Regen Lite? On extended Idle

Keith Browning · February 14, 2021

I had been involved with an ambulance that "after idling more than three hours the engine starts shaking."

Initially I performed an inspection and checked for codes. None. So I started the truck and let it idle for several hours. Nothing. Then realizing this is an ambulance the "module" power would normally be turned on which I then did and let the truck idle several hours more however the module software demanded the idle be up around 1800 RPM. Not unusual. I then verified that the engine sounded muffled and indeed it was shaking like it was misfiring. Still no codes. I wanted to check power balance and monitor some PIDs however the ambulance "module" was using the DLC so I couldn't do anything with a scan tool when it was acting up. I gave it one more try with IDS connected, module disconnected and idling for hours. Then it happened.

Suddenly the turbo spooled up and the RPM's raised to 1000. I was monitoring the EGT sensors and DPF_REGEN_STAT among other things and began to notice the EGT's climbed to around 800*f and remained there for 20-30 minutes. The regen status PID never changed but it sure looked like a regen event to me - soot can be burned off at temperatures of 600*f + which is more like a "passive regen" and EGT temperatures one might see while driving the truck. But it never said it was in regen despite this event clearly being controlled.

Contacted the hotline about the scenario and it was stated that the ambulance module was causing the idle concern. Okay. I agree with that but how? I pressed three times about the apparent regen and avoided the question completely. At this point I am convinced there is something in the calibration that burns the exhaust but not a full blown regen. As for the customer's concern I am thinking this regen event that wants to set the RPMs to 100, raise back pressure and adjust fueling is not happy with the 1800 RPMs the ambulance module is commanding.

Thought I would share this and see if anyone has come across something like this.

forddieseldoctor · February 14, 2021

Interesting. I would guess that it’s something to help keep the filter warm so that it don’t get plugged tight.

@PTT_W_ARod · February 21, 2021

Interesting, thanks for sharing!

Keith Browning · March 2, 2021

Quote

SSM 49430 - 2011-2021 F-Super Duty, 2016-2021 F-650/F-750 – High/Elevated Idle After Extended Idle Periods – Selective Catalyst Reductant (SCR) System

2011-2021 F-Super Duty and 2016-2021 F-650/F-750 vehicles equipped with a 6.7L engine may exhibit a high/elevated idle condition. During prolonged idle time, vehicles may experience this high/elevated idle to reduce buildup of unburned hydrocarbons from the SCR system. The powertrain control module (PCM) estimates hydrocarbon levels in the SCR and may increase idle speed to remove them. Idle speed will be increased to 1000 revolutions per minute (rpms) for ambient temperatures near 26°C (80°F) and may increase to as high as 1200 rpms at -40 °C (-40°F). These elevated idle periods can last from 20-40 minutes, depending on ambient temperatures. During power take off (PTO) use and already using idle set point control, the elevated speed is disabled. It is required that the operator monitor the vehicle and adhere to the Exhaust Filter warning messages.

Stumbled on this today... but it makes no mention of the elevated EGTs, turbo spooling and change in the sound of combustion.