I've been struggling with troubleshooting a p0302 misfire code on my 04 wrx. I've read Donkey's sticky post and the following is what I have done so far. Any suggestions are appreciated!!
Previously the car was showing cylinder 2 and 3 misfire codes. Now after changing the spark plugs to new ones and swapping the coils from good cylinders to cylinders 2 and 3 the misfire code on cylinder 3 hasn't come back. However cylinder 2 misfire codes are still showing up.
The following was taken from nasioc.com for troubleshooting misfire codes and I've noted which steps I've taken so far in the order performed.
1. Wrong, worn or incorrectly gapped spark plugs. Generally NGK work best gapped between .028"-.030".
New NGK plugs were properly gapped and installed
2. Bad/loose coil pack or coil pack connector. Test coil pack and move to other cylinder to see if DTC changes. If so this would indicate a coil pack issue. Also check the tower boot for corrosion.
Done! After swapping coils 2 to 4 and 3 to 1 cylinder 3 now does not register misfire codes. Only cylinder 2 does.
2. Clogged/dirty/bad injectors or fuel filter. Try changing the fuel filter. The maintenance schedule for the filter is every 30K miles. Have the injectors professional cleaned or at least run several bottles of a good injector cleaner through the gas tank. 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) You can swap injectors from another cylinder and see if the misfire follows. If so this would indicate an injector issue if it does move..
I've been running basic fuel injector cleaner this whole time.
3.Poor grounds/grounding. Clean the battery ground cable and ones that run to the intake manifold. Make sure all are connected. These are sensor grounds and must be kept clean.
I made a point of cleaning all the grounding points on the intake manifold and I even made a simple new grounding kit grounding multiple points on the intake manifold to the ground on the battery and frame.
4. Dirty MAF sensor. This causes an incorrect airflow readings. Misfires can result. Clean with CRC MAF cleaner or NON chlorinated brake cleaner. Make sure you are actually cleaning the MAF sensor and not just the IAT sensor. Common mistake.
I took the maf sensor apart and cleaned the sensor with sensorkleen
5. Check valve clearances & compression. Leak down/compression test.
I didn't get a chance to check valve clearances but a compression test showed consistent compression across all 4 cylinders.
6. Cam timing. Check cam timing per the service manual. Clean cam and crank sensor face.
The dealership took a look at the timing belt and determined that it was a tooth off and has removed the timing belt and re-installed it properly. $1400.00 later the car is still showing cylinder 2 misfire codes.
7. The bugeyes were plauged with misfires.
Updating the ROM in the ECU to the latest revision from Subaru helps alleviate most false misfire issues. This can be done through the stealership or opensource software. Mine isn't a bugeye its an '04 but the dealership did perform an ecm update to the ecu in an attempt to fix this. However the cel has come back even with the update.
8. Carbon build up in heads/cylinders. You can use Seafoam or top end cleaner as well as other type of carbon remover.
Today I swapped cylinder 2 injector with cylinder 4 injector to rule out any injector issues I may be having. I also ran half a can of seafoam in the bpv vacuum tube and the other half in the gas tank. *fingers crossed*. I noticed it did smoke quite a bit but I took it for a spirited put down the highway. idle seems a little smoother but I'm not sure if is just in my head. I did notice a bit of smoke coming out of the engine bay around the turbo area. Would this cause my misfire? I took a look but can't figure out what is leaking in the area. its just a small cloud of white smoke when seafoam is used.
The following are next steps to take according to Donkey's post but which of the steps should be done first?
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).
Haven't performed this check yet but I believe I have exhaust/boost leak around turbo. exhaust fumes can be seen when seaform is introduced into the system around the turbo however I can't seem to find the source.
Excessive PCV blow by. PVC gases will effectively lower the octane content of gasoline/petrol and can cause misfires along with knock. Get a catch can or air/oil seperater. I haven't done this yet but is there a way to check if there is excessive pcv blow by? or is this a simple fix?
Faulty fuel pressure regulator or fuel pump. Check fuel pressure. It should be bewteen 35-38psi idle @ sealevel. Removing the vac line at idle should give you 43 psi. The FPR is a 1:1 rising rate. For every 1 psi manifold positive pressure the fuel pressure should rise 1 psi.
What is the easiest way to test for a bad fuel pressure regulator or fuel pump?
Faulty front O2 sensor Replace with new
Anyone know how much a sensor might be? Anyone have a spare they would want to sell?