HELP: 2015 starts and idles but will not take throttle - Chevy and GMC Duramax Diesel Forum
11-16 LML Duramax Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine , Transmission, Etc.

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post #1 of 8 (permalink) Old 12-19-2019, 07:36 AM Thread Starter
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HELP: 2015 LML Duramax starts and idles but will not take throttle

Need some help on figuring this one out. 2015 GMC Sierra 2500HD Duramax - 125K miles - Single owner - All stock. Historically this has been an intermittent problem that has occurred a half a dozen times or so now over the last 50K miles. It hasn't occurred in over a year (around 20k miles), until last night. It was driven to work in the morning (45 min drive), perfectly fine. Started the truck after work and it fired up and idled fine, but when attempting to drive it just sputters and bucks around when the go pedal is pressed. If you put it park and press the throttle it won't rev smoothly, and won't go to much more than 1300 rpm. It pulses like a smoker pulling tractor building power/boost before dumping the clutch.

In the past, stopping and restarting the truck has resolved the issue. Last night, around 25 restarts and it was still acting the same.

The truck has been randomly setting a P049D, that comes and goes. I checked the codes and this was the only code stored.

I suspected possible fuel restriction, but using a Kennedy Diesel test gauge showed only 2" of vacuum.

On a whim, I disconnected both negative battery cables. Cycled the ignition 2 times. Then reconnected the battery cables. The truck started and instantly ran perfectly. It would rev out smoothly and at 3K RPM I still only showed 4" vacuum on the test gauge. Drove the truck home and it ran flawlessly.

6:30 this morning, went out to head to work and it's doing the same thing. Not drivable. Before I try to 'reset' the thing again, what else should a guy check to pinpoint the issue with this animal?

2007 Classic CCSB LBZ

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post #2 of 8 (permalink) Old 12-19-2019, 07:44 AM
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This wouldnít make sense if itís an intermittent issue, but itís not fuel gelling is it?

Possibly a bad FPR? I could see that being intermittent. Do you have any way of watching your desired an actual fuel pressure? Youíll probably see your actual rail pressure bouncing around when the issue comes up.


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post #3 of 8 (permalink) Old 12-19-2019, 07:51 AM Thread Starter
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I don't think it's fuel gelling. If it was, it should have shown up on the vacuum gauge, and it would not have been resolved by the battery disconnect/computer reset.

I'm not sure if my Actron will show desired/actual rail pressure, but I believe if there was a variance in desired vs. actual it would set an ODBII code? Good thought. I need to see what I can read with my scan tool.

Are the FPR's on these trucks mechanical or electrical?

2007 Classic CCSB LBZ
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post #4 of 8 (permalink) Old 12-20-2019, 05:40 AM Thread Starter
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Got this figured out last night. The EGR valve was stuck open at 55%. My Actron scan tool showed the actual vs commanded EGR position and while the truck was being stupid, I could see the ECM was commanding 0% open, but the valve was actually stuck around 55%. A few key cycles later, and a few light hammer taps on the EGR valve, it free'd up and starting moving to commanded position. Instantly the truck runs flawlessly again. New EGR valve ordered.
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2007 Classic CCSB LBZ

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post #5 of 8 (permalink) Old 12-20-2019, 07:07 AM
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Sounds like a good scan tool. Thanks for posting solution.

2012 3500hd srw 4 wd Jamco exhaust Kennedy dual lift pump Trifca bed cover B& W gooseneck hitch Western Diesel fuel filter relocation bracket
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post #6 of 8 (permalink) Old 12-20-2019, 08:06 AM
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Which model of Actron are you using?

2016 3500 HD Denali 4WD, CCSB, FuelBox 57 gallon Aux Tank, Edge Insight Monitor, Otherwise 100% Stock
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post #7 of 8 (permalink) Old 12-20-2019, 08:33 AM
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I chased a similar problem for a few years before someone finally listened to my son-in-law's original suggestion that the EGR Valve might have something to do with it. It always seemed to happen only when I was towing my boat or travel trailer so it was quite frustrating, not to mention expensive: I spent around $4K at the dealers paying for parts and labour that had no effect before I took it to my local mechanic shop who immediately sent it back to the dealer again for a computer flash upgrade. Oh! there's codes and it's the EGR Valve that's so dirty it doesn't function any more...who'd a thunk it? When the shop opened it up to replace the valve they found the intake hoses and EGRV were super dirty and the EGRV was corroded.

The reason it was so dirty was probably due to my wife using the truck as a daily driver to a job that was about 5 minutes from home. Five days a week, four 5 minute trips a day (home for lunch) for a few years is not good for a diesel!!

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2005 GMC Sierra 2500HD LLY totally stock
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post #8 of 8 (permalink) Old 12-20-2019, 10:10 AM Thread Starter
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Quote:
Originally Posted by Fredn3ck View Post
Which model of Actron are you using?
It's a CP9680

2007 Classic CCSB LBZ
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