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Old 02-29-2012, 12:39 PM   #1
quazimoto
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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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Old 02-29-2012, 12:51 PM   #2
WhiteBgeye02
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this deserves a sticky! i am sick off ppl posting about misfires. if you check all this and still cant figure it out it may be time for the professionals to figure it out.
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Old 02-29-2012, 01:41 PM   #3
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You can move injectors the same way you explained the coil pack procedure to see if the misfire follows.

I have in the past slightly..."I MEAN SLIGHTLY" twisted the prongs to the coil packs and re-installed to ensure contact is being made inside the connectors.
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Old 02-29-2012, 01:53 PM   #4
BlueWagon02
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I have seen the same or similar post at clubwrx.net, and an additional post may be helpful for issues that could cause a misfire on all cylinders, not just one or two.
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Old 02-29-2012, 01:57 PM   #5
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Quote:
Originally Posted by 2gnt2wrx View Post
You can move injectors the same way you explained the coil pack procedure to see if the misfire follows.

I have in the past slightly..."I MEAN SLIGHTLY" twisted the prongs to the coil packs and re-installed to ensure contact is being made inside the connectors.
Updated! Yeah forgot to put that in there.
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Old 02-29-2012, 02:00 PM   #6
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Awesome list. Saves some $$$$ by doing these simple tests for sure
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Old 03-01-2012, 09:21 AM   #7
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Quote:
Originally Posted by BlueWagon02 View Post
I have seen the same or similar post at clubwrx.net, and an additional post may be helpful for issues that could cause a misfire on all cylinders, not just one or two.
Yeah,I made that thread as well . Good idea about the multiple misfires.
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Old 03-01-2012, 09:47 AM   #8
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i also believe there is a new rom you can flash onto your car to fix misfire problems. would have to check around romraider forums though.
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Old 03-01-2012, 01:43 PM   #9
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Quote:
Originally Posted by WhiteBgeye02 View Post
i also believe there is a new rom you can flash onto your car to fix misfire problems. would have to check around romraider forums though.
You can turn off the roughness monitors for each cylinder "If you know it's false". While not advisable, you will be able to tell if your car is really misfiring.
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Old 03-01-2012, 02:32 PM   #10
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Include links for how to's and this should be a sticky for sure.
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Old 03-01-2012, 04:07 PM   #11
quazimoto
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Quote:
Originally Posted by WhiteBgeye02 View Post
i also believe there is a new rom you can flash onto your car to fix misfire problems. would have to check around romraider forums though.
It's any ROM.

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Old 04-01-2012, 02:21 PM   #12
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Cleaning the evap purge valve solved my misfire on cylinder #1 issue. It must have been getting stuck open or it was in backwards. Arrow for "to e/g" should point to the left (toward air intake).
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Old 04-01-2012, 05:26 PM   #13
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Quote:
Originally Posted by quazimoto View Post
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.

Don't Subaru use a hot wire style MAF sensor instead of an IAT? (on 02+ atleast) Or do you mean MAP?
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Old 04-01-2012, 06:10 PM   #14
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The iat is in the same housing as the maf. Only when you first look at it, the iat sensor is the one that is easily visible. Where the maf is up inside the plastic tube/housing, barely visible.
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Old 04-01-2012, 07:39 PM   #15
quazimoto
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Quote:
Originally Posted by TwoFifty View Post
Don't Subaru use a hot wire style MAF sensor instead of an IAT? (on 02+ atleast) Or do you mean MAP?
I mean exactly what I said....... Have you not bothered looked at your MAF sensor? I have. There are several tutorials on here on how to clean the MAF sensor on a Subaru. Picture of a Subaru MAF sensor for reference............you tell me The amber bulb is the IAT sensor

Last edited by quazimoto; 04-14-2012 at 07:50 AM.
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Old 04-01-2012, 08:11 PM   #16
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Quote:
Originally Posted by quazimoto View Post
I mean exactly what I said....... Have you not bothered looked at your MAF sensor? I have. There are several tutorials on here on how to clean the MAF sensor on a Subaru. Picture of a Subaru MAF sensor for reference............you tell me
Yes i am well aware of what my MAF looks like

I do however see where people go wrong now though, i'd never really thought of it like that before as i'd just always referred to the whole thing as the MAF, that's why i was getting confused

Last edited by TwoFifty; 04-01-2012 at 08:21 PM.
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Old 04-01-2012, 08:46 PM   #17
bryan.paradise
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Yeah well unfortunately, the "professionals" at the Subaru dealership near me want to charge an arm and a leg to troubleshoot and not take responsibility when they don't fix a problem. Ridiculous.
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Old 04-01-2012, 09:28 PM   #18
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I was chasing a miss fire for ever.... I changed my plugs and coil packs and runs vibration free
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Old 05-01-2012, 07:33 PM   #19
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All but number 3&10.

Why i didnt check for 3; the heads i have currently are in good condition and i have them built with oem valves, buckets, springs and retainers.

Why i didnt check for 10; i have the 4eat auto trans and all pulleys are brand new OEM.

What about PCV Blowby?
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Old 05-23-2012, 05:01 PM   #20
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could a bad MAP sensor cause a buck or misfire?
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Old 05-23-2012, 07:07 PM   #21
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Not that I know of. The ECU only uses the MAP sensor to reference boost pressure unless the MAF fails. Then the ECU will switch into a "fail safe" speed density mode.
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Old 05-23-2012, 07:39 PM   #22
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Quote:
Originally Posted by shwagondawheels View Post
could a bad MAP sensor cause a buck or misfire?
you would get a CEL for that

is the CEL on??

what codes??
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Old 05-23-2012, 10:06 PM   #23
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Quote:
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Not that I know of. The ECU only uses the MAP sensor to reference boost pressure unless the MAF fails. Then the ECU will switch into a "fail safe" speed density mode.
ok so the MAP sensor in dedicated to the boost map only?

the other cars i,ve had misfire or buck from a bad MAP sensor where MAFlless cars (obviously speed density w/ maybe alpha n blend map on a n/a car) reason for my thought

it's the misfire/buck in the other thread(s) lol
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Old 05-23-2012, 10:10 PM   #24
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Quote:
Originally Posted by Uncle Scotty View Post
you would get a CEL for that

is the CEL on??

what codes??
random multiple
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Old 05-23-2012, 10:12 PM   #25
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Uncle scotty, the codes my car is throwing are p0301 p0302 p0303 p0304
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