Originally Posted by ArmyofOne
I was watching the injectors pulse on the scope in the shop. Every time the tick was audible with the truck on the dyno, a spike showed on the scope. The injectors in the Hemi's with MDS "tick" when the fuel in the rail bypasses the injector because its closed. I cant really think of any other way to explain it, but my dealer spent 35 days and went to great lengths, even paying for dyno time at a contracted shop, to get to the bottom of the ticking noise described, and that was the verdict. If you don't buy it, I don't know what to say, other than I dont know why a dealer and the service manager would willingly go that far to get to the bottom of it and then give me the wrong answer. They drove new trucks, and used trucks, and my truck. They had my truck hooked up and then hooked up a new one for comparison, and mine checked out with nearly identical results and readings to every truck it was tested against...6 in total (3 brand new and 3 used 4th gens).
Call me a skeptic.
As far as I know, when decelerating from 60, as the OP wrote, ALL injectors would be de-activated, not just the MDS ones. That alone rules out this theory. Cars have been cutting injection during deceleration for years now. Also, under light throttle the majority of fuel bypasses all the injectors anyways, so that's nothing new. Add this: If you saw a spike on an O-scope- how could you see it if it wasn't being fired? Also, all the engine parts are still moving at rate, so a spike on a scope could appear to you to align with any event. But mostly, an unpowered injector has no electrical pulse applied, and would have zero uncompressible fuel movement as a result, so I can't see it from my house. Maybe, with a stretch just maybe a fuel rail line, or hose. There has to be physical movement to create noise.