Miss-fire on #2 spark plug in a 96 subaru legacy

My car will drive fine, then @ 60 mph or above sometimes it will sputter and the check engine light will blink on. I brought it to my mechanic and plugged it in. Miss-fire on some spark plugs. They replaced all spark plugs and wires. The car is sill doing the same thing. My mechanic plugged it in again and now just a miss fire on #2 plug. (even after new wires and plug) Only seems to happen once the car is warmed up. If left sitting for 15 hrs the check engine light goes off completely. Only to come on again, after driven 25 or more miles. Any ideas of what could be wrong?

Those codes are not actually so specific that they can tell you whether the problem is in the plug not firing. You probably have a P0302 code - which is a “cylinder” 2 misfire - not a “plug” 2 misfire. Verify that the actual codes have been P030X and report if not.

Anyway, a “cylinder” can misfire for a number of reasons. Lack of spark, too little or too much fuel, or lack of sufficient compression.

Before doing anything else it would be wise to have the compression checked. If that is good ("good would mean something in the neighborhood of 170 psi or better with all cylinders very near the same).

Then move past ignotion & on to fuel.

Thanks for the tip. Its at the mechanic now. He should be getting back to me soon about what he finds. Are cylinder problems usually expensive? Could I have done more damage by driving it?
Thanks for your help.

It’s also possible to get a misfire code when the valves get out of adjustment. When the engine heats up, the steel valve stem expands (lengthens) faster than the aluminum head does, causing the valve not to seat properly. Then when the engine cools off after use, the valve stem contracts and the misfire code goes away.

The way to check that out is by a compression test, but the test must be done with engine hot (after check engine light comes on). The alternative is to check the valve lash with the engine cold.

I will check to see if my mechanic has done a compression test. This sounds like the problem i am having. Would the fix be an expensive head gasket?

Do you want the truth or shall I lie to make you feel better? Head problems are one of those major surgery things that are on the expensive side.

However, there’s no reason to assume it is likely. You just check this kind of thing out to avoid wasting money on other things like ignition coils or fuel injectors and the like. Misfire problems are pretty common and most are just from relatively minor and routine things.

How many miles are on the car and how well has it been maintained according to the required schedules?

The car has been great…so far. We bought it from a bank repo. Unfortunately there were no prior records. We had our trusted mechanic look it over and gave it a good report. We avoided buying a outback in our price range b/c of head gasket problems. It has 175,000 miles, and im hoping to get 100,000 more.

While it’s seldom done by mechanics, whenever an engine performance problem exists a compression test must always, always, always be performed. One must weed out the possibility of any engine mechanical faults or head down the path of throwing every part in the book at it.

Generally the first thing looked at is the spark plugs. The plugs are out so for crying out loud stick the compression tester on it at that time.

Valve lash will tighten up as the engine warms up and lash is something that should be inspected and adjusted as necessary every 30k miles. Like the compression test and the dodo bird, this is also something that is apparently non-existent.

It’s not difficult to connect a vacuum gauge to the intake manifold and check the vacuum while the engine is running. Any compression or valve lash problem (they’re related) will be apparent right off the bat.
Any anomaly in the vacuum would definitely be a sign to run a compression test, which should have been done while the plugs were out.

If this does turn out to be a valve lash problem a tight intake valve may be surviveable. A tight exhaust valve means problems. These problems may be present after adjustment or they may not surface for months and many miles. This means a valve job. Hope that helps.

I am kind of leaning toward a fuel delivery problem. If the fuel filter hasn’t been replaced you might try that and if that doesn’t help then the fuel pump may be the trouble.
Cigroller an OK4450, what do you guys think about that senario?

I’d say its certainly within the realm of possibility - checking the pressure is another thing to add to OK’s list of easy things to do. The only thing is that I’d suspect that a general fuel delivery problem wouldn’t only shop up in one cylinder. Certainly a #2 injector problem is in the realm of possibility.

There’s another possibility, but it’s rare, and it applies only to the 2.2 liter engine. If your car has the 2.5 you can ignore this post.

My '96 Legacy (2.2) once had a misfire caused by a “traveling valve guide.” The Independent Subaru specialist who correctly diagnosed this condition told me he’s only ever seen it on the 1996 model year cars, but he has seen several cars with this problem.

A valve guide can become loose in the cylinder head, and every once in a while it moves very slightly into the cylinder and prevents the valve from fully closing, which results in a misfire and turns on the CEL. I could drive for weeks between misfires, and the CEL would go off, then, seemingly at random, it would happen again.

If this is the case, and I hope it’s something much more simple, the solution is to install a rebuilt cylinder head, which is rather expensive. This condition must be verified before you even think of such a drastic remedy.

The only other time I ever had a misfire in this car the cause was a faulty spark plug. And the plugs were not very old.

Good luck. I hope your problem is something in the ignition system, and not a traveling valve guide.