I've tested the engine on two separately powered (with different power supplies) sections of track on my layout, and I've also tested several of my other Bachmann F7 engines on my layout. All engines run fine except this particular one.  So, it doesn't look like it's my track circuitry.
I'm guessing it's a short internally in the motor inside the engine. The next step for me will be to replace the motor with a spare unit I have and see what happens.

Thanks for the response... I've had them connected and separate and the same problem occurs. Both engines will stall.... I figure it's a short somewhere in the F7 chassis.. I just can't figure out where it is. I've done a continuity check and there are no problems that I can find. I'm wondering if it's in the windings of the actual motor.   I might try replacing the motor with a spare that I have to see if the problem is internal to the motor. If its not that, I really have no idea where the problem is.

Greetings,
I'm having a problem with a Bachmann engine and I hope someone can give me some help. I have a New Old Stock (NOS) Bachman Spectrum N scale F7 Diesel chassis that is having an electrical problem. When I run the engine on my layout, it runs strong with no problems for several seconds. It then stalls and stops, but then starts running again. The amount of time and distance varies from one or two seconds to several seconds between stalls, and it doesn't always stall in the same locations. If I place the engine in tandem with another powered engine, it will cause both engines to stall and stop.  I have taken the chassis apart to lube it, and to check all the electrical connections and contact points. But I don't see anything that looks like a problem.  Can anyone please offer any suggestions as to what might be wrong?  Thanks...