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Old 07-14-2013, 09:03 PM   #1
jesseber
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Unhappy TERRIBLE hesitation/lean AFR at low rpms. Particularly from a stop.

Just finished having my motor built on my 2004 STI and met up with my tuner (who has always given me solid tunes) to give me a break in tune but no matter what he tries the car goes EXTREMELY lean and hesitates like f'ing crazy to get moving from a stop until about 2700 when it suddenly runs like a charm.

This happens about 75% of the time, otherwise it gets moving perfectly fine. The issue also occasionally affects other gears as well at low RPMs (though not as much and not near as bad) and the car also is hesitating and not lettting me rev past the low 2000s during neutral revs about 50% of the time.

Car is idling at a rock solid 14.7 afr.

What is going on??? Spark plugs? Injectors?

Mods include FP Red, 1100DWs, and other supporting mods. Tuning is on Cobb AP.
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Last edited by jesseber; 07-14-2013 at 09:39 PM.
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Old 07-15-2013, 06:01 AM   #2
dstroy
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Did you check your fuel pump/regulator/controller already?

Last edited by dstroy; 07-15-2013 at 06:08 AM.
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Old 07-15-2013, 12:58 PM   #3
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AFRs are still target when WOT?
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Old 07-15-2013, 01:14 PM   #4
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Quote:
Originally Posted by SlimJim8804 View Post
AFRs are still target when WOT?

Can't go WOT. Brand new motor build.
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Old 07-15-2013, 01:15 PM   #5
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Quote:
Originally Posted by dstroy View Post
Did you check your fuel pump/regulator/controller already?
Just the regulator which seemed fine.
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Old 07-15-2013, 02:11 PM   #6
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The nuetral revs, that's a bit odd.

The rest of it sounds like it can stem from bent or kinked fuel hoses or a faulty regulator or coinciding vacuum assembly.

Have you checked static and dynamig fuel pressure?

-Mark
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Old 07-15-2013, 02:22 PM   #7
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Quote:
Originally Posted by APM Tuned View Post
The nuetral revs, that's a bit odd.

The rest of it sounds like it can stem from bent or kinked fuel hoses or a faulty regulator or coinciding vacuum assembly.

Have you checked static and dynamig fuel pressure?

-Mark
At idle the dynamic fuel pressure on the gauge is at 42psi.
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Old 07-15-2013, 02:35 PM   #8
jesseber
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^^ (Tuner) ^^
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Old 07-15-2013, 04:56 PM   #9
dstroy
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Have a friend watch your pressure to see what it does, if it drops at idle, signs point to bad or going bad relay/fuse/wiring/pump/fpc. Or maybe a partially clogged filter.
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Old 07-15-2013, 05:52 PM   #10
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Quote:
Originally Posted by CorrPerformance View Post
At idle the dynamic fuel pressure on the gauge is at 42psi.
Okay, do you have a system that can allow you to drive the car to see what's going on when it stumbles? Idles offer no load, that's why i ask.

-Mark
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Old 07-15-2013, 10:00 PM   #11
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Quote:
Originally Posted by APM Tuned View Post

Okay, do you have a system that can allow you to drive the car to see what's going on when it stumbles? Idles offer no load, that's why i ask.

-Mark
Would watching the regulator gauge during a free rev stumble help at all? Trying to do what I can on my end.
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Old 07-15-2013, 10:39 PM   #12
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Yeah, it'll tell you to either continue troubleshooting the fuel system or look for something else. You'd be looking for a significant drop in pressure.
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Old 07-17-2013, 03:03 PM   #13
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Gonna pull and replace the fuel pump today and then check the FP gauge under throttle/stumble.
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Old 07-17-2013, 11:47 PM   #14
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Replaced fuel pump. No difference. Still 42psi at idle, climbing to ~55psi under sputtering free rev.

Having played with it more, I have to say the hesitation is the worst whilst going into 1st. Almost impossible to get going when it stumbles.

Update: Moved it out of the way of my driveway a few minutes later and it acted absolutely perfectly well behaved (for the two times I gave it pedal while semi-walking it). Gave it some free revs afterwards and after a few it started stumbling again.

Also, just caught p0458 (Evap) but if I'm not mistaken that's because of my new Perrin fuel rails/lines, correct?

Last edited by jesseber; 07-17-2013 at 11:54 PM.
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Old 07-18-2013, 09:41 AM   #15
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Hey you did not mention that you also have intake camshaft position sensor DTC (p0021) that keeps popping out from time to time and also P0011. Having those DTCs coming on will also render the car from operating normally. I mentioned these to you from the day I got to the mechanic shop and connected to the AP unit to try to tune it.
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Old 07-18-2013, 09:45 AM   #16
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Hang on... You got an evap code? did you by chance NOT hook the evap purge line on the manifold back up? Because that would give you a pretty significant vacuum leak.
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Old 07-18-2013, 09:50 AM   #17
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And if your AVCS solenoid/related wiring is failing it would cause problems similar to this.
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Old 07-18-2013, 02:51 PM   #18
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hmmmm, looks like there are other things going on here...

-Mark
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Old 07-18-2013, 02:53 PM   #19
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Quote:
Originally Posted by CorrPerformance View Post
Hey you did not mention that you also have intake camshaft position sensor DTC (p0021) that keeps popping out from time to time and also P0011. Having those DTCs coming on will also render the car from operating normally. I mentioned these to you from the day I got to the mechanic shop and connected to the AP unit to try to tune it.
Corr, if your tuning this thing (or trying to get it tuned but having ^those issues)....clearly there's another problem going on.

huh, odd that things get left out randomly.

-Mark
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Old 07-18-2013, 04:02 PM   #20
jesseber
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Quote:
Originally Posted by dstroy View Post
Hang on... You got an evap code? did you by chance NOT hook the evap purge line on the manifold back up? Because that would give you a pretty significant vacuum leak.
I didn't do the install so I'm not sure. How can I check? Again I'm using a Perrin fuel system.

Last edited by jesseber; 07-18-2013 at 04:21 PM.
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Old 07-18-2013, 04:04 PM   #21
jesseber
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Quote:
Originally Posted by CorrPerformance View Post
Hey you did not mention that you also have intake camshaft position sensor DTC (p0021) that keeps popping out from time to time and also P0011. Having those DTCs coming on will also render the car from operating normally. I mentioned these to you from the day I got to the mechanic shop and connected to the AP unit to try to tune it.
Yeah I totally forgot about that code. I haven't seen it since, though.
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Old 07-18-2013, 05:00 PM   #22
dstroy
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You need to do a leak test to rule out any vacuum leaks.
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Old 07-18-2013, 05:13 PM   #23
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Quote:
Originally Posted by dstroy View Post
You need to do a leak test to rule out any vacuum leaks.
Yeah I'm gonna bring it back to the shop in the morning and have them look into the problem but we're gonna start with a smoke test.
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Old 07-18-2013, 05:26 PM   #24
dstroy
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Yeah I'm gonna bring it back to the shop in the morning and have them look into the problem but we're gonna start with a smoke test.

same thing, less messy
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Old 07-19-2013, 04:32 AM   #25
BURNING4ORCE
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Quote:
Originally Posted by jesseber View Post
Replaced fuel pump. No difference. Still 42psi at idle, climbing to ~55psi under sputtering free rev.

Having played with it more, I have to say the hesitation is the worst whilst going into 1st. Almost impossible to get going when it stumbles.

Update: Moved it out of the way of my driveway a few minutes later and it acted absolutely perfectly well behaved (for the two times I gave it pedal while semi-walking it). Gave it some free revs afterwards and after a few it started stumbling again.

Also, just caught p0458 (Evap) but if I'm not mistaken that's because of my new Perrin fuel rails/lines, correct?
That code is for the pump if you didn't seal the black rubber gasket properly for the tank,re-used the old one, also dirt debri causing mating surface leaks. I usually just turn off the cel, silicone the gasket a it, or replace with a new one. Code comes on here and there on different occasions usually long drives if it's leaking and a feint of raw fuel smell inside the cabin.
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