ECU's on fuel Injected Engines

at the example of the 3.9 Range Rover engine

Sorry for the sometimes not absolute correct names, text translated from french

This procedure should be similar on any engines using an flap for measuring the air flow. Those who use Lucas ECU box and an Hot Wire to monitor air flow are slightly different. We used this procedure successfully on many different cars. But it's at your risc. And you may well damage a component beyond repair if you screw it up.

Cold start enrichment Connector to the ECU

P= pump relais

M=main relais

S=steering relais

Air flow sensor - connector Flap position sensor
Resistance box Timed thermal contact Air mixture valve Coolant temperature sensor Constant energy coil

 

Feeding of the electronic regulator

(This is the ECU box)

Possible fault:
Connect Voltmetre between Pin 10 and ground. Contact.

No reading: Check cables and connectors, check Main relais by substitution of a new unit (this is genuine LR instructions...)

Lower than 11 V: Check cables and connectors for a bad or corroded contact

Normal result:
11-12.5 Volts
 

 

Fuel pump contacts Possible fault:
Connect Voltmetre between Pin 20 and ground. Contact. Air flap closed

When closed: Something else than =V when flap closed: check switch on air meter (flap) housing

When moving: No reading: Check wire harness from relais to air metre, then from air metre to relais of fuel pump. Check the relais by substitution of a new one. Check the pump by connecting a wire directly from battery + and - to the pump

Normal result:
0 V when closed, 11-12.5V when flap moving
 

 

Starter rotation signals
Possible fault:
Connect Voltmetre between Pin 4 and ground. Turn the engine over with the starter.

No reading but starter turns: Check wiring harness from ECU to relais and electronic regulator

No reading and starter does not turn: check starter and starter relais.

Reading under 8V: check batterie (connect another one) and starter

Normal result:
8-12V
 

 

Air metering valve
Possible fault:

Connect Ohmmetre:

between Pin 6 and 8: 360 ohms

between Pin 6 and 9: 560 ohms

between Pin 8 and 9: 200 ohms

Differing values: check cables with ohmmetre, check air metering valve but make sure it's completely closed.
Normal result:
above values + 10 ohms
 

 

Water temperature sensor
Possible fault:

Connect Ohmmetre between Pin 13and ground

Differing values: Check cables and connector, change sensor if readings still differ

Take only short readings as sensor may be damaged by heat from curent from ohmmetre

Normal result:

-10°C = 7-11,6 kohms

+20°C = 2,1 to 2,9 kohms

+80°C = 0,27 to 0,39 kohms

 

 

RPM signal
Possible fault:

(constant energy ignition)

Make a connestion between - of the coil and Pin 1. Connect voltmetre between Pin 1 and ground

No reading: check the connectors between coil and regulator
Normal result:
Fluctuates between 6 and 9V
 

 

Injectors
    Possible fault:
Injector 7 Connect ohmmetre between Pin 14 and 87 of main relais

Reading below normal: Disconnect one after another the injectors until you find the one with low or 0 resistance. Replace.

If all are OK you must check the wiring harness and connectors as well as the resistance bloc

Injector 8 Connect ohmmetre between Pin 28and 87 of main relais
Injector 2 Connect ohmmetre between Pin 31 and 87 of main relais
Injector 4 Connect ohmmetre between Pin 30and 87 of main relais
Injector 3 Connect ohmmetre between Pin 33 and 87 of main relais
Injector 5 Connect ohmmetre between Pin 32 and 87 of main relais
Injector 1 Connect ohmmetre between Pin 15 and 87 of main relais
Injector 6 Connect ohmmetre between Pin 29 and 87 of main relais
Normal result:
Between 7 and 10 ohms
 

 

Injection ramp
Possible fault:
Mount the manometre on the flexible line to the cold start enrichment injector. Contact and move the air flap to close the electric circuit of the fuel pump

Pression 0: Check if fuel pump gets 12V, if not so replace the relais of the pump and then the main relais.

If the pump gets 12 V check it's ground (a common fault) by laying a wire directly to the ground. If it still does nothing chances are good the pump is shot. Take it out and check it again on the bench.

Pression out of limits (above or below): Check for leaks on the complete circuit, coloring around line connections and leaking injectors, then pressure regulator and anti-return valve- in this order.

Normal result:
2,4 to 2,6 kg/cm2
 

 

Air Mixture Thermovalve
Possible fault:
Connect ohmmetre between Pin 34 and 87 of the fuel pump relais No reading: Check wiring and connectors between fuel pump relais and air mix valve as well as electronic regulator. Than disconnect valve and check it by ohmmetre
Normal result:
30 - 40 ohms
 

 

Cold Start enrichment injector
Possible fault:
Disconnect timed termocontact. Successively ground the wires. Connect ohmmetre between Pin 4 and ground

No reading: Check wiring and connectors between ECU, cold start injector and temporised thermocontact.

Cut off: Check wires, connectors and cold start injector

Normal result:
0 - 5,0 ohms
 

 

Air temperature sensor
Possible fault:

Incorporated in the air flow sensor

Connect ohmmetre between Pins 6 and 27

Take only short readings as sensor may be damaged by heat from curent from ohmmetre

Reading unlimited: disconnect flow meter, connect Pins 6 and 27. If reading is now 0 the sensor is faulty. If reading still unlimited check wiring and connectors as well as ECU connector
Normal result:

-10°C: 8,26 to 10,56 kohms

+20°C: 2,28 to 2,72 kohms

+50°C: 0,76 to 0,91 kohms

 

 

Air flap position sensor
Possible fault:
Set multimetre on TENSION, reconnect ECU, contact  
Measure tension between green (-) and yellow (+) by the back side of the connector block near the ECU

4,3 (+- 0,2V)

Lower or 0: check wiring and connectors

Measure tension between green (-) and red (+) by the back side of the connector block near the ECU

0,325V (+0,35V)

Loosen screws and rotate sensor until reading is correct

The tension must grow progressively in the same manner as you open the air flap

Progressive from 0,3 to 4,5V

If the reading jumps or fluctuates you must change the sensor.

 

Deceleration shut off relais
Possible fault:
Disconnect the - wire from coil to relais. Contact off. Connect ohmmetre between Pins 1 and 30 of the relais Unlimited is correct. Anything else: Check wires and connectors, then replace relais by a new one.
Contact The resistance must drop to 0. Anything else: Check wires and connectors, maybe even the vacuum switch.
Repeat the measurement at least once.  

 

Air flow sensor
Possible fault:
Reconnect ECU. Contact. Pull back the rubber sleeve on the connector. Connect voltmetre between Pin 6 (+) and Pin 9 (-) 1,55V (+- 9,1V) This figures from the genuine book but I strongly suspect a fault here. I think it should read +-0,1V
Connect voltmetre between Pin 9(-) and Pin 7(+) 3,7V +-0,1V
Open the flap slowly: The tension must drop 1,6V +-0,2V
Abnormal results: Change the sensor

 

Air flow sensor
Possible fault:
Disconnect ECU. Contact. Pull back the rubber sleeve on the connector. Connect voltmetre between Pin 8 (+) and Pin 9 (-) Abnormal reading: Change sensor
Normal result:
4,3V +- 0,2V