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Mercedes M103

Injector rail

First, remove air filter. Then, remove mechanical injectors with distributor.

Use fuel rail with pressure regulator from the M104 engine.

Cut fuel injectors places to put new injectors in place.

Secure fuel rail

Install new idle valve fitting. Old idle valve connections are unusable now.

Idle valve

Before installing, clean valve internals with carburettor cleaner, and lubricate with the oil. Don't use WD40, it is not lubricant.

MAP sensor

MAP sensor location is very important for decent engine operation. Locate MAP sensor exactly like on photo.

Drill 13mm hole for sensor tip. Cover drill tip with grease to catch the debris.

Seal hole with a sealant. Sufficient sealing paste must be applied because the surface of the intake manifold is rough.

Secure sensor with included screw.

ECU and wiring


Disconnect battery when working with the electrical system. Connect battery back only when engine have to be started.

ECU is dust and splashproof. It cannot withstand continuous water contact or pressurized water. Do not install ECU with cable upwards. In this case, water and moisture will flow off the cable into ECU.


Wire colors are not fixed, and can be changed. Wires are labeled. Refer to labels to determine wire purpose.

Wiring harness for 4 and 6 cyl engines are unified. On a 4cyl engine you will have 2 extra injector connectors - those are closer to the ECU connector. You can cut those connectors or leave unconnected.

Put ECU next to the stock unit. Pull required wires from the harness.

All wires should be connected in parallel. Otherwise will be mentioned explicitly.

Connection to the 25pin ECU

  • 1 Power 12V
  • 2 GND
  • 5 FULL SW
  • 8 Lambda - disconnect from the stock ECU
  • 13 IDLE SW
  • 21 CLT
  • 25 AN

Connect DH wire to the ground

Connection to the 55pin ECU

  • 6 GND
  • 9 Power 12V
  • 13 Lambda - disconnect from the stock ECU
  • 16 CLT
  • 27 AN
  • 46 FULL SW
  • 47 IDLE SW

Connect DH wire to the ground

Lambda sensor

Attention! Make sure to disconnect the lambda from the stock ECU to avoid interference.

If you don't have lambda sensor, or your sensor is malfunctioning, you should install universal Bosch sensor 0258986507 or 0258006537

Connection diagram:

  • white wires - to the heating connector
  • black - signal to the ECU
  • gray - to the ECU ground

Air conditioner

Connect EXT wire to the air conditioner clutch wire. It is used for maintaining idle RPM while air conditioner is operating.


Normally, you will use Bluetooth interface to connect to the ECU. In rare cases, BT connection is unreliable, so you can use K-Line instead.

To connect K-Line cable, you should prepare 3 wires:

  • 12V
  • Ground
  • K-line

Pinout of the K-Line cable:

Pinout of the car OBD2 connector

Other wires

There are other wires, not mentioned in this manual. They are reserved for future use. Isolate and hide unused wires into the harness.

Additional info

Stock ECU pinout

  1. Main relay power (Yel)
  2. Ground (Brn)
  3. Idle speed control valve control (Red/Wht)
  4. -
  5. Full load throttle (Gry/Yel)
  6. Speed sensor (Grn/Yel)
  7. Ground/Return for cool. sensor (Brn/Wht)-Coolant sensor return for MY 1988 California version
  8. Oxygen sensor input (Grn)
  9. Fuel pump relay A/T (Grn/Blu)
  10. Electro-hydraulic actuator control(Brn/Blk)
  11. Altitude sensor (Blu/Red)
  12. Electro-hydraulic actuator supply (Brn/Blk)
  13. Closed throttle (Brn/Yel)
  14. -
  15. Check engine indicator (Red/Grn)
  16. Ignition switch (Vio)
  17. Air flow sensor Input (Blu/Wht)
  18. Air flow sensor reference (Blu/Grn)
  19. A/C compressor (Blu/Yel)
  20. Ground (Brn/Red)
  21. Coolant temperature sensor (Grn/Red)
  22. -
  23. Diagnostic
  24. Deceleration micro-switch input (Gry/wht)
  25. TD signal (Grn/Yell)

  1. Supply Battery voltage
  2. Purge valve
  3. 02 sensor heater voltage
  4. Idle speed control valve
  5. Intake Air temperature sensor
  6. Chassis ground
  7. Impulse readout, malfunction memory
  8. -
  9. Supply voltage
  10. Deceleration fuel shut-off microswitch
  11. Start signal
  12. -
  13. 02 sensor signal
  14. Intake air temperature sensor
  15. -
  16. Coolant temperature sensor
  17. -
  18. Diagnostic signal 02 sensor heater
  19. Ground ECU
  20. Start valve activation
  21. -
  22. -
  23. Idle speed control Valve
  24. Check engine warning lamp
  25. -
  26. Data exchange with EZL ECU
  27. RPM signal
  28. Selector lever position
  29. Speed signal
  30. Lambda output, on/off ratio
  31. Air flow sensor supply voltage
  32. 02 sensor wire shielding
  33. -
  34. Air flow sensor ground
  35. Ground
  36. -
  37. Electro hydraulic actuator (+)
  38. EGR valve
  39. Transmission shift point control
  40. -
  41. Supply voltage
  42. Air pump control signal
  43. -
  44. -
  45. A/C compressor engagement signal
  46. Full load throttle signal
  47. Closed throttle signal
  48. -
  49. -
  50. -
  51. -
  52. Air flow sensor input signal
  53. -
  54. -
  55. Electro hydraulic actuator (-)

MAP sensor pinout

Invent Jetronic ECU pinout

View at the ECU connector

8 7 6 5 4 3 2 1

(*) - АС input is available starting from ECU version 2.3


  • MAP - absolute pressure sensor
  • TPS - throttle position sensor
  • IAT - sensor air temperature
  • CLT - coolant temperature sensor
  • DH - Hall sensor
  • AFS - airflow sensor
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