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Old 02-29-2012, 12:39 PM   #1
quazimoto
Scooby Guru
 
Member#: 70395
Join Date: Sep 2004
Chapter/Region: MAIC
Location: Da-boonies,Va
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5-10x a week an individual posts about having a misfire issue (MAINLY BECAUSE OF THE INABILITY TO USE THE SEARCH FEATURE!!!). This is a very common problem and there are alot of threads addressing this very problem. So here are the possible issues and solutions (read this first,then post about an issue if you have no resolution after trying said solutions):


MISFIRES


1. Wrong, worn or incorrectly gapped spark plugs. Generally NGK work best gapped between .028"-.030".

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..

3. Check valve clearances & compression. Perform a leak down/compression test first.The FSM has the valve clearance specs. This is a complete PITA with the motor in car.

4. Dirty or faulty 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.Also try swapping with a know good MAF to determine if the MAF is possibly bad.

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.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.

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

8. 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.

9. Carbon build up in heads/cylinders. You can use Seafoam or top end cleaner as well as other type of carbon remover.

10. Lightweight flywheels or crank pulleys. (phantom misfires) Can cause false misfires. Opensource tuning can disable.

11. 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.Make sure the connection to the coil pack is clean and tight. If the clip on the connector is broken,find a way to secure it.

12. 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.

13. Faulty front O2 sensor
Replace with new


14. Damaged crank timing gear

15. Misfires all cyclinders: Coil pack connectors mixed up (correct way:black to back,white to front),light weight flywheel,bad/unplugged crank or cam sensor,incorrect gapped plugs,cam timing off,bad front O2 sensor,poor grounding,fueling issue (fuel pump,fuel pump controller,FPR)

Flashing CEL (02-05 2.0L only) = Gross misfire. Doesn't always store as a DTC as it is momentary. For the most part diagnosis is the same as the above suggestions. This is more severe than the standard misfires and causes potential catalytic damaging consequences.

FYI-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.

Hope this helps! Will add as other causes are found.
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Last edited by quazimoto; 10-11-2015 at 08:12 AM.
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