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Old 12-29-2012, 06:18 PM   #1
BlueSubeDude
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2006 WRX TR

Default AF Correction +25% Pumping Brakes

My random misfire is driving me crazy...

Symptoms:
I have an inconsistent misfire on cylinder 1. This usually happens after I pull out of the driveway and drive a few blocks to a stop light. When I approach the light I notice that the engine idles roughly and then settles out after a while. At this point I get the CEL for Cylinder 1 misfire. It doesn't happen all the time.

Observations:
I notice that my car idles smoothly when the car is cold (open loop) and when the car is completely warmed up I don't have the problem. It usually happens about 3 minutes after I start driving out of the driveway. I used the AP to look at the AF Correction 1 and have noticed that when I'm on the brake the AF Correction goes above 10%. As a test, I pumped the brakes and found that the AF goes all the way up to +25% and the engine rpms change. At idle the AF Correction hovers +/-8%.

Car/Mods:
2006 WRX Stock with K&N Filter. The Airbox has broken tabs so I tied the box down with rope (been running like this for a couple of years). Cobb Stage 1 Map (does the same on stock map). I also have a small evap leak somewhere, but it's been fine for over a year (p0442). I recently changed plugs NGK iridiums, 0.03" gap. Compression hovered about 150 +/-2% on every cylinder.

What do you guys/gals think?
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Old 12-29-2012, 09:33 PM   #2
Cobb Tuning
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If it happens while pumping the brakes, which requires vacuum power, it would likely indicate an intake tract leak (probably post-TB). It's possible the brake booster supply hose itself is torn.

Cheers

Lance
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Old 12-29-2012, 10:19 PM   #3
BlueSubeDude
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Quote:
Originally Posted by Cobb Tuning View Post
If it happens while pumping the brakes, which requires vacuum power, it would likely indicate an intake tract leak (probably post-TB). It's possible the brake booster supply hose itself is torn.

Cheers

Lance
I checked the brake booster vacuum hose, and everything seemed okay. When I pulled off the hose on the booster side I heard a "swoosh" of air which indicates that it was holding vacuum. I sucked on the hose (I know...very crude and unsanitary) and the hose held a vacuum. The check valve seemed to function properly too. Would I need a stronger vacuum to check the hose?

Do the diaphragms in the brake booster ever leak?

So with your response my misfire sort of makes sense. I'm guessing that my car is still in open loop when I get on the brake at the first stoplight and doesn't accommodate for the extra leaked air from using the brakes, which results in a misfire. Is my logic sound or am I missing something? If this is the case how come only cylinder 1 misfires? Based on my understanding cylinder 4 is connected to the brake booster line and would probably be the cylinder that misfire.

I appreciate the help.

Thanks
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Old 01-01-2013, 08:04 AM   #4
danger1138
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Happy new yeArs.. I read this thread yesterday, so i went ahead and pumped the brakes while car was idling and the AF correction 1 went from hovering around ~4 all the way to +25.. So maybe an intake tract leak.. How can i test for where the leaks actually coming from? Seafoam?
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Old 01-01-2013, 12:30 PM   #5
danger1138
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Bump..
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Old 01-01-2013, 08:24 PM   #6
nmlittlebigman
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Old 01-02-2013, 10:04 AM   #7
Cobb Tuning
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Quote:
Originally Posted by danger1138 View Post
Happy new yeArs.. I read this thread yesterday, so i went ahead and pumped the brakes while car was idling and the AF correction 1 went from hovering around ~4 all the way to +25.. So maybe an intake tract leak.. How can i test for where the leaks actually coming from? Seafoam?
You can do a pressure or smoke test of the intake tract. As nmlittlebigman stated, there are DIY methods for a pressure test. Most Subaru performance shops (and other repair shops) will also have the ability to do a pressure or smoke test.

Bill
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Old 06-10-2013, 11:50 AM   #8
BlueSubeDude
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It's been awhile, and I'm still having this problem. I bought a vacuum gauge and hooked it up to the the location that feeds the brake booster and the vacuum held.

It's starting to get worst because I notice it everytime I brake hard. When I come to a stop, the engine idles really roughly and usually settles down after 10 secs or so. Sometimes throws a misfire CEL because it's not getting enough fuel. I found that if I blip the throttle as I come to a stop things are okay and there's not a huge a/f correction.

Thoughts anyone?

Update: Another observation I made today. I was watching the short term fuel trims and noticed that everytime I got off the gas after cruising to coast, it would jump to +15-19% for a few seconds then settle back down. Looks like the braking just coincided with getting off the gas pedal. Anyone know why the fuel trim would jump up when coasting after cruising? Bad fuel pressure regulator? Clogged fuel filter?

Last edited by BlueSubeDude; 06-10-2013 at 07:41 PM. Reason: update
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Old 06-10-2013, 10:31 PM   #9
danger1138
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Its is most likely an issue with your brake booster line. It operates off vaccum
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Old 06-10-2013, 10:31 PM   #10
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^^ operates off vaccum so u might have a leak there. Check it out.
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Old 06-12-2013, 09:41 AM   #11
BlueSubeDude
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I hooked up a vacuum gauge to where the evap line goes into the cylinder 1 runner and vacuum held steady at 18inHg so I don't think it's an intake manifold leak.

Just for kicks, I pulled the TPS connector to force the car into open loop. With the AP I monitored the roughness, and in open loop there was absolutely no roughness. In closed loop the roughness would consistently count at idle. Since open loop ran smoothly, I can rule out the following: injectors, spark plugs, compression.

I'm left with either a bad sensor or an exhaust leak before the front O2 sensor?

How do I test the MAF/Front O2 before spending $$ on the parts?

Anyways, I have a fuel filter coming because it's long over due (went to the dealership and they said the fuel filter isn't a serviceable item so I never changed it). Maybe this will help....

Last edited by BlueSubeDude; 06-13-2013 at 01:06 AM.
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Old 06-14-2013, 11:51 AM   #12
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I bit the bullet and took my car to a subaru specialist. As soon as I said 06 wrx he told me it's probably exhaust valve tightness so he's going to check the clearances. According to him the 06/07 wrx's are notorious for this and he's seen tons of exhaust valve tightness on these cars causing misfires.
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Old 05-08-2014, 11:31 PM   #13
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Bumping this to clear some misinfo in here. Came across this thread while doing research on AF Learning.

Found that my car also causes short term learning to spike and max out at +25% while pumping the brakes and idling (not taking your foot off the brake).

This seems to be a normal and not an indication of a mechanical issue. My car does it, (Cobb SF intake + TP tune) my coworkers bone stock 2013 WRX with 4K miles does it, and my wife's 2003 Pontiac Vibe (Toyota 1.8 NA engine) also does it. The Toyota only goes up to about +15% though.

Edit: Answered by atomicfire

Last edited by meebs; 05-19-2014 at 10:11 PM.
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Old 05-12-2014, 02:24 PM   #14
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The brakes are vacuum powered. When you pump the brakes you are intriducing extra air into the intake system. This is normal operation.
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Old 05-16-2014, 06:14 AM   #15
Bo0stcreep
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Its am electrical issue. Can you monitor voltage as you are pumping the brakes? Probably dips down into the 12's? Thats just the car correcting the A/F due to the voltage drop.
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Old 05-19-2014, 10:10 PM   #16
meebs
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Quote:
Originally Posted by Bo0stcreep View Post
Its am electrical issue. Can you monitor voltage as you are pumping the brakes? Probably dips down into the 12's? Thats just the car correcting the A/F due to the voltage drop.
No. It is NOT an electrical issue. The extra air in the intake manifold needs extra fuel to burn correctly.


Quote:
Originally Posted by atomicfire View Post
The brakes are vacuum powered. When you pump the brakes you are intriducing extra air into the intake system. This is normal operation.
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Old 05-23-2014, 05:08 PM   #17
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All cars do this because you are putting a load on the charging system in which it cannot keep up, so in turn the voltage drops. Which means voltage to the injectors drop, in turn the car sees it start to go lean and adjusts accordingly, by adjusting PW to the injectors.
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Old 05-24-2014, 11:06 AM   #18
meebs
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Quote:
Originally Posted by Bo0stcreep View Post
All cars do this because you are putting a load on the charging system in which it cannot keep up, so in turn the voltage drops. Which means voltage to the injectors drop, in turn the car sees it start to go lean and adjusts accordingly, by adjusting PW to the injectors.
Preposterous. There is no different "load" on the electrical system by pumping the brakes versus just stepping on them and holding your foot there. What is draining the system? The brake lights are "on" while holding your foot down (not pumping), and "on" while pumping the brakes (again not taking your foot off completely).

It is a non-issue. There's no need to keep throwing theories out about this; the test I did showed that a BONE stock 2013 exhibits the same behavior.
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Old 05-24-2014, 11:19 AM   #19
Bo0stcreep
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Quote:
Originally Posted by atomicfire View Post
The brakes are vacuum powered. When you pump the brakes you are intriducing extra air into the intake system. This is normal operation.
Quote:
Originally Posted by meebs View Post
Preposterous. There is no different "load" on the electrical system by pumping the brakes versus just stepping on them and holding your foot there. What is draining the system? The brake lights are "on" while holding your foot down (not pumping), and "on" while pumping the brakes (again not taking your foot off completely).

It is a non-issue. There's no need to keep throwing theories out about this; the test I did showed that a BONE stock 2013 exhibits the same behavior.
For one, pumping the brakes you are not introducing any additional unmetered air into the engine, its already been accounted for.


Second Why is it that when just the brake lamp switch in engaged over and over again ( not pumping the brakes, tapping ) just enough to get the brake lights to come on, it still shows the same symptoms?
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Old 05-24-2014, 11:25 AM   #20
Alaskan EJ20
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log your maf voltage, I had an issue were the maf voltage would go hay wire after wired stuff like that, it would weirdly run ok, 1.32-1.35 on a 2.5l with stock air box, and then the voltage would double and go waky when I did stuff like brake and use the heat and ac. new maf solved it, also look up break boost leaks,
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Old 05-24-2014, 12:24 PM   #21
meebs
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Quote:
Originally Posted by Bo0stcreep View Post

Second Why is it that when just the brake lamp switch in engaged over and over again ( not pumping the brakes, tapping ) just enough to get the brake lights to come on, it still shows the same symptoms?
Tapping is still actuating the brakes.

Holding the brake with the tail lights on - does not cause the issue. The constant electrical load to run the lamps is not causing it.

I don't even know why this needs to be discussed any further it is NOT an issue if a bone stock 2013 does it.
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