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Good morning AdkLooch,

We regret to hear that you are experiencing these engine concerns in your Silverado, and apologize for any inconvenience you have experienced as a result. We would be more than happy to reach out to your dealership for clarification on the diagnosis, and see if it would be appropriate to get you back in. If this is something that interest you, please send us a private message with your VIN, full contact information and involved dealership.

All the best,

Julianne M.
GM Customer Care

AdkLooch said:

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?
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