Diagnosing misfire

[Stphnhrrng]

So' date=' in diagnosing the misfire, have you tried swapping parts to other cylinders to see if the misfire code moves to another cylinder? That's usually my first step in diagnosing a misfire. I know you changed a lot of these parts, but it still might be worth it to try. At least that would rule out if one of the plugs/wires/injectors isn't working properly. Next I would do a smoke test. I understand that it's NA, but vac leaks affect NA cars too. I'd also run a can of seafoam through the intake to see if that changes anything. 200K could have a bunch of carbon buildup on the valves. Just my thoughts on cheap or free things you could try before firing the parts cannon at it.[/quote']

 

When the dealership was tearing through it they checked for vac leaks, there weren’t any. they also tried switching around all the parts even if they were new. They visually checked the valves and stuff, I might try seafoam anyways to be safe but I kinda doubt it’d do anything. How do you run it through your intake though? I always thought it was a liquid you put in you gas or your oil before an oil change

[Stphnhrrng]

I read that low idle was because of the battery being disconnected and it needed to re-learn. So I was driving to work this morning and about 30-40 mins into the drive the check engine light started blinking, car was shaking really badly, and lost most of it’s power. Pulled over at a nearby autozone, cylinder 2 misfire. Called the dealership that was just looking at it, they said it was shaking because of a bad wheel bearing, and that if I brought it back in and paid for a couple more hours they’d check valve clearances and the ECM, even though they told me that they would check valve clearances when I had them working on it last time. Thinking about finding a smaller subaru mechanic in the Salem, OR area if I can’t figure out what’s wrong with it.

[apexi]

I'd have an independent shop check it out, I wouldn't bring it back to the dealership. I'd also just try cleaning the maf sensor for kicks as mentioned in post 8. If the car isn't properly detecting how much air is coming in, that could definitely cause your issues.

[Stphnhrrng]

I'd have an independent shop check it out, I wouldn't bring it back to the dealership. I'd also just try cleaning the maf sensor for kicks as mentioned in post 8. If the car isn't properly detecting how much air is coming in, that could definitely cause your issues.

 

Yeah, I had a mobile Subaru mechanic come take a look after the dealership, wish I had waited and looked myself first cause they just didn’t plug the cylinder 2 injector in properly so after about an hour it fell off the injector. I’m waiting for him to be free so I can have him try to find the original problem now, in the meantime I already replaced the MAF, and it didn’t change much. No vac leaks, cylinder 2 compression is perfect, new plugs, wires, coils, injector. all of the above either I or the dealership swapped with another and nothing changed. (with the exception of the coil I think). At this point I have no clue what could possibly cause it. Dealership pulled timing cover and looked in there and said it looked normal, no missing teeth or anything. Valves haven’t been checked but I would think it would effect the compression if there was a problem.

[Stphnhrrng]

I agree but again wanted to give a potential culprit (with weak ignition coil at high mileage) even though it's most likely something else.

 

So I have to concede, I went to the dealership here in Salem and asked about the plug gap, stock gap is 0.039-0.043. I just wanted to apologize for doubting/arguing with you, and wanted to let people know that they shouldn’t trust the owners manual. That being said, I doubt a couple 1/1000ths of an inch would make much difference, but you were right either way

[Pleides]

Have we even discussed when the misfire occurs? At a certain RPM? Certain weather?

 

Has the car been sitting in quarantine for a long time with gas that potentially could have gone bad?

 

Have you had a technician sit with a computer plugged into OBD2 to see if any parameters go haywire when the car misfires?

 

Are your O2 sensors in OK shape? These can commonly show symptoms of failure on Subarus without giving a check engine light, or cause other issues.

 

Is your intake air filter OK?

 

Any sensors going bad? What about the PCV/EGR system?

 

Might be a last resort, but if some CANBUS business isn't getting enough voltage, a bad alternator or battery might cause issues with misfiring, but that's a stretch.

[Stphnhrrng]

Btw, figured I would update everybody trying to help. About two months ago I pulled my rad cap and found some slurry under there, bad head gasket. I just got around to pulling the engine and starting it last weekend. I took my heads to a machine shop and they resurfaced it for the new gaskets, but he also told me that a couple of the exhaust valves had some carbon buildup under them and weren’t sealing correctly. He chipped it away and then vacuum tested and it sealed perfectly afterwards. When I got home I inspected it and what do you know, it was cylinder 2. So whether it was the bad head gaskets or a stuck exhaust valve causing the misfire, I’m not positive. I would guess the valves though. Hopefully that fixes it. I have it mostly put back together, buying new spark plugs right now, (not 0.44 gap this time) and then renting a cherry picker hopefully tomorrow to change the clutch and throwout bearing before I put the engine back in. Wish me luck! Also one of my valve cover screw holes got stripped out. What are your thoughts on re-tapping the hole?

[apexi]

buying new spark plugs right now, (not 0.44 gap this time)

 

What are you going to set the gap to? A .044" gap won't cause any issues at all, zero.

Edit: Just want to make sure you're not going to go to small of a gap, like turbo small at .030" or something.

Edited April 17, 2021 by apexi