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Jim_Coupe
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« on: April 11, 2016, 06:36:43 AM »
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When i changed my exhaust to 3" with lower backpressuer my idle at warm engine now occilates up and down when i do a first start. It dissapears after a while.. I suspect it is due to lower backpressure in the exhaust and i need to adjust a PID value somewhere..
Any thread I can read more about this here?
/J
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E85oholic
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nyet
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« Reply #1 on: April 11, 2016, 08:56:16 AM »
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I have the exact same problem with a 1.8t wb car.
Fine on cold start until closed loop kicks in, then hunting until coolant temp reaches 89C-90C, ON the dot.
It is repeatable, does it EVERY time.
Cat heating disabled, warmup fueling is dead bang on.. idle trims are 0
tried raising idle torque reserve, no effect. Also tried higher idle rpm up to 1000, still hunts.
Works fine with AC on.
Would post logs but they're huge, i have the whole start cycle from cold to 90C if anyone needs it; I can post it.
I can understand needing to tweak the idle PID, but what is changing over at 90C such that is is fine (other than the thermostat opening)?
If i ever figure out the problem I will post here.
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« Last Edit: April 11, 2016, 08:59:53 AM by nyet »
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ME7.1 tuning guideECUx PlotME7Sum checksumTrim heatmap toolPlease do not ask me for tunes. I'm here to help people make their own. Do not PM me technical questions! Please, ask all questions on the forums! Doing so will ensure the next person with the same issue gets the opportunity to learn from your ex
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adam-
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« Reply #2 on: April 11, 2016, 09:56:23 AM »
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What's been changed hardware wise? No issues here.
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nyet
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« Reply #3 on: April 11, 2016, 10:10:50 AM »
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What's been changed hardware wise? No issues here.
The 1.8t i'm working on has a ton of changes - injectors, exhaust, turbos, etc. so i'm not sure where to start. Not sure about Jim's car, of course. |
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ME7.1 tuning guideECUx PlotME7Sum checksumTrim heatmap toolPlease do not ask me for tunes. I'm here to help people make their own. Do not PM me technical questions! Please, ask all questions on the forums! Doing so will ensure the next person with the same issue gets the opportunity to learn from your ex
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TijnCU
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flying brick
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« Reply #4 on: April 11, 2016, 10:51:12 AM »
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What kind of rpm fluctuations are we talking about?
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nyet
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« Reply #5 on: April 11, 2016, 01:55:52 PM »
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400rpm or so.
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ME7.1 tuning guideECUx PlotME7Sum checksumTrim heatmap toolPlease do not ask me for tunes. I'm here to help people make their own. Do not PM me technical questions! Please, ask all questions on the forums! Doing so will ensure the next person with the same issue gets the opportunity to learn from your ex
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dream3R
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« Reply #6 on: April 11, 2016, 10:29:24 PM »
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injector p/w ok?
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nyet
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« Reply #7 on: April 11, 2016, 10:48:34 PM »
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injector p/w ok?
Yes. Injectors are fine. Everything is fine for the first 110 seconds (open loop) and after the motor reaches 90C, which means either the pump is loading the motor just enough to hide the problem after the thermostat opens, or I'm missing something in the ECU. |
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ME7.1 tuning guideECUx PlotME7Sum checksumTrim heatmap toolPlease do not ask me for tunes. I'm here to help people make their own. Do not PM me technical questions! Please, ask all questions on the forums! Doing so will ensure the next person with the same issue gets the opportunity to learn from your ex
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dream3R
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« Reply #8 on: April 11, 2016, 11:44:44 PM »
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Yes. Injectors are fine.
Everything is fine for the first 110 seconds (open loop) and after the motor reaches 90C, which means either the pump is loading the motor just enough to hide the problem after the thermostat opens, or I'm missing something in the ECU.
Exactly my point log p/w from cold to warm up. |
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Jim_Coupe
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« Reply #9 on: April 12, 2016, 01:02:58 AM »
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Same here around 400 - 800 rpm.... I happened when i changed Exhaust+Intakemanifold. This occured also before i tuned my engine (OEM MAF + Injectors + OEM File) when i had the exhaust system disconnected (O2 sensors connected).
My theory is that the idle is very fine tuned agains the backpressure of the OEM exhaust system.. It feel like a value in a PID loop somewhere need to be adjusted. The "P" factor should be lowered abit.. hmm or maybe more timing advance @ idle to keep it alive.
What is p/w dream3R?
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« Last Edit: April 12, 2016, 01:20:28 AM by Jim_Coupe »
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E85oholic
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prj
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« Reply #10 on: April 12, 2016, 01:44:36 AM »
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Back to school.
Backpressure does not change on idle from a bigger exhaust.
Backpressure is restriction due to high flow. At idle even a 2" exhaust is more than sufficient for your engine.
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Jim_Coupe
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« Reply #11 on: April 12, 2016, 03:06:55 AM »
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Yes that sounds correct in my ears and I will not argue with that.  But i have experienced very unstable idle when I example wise took of the headers on my old 5cyl s2. |
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« Last Edit: April 12, 2016, 03:10:26 AM by Jim_Coupe »
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E85oholic
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eibxmatic
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« Reply #12 on: April 12, 2016, 06:04:25 AM »
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Sounds a bit like oscillating stalling protection
Is the throttle plate angle jumping ?
Could be caused by a leak pre O2
Maybe rising egt after warmup will heat exhaust enough to close the leak itself
Just a thinking
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nyet
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« Reply #13 on: April 12, 2016, 09:55:40 AM »
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Exactly my point log p/w from cold to warm up.
I have that. What am I looking for? the p/w oscillates along with the throttle plate and timing as the idle PID tries to control the speed. They don't appear to be bottoming out. I can raise the idle to 1000 rpm, and/or increase torque reserve to bring up load, and the problem still occurs, so I don't think it is an injector problem. And I can't imagine the water pump load alone is enough to explain what I'm seeing. |
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« Last Edit: April 12, 2016, 09:58:40 AM by nyet »
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ME7.1 tuning guideECUx PlotME7Sum checksumTrim heatmap toolPlease do not ask me for tunes. I'm here to help people make their own. Do not PM me technical questions! Please, ask all questions on the forums! Doing so will ensure the next person with the same issue gets the opportunity to learn from your ex
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nyet
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« Reply #14 on: April 12, 2016, 09:56:52 AM »
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Maybe rising egt after warmup will heat exhaust enough to close the leak itself
It stabilizes EXACTLY at 89.5-90C, every time.... |
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ME7.1 tuning guideECUx PlotME7Sum checksumTrim heatmap toolPlease do not ask me for tunes. I'm here to help people make their own. Do not PM me technical questions! Please, ask all questions on the forums! Doing so will ensure the next person with the same issue gets the opportunity to learn from your ex
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