Outback missfire

subaru
outback

#1

My girlfreind has a subaru outback that comes up with a “miss fire on cylinder one” code. The wires, plugs and coil was replaced. The check engine light still goes on. It runs ok until the engine gets hot then the engine sputters. One guy suggested a burned valve. Getting expensive any ideas???


#2

What year is this Outback, and which engine does it have? The mileage would also be helpful.

“One guy suggested a burned valve.” What was the basis of this suggestion? Did he do a compression test? Did anyone do a compression test?

A bad fuel injector can cause a misfire. So can a clogged fuel filter. Throwing parts at the car isn’t going to fix it. Testing of individual components will eliminate them as the source of the misfire by the process of elimination.

Not all misfires are ignition related.


#3

A misfire problem can be one of the most difficult engine problems to solve I think. There may be a problem with the cam sensor as it heats up. I would check that signal waveform as the engine heats up to see if there is a change in it. Swapping injectors with another may help pinpoint a trouble there.


#4

A burned valve is entirely possible if the valve lash has never been inspected and adjusted as necessary.
My perpetual recommendation when it comes to an engine performance problem is to ALWAYS run a compression test when the spark plugs are out. You’re 99% of the way there with the plugs out so rule out a mechanical malfunction right then and there.

If the valve lash is on the tight side (with some clearance) this could explain sputtering when hot. The metal expands when hot and a few thousandths of valve lash clearance can become less than zero; which means the valve is being held open a bit.
If this has been going on for a while adjusting the valves may help in the short term but down the road valve problems may surface no matter what because the valve, or valves, are damaged goods.

A vacuum gauge can also be connected to an intake manifold vacuum hose. If a cylinder has low compression due to rings or valves then it will show up on the vacuum gauge instantly.


#5

I would think a burned valve would show up cold or hot. What about a bad injector (if it’s multiport). A compression test will nail down a burned valve.


#6

Swap #3 fuel injector with another. If the misfire follows, it’s a bad fuel injector.


#7

Year, milage, brief maintenance history…
That info would be helpful.