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03-01-2020, 02:41 PM | #1 |
Scooby Newbie
Member#: 309719
Join Date: Feb 2012
Location: Dayton OH
Vehicle:2012 Forester XT |
2012 FXT EJ257 engine - rough idle, occasional P0301, misfires on hot start
Summary: The car starts and runs fine from cold. But, if the car is fully warmed (e.g. highway driving) then stopped and re-started within 10-20 minutes, it is hard to start, the idle is very rough, there may be a CEL (typically P0301 or P0302 or even all 4 cylinders).
You don't need the CEL to know that the idle is rough - it is very noticeable (car shaking!) After a few minutes of driving, the problem goes away. And, after a day or so, the CEL may even go away (if you haven't repeated the stop-restart-hot sequence). The CEL will usually clear itself! If the car is stopped when hot but allowed to sit for 30-45 minutes, it re-starts normally. If the car is started, driven on short local trip, it re-starts normally. This problem can be duplicated. ------- Vehicle: 2012 FXT with 114k miles, EJ257 engine - The vehicle is in mostly stock condition, but with a Mishimoto CAI and Cobb Stage 1 tune. Removing the tune and/or removing the CAI had no effect of the problem. - The problem existed before the 105k timing belt service - it existed afterwards. I did the timing belt service myself, re-checked it once, and had another garage re-check it a second time (see below). ------ Efforts to Date (more or less in the order done): - Replaced 4 spark plugs - NGK Iridium IX LFR6AIX-11 re-gapped to .028 - Battery and alternator checked at local battery shop - both checked out fine. ----- - Cylinder Pressures: ~125 on all cylinders cold* - Leak-down test Cylinder 1 - normal* - Engine smoke test - no vacuum leaks detected* - Switched locations of coil-on-plug packs - no effect.* - Checked timing belt installation - all good* - checked everything the ECU could tell them, in the garage and on the road... all good. The valve timing was spot on.* *All above services were done by Foreign Exchange in Dayton. They could duplicate the problem but not solve it. ----- - MAF cleaned (not noticeably dirty) - Replaced 4 Injectors - genuine Denso 2970013 - Replaced Front O2 sensor - Denso 2349108 - All accessible grounding points cleaned - All accessible engine bay electrical connectors cleaned with electronics cleaner. - Replaced Rear O2 sensor - Subaru 22690AB06A - Replaced both engine ground straps - Subaru 81831AG000 2x Miscellaneous: - I monitor the vehicle gas mileage - it has not changed (~22.5mpg overall for the last 30k miles). I have always used 93 octane gas, usually from a Mobil-serviced gas station. - This vehicle is a daily driver. It runs fine on the highway - really great, in fact. The stock turbo will easily generate 12 lbs of boost and hold it until I run out of road. Idle vacuum is ~15"Hg. - With Rotella T6, the engine uses no oil in 5000 miles. With Mobil-1 0w30, it uses about 1/2 quart in 5000 miles. Cold start oil pressure is 105psi+. Hot running oil pressure is 85psi at 2700rpm. - The engine acts like some system or valve is not re-setting properly, or maybe it's failing - on it's last leg - so hot re-starts are problematic. I think this is more likely the problem, rather than something mechanical. - Or, maybe some valve or sensor is getting heat soaked when the hot engine is stopped. The sensor continues to fail until the car is driven a bit, causing the part to cool down. But which valve? What sensor? Where to? what next? This has been going on for 10,000 miles and I'm running out of ideas.
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03-02-2020, 09:18 AM | #2 |
Scooby Guru
Member#: 108051
Join Date: Feb 2006
Chapter/Region:
AKIC
Location: Oneonta, NY
Vehicle:2005 WRX STi WRB |
Sound like fuel aeration or vapor lock. How old is fuel pump? What's fuel pressure under all conditions? Like cold start hot start and running?
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03-02-2020, 06:04 PM | #3 |
Scooby Newbie
Member#: 309719
Join Date: Feb 2012
Location: Dayton OH
Vehicle:2012 Forester XT |
The fuel pump and fuel filter are both original, so maybe 8-9 years old (vehicle was built in 09/2011) . No information on fuel pressure. I would think a low-pressure/inadequate pressure issue might appear at highway speeds or under load - exactly where the vehicle is running quite well.
I have not (yet) replaced the fuel filler cap. But, it's really due for replacement, problem or not. As noted, this problem has been going on for quite a few miles and months. Cold(er) weather did not seem to make a difference. |
03-02-2020, 06:16 PM | #4 |
Scooby Specialist
Member#: 29292
Join Date: Nov 2002
Chapter/Region:
SCIC
Location: Orange County CA
Vehicle:2004 WRX wagon silver |
have you cheked your coils?
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03-02-2020, 09:29 PM | #5 |
Scooby Newbie
Member#: 309719
Join Date: Feb 2012
Location: Dayton OH
Vehicle:2012 Forester XT |
The Foreign Exchange mechanic tried moving the coil-on-plug packs around to see if it might change the order in which cylinders were missing. No change.
I can't envision all four coils failing about the same time. And, if they (or even one of them) was failing, I would think it would show up in fast highway driving. I've got a set of working coils off a 2006 FXT sitting in my garage. They have a different part number but I suspect they would work. Does anybody know the difference in coil packs from 2006 to 2012? It might be an interesting swap. |
03-02-2020, 10:42 PM | #6 | |
Scooby Guru
Member#: 108051
Join Date: Feb 2006
Chapter/Region:
AKIC
Location: Oneonta, NY
Vehicle:2005 WRX STi WRB |
Quote:
Doing a fuel pressure test won't tell you much about flow. You need to verify the pump is delivering what it's rated for. Next I'd inspect the injectors. But if all 4 cylinders are misfiring I'd also check the crank sensor and or cam sensors. If only on bank is misfiring I'd check the corresponding camshaft sensor and or avcs system. |
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03-03-2020, 06:14 AM | #7 |
Scooby Newbie
Member#: 309719
Join Date: Feb 2012
Location: Dayton OH
Vehicle:2012 Forester XT |
Injectors were the original suspect - all 4 were replaced. No improvement.
The coils were shuffled around several times - no changes were noticed. One reason we decided the coils were not at fault is that they're relatively 'cool' - air flow over, etc. I'm seriously thinking about the cam and/or crank sensors. |
03-03-2020, 10:07 AM | #8 |
Scooby Guru
Member#: 108051
Join Date: Feb 2006
Chapter/Region:
AKIC
Location: Oneonta, NY
Vehicle:2005 WRX STi WRB |
Again check fuel temp also. Fuel tend to start and evaporation process in the rail when heat soaked.
You can try this for an easy and cheap diagnosis. Remove the hood.. drive car let it sit and restart see what you get. Report back! |
03-03-2020, 10:11 AM | #9 |
Scooby Guru
Member#: 108051
Join Date: Feb 2006
Chapter/Region:
AKIC
Location: Oneonta, NY
Vehicle:2005 WRX STi WRB |
And you can check fuel flow by removing line powering pump by jumping relay if it's a walbro 255lph convert 255lph to lpm. Divide that in half power pump for 30 seconds measure your fuel that it output.
Varifty you're holding fuel pressure on shut down. Always leave key on for second before you start so fuel can prime system. |
03-03-2020, 11:05 AM | #10 |
Scooby Specialist
Member#: 59892
Join Date: Apr 2004
Chapter/Region:
South East
Location: Summerville, SC
Vehicle:2004 TP Tuned GT30R .82 JBP STi |
I had a very similar issue with my EJ257 a while back. Did a lot of hunting, replacing things to no end. The problem ended up being my oil control valves. While they bench tested within spec, they were a little off from each other. I replaced them and haven't had an issue since. I hope that might help.
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03-03-2020, 11:08 AM | #11 | |
Scooby Guru
Member#: 108051
Join Date: Feb 2006
Chapter/Region:
AKIC
Location: Oneonta, NY
Vehicle:2005 WRX STi WRB |
Quote:
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03-03-2020, 11:18 AM | #12 |
Scooby Newbie
Member#: 309719
Join Date: Feb 2012
Location: Dayton OH
Vehicle:2012 Forester XT |
I will check holding fuel pressure after shut down. When I did the injectors, I did not detect any pressure in the system when I pulled the first injector, but the engine had been off for several hours and everything was cold.
FWIW, I always leave the key on for a few seconds before start up. I am seriously looking at the crank and cam sensors. I'm not sure whether this is a hellish job or a snap (probably the former :-). ----- This morning, I drove the car ~40 miles to a location for my job - mostly highway miles. My car ran flawlessly on the trip down. I was done in a couple of hours, left, and drove home. Again, it ran flawlessly - even better. While none of the things listed up above solved my problem, they sure as heck made the car run well. On the trip back I chased an STi north along I-75. Despite misty weather, we both had a good time and my car was running at 110%. That's what is so aggravating about this problem. |
03-03-2020, 11:24 AM | #13 |
Scooby Guru
Member#: 108051
Join Date: Feb 2006
Chapter/Region:
AKIC
Location: Oneonta, NY
Vehicle:2005 WRX STi WRB |
I can't believe I missed that in your original post that hot running oil pressure of 85psi at 2700rpm is a lot! That's way to high is your gauge accurate?
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03-03-2020, 11:29 AM | #14 | |
Scooby Guru
Member#: 108051
Join Date: Feb 2006
Chapter/Region:
AKIC
Location: Oneonta, NY
Vehicle:2005 WRX STi WRB |
Quote:
I'm kinda ruling out the sensors as the car runs good for you any other time. But if fuel pressure isn't holding that will cause things to lean out especially in boost. What are fuel trims? |
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03-03-2020, 11:41 AM | #15 |
Scooby Guru
Member#: 108051
Join Date: Feb 2006
Chapter/Region:
AKIC
Location: Oneonta, NY
Vehicle:2005 WRX STi WRB |
I'd verify you're getting oil pressure to the avcs solenoids you should see 10psi every 1k rpm 20psi at idle is ideal.
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03-03-2020, 02:20 PM | #16 |
Scooby Newbie
Member#: 309719
Join Date: Feb 2012
Location: Dayton OH
Vehicle:2012 Forester XT |
Regarding Oil Pressue: with Rotella T6 5w40, the engine uses no oil in 5000 miles. With Mobil-1 0w30, it uses about 1/2 quart in 5000 miles. Cold start oil pressure is 105psi+. Hot running oil pressure is 85psi at 2700rpm; Idle oil pressure 20-24psi at 700rpm. All of this comes from a Defi gauge.
Regarding fuel pressure, it is the stock regulator. The car runs great in boost. It runs great all the time except when it's stopped hot and then re-started within 10-20 minutes. If the fuel pump was on the fritz or the fuel filter clogged, I would expect all sorts of engine problems at speed or boost. In fact, the only problem is lack of road. My theory on sensors is that one of them (Cam sensor Bank 1 most likely) is somehow getting heat soaked when the hot engine is stopped and does not become completely functional until I've restarted and underway or until it is allowed to cool - whichever occurs first. But, so far, my theories have not been correct :-( |
03-03-2020, 02:30 PM | #17 | |
Scooby Newbie
Member#: 309719
Join Date: Feb 2012
Location: Dayton OH
Vehicle:2012 Forester XT |
Quote:
If I use Mobil-1 5w30, the hot running pressure is 80psi at 2700rpm at time of oil change, dropping to 70psi at 2700rpm after 3000 miles. Mobil-1 Ow30 is much more robust - almost as solid as Rotella T6. |
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03-03-2020, 03:21 PM | #18 | |
Scooby Guru
Member#: 108051
Join Date: Feb 2006
Chapter/Region:
AKIC
Location: Oneonta, NY
Vehicle:2005 WRX STi WRB |
Quote:
And that is still a very high oil pressure for hot cruise speed. Your defi oil psi gauge might have it's sensor going bad. |
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03-03-2020, 08:07 PM | #19 | |
Scooby Newbie
Member#: 309719
Join Date: Feb 2012
Location: Dayton OH
Vehicle:2012 Forester XT |
Quote:
The VDO mechanical gauge setup on an '06 FXT (EJ255 engine) measured about the same pressures and the same clear differences between Mobil-1 5w30 and Rotella T6 5w40. The VDO gauge measured pressure directly off the oil gallery hole very close to the PCV valve (about 2" away, as I recall) - no sender involved. I have about 4 years of pressure experience from that vehicle. At least for the 2012 FXT, I am comfortable that the oil pressure is 'normal'. And, normal or high, it's unclear how it would impact the hard-start-when-hot problem. Last edited by davefedex5358; 03-04-2020 at 01:54 PM. Reason: update images |
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03-04-2020, 12:43 AM | #20 |
Scooby Guru
Member#: 108051
Join Date: Feb 2006
Chapter/Region:
AKIC
Location: Oneonta, NY
Vehicle:2005 WRX STi WRB |
Just my opinion from what I've seen. Don't believe it has anything to do with your hot start issue.
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03-04-2020, 11:03 AM | #21 |
Scooby Guru
Member#: 108051
Join Date: Feb 2006
Chapter/Region:
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Vehicle:2005 WRX STi WRB |
You can locate the fsm and find the resistance values for the cam sensor and the pins corresponding to the test. Check this on a cold and hot sensor. That will tell you if the cam sensor is the issue.
Are they factory cams? What else did you change on the build before having the issue? Besides injectors which I sent you the test procedure on in a PM. |
03-04-2020, 01:49 PM | #22 | |
Scooby Newbie
Member#: 309719
Join Date: Feb 2012
Location: Dayton OH
Vehicle:2012 Forester XT |
Quote:
Nothing else was changed in the build. As an early step in trying to solve the 'problem', I removed Cobb S1 tune - no change, although the vehicle did not run as well. I also tried removing the Mishimoto CAI - again, no change. |
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03-04-2020, 02:46 PM | #23 |
Scooby Guru
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Join Date: Feb 2006
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Vehicle:2005 WRX STi WRB |
Did you verify the fuel pressure yet?
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03-04-2020, 10:12 PM | #24 | |
Scooby Newbie
Member#: 309719
Join Date: Feb 2012
Location: Dayton OH
Vehicle:2012 Forester XT |
Quote:
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03-05-2020, 07:04 AM | #25 |
Scooby Newbie
Member#: 400179
Join Date: Aug 2014
Vehicle:2009 wrx |
when mine had hot misfires it turned out to be tight valve clearances. they get tighter over time, eventually going below spec. you cold try doing another compression test when the engine is very hot, although that's a pain (literally).
when the engine cools off, the valve clearances relax a bit, and it runs better. |
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