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I have acquired some of the recent Intermountain HO SD40-2's with the ESU sound decoders. When I have them in consist running as a pair or trio they seem to surge which in turn creates an accordion effect in the train. It does it a lot at slower speeds and I don't notice it as much at higher speeds. When I run them individually I don't seem to have the problem. Is there something that I have to program in the decoder? Nate
I forgot to add in my post that I am running them with DCC and that I have other loco's that do not have this problem so I don't believe it is a power supply issue. Nate


Active Member
Sounds like you need to disable DC mode. Not sure what needs programmed for that ESU decoder. Look in the manual, or look it up on their website.

Also, what DCC system do you have? Are you using Advanced consisting mode, or basic consist mode?

Mark R.

Custom Painter
Sounds like the BEMF in the units is fighting with each other. If all the engines in the consist aren't properly speed matched to each other, the BEMF will get false indicators as to what to do when the other units are pushing or pulling it.

Try setting CV49 to 18 in the units to turn the BEMF off and see if it helps. CV49 to 19 turns it back on.

Thanks to everyone for the suggestions. I was called away from home but will apply what has been said and post an update when I return! Nate

Mark R.

Custom Painter
Engines in consists should have the BEMF turned off. ANY external exertion on an engine with BEMF turned on will cause the engine to immediately try to compensate by either trying to slow down or pick up.

If one engine runs even slightly faster than the other, it will try to push the second engine. The BEMF sees this push and tries to slow the motor to maintain the set speed. The first engine sees this slow down and IT'S BEMF tried to speed up to compensate. In the end, the two engines are constantly fighting back and forth to maintain the set speed.


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