I have a 2018 Cummins (144,000 miles) with 68RFE transmission, and everything is stock.
I recently had an oil leak behind the timing chain, which the dealer fixed. I also had an SCT tuner running the 20hp tow tune.
When I'm driving about 40 mph and let off the pedal and let the rpm drop down around 800 rpm and then lightly touch the pedal, the motor knocks extremely loud for about a second. It sounds like the fuel is igniting early.
I took the tuner off, and it still does it. Can this be caused by the dealer removing the timing chain our what could cause this?
The dealer can't find any problems with it.
It has been there a week, and they told me to drive it until it gets worse, but I'm afraid it will damage the motor.