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Old 10-03-2013, 01:33 PM   #1
Sethk1980
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Default engine stutter when under load

Hey folks. Ive got an interesting issue. My car drives wonderfully when normal driving is taking place- but then the pedal is applied, 70% of the time it stutters and sputters and backfires at around 1/2 throttle. In neutral, it revs fine and fast, no issue.
I have, in my 02 wrx, a jdm ej207 with the following mods:

*16g turbo upgrade, 18psi (with the issue it rarely breaches 10psi)
*Perrin silicone turbo inlet with short ram air intake
*big tmic with silicone hoses
*550cc yellow side feed injectors
*Walbro 255lph fuel pump
*fully catless exhaust
*race header
*3 inch catless bellmouth dp
*3 inch catless stainless mandrel bent exhaust
*jdm tgvless intake on phenolic spacers
*12lb flywheel
*Grimmspeed 3 port boost controller
*probably other things I cant remember

The system has been boost leak tested, so thats not the issue. Any ideas or input or suggestions would be wonderfully appreciated! Im stuck in a rut and out of ideas. Its also running a Cobb ap v2, btw.

Thanks for reading!
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Old 10-03-2013, 01:35 PM   #2
zman17
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Are you running a custom tune or just a cobb off the shelf map?
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Old 10-03-2013, 01:49 PM   #3
Sethk1980
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Custom tune from iaperformance. Also I cant do a wot test run bc when I roll into wot it starts stuttering really bad. Also, when I have the Cobb plugged in...the car seems to run much worse.
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Old 10-03-2013, 02:28 PM   #4
danger1138
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Whats the spark plug situation like? Ever throw any check engine light codes?
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Old 10-03-2013, 05:27 PM   #5
Sethk1980
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Bank one running lean code, but thats it. Plugs are brand new ngk iridium 9s
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Old 10-04-2013, 09:29 AM   #6
Sethk1980
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Bump for insight
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Old 10-04-2013, 09:47 AM   #7
nmlittlebigman
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Bad MAP sensor (Manifold Absolute Pressure) is my guess.
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Old 10-04-2013, 09:57 AM   #8
Sethk1980
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Care to elaborate as to why (
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Old 10-04-2013, 09:59 AM   #9
easterbran
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Bad O2 sensor?
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Old 10-04-2013, 10:23 AM   #10
danger1138
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Yes was leaning towards bad o2 after what u stated. J
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Old 10-04-2013, 10:46 AM   #11
nmlittlebigman
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Quote:
Originally Posted by Sethk1980 View Post
Care to elaborate as to why (
Because the ecu uses it (among other things) to determine load which in turn determines fueling and timing.
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Old 10-04-2013, 10:50 AM   #12
johnnyrizzo
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Default Major Problem: 2011 WRX upgraded to AccessPort v3

2011 WRX
I bought it with 20k miles on it. Car already had invidia catless dp and magnaflow exhaust. Had previously been tuned with an older accessport. However the ap did not come with the car.

*Note: at this point the car runs really well and I have put almost 1,000 mile on it with no issues.

So I bought a v3 and installed it the other night. Now no matter what OTS map I run, the fuel cuts at 2psi boost. Of course I have now lost the map that was on there originally. I uninstalled the ap and tried driving around with the stock ecu setting. It still fuel cuts around 5-10 psi.

Any ideas?
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Old 10-04-2013, 11:00 AM   #13
nmlittlebigman
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Quote:
Originally Posted by johnnyrizzo View Post
2011 WRX
I bought it with 20k miles on it. Car already had invidia catless dp and magnaflow exhaust. Had previously been tuned with an older accessport. However the ap did not come with the car.

*Note: at this point the car runs really well and I have put almost 1,000 mile on it with no issues.

So I bought a v3 and installed it the other night. Now no matter what OTS map I run, the fuel cuts at 2psi boost. Of course I have now lost the map that was on there originally. I uninstalled the ap and tried driving around with the stock ecu setting. It still fuel cuts around 5-10 psi.

Any ideas?

Start another thread so we don't hijack the original poster.
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Old 10-04-2013, 11:17 AM   #14
Sethk1980
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Ok, just noticed that my pressure control valve is plugged into the wiring harness...but no lines are running to it, one of which is broken and taped over.
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Old 10-04-2013, 04:49 PM   #15
Cobb Tuning
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Default

Do you have any logs? Have you tried working with your tuner to see if they have any input?

Is this something that started happening recently? Or has it been going on since the car got tuned? Has anything been changed on the car recently?

The lean code is definitely concerning and will give you and idea as to what could be the problem. You may have a pre-turbo intake leak. Your front O2 could be worn/failed. Your MAF could be worn/failed. Your MAF scaling and/or injector scaling in your tune could need some work. Those are all just guesses though.

- Chris
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Old 10-04-2013, 04:58 PM   #16
Sethk1980
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Thanks Chris. Ive actually got 2 tuners on it, and plenty of logs. The system was leak tested from the short ram, before the maf, with no leaks. Scratching my head for a couple months now, as its a jdm swap in. Been running this way since before the tune, so its pre existing
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Old 10-04-2013, 05:00 PM   #17
loather
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Among the mods listed I don't see an aftermarket fuel pressure regulator - Could the fuel pressure be fluctuating, causing the stutter?
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Old 10-04-2013, 05:57 PM   #18
Sethk1980
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Thats correct, I dont have one- and its on my list of curiosities, but apparently there are a few potential issues here, im just trying to see if theres a way to pinpoint something specific so I dont try the buy everything approach lol
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Old 10-04-2013, 06:30 PM   #19
loather
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I totally get that - it's easy to do the shotgun approach until the cash runs out

The way the FPR works is that it should be at a constant pressure until the manifold is under boost - then fuel pressure rises 1:1 - 1 psi manifold pressure => 1 psi fuel pressure increase. Hook up a fuel pressure gauge and see what's going on when it starts to flake out. If you see the pressure drop or fluctuate, you know you have a likely candidate (the other candidate for low fuel pressure is that the fuel pump is faulty, but Walbros are pretty reliable ...)
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Old 10-04-2013, 07:45 PM   #20
Sethk1980
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Well I just noticed a code p0031 heater cintrol circuit low bank 1 sensor 1. That help out any?
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Old 10-04-2013, 08:35 PM   #21
nmlittlebigman
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Quote:
Originally Posted by Sethk1980 View Post
Well I just noticed a code p0031 heater cintrol circuit low bank 1 sensor 1. That help out any?
Front O2 sensor bad or failing. That could explain alot of your symptoms.
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Old 10-04-2013, 08:40 PM   #22
Sethk1980
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Welp I guess thats where ill continue spending lol. That seems to be a one problem issue, as I already checked the connectors and theyre fine.

I also started snooping around the bay and found that my ebcs wasnt completely hooked up correctly (didnt seem to affect performance), and my purge control solenoid valve was plugged in, but no lines were hooked to it at all (I hooked them up correctly).
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Old 10-05-2013, 11:02 AM   #23
Drewswrx
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Check the plugs. I say this cause I had the same exact problem and my car was running super lean. I check the plugs and turns out I had a cracked plug.
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