Lml stuck full throttle issue help! - Chevy and GMC Duramax Diesel Forum
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post #1 of 3 (permalink) Old 08-30-2019, 11:40 AM Thread Starter
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Lml stuck full throttle issue help!

This will be long winded as id like to provide as many details as possible.

New(ish) lml owner here. Truck is a 13, slt ecsb- loaded, adjustable pedals
Deleted- afe dp back, mini Maxx (lowest setting), afe intake. (Yes, I’ll make a signature with that info when I figure out how!)
194k miles. Fresh delvac 15/40 and fresh delco fuel filter. Truck was dealer serviced prior to me- nothing on the Carfax as far as engine being opened up meaning original cp4, original injectors, head gaskets, etc. Rail pressure according to the mini max runs 4100-29500. Running Howe’s treatment and going a little heavy on the mix (trying to preserve the cp4).

Before we get too far- yes I’ve searched, no my floor mat isn’t stuck over the pedal (don’t even have them yet, auction truck!), cruise is off, the pedal returns up when it happens, and the mini Maxx shows 0 percent throttle.....but the truck is wide open running through the gears uncontrollably. I should also state that this truck got deleted after $3700 worth of nox sensors, dp sensor, urea tank, lines, labor, etc from a quirk Chevrolet in Massachusetts. I suspect there might be an issue in the harness, and this is why the previous owner ditched it. I didn’t really care as my state doesn’t do emissions so I bought the truck very cheap after a wholesale dealer got it and i immediately deleted it.

I noticed an issue after I deleted it, just reviving it up on the lift still to see how she sounded. I blipped the throttle to the floor for a split second and it soared over 3 grand and stayed there for 4-5 seconds which is a considerably long time to hear it scream with no load on it. I thought that might just be normal when the trucks in park.
I had about 3,000 problem free miles on the delete bud hadn’t had my foot to the floor (never really a need) until yesterday merging with a 28’ boat trailer and when I backed out of the throttle, the truck stayed full tilt- shifted and kept pulling. I stabbed the throttle several times and it wouldn’t come down, brakes were useless so I killed the key which is probably awful for the turbo to cut oil to it while it’s spinning that high but I had no choice. I pulled over, fired the truck back off and it was back at idle and seemed okay.
I got myself to a safe stretch with no cars around, changed the mini Maxx to display tps percentage and floored it again just to try to duplicate the problem and it happened again- tps went to zero but the truck stayed wide open. This time I rode it out and after 10 seconds or so it came back down on its own.
Something to note- I don’t believe it’s “running away” as In burning it’s own oil via turbo seals or being overfilled or anything like that. I killed the key the first time and it shut right off. No smoke that I could see, no blue/white not even a black haze.

I’ve seen one other issue in my searching where the dealer replaced someone’s pedal assembly and all was well, but something tells me it’s not in the pedal since my tps signal drops as it should and the pedal isn’t physically stuck. I know the truck should throw a tps miscorrelation code and shut down to an idle/reduced engine power for something like this but it doesn’t.

I dropped the trailer at a buddy’s farm and limped the truck home as I’m hesitant to get myself into a bad situation, right now it seems to only happen at full throttle but who knows if it could escalate and take off whenever it wants.

I’m a new lml owner, stepped up from an lb7. Need to ask What is the throttle valves purpose? Strictly EGR? If it’s getting blown open under boost could this introduce more air and maybe the truck adds fuel to compensate and takes off? I didn’t delete the throttle valve, just unplugged the egr and various connectors via the mini Maxx manual.

Could this be an issue with the mini Maxx calibrations/tune files? Something corrupt? Is there something else I should unplug? I did read that the differential pressure sensor needs to stay plugged in or you’ll experience stuff like this....I left the sensor under the bed and plugged in but just took the lines off it. Also- I unplugged the big connector on the frame rail when I deleted it and insulated it all up- does the pressure sensor run through this plug? Maybe I have the sensor physically plugged in but interrupted it in that big harness? I did trace the wires as far as I could and they tied in north of that big connector but I don’t know if they make a u turn in the harness somewhere and go back through it?

Any help on how to go about diagnosing this would be appreciated! I do have hp tuners/vcm scanner for my lsx stuff so I can log much more than the mini can if more information is needed.

Hopefully this is the right forum section to post this in- it’s a 911 situation for me...I can limp the truck around but I have a customers boat in limbo as it sits at a friend’s farm and I’m too nerved up to hook back onto it and get it to my shop. Thanks again in advance to anyone with advice.
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post #2 of 3 (permalink) Old 08-30-2019, 04:01 PM
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That sounds scary dangerous!

On a side note, my minimaxx wont tell me rail pressure? Do you have the update for it?

2014 2500 LML SRW
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post #3 of 3 (permalink) Old 08-30-2019, 04:56 PM Thread Starter
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Originally Posted by jrry261 View Post
That sounds scary dangerous!

On a side note, my minimaxx wont tell me rail pressure? Do you have the update for it?
I do not! I bought it used, it doesn’t say rail pressure. In the gauge setup it’s under “icp”
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