The MPI MPXpress is a line of diesel-electric locomotives built by MotivePower (a subsidiary of Wabtec) for commuter rail service.

MPXpress locomotives were built with a high percentage of re-manufactured parts including diesel engines, major electrical components, trucks, and frames.

Cabs, fuel tanks, electronics, HEP package, and other replaceable parts such as wheels and couplers were new when delivered.

Compared to a locomotive with a separate HEP generator, the prime mover had to constantly maintain a higher RPM in order to supply power to the passenger cars.

[4] The MP36PH-3S was the first variety of MPXpress locomotive to be built and the launch customer was Metra, a commuter railroad in the Chicago area.

Starting in 2015, Metra began converting its MP36PH-3S locomotives to the MP36PH-3C specification by removing the static inverter and replacing it with a separate HEP generator.

The MP40PH-3C introduced a new prime mover, the larger 16-cylinder EMD 710G3B series diesel engine, capable of generating 4,000 hp.

The MP40PH-3C was developed in response to a bid request from GO Transit for locomotives capable of generating 4,000 hp, hauling 12 passenger cars and traveling at speeds up to 93 mph (150 km/h).

MotivePower removed the EMD prime mover and HEP motor and replaced them with the twin Cummins engines.

[13] Initially GO Transit had planned to convert a total of ten MP40PH-3Cs to the new MP54AC standard; it later ordered 16 additional newly built MP54AC locomotives instead.

Both the MP54AC and F125 have struggled to find customers, unlike the Charger series, which has sold more than 350 units including large orders from Amtrak and Via Rail.