Subaru misfire

I have a 2005 Subaru Impreza that misfires. It can happen at most any speed, not sure at RPMs above 4500. I can always make it happen if I turn the air conditioner off and then back on. I have replaced the plugs, wires, front oxygen sensor and ignition coil.

I also ran a can of injector cleaner through it.

The check engine light sometimes comes on, and the code was for misfire on 3

Were there any other codes?

What did your #3 spark plug look like when you pulled it out? Compare to the others.

You can try swapping your #3 fuel injector with another to see if the misfire moves with the injector.

Checking the compression would not be a bad idea.

Hope that the fuel injector is just dirty or plugged. The can of injector cleaner probably wasn’t enough. Do like cigroller suggests and swap injectors or just take out #3 and look at the spray pattern. Or just replace it.

The fuel injector will be a lot cheaper than a compression problem.

The plug on three looked good yesterday. I took the car in for a tune up a few months ago. The only thing they did was change the plugs for 100 dollars. Stilll had the occasional misfire. No check engine light until last week.

I have since changed the other items listed, oxygen sensor, wires, and coil pack.

When I took out the plug in three last night it looked clean, light gray ash, and good gap. replaced it and still the same problem.

How hard is it to replace an injector??

To swap injectors you’ll need to pull the fuel rail - you’d want to have a repair manual for the car ($20 at an auto parts store for a bare bones Haynes or Chilton’s).


Any time a performance problem exists a compression should always be run as a first step. A cyl. that is down will never run properly and knowing this in advance can save a lot of time and money spent throwing parts at it.

If the compression is down the most likely cause would be tight valve lash; which should be inspected about every 30k miles and is seldom ever done.

Inspecting compression should be done no matter the age of the car or the mileage. In a perfect world a late model and even low miles car should not have a compression problem.
In the real world problems do occur so weed this potential problem out in advance.
I’ve seen a number of low miles vehicles that have suffered or were a heartbeat away from suffering valve and cylinder head problems due to this very issue with the worst example being a Subaru that only had 7k miles on it. Both cylinder heads were totally trashed to the point where they were not even repairable.

Hopefully this is not the case but considering the items you’ve changed have not fixed the problem it’s a good idea to back up a step and check the compression.

Thanks I will check it out