Leave well enough alone!

First suggestion, don't use the front coupler!

I think what you describe may be a pinched wire for the front coupler, so when it's energized it's causing a surge and creating the issue you see.

I have the same locomotive, and changing the ID should not affect anything, and certainly not cause what you see!

I have a K-Line B6 switcher that had the same problem.  Firing the front coupler led to full speed takeoff.  I replaced the coupler with an Atlas coupler for their Erie Built diesel (Atlas part number 680805) and everything has been great since then.

No reason I can think of that the coupler would do that, I have to suspect a wiring issue.

Well, it took me three hours and a lot of removing and replacing parts, but I traced the two front coupler wires from the coil all the way back to the board. Nothing was pinched.  I couldn't see a wire anywhere that looked in distress.  Maybe it's a board problem?  Man, a sloped back tender 0-4-0 that has to do its yard switching from the tender side is a bummer.

Not sure what to do next except try the coupler replacement, I guess.  If I can find one.   

Just Disconnect the front coupler, and try the engine. It should show if the front coupler needs replacement.

Can you measure the ohms of the coupler?  Could be an internal fault.  What gftiv, states is good way to isolate the actual coupler, versus the coupler command.

The other area to check is the mother board.  It could be a bad trace there, but I would take the easy path and check coupler first.

What happens if you go back to original ID?    G

I will be more than amazed if the TMCC ID has anything to do with this issue.

I have a K line b6 0-6-0 with TMCC that had the same "coupler fire - high speed launch" issue.

I believe that mine was being caused by excess smoke fluid reaching sensitive electronics.

Well, the problem is solved.  First I was going to go back to the original ID# and if that didn't work do the coupler things you guys suggested.  But I happened to stumble across the manual for the engine this morning and saw the reprogramming procedure in it. Tried that and when I powered back up afterwards everything was back to normal. The ID# to which I had changed worked fine.

I wish I understood this stuff better. I am happy it worked, but cannot understand how the boards can suddenly be made to function correctly by going through that procedure.  What happens to them that reprogramming "fixes."  And, of course, the bigger question is why would I not be smart enough to try that first?  Duh! 

I sure do appreciate all the help!!       

That's certainly a first!  Question.  Does this unit have an ERR Cruise Commander M installed?  Those can go nuts if you don't have the correct engine type, but the stock DCDR doesn't have that problem.

No ERR Cruise Commander installed.  I bought this thing new way back when it was first produced and just started using it now that I actually have track to operate on.  It's in original condition from then.

I ran this engine for the very first time several months ago and then put it back in the box until more layout building was done.  Yesterday I brought it back out put in on the track and ran for a few minutes then did the ID# change.  Maybe there was a derailment or something from that first run.  But I thought reprogramming would be necessary because, as the manual puts it, the thing would demonstrate "..unresponsiveness in command mode."  In this case it was just the coupler/rocket issue.  Everything else was fine.   

Bucky,

   When a Tmcc engine develops problems the first thing to do is a reprogram, this is for all manufactures. It saves a lot of time. All manuals have the code for the particular engine or you can use the attachment. 

I agree Bill, but I am amazed that this particular issue is caused by reprogramming.  I guess you never know.

Downloaded the attachment, Bill.  Thanks.  Obviously always the first step from now on.  I just wish I knew why it did what it did, but it worked so I'm moving forward. 

I feel your problem is as John first stated.