I would like to MU or DH 2 LL SD9s together but one has a loksound decoder and the other is plug & play TCS. They both ran good together before decoders but now one starts way before the other. I changed the cv for Vstart but cant seem to get the speed curve to accelerate smoothly.
You might also want to try working with Vmid and Vhigh as well to get them to run close. They just have to be close, not dead on perfect. Too far off and they will buck back and forth, but it doesn’t have to be absolutely perfect at all speeds.
Failing that, you may have to program in a speed curve to one or both units.
Which DCC system do you have? If it supports Ops Mode programming you can start both locos and adjust the one on the fly while they are running. Put them near each other but not coupled and adjust til they stay about the same distance apart.
–Randy