[AdkLooch]

Fellas,

Here's the issue I'm having in a nutshell: take foot off of accelerator when going downhill to maintain speed. Press accelerator once at the bottom of the hill (and beginning to go up another hill) to maintain or increase speed - at this point there is no response from the throttle until the accelerator is pressed far enough at which point the transmission upshifts and the RPM's jump. During the "lag" there is noticeable tap/ping/knock/what-have-you noise.

What I've found in the data is that during the period when my foot if off of the accelerator (coasting downhill) the engine switches to open loop and the long term fuel trims for each bank go negative. When I get back on the gas the engine switches back to closed loop and the lag begins.

From what I've gathered, in open loop the ECM is relying more on sensor data (other than O2 sensors) and in closed loop is relying more on O2 sensor data and tables. Assuming that is all correct, what could be causing such a difference in performance between open and closed loop? If everything is operating correctly I imagine there shouldn't be much difference in the way the truck runs whether in open or closed loop. What gives?

 

[AdkLooch]

Thanks for the reply. The truck is a completely stock 2016 with only 1300 miles on it. It was definitely up to temperature when I logged the data and there are no codes. I haven't shown the data to the dealer but I have had it in a few times for the same lack of power issue - they tell me its normal but I'm inclined to disagree.

 

[AdkLooch]

Most of what I've read at this point says the same thing - decel mode. Should there be such a difference in performance when switching between the two? One would think that there should be no noticeable difference in performance and power whether the is engine looking at all the closed loop sensor data versus the open loop sensor data - the big assumption being that all the tables have correct values and all of the sensors are working correctly. I would think the transition between the two operating modes should be transparent to the driver. Of course, GM could just be making a s**t product but I'm not quite there yet. I've had three loaner Silverados, all of which ran great.

 

[AdkLooch]

Thanks for taking the time again to reply. If by VCM you are referring to active fuel management, I always drive in M5 (unless on the highway which is very rare) to purposefully keep the vehicle in V8 mode.