Duramax Diesels Forum Truck of the Week
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Old 11-13-2017, 05:44 PM
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Default hard starts

This has been an issue for a couple years now, but it has gotten much worse. When I start the truck at 45 degrees or under, it knocks like crazy, idles like crap and smokes the shop completely out in a few seconds. Once It warms up for a minute or so, the idle smooths out and it runs fine. Truck runs great, balance rates when warm are all great, I just replaced all 8 glow plugs last year in hopes of solving the issue but it didn't help at all. When I replaced the glow plugs, I verified the relay was working via a test light. About 5 seconds after the light expires I can hear my lift pump ramp way up and the volt meter goes up, so I'm assuming the relay is still working.
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Old 11-13-2017, 05:53 PM
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My old rattly 94 12 valve cummins daily driver with 270,000 miles starts with ease, smooth and hardly smokes at 10 degrees. really confused why this common rail is so horrible.
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Old 11-13-2017, 06:00 PM
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I have a 325,000 mile LB7 with lowered compression, no intake air heater, +75% race injectors, and mine starts clean at 13įF with no rattle or smoke.

I really don't know why these common rails are so horrible. LOL

There is clearly something wrong with your specific truck. What all has been done to the truck? If it is tuned, that's probably the issue.

Edit: signature says PPEI tuning. Try flashing it back to stock and try a cold start.

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Old 11-13-2017, 06:18 PM
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I do have the intake heater deleted. I don't have the stock file for the truck anymore. Long story, but it involves my original ECM being bricked. running it on 1 or 5 on the dsp doesn't seem to make a difference. It has 81,000 on the clock. I believe I replaced the injectors at 68,000. It seems to start fine when its warm, so I don't think its a leaking injector.
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Old 11-13-2017, 06:21 PM
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I bet it is tuning. If you know someone nearby that you could borrow a stock ECU from, you could do that. Just do the 30-minute anti-theft relearn, then let it get cold and see what happens.

You could also try and get a dealer to flash a stock file on, or find one online. This assumes you have the ability to put your PPEI tune back on. Also, you might be able to contact PPEI and see if they kept the stock tune.
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Old 11-13-2017, 06:24 PM
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I do still have the stock file, but I don't think it will work in the new ecm?
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Old 11-13-2017, 06:24 PM
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Quote:
Originally Posted by danzick View Post
I do still have the stock file, but I don't think it will work in the new ecm?
It should work just fine. Just do a full flash to remove the DSP5 code, or it will get angry. And do a full flash to put the DSP5 tune back when you're done testing.
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Old 11-13-2017, 06:29 PM
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thanks, I will give it a try. I also emailed Kory a copy of my dsp5 file to double check everything.
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Old 11-13-2017, 07:12 PM
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What glow plugs did you use? I replaced mine with 8 Diesel rx plugs and didnít get any codes for a couple weeks but truck was knocking and smoking and shaking real bad. The codes finally showed up and had 6 bad plugs. Replaced them all with 8 ac delcos and the truck fires right up now no smoke or nothing. This is how bad it was and still didnít throw codes for 2 weeks lol.

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Old 11-13-2017, 07:53 PM
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All new acdelco
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Old 11-13-2017, 07:55 PM
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That video it's pretty dang accurate. But more on a colder say. Say 20 degrees or lower.
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Old 11-13-2017, 08:45 PM
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Thats been my life for a long time. I joke that my truck acts like an old Detroit when the temps get below 35*. I know my problem stems from poor injectors.
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Old 11-13-2017, 11:05 PM
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It could be injectors, but with how low the miles on them are, unless they were junk injectors, it is probably tuning. Not many tuners alter the cold start tables (and there are a lot of them), so it can get cranky as tunes get more aggressive. And honestly, even GM's stock cold start tuning was kind of crap. I made improvements to that when my motor was stock even.

With some effort (OK, a lot of effort), you can even have a built motor with big injectors start and run clean in the cold:
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Old 11-14-2017, 06:59 AM
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interesting. I will have to see what Kory says. They were LDS injectors.
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