Problem putting together an O gauge layout with some older components: Puzzling inconsistent response with Cab1 controller.

Sounds more like a track issue than any thing else.  Since Atlas track does not that the outside rails connected, it could be caused by the traction tires that keep wheels on that side from picking up power.  Try putting a lighted caboose on track where engine stops to ensure there is power and that would also bridge power to both outside rails.  Also, Atlas switches are known for not passing power through due to small connecting wires burning out.

Good luck and keep us posted,

Don

Newer (conventional?) engine goes around just fine, but older conventional engine runs a little bit, then stops.  Have you serviced (lube, oil and clean) the older engine lately?  If it's been in storage a long time, it may need servicing to run properly.  Same goes for track if it's been stored a long time!

Chuck

@DGJONES posted:

...Since Atlas track does not that the outside rails connected, it could be caused by the traction tires that keep wheels on that side from picking up power.  Try putting a lighted caboose on track where engine stops to ensure there is power and that would also bridge power to both outside rails.  Also, Atlas switches are known for not passing power through due to small connecting wires burning out....

Not clear from the original post if the problems occur with TMCC, but this could affect the signal.

Do you have a sufficient number of power drops around the layout from your power supply ? 

Adding jumpers between track sections helps with connectivity/continuity issues between track pieces, but does not increase power to remote parts of the layout.

I would also test around the layout with a voltmeter to see if all parts of the layout are getting correct voltage, especially under load.

Using new Williams 44-ton switcher - ran smoothly  around mainline loop X one. Older conventional loco - stalled halfway around and wouldnʻt respond. Repeat again with new loco and then older one - stopped after short distance passing one turnout and then wouldnʻt respond. Tried again with the switcher and no response at all (i.e. turned knob multiple times etc) and then took off like a bat out of ...

This sounds as though it may  be a problem with weak feeds of power, especially if the older engine has the old pulmor motor.  You state that you added jumpers but if these a with alligator clips, that may not carry sufficient power the older engine needs. when you run the old locomotive and it stops, carefully check the jumpers close to the area where it stopped and see if they feel warm or hot, if so you need better conductivity on your track work. Make sure all track connections are clean and tight, it may help to put a little rail-zip on the pins. Please keep us appraised of your progress.

Ray