Lionel MPC engine randomly slows down

It may not be random since it always slows down if "really slow on the side of the loop away from the power pack connection".  You may have to check out that track section and middle rail connections with other locos or a voltmeter.

Charlie

@BenLMaggi posted:

...tracks are clean, the connections between sections seem fine, and I doubt I need an extra set of jumpers to get the current 5 feet from the transformer...

Well, it's FasTrack, so you probably do. The U36B does draw more power than the can-motored modern stuff and it will show if there are high resistance track joints.

Thanks.

If you have another Pullmor powered diesel, see if it exhibits the same behavior.

@Choo Choo Charlie posted:

You may have to check out that track section and middle rail connections with other locos or a voltmeter.

Charlie

A volt meter could show full voltage unless there is a load. I would use an ohm meter. Put one test lead on each side of the joint.  Any thing higher than 1 ohm is a bad connection. It should also show up using similar locos, like he says.

None of my other engines do it.

Check any solder connections to make sure they are tight.

They actually draw enough current that a poor connection may be warm to the touch.  I have used one of those inexpensive IR gun style thermometers from Harbor Freight to locate 'hot spots' due to poor track joints.

@CALNNC posted:

They actually draw enough current that a poor connection may be warm to the touch.  I have used one of those inexpensive IR gun style thermometers from Harbor Freight to locate 'hot spots' due to poor track joints.

The IR gun would be much safer than using your hand. I once had a bad connection at a lockon and found it glowing red and singeing the carpet during a running session!

Ben does the motor sound change when the loco slows down?

My brother used to have an 8556 Chessie switcher that would sometimes "get stuck in low gear."  While running, the loco would shudder a little and emit a louder-than-usual growling sound.  When we were kids we thought this was cool.  When I got older, I discovered that it was due to excessive thrust play in the armature.  As the brushes wore down, the armature shaft could shift further into the nylon brush plate on top of the motor, affecting the mesh with the worm wheel down in the truck.  The fix was to add a screw to the brush plate, limiting upward travel.  Some locos had an Allen screw for this purpose installed in the brush plate at the factory.

The MPC diesels are basic designs that can provide years of use (abuse?) once these types of initial quality issues are addressed.  Good luck and please post back with what you found.

check between the truck and chassis plate. if it's missing the small ground spring they can behave kinda like that without the ground spring.