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Happy and Holy Easter to all.

This engine began this right out of the box. Initial, gentle, gradual throttle increase to less than half produced a full speed runaway. Only my lightning like reflexes prevented an unplanned off the table launch adventure. My aperture relaxed, and I advanced the throttle ever so slowly, and you can see the results in my crummy videos. I contacted the dealer, and this was his response - “Best guess from the videos is that one of the pick-up rollers has a short or isn't wired correctly. Should be an easy fix. Send it back to me.” As it was a brand new item, I was reluctant to accept a repair, and asked for, and was granted, an exchange. Good customer service. It is otw back, and the exchange will be shipped. I post this here not to complain, but for the intellectual exercise of discussing what the likely culprit could be.

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Last edited by Mark V. Spadaro
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Simple, the tachometer is not reading the flywheel. This causes the motor control to ramp up voltage/pwm to the motor attempting to reach the target speed and when it finally cannot over a time period (because the tachometer is not working) it STOPS in safety to reduce the risk of locked motor burnout.

Your video demonstrates exactly what to expect on a diesel MTH PS3 with a tach problem. You happen to be running in conventional so you can limit track voltage and thus top speed. The symptom is ramp up of speed and then sudden stop after distance. If it was steam, not diesel, you also would get no chuff sound and no matching puffing smoke- again because non functioning tach.

Again,  simple answer- the tach subsystem is not working. Lots of ways that could happen- sensor not aligned to flywheel, broken wire, or other failure.

Again, the MTH PS2 and PS3 uncontrolled runaway is worse with full track voltage when running in command mode (DCS) but ALSO happens in conventional because MTH always uses speed control closed feedback using the tach by default. You can turn off "cruise" speed control using a command, but better to fix the problem and on steam you have to fix the tach or else chuff and puff don't work.

You had the engine replaced but knowing this symptom, what it means, is valid for again PS2 and PS3 engines, also MTH Locosound. I even could happen on Odyssey equipped Lionel engines, even Lionchief plus and higher.



Your video demonstrates exactly what to expect on a diesel MTH PS3 with a tach problem. You happen to be running in conventional so you can limit track voltage and thus top speed. The symptom is ramp up of speed and then sudden stop after distance. If it was steam, not diesel, you also would get no chuff sound and no matching puffing smoke- again because non functioning tach.

I have one of these diesels that operates correctly. It appears the diesel rpms are not ramping up either.

Further supporting your diagnosis in case others should have a similar issue and come across this thread.

On a side note. This h10-44 is a superb performer with great sounds. I'm running mine via a Lionel tpc unit and a Legacy handheld.

With stall speed set at 5.5v it is an outstanding crawler that is excellent for switching. It runs as smooth as any Legacy diesel I have ever owned.

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