Duramax Diesels Forum Truck of the Week
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Old 01-07-2018, 03:42 PM
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Default rough idle - need some guidance

Can anyone explain what can cause this? I tried to post my log but it keeps telling invalid file, so if someone can tell me how to change the file so I can post it up, let me know .

Issue: Commaned mm3 jumps up randomly 8-10mm3 causing a slight lopey ide. After 5-10 seconds it goes away. Only does this on cold starts, and fuel rail pressure seems to hold pretty dang steady. I can't wrap my head around why my commanded mm3 jumps up randomly?
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Old 01-07-2018, 07:00 PM
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Did you ever figure out your fuel pressure issues? Does this issue happen in the base and dsp tunes?

Have you tried the stock tune?

You shouldn't mess around with any of the idle areas of the fueling tables. Leve them stock. That goes for Torque reference, Main Injection, and Fuel Pressure.

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Old 01-12-2018, 11:07 PM
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I've tried putting all idle fueling areas 100% stock, with the same result. I've tried a few different base tunes, thinking maybe that could be the case. Tomorrow I'm uploading a stock tune that I can try out to see if the issue is still there. If it is I'm at a loss, maybe some corrupted files? It's crossed my mind to take it to GM and have it flashed. It only does it below 25-30*. However, after that, the colder it is out the worse the lopey idle becomes. My pulse at idle will jump from 900-1000us to 1300-1400us, and its only for one frame on the log. It then returns to the normal 900-1000us. I wish I could post my log


Yep got the fuel press. issues sorted out!
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Old 01-12-2018, 11:17 PM
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Here's one of the dsp files I've tried
Attached Files
File Type: ctz Davis_NEW_Winter.ctz (1.56 MB, 7 views)
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Old 01-13-2018, 01:31 PM
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Did it this morning with a stock tune as well
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Old 01-13-2018, 07:40 PM
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take anything that I'm saying with a grain of salt, because this is the internet and I'm no tuning genius... but took a quick look and I'm a bit confused by the timing changes at 10mm3 you've chosen, as well as a few other things like ECT timing changes. It might be why it's running so badly at idle. Also, you shut off the EGR instead of leaving it on and tuning the parameters to keep it from coming on; that's a no-no on the LMM. I have some stock known good tunes from my LMM and some friends LMMs if you want me to email you something to start over with?
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Old 01-13-2018, 11:35 PM
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I thought the same as you, that possibly what I was trying to achieve via timing correction on cold starts was the culprit, and I did reverse what I did. However, the issue remained. I'm doing the corrections to add timing at idle, even at operating temp. Not abunch, but 1.5-2* or so.

I just stumbled upon the egr tables. I was not aware of that known "no no" until I did some reading last night. I went back and left all the EGR tables factory, besides changing the settings so it never comes 'on'.

And pay no attention to dsp#1 I was just playing with timing at low mm3 values to see how much more heat I could get to the charger. So when your towing, and "coasting" down a hill, I was seeing if I could help keep the charger warm. Hoping when its time to fire back up the hill the charger will come in a bit quicker. Its a work in progress lol.

Thanks for the reply!!
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