IF YOU HAVE A MISFIRE CODE ,PLEASE READ THIS!!!

[Donkey]

*This is not a thread for posting your own misfire problem!*
Please start your own thread in the General Maintenance & Troubleshooting forum. Feel free to post your own resolution to misfire problems though.

Once or twice a week an individual posts about having a misfire issue. This is a very common problem and there are alot of threads addressing this very problem. So here are the possible issues (read this first,then post about an issue if you have no resolution after trying said solutions):

MISFIRES

1. Wrong, worn or incorrect gapped spark plugs. You should run only NGK stock range plugs gapped to .028.

2. Clogged injectors/dirty fuel filter. Try changing the fuel filter. The maintenance schedule is every 30K miles. Have the injectors cleaned or at least run several bottles of a good injector cleaner through the engine. Also make sure you are using the correct octane gas! Either 91 or 93 unless you are specifically tuned for another octane!! (IE: race gas or E85).

3. Check valve clearances & compression. Leakdown/compression test.

4. Oil or dirt build up on MAF sensor. This causes an incorrect load reading which make for AFR corrections out of line. Misfires can result. Remove the sensor, place in plastic bag. Spray out with CRC MAF cleaner or NON chlorinated brake cleaner.

5. Vacuum leaks or preturbo leak. Check where the FPR hose connects (generally you could get a P0457 or P0171 with this as well). Check the turbo inlet pipe where it connects to the turbo. This pipe is famous for ripping and causing a huge preturbo leak (P0171 as well).

6. Clean the battery ground cable and ones that run to the intake manifold. These are sensor grounds and must be kept clean. Clean coil pack grounds (bolt holes).

7. Cam timing. Check cam timing per the service manual. Clean cam sensor face.

8. Excessive PCV blow by. PVC gases will effectively lower the octane content of gasoline/petrol.

9. Carbon build up on motor. Real common on EJ205's. Get some BG Chemtool, GM top end cleaner or other type of carbon remover. GM top end cleaner seems to work really well.

10. Lightweight flywheels or crank pulleys. (phantom misfires) Clean crank sensor face.

11. Bad/loose coil pack or coil pack connector. Test coil pack and move to other cylinder to see if DTC changes. Also check the tower boot for corrosion.

Misfires all cylinders: Coil pack connectors mixed up (black to back),light weight flywheel,bad/unplugged crank or cam sensor,incorrect gapped plugs,cam timing off.

[Anub1s]

Thanks for writing this up Donkey. Misfires are one of the hardest things to track down and they're almost impossible to diagnose over the internet. This gives people a great place to start.

[1198S]

Yesterday I've replaced 4 plugs and 1 coil pack. P0304 came back today. I've did some of the things that Donkey posted, cleaned the MAF sensor, clean the coil pack connectors, replaced the PCV valve and pure in 2nd bottle of injector cleaner. I also replace the air filter and fuel filter as well.

It seem to be improving as I drive home this afternoon. I hope this will fix it, next step will be cleaning the grounds and add more fuel injector cleaner.

Thanks for the posting.

[Donkey]

Misfires are definately a P.I.T.A. to track down! Especially on bugeyes!

[zax]

Great post!

10. Lightweight flywheels or crank pulleys. (phantom misfires)

I have heard this, but never really knew the reasons for this occurrence. Care to clarify?

[Donkey]

Great post!

I have heard this, but never really knew the reasons for this occurrence. Care to clarify?

Apparently it has to do with the crank's rotation speed and how the ECU interprets it via the crank sensor.

[EvoEatr]

I think the check valve clearances should be moved to like number #2 or #3 position fore Ive dealt with alot of these misfire codes for years and with my experience if its not a plug/coil pack/ backed out or broken wire somewhere, than it seems to be the valve clearances, we've had more than a couple higher mileage WRX's with tight valves... Of course unless your rating them in terms of intrusiveness... Just my opinion of course... BTW excellent idea for a sticky....

[Donkey]

I think the check valve clearances should be moved to like number #2 or #3 position fore Ive dealt with alot of these misfire codes for years and with my experience if its not a plug/coil pack/ backed out or broken wire somewhere, than it seems to be the valve clearances, we've had more than a couple higher mileage WRX's with tight valves... Of course unless your rating them in terms of intrusiveness... Just my opinion of course... BTW excellent idea for a sticky....

Done! You guys change out the shims/buckets with the motor in car?

[EvoEatr]

Done! You guys change out the shims/buckets with the motor in car?

Yup, Its a tight fit but It can be done.. we have a pretty decent assortment of them, fore personally whenever I have one that needs adjustment I order a couple bucket sizes smaller and a couple larger just in case...extremely tight clearances japan haha

[nunez07c]

Ok, so I really need help on this I got the P0304 code. So far I've cleaned the MAF, Changed the FPR hose (fixed P0171), cleaned injectors, changed the spark plugs 1000 mi ago, and this afternoon changed two coil packs (rear driver and passengers side)... Basically now I'm stumped, I don't know what to do next, FYI the idle tends to move up and down ( don't know if it is because its cold engine since i sometimes also occurs when the engine is warm.)



Thanks in advance to all that help me .. .. . .. .

[Anub1s]

Ok, so I really need help on this I got the P0304 code. So far I've cleaned the MAF, Changed the FPR hose (fixed P0171), cleaned injectors, changed the spark plugs 1000 mi ago, and this afternoon changed two coil packs (rear driver and passengers side)... Basically now I'm stumped, I don't know what to do next, FYI the idle tends to move up and down ( don't know if it is because its cold engine since i sometimes also occurs when the engine is warm.)



Thanks in advance to all that help me .. .. . .. .

What year WRX? With the idle going up and down, I'd suggest cleaning and re-gasket-ing your IACV if applicable.

[1198S]

My 02 has 197K miles on it. I keep getting the P0304 I found out that it is sticky valve in # 4 cylinder. Only when I'm hard on the gas when the car is not fully warmed up. If the car is warmed up before I drive I don't get the code.

I'm going to keep driving like that. Will be throwing in STI block will rebuild the heads then.

[nunez07c]

Ooo forgot, I have an 04' WRX. I really have no clue what to do next and I'm not planning on spending 2k on this issue, cause I'm saving that for the possibility of a spun bearings my uncle (mechanic) said he heard, so possible rebuild ( which I have no idea what to get)




THanks guys, either way your all awesome.

[Anub1s]

Ooo forgot, I have an 04' WRX. I really have no clue what to do next and I'm not planning on spending 2k on this issue, cause I'm saving that for the possibility of a spun bearings my uncle (mechanic) said he heard, so possible rebuild ( which I have no idea what to get)




THanks guys, either way your all awesome.

If you have a spun bearing, you have a spun bearing, you'd be hearing knock and possibly other noises along with deminished oil pressure, they wouldn't be just random come and go things. I wouldn't worry too much about that until it's actually a problem.

What I would recommend is cleaning that IACV, which you do have since you have an '04, and make sure that you use a new gasket when reinstalling. There are how-to's on this board, so do a quick search and it will yield the information you need in order to do it.

Beyond that, I would recommend a compression and leak down test be performed to make sure your engine is still within spec. A blown piston will cause a misfire, so hopefully this isn't the case, but it's good to rule out.

[Donkey]

Ok, so I really need help on this I got the P0304 code. So far I've cleaned the MAF, Changed the FPR hose (fixed P0171), cleaned injectors, changed the spark plugs 1000 mi ago, and this afternoon changed two coil packs (rear driver and passengers side)... Basically now I'm stumped, I don't know what to do next, FYI the idle tends to move up and down ( don't know if it is because its cold engine since i sometimes also occurs when the engine is warm.)



Thanks in advance to all that help me .. .. . .. .

Unless you have tried everything on the list above then thats what to do next.

*Check valve clearances & compression. Leakdown test.
*Clean the ground cables that run to the intake manifold. These are sensor grounds and must be kept clean. Clean coil pack grounds (bolt holes).
*Check cam timing
*Carbon build up on motor. Real common on EJ205's. Get some BG Chemtool, GM top end cleaner or other type of carbon remover. GM top end cleaner seems to work really well.