heard of this. Subie-newbie67 says the 2.5`s with HLA`s don`t use shims, is this correct? if this is the case then the valve is most likely to be burned? Right?

Holding the throttle open allows the maximum amount of air into the cylinder during the test. With the throttle closed you may only get half as much compression as there should be.

Only removing the spark plug from one cylinder also brings down compression because it slows down the cranking speed of the engine.

To get an accurate compression test you need to remove all 4 plugs, and crank the engine with the throttle held wide open. You should then test the other cylinders to see if that cylinder is low compared to the others, and by how much.

 

A more conclusive test for a burned valve is a Leakdown test, which requires shop air around 100psi.