Mercedes M103

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

Airflow sensor plate is not needed any more. Remove it, and fix moving part beneath with a plastic strap.

Injector rail

To install injectors properly, you need to cut part of the intake manifold like on photo below

Then, install injector sleeves using engine sealant.

Insert injectors. First - into the fuel rail. Then - into the manifold.

Bend the metal brackets of the rail and drill an hole on each bracket to insert the screw that will hold it to the intake manifold.

Idle valve

The stock air supply scheme from the Idle valve cannot be used.

Install new idle air supply fitting under the throttle. Connect the air supply hose from the idle valve.

Idle valve is left connected to the stock ECU.

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 really important to ensure a good engine operation. Locate MAP sensor exactly as shown on photo.

Drill 13mm hole for the sensor and 8mm for the bolt that will secure it. Cover the drill tip with grease to catch the debris, it is reccomended to clean the intake manifold after drilling the hole to ensure that no metal debris is left in it.

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. Apply sealant to the thread, to prevent air leaks and unscrewing.

Never install any sensor with the wires upwards, water will flow off the cable and shortcircuit the sensor.

Warning

It is prohibited to install MAP sensor in place of cold start injector.

ECU and wiring

Warning

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, so it is reccomended to install it in a dry and safe place. Do not install ECU with cable upwards. In this case, water and moisture will flow off the cable into ECU.

Warning

Wire colors are subject to change. If wires have text labels - use labels to identify wire purpose.

Wiring harness for 4 and 6 cyl engines is unified. On a 4cyl engine you will not connect 5th and 6th cylinders.

Attention

Normally, wires has printed labels. Refer to the wire colors ONLY IF LABELS ARE NOT PRESENT.

The best spot to install the ECU is next to the stock unit. Stock ECU location:

W124 - under the hood next to the battery
W126 - front passenger legs compartment

Pull required wires from the harness. All wires should be connected in parallel to the original ones, otherwise it will be explicitly mentioned.

Connection to the 25pin ECU

1 - 12V
2 - GND
3 - IDLE (optional, read Idle Control section below)
5 - K-FULL
8 - Lambda - disconnect from the stock ECU
13 - K-IDLE
21 - CLT
25 - AN

Connection to the 55pin ECU

6 - GND
9 - 12V
13 - Lambda - disconnect from the stock ECU
16 - CLT
23 - IDLE (optional, read Idle Control section below)
27 - AN
46 - K-FULL
47 - K-IDLE

Idle control

Stock Mercedes IAC controller is working fine, you can leave it as is. If you want to control IAC valve with Invent - disconnect the wire from the stock ECU and connect it to the IDLE wire.

Attention

Only 2-wire idle valve is supported. For 3-wire valve, external circuit is needed. For more information, look into additional info section at the end of the document.

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

Stock lambda probe has 3 wires: ECU signal, ECU ground, heater +12. It has no heater ground wire, because the exhaust pipe is used as a ground.

New lambda probe has 2 separate heater wires, and the heater has no connection to the sensor housing, which is a more robust design.

Connection diagram:

white wires - to the lambda heating connector, or to the fuel pump supply
black - signal to the ECU
gray - to the ECU ground

LPG

Connect the EXT wire to the gas supply valve, turn on the LPG mode by EXT input in the settings. Now the ECU will adapt to work on gas fuel.

If you have a carburetted LPG system - you do not need to cut the power of gasoline injectors. Check Turn off injection option and fuel will be cut by the signal from the EXT.

Air conditioner

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

K-Line

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
A	IDLE	INJ1	INJ2	INJ3	INJ4	INJ5	INJ6
B	+12V	CLT	TPS	AN	KLINE	EMUL	IDLE SW	FULL SW
C	GND	5V OUT	IAT	MAP	LAMBDA	EXT	DH	AC*

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

3-wire IAC valve

It has two windings - one for opening and the other for closing.

To connect this valve, an external circuit is required. A MOSFET with a current of >5A and a voltage of >55V is used.

The dotted line indicates the IAC.

Abbreviations

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