Note on the 4M51:

The 4M51 is a relatively rare industrial or marine diesel engine (part of the Mitsubishi 4M series). Unlike automotive ECUs, industrial diesel ECUs often have non-standard pinouts, varying wire colors, and different sensor configurations depending on the application (generator, excavator, pump, etc.). This report outlines the methodology for deriving a verified pinout.

Connector A (22 pins) – Engine Inputs/Sensors

5.2 Erratic Idle

  1. Back-probe A06 (Gray wire) and A01 (sensor ground).
  2. Key ON, engine OFF: Voltage should be ~1.8V (atmospheric).
  3. At idle: ~1.0V (vacuum).
  4. Under load/boost: Should rise to ~3.5V.

For performance tuners using the 4M51 in marine or off-road racing, pinout work is essential for ECU cloning.

120-pin rectangular connector

The 4M51 ECU typically uses a (similar to Mitsubishi Heavy Industries industrial ECUs), arranged in 2 rows (A & B).