Engine Revs to Redline on Cold Start 6.2L

Rob Mugs · November 25, 2020

That's crazy, almost reminds me of a runaway diesel.

I'd definitely bring that in

Denny NWO · November 26, 2020

I showed the video to the mechanic at the dealership, its going in today.

mafd2 · November 26, 2020

Can you post the video on youtube and add the link here?

Denny NWO · November 28, 2020

Here is the dealership technicians report: Nov 25 - Scan, no ECM codes stored and no bulletins apply. Codes U0140, U0131, U0151, U0102 and U0146 are set history in the BSCM which is related to bulletin 20-NA-155. A new BSCM cal is available to correct condition. Called TAC, no help. Removed the induction pipe at the throttle body, no sign of moisture or anything that would affect the throttle blade. The accelerator pedal is free of obstacles and does not appear to have anything that could hold it down. Parked truck outside over night. Next morning, Nov 26 - install the scan tool, monitor the induction data list and start. The engine RM flared up to 1850 then quickly down o a normal cold idle. The impression I got was an engine start with an incorrect idle learn. Found the idle compensation at 67% which seems high for a vehicle with 12K mileage. Inspect throttle body, completely clean. Correction: No repair possible today and no problem was found. I did install the latest BSCM cal, prog code 28YN51521209 for customer satisfaction and just in case it's related. Wipe down throttle body and perform an idle compensation relearn. Run and clear codes. The engine started without the flair this time. Customer to retry.

I will give it some time and see if it happens again and post if it happens again....or not.

Edited November 30, 2020 by Denny NWO

Denny NWO · November 28, 2020

On 11/26/2020 at 9:03 AM, mafd2 said:

Can you post the video on youtube and add the link here?

mafd2 · November 28, 2020

Wow! Unbelievable... As said above it's like a runaway Detroit diesel from years back. I hope it gets figured out. Keep us updated and thanks for posting the video.

Rob Mugs · November 29, 2020

11 hours ago, mafd2 said:

Wow! Unbelievable... As said above it's like a runaway Detroit diesel from years back. I hope it gets figured out. Keep us updated and thanks for posting the video.

Been around one or two... even had a deuce n a half that had been messed with run away on me

For those that haven't seen what happens

Denny NWO · November 30, 2020

I went to work today and after 10 hours of sitting outside in 20F cold, it started and fluttered and flared up to about 2000 RPM for 2 seconds then ack to idle and bounced up and down a bit. I never took my foot off the brake and did not touch the throttle. Video is noisy at the end as an aircraft was flying over on approach to the airport and I shut the drivers door. Guess the BSCM update didn't do much.

Edited November 30, 2020 by Denny NWO

Jay P · November 30, 2020

Check the under hood fuse box bolts. Your issue isn't on the list but it's worth a look. See attached.

Jay

BUELLTIN.pdf

kodiakdenali · November 30, 2020

Subscribing because mine just did something strange to me today, not what yours is doing though, but right after startup during the gauge sweep it sounded like it reved up to 1500-2000 or so, then right back to idle. it wasn't cold though, maybe 5c, in the garage. it was the second start but still cold. I was just moving it around to put the winter tires on it, a couple months too late! I'm not going to worry about it unless it happens again, but I'd like to hear what your final resolution was.

speaking of all of this, not that this situation seems likely to cause a runaway, but does anyone know how to do an emergency shutdown on this truck? this is something that I think keyless start systems need to get standardized on. I had a Ford once where you could do an emergency shutdown by holding the button for about a second. annoyingly it would only restart in park, it would not restart in neutral. I have had 2 FCA cars which as far as I can tell have no way to do an emergency shutdown at all, which is honestly rather scary. What would you do if you had a sudden coolant leak? or an loss of oil pressure? or a fuel line comes loose and you've got flames shooting out from under the hood...and the only way to stop the fuel pump from pouring fuel onto the fire is to get from your 85mph interstate speed to a complete stop to get the transmission in park before it will allow you to shut off the engine? especially with vehicles that have EPAS now (electric power assisted steering) and knowing that the vacuum in the brake booster will still give you one or two brake applications with power assist before you turn out of boost, it would seem that being able to shut down the fuel supply from the fireball under your hood is way more important for your safety than preventing engine from being able to turn off while in motion.

Denny NWO · December 3, 2020

It did a slight flare on the post from Sunday but on Monday, it went to 3500RPM for almost 8 seconds. Tuesday it started normal and Wednesday (tonight) it sputtered on start up and only slightly flared up. Every time this happens, it has been sitting outside for 8-10 hours after finishing work in temperatures just below freezing. It never does it in the morning at home parked in my heated garage. Here is Monday's start up. I have my foot on the brake the entire time and lift it at the end. It going back to the dealership tomorrow.

Denny NWO · December 3, 2020

On 11/30/2020 at 2:32 PM, kodiakdenali said:

Subscribing because mine just did something strange to me today, not what yours is doing though, but right after startup during the gauge sweep it sounded like it reved up to 1500-2000 or so, then right back to idle. it wasn't cold though, maybe 5c, in the garage. it was the second start but still cold. I was just moving it around to put the winter tires on it, a couple months too late! I'm not going to worry about it unless it happens again, but I'd like to hear what your final resolution was.

speaking of all of this, not that this situation seems likely to cause a runaway, but does anyone know how to do an emergency shutdown on this truck? this is something that I think keyless start systems need to get standardized on. I had a Ford once where you could do an emergency shutdown by holding the button for about a second. annoyingly it would only restart in park, it would not restart in neutral. I have had 2 FCA cars which as far as I can tell have no way to do an emergency shutdown at all, which is honestly rather scary. What would you do if you had a sudden coolant leak? or an loss of oil pressure? or a fuel line comes loose and you've got flames shooting out from under the hood...and the only way to stop the fuel pump from pouring fuel onto the fire is to get from your 85mph interstate speed to a complete stop to get the transmission in park before it will allow you to shut off the engine? especially with vehicles that have EPAS now (electric power assisted steering) and knowing that the vacuum in the brake booster will still give you one or two brake applications with power assist before you turn out of boost, it would seem that being able to shut down the fuel supply from the fireball under your hood is way more important for your safety than preventing engine from being able to turn off while in motion.

The Start/Stop button will shut the engine down. One time when the RPM took off to park redline (3500RPM), I just hit the start/stop button and it shut down immediately. I waited a few seconds and hit the start button and the engine started normally.

Denny NWO · December 13, 2020

So it went to the dealer a second time and they flashed a new BSCM calibration and it started fine until yesterday and it did its random start and redline. Tonight it fired and stalled then the starter cranked for 7 more seconds and it fired and redlined and held until i kicked the throttle pedal. It's going back to the dealer for a third time and they will keep it until they figure out the problem.

2019 AT4 Cold Start High RPM after long crank.mov

Edited December 13, 2020 by Denny NWO