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Old 12-22-2017, 01:23 AM   #1
serrius
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Default 15 wrx misfire? I think?

Leave the gym, turn car on and immediately rough idle. Pull the access port counts and cyclinder 4 is going crazy going up to 100 and cyclinders 1-3 show 15. Car sounds like a EJ.

3 miles from home so figure I’ll hazard light my car home slowly. Half way through the drive everything reverts back to 0 and the car is running perfectly fine. Engine reverts back to same FA noise. DAM stayed at 1 the entire time.

Let it sit a hour then go for a drive and is like nothing ever happened. Did some mild pulls and everything is perfect.

What the **** happened? Lmao
This is my fourth Subaru and it’s bringing back EJ memories!
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Old 12-22-2017, 01:32 AM   #2
Master467
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Fouled plug, dying coil pack, dying injector. That's where I'd start looking.

Could be a bad ground, but that shouldn't just screw with one cyl.
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Old 12-22-2017, 01:59 AM   #3
serrius
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IS there a way I can see if the injector is dieing through the accessport?
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Old 12-22-2017, 08:39 AM   #4
Perscitus
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Sadly no. Injector PW, DC, Fuel Trims, Fuel Pump DCs wont expose it.

Sounds like you clogged up the injectors, especially #4. Bad/contaminated fuel, dirty pre filter, in-tank LPFP filter will do it or..
have you by any chance ran the tank dry (to E) and drove say 10-25 miles like that? Or have a habit of running the tank nearly dry? That will do it.

Last edited by Perscitus; 12-22-2017 at 10:18 AM.
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Old 12-22-2017, 10:41 AM   #5
Schoat333
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How many miles are on the car? Any mods besides the AP?
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Old 12-22-2017, 04:16 PM   #6
serrius
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STAge 2 with water injection with all supporting cooling mods. Uh tank wise, the car sits a lot . I have a another car I drive more.
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Old 12-22-2017, 07:38 PM   #7
Perscitus
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Sitting a lot is no big deal unless it sits nearly empty.

The question is do you tend to run it dry or nearly dry or did you do that recently?
If so, you clogged the injectors, particularly #4. I bet if you swapped it over to Cyl 1 or 2, the misfires would follow. If so, you've got your culprit.
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Old 12-23-2017, 02:50 AM   #8
danoz
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Do you have a check valve in you water/meth injection? Where is it located in the system?
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Old 12-23-2017, 10:12 AM   #9
gn4rwhals
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Quote:
Originally Posted by danoz View Post
Do you have a check valve in you water/meth injection? Where is it located in the system?
Check valves are a must, learned that with a kit I helped install.
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Old 12-23-2017, 11:16 PM   #10
serrius
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Edited below

Last edited by serrius; 12-23-2017 at 11:26 PM.
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Old 12-23-2017, 11:25 PM   #11
serrius
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Yes on the valve , tapped into my intercooler ( mishimoto ). There have been plenty of times Of me driving with the gas light on, more just out of laziness of getting gas tomorrow.
I have a S4 which I drive 90% of the time, so I’m sure it’s sat with the gas light on for a few days. Never gave it thought that it could clog the injectors. Learn something new everyday huh

I ordered a injector flush kit so I’ll just pull the injectors and clean them and run a few bottles of cleaner also. I’ve been driving the wrx since and it’s running perfect. No low oil, no dam changes, AFR/DAM good. Actually the only hiccup I’ve ever had owning the Subaru since 2015, I literally baby this thing and am critical on all parts and maintence.

no misfires what so ever after the event except the occasional 1 count ever now and then which has happened since it had 300 miles - its Normal for cars to have minimal roughness during a drive. Literally stopped and went back to normal when I was lugging it home. All good now, Nothing across all cylinders
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Old 12-24-2017, 08:56 AM   #12
Perscitus
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Sounds good and yes, you most likely sucked up some debris from the tank.
It cleared this time, sometimes it doesn't (got lucky).

When she's at 30 or 60K swap out the in-tank pre-filter and LPFP filter.
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Old 12-26-2017, 11:03 PM   #13
serrius
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Spoke to soon!

Put in new coil packs along with spark plugs. The misfire only happens towards the very end of my power band near red line only in 2nd and fourth gear in cylinder 4. I get counts anywhere from 1-8. Third gear wot produces one count very rarely at the end of the band which I attribute to the engine going back to a moderate Rpm as I let go of the throttle. I ran 3 bottles of injector cleaner for safe measure.

I’m just stumped. I emailed my tuner on possible fuel trims since I never really monitored roughness before and all my tune pulls are in 3rd so I could have had this prior and not had a clue.

Fuel pump, clogged injector 4 or fuel trims? But if it was a clogged injector why only at the end of WOT and not during the whole thing? Pulling the injectors looks like a pain in the ass so I’m trying everything before I attempt on removing them.
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Old 12-27-2017, 06:05 AM   #14
serrius
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Just purchased a DW65c to rule out the fuel pump but I’m a little confused on the in tank filter. The DW has its own filter I get that but The 15 wrx doesn’t seem to use the big white container fuel filter which previous models used that went inside with the pump.

Upon searching I found this 42072AA121 but it goes to the secondary fuel pump sender.

Where is the secondary fuel pump sender?
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Old 12-30-2017, 12:46 AM   #15
VelosoWrex
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Default 15 wrx misfire? I think?

Change your gas, believe it or not I’ve had the same issue and swapped my plug and changed the coil packs around and nothing. Emptied my tank and filled up with fresh 93 and boom, problem solved. Something so simple and it seems impossible to locate the issue. Did compression test to be safe and came back in perfect condition. I even ran injector and fuel pump cleaner through before I refilled and after I refilled.
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Old 12-30-2017, 07:53 AM   #16
Elbert Bass
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Quote:
Originally Posted by serrius View Post
Just purchased a DW65c to rule out the fuel pump but I’m a little confused on the in tank filter. The DW has its own filter I get that but The 15 wrx doesn’t seem to use the big white container fuel filter which previous models used that went inside with the pump.

Upon searching I found this 42072AA121 but it goes to the secondary fuel pump sender.

Where is the secondary fuel pump sender?
On the left side of the fuel tank.
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Old 12-30-2017, 10:04 PM   #17
Mohaj
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Only time I experienced the "backfire" on the FA20 on my 2015 WRX was after 2 weeks of Chevron CAN 91. Happened at 3500-4000' of elevation on CA/OR border on morning startup on my way home to Seattle (hwy 395).

Car has sub 24,000 mi on it and only time I've ever experienced that. I am convinced it is a quality of gas thing. I put nothing but Shell in the car, and 3 pump Shell as much as possible.

I am fully convinced quality of gas is a massive factor in performance of these engines.

I'm only stage 1 OTS Cobb and have seen the DAM differences in different gas station additives. Shell is my go to. Food for thought, hope it helps
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Old 04-02-2021, 06:41 AM   #18
ASELppl
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I realize this is a dead thread but I’m wondering if you ever found a solution? I am currently trying to diagnose almost the exact same issue. Did the new fuel pump solve the issue? If you see this reply please let me know!
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