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Subaru Forster 01 - cyl 2 miss fire check engine light

Subaru Forster 2001 Check engine light

Code was a cyl 2 miss fire - Replaced plugs & wires - Fuel filter

When the old plug was removed from cyl 2 the color was good. Ran two tanks with fuel injector cleaner.

Takes about 2 days for the check engine light to turn back on - with a cyl 2 miss fire and sometimes a O2 sensor problem - Engine runs ok - Loss of fuel mileage from 30 to 26 MPG - When first started the engine RPM is ok until I start to drive. I only drive about 100 feet to a stop sign and the engine RPM will run up to about 2200 when the clutch is depressed. If I let out the clutch to load the engine the RPM will drop to about 800 and stay there after I depress the clutch again. Talked to a local garage and they want to replace the head gaskets. They think the head gasket is leaking internal to the #2 cylinder and causing the miss fire. No sign of coolant leaks or coolant usage. No oil usage. About 96,000 miles on car. Only the # 2 cyl mis fire errors there are no errors for the other cylinders.

Thinking about replacing the O2 sensor and or the ignition coil.

Any other ideas that I can check or test to prove or disprove the idea of a bad head gasket ?

a faulty head gasket does not automatically mean loss of coolant or even overheating. the symptoms will vary based on where the head hasket may be faulty.
the garage should not be wild guessing at a head gasket problem and unfortunately, that happens far too often.

running a compression test should be the first step followed by connecting a vacuum gauge. the latter will also give an indication of a head gasket problem along with verifying if an intake vacuum leak is present. depending on where a vacuum leak is located it is possible to get a cyl. specific miss because of the engine design.
actually, the high/erratic idle could be the sign of a faulty idle air valve, vacuum leak, etc.

depending on the compression/vacuum readings tight valve lash should be considered. i disagree (strongly and completely) that valve lash on mechanical lifter engines can be ignored for the ridiculous time frames the car makers specify; which is often 100k + miles.
odds are the majority won’t have a problem but a certain % will and this means a moderate amount of pricy engine work if applicable.

jmho, but compression test first and do not accept guessing at a head gasket diagnosis.

I agree on ok4450 analysis of the head gasket issue ruling out or in. Its pretty common in this particular motor sadly. If diagnosed as head gasket you may qualify for this if lucky

Howdy could some leaking antifreeze into the engine be causing the oxygen sensor to trigger the engine light? See my problem 93 taurs head gasget issue post a few days ago sounds kinda similar… let me know what ya think after reviewing it.
My darn check engine light has not come back on since adding that bottle of barts radiator stop leak.

Thanks for the different items to check. Will look into them this weekend.

What should I see for the average compression levels on this type of engine 2.5L
What should I see for vacuum levels ?


I think the compression should be around 165 to 180 lbs normally. The main thing is they all should be close to each other, within 10 to 15 lbs. Vacuum readings will be same as any other engines; readings vary, depending on the throttle position.

By swapping the ignition coils you can see if the missing cylinder changes with it. Others have changed out the O2 sensor and have had success doing that, so your idea may work there. Before doing that though you may want to try running some Seafoam through the intake while revving the engine to try and remove any carbon in the cylinder that may be the cause of this trouble.

You say, as you come to a stop, you are depressing the clutch pedal, and…what is your other foot doing? Depressing the brake pedal? And, the rpm go up. When you want to go, you let off the brake pedal as you’re letting up the clutch pedal, and the rpm comes down.
Try this: drive the car. When you want to stop, use the hand (parking) brake, only. Results?