Multimeter Checking Procedures for the 3.9 Engine

In case of differing measurements first inspect the wiring drawn in bold lines

1. Check voltage from batterie to the ECU On the multimeter the battery voltage must show. (minimum 10V)
Possible fault: Check earth

 

2. Check voltage from ignition to the ECU On the multimeter the battery voltage must show.
Possible fault: Check earth

 

3. Verify if main relay works - first step  
Multimeter must show battery voltage. If 0 Volt see next step

 

4. Verify if main relay works - second step  
A = must be battery voltage, if OK ECU possibly faulty, B = must be 0 Volts when ignition off

 

5. Verify if pump relay works  

If the relay is OK go to 6		 Listen to a "click" from the pump relay

 

6. Verify pump relay circuits  

Pin 87 must show battery voltage if other conditions fullfilled.

If so, the ECU is suspect.

 

7. Check if fuel pump gets current  
If the pump is the in-tank model with connectors on the upper side of the tank- and inaccessible. However there is a connector not far away up the wiring harness where you can check voltage.

 

8. Check engine rpm signal and resistance  
Check if Pin 39 has battery voltage on the multimeter. Check resistance between coil and Pin 39 (6,8 kohms)

 

9. Check injectors (Pin 13 is for injectors 1,3,5,7)  

Reading of 5-6 ohms=1 injector suspect

Reading of 8-9 ohms=2 injectors suspect

Reading of 16-17 ohms=3 injectors suspect

Reading of more=get your gun and shot it!

  

 

10. Check injectors (Pin 11 is for injectors 1,3,5,7)  
Connect ohmmetre between Pin 2 and 11. Reading of 4-5 ohms is OK.

Reading of 5-6 ohms=1 injector suspect

Reading of 8-9 ohms=2 injectors suspect

Reading of 16-17 ohms=3 injectors suspect

Reading of more=get your hammer and give it a good tap!

  

 

11. Fuel temperature sensor  


NB: If your fuel temperature is over 80°C or 176°F - let all go and run! That thing will blow any moment

°C

°F

Correct read in ohms.

-10°

0°

20°

40°

60°

80°

100°

14°

32°

68°

104°

140°

176°

212°

9100-9300

5700-5900

2400-2600

1100-1300

500-700

300-500

150-200

 

12. Coolant sensor check  
Connect ohmmetre between Pin 25 and 7.
°C °F Correct read in ohms.

-10°

0°

20°

40°

60°

80°

100°

14°

32°

68°

104°

140°

176°

212°

9100-9300

5700-5900

2400-2600

1100-1300

500-700

300-500

150-200

 

13. Verify air bypass valve  

Connect multimeter between Pin 26 and 1.

Correct reading: 48-58 ohms. If not verify wiring

 

14. Verify air bypass valve - second part  

Connect multimeter between Pin 28 and 29.

Correct reading: 48-58 ohms. If not verify wiring

 

15. Check throttle potentiometer  

Connect multimeter between Pin 25 and 3.

Correct: 5000 ohms, if different go to next step

 

16. Check throttle potentiometer - second part  

Connect multimeter between Pin 20 and ground

Throttle closed: 0,29V-0,36V

Throttle open 4.6V-5,0V

Important: Voltage must grow linear when moving flap and must not jump

 

17. Check Hot Wire Mass Airflow Sensor  

Connect multimeter between Pin 35 and ground

Correct: 0,3V-0,6V

 

The following steps must be taken with some precautions. The fuel system must be depressurised as pressure stays inside the lines and a dangerous spray will occur when you open them. Also the slightest dirt particle in the system upstream of the filter (nearer to the engine) will definitely deteriorate the system. Some spilling can't be avoided, so take care.

How to depressurise the system:

  1. Switch ignition off! Take fuel pump relay out of his holder.
  2. Start the engine . It probably will start but soon will cut off when the remaining pressure drops.
  3. Ignition off.
  4. Insert fuel pressure manometre into the fuel line between the fuel rail and the filter, near the filter at the back of the car.
  5. Put the fuel relay back in place
18. Fuel Pressure check  

Correct reading: 2,4-2,6 kg/cm2

or 34,0-37,0 psi

AND a pressure drop of not more than 0,7 kg/cm2 or 10 psi in one minute.

 

19. Injector leak test  

Injectors may leak. Take all the injectors out but don't disconnect them from the fuel rail. Put some sort of receptable under them and switch on ignition. Any injector that gives off more than 2 drops a minute must be replaced.

If you have to replace a leaky injector you must inspect the spark plugs for fouling!

Take care: The following steps are more dangerous as the spray can ignite quite easily

20. Injector flow test (left bank, 1,3,5,7)  
Ground Pin 13 and 16. This will cause the injectors to open. Place a large receptable under the injector, maybe a bottle or so. A correct injector will flow 167 cm3 per minute!

 

21. Injector flow test (right bank, 2,4,6,8)  
Ground Pin 11 and 16. This will cause the injectors to open. Place a large receptable under the injector, maybe a bottle or so. A correct injector will flow 167 cm3 per minute!

 

22. Gear input switch (Inhibitor switch) (automatic trans only)  

Connect multimeter between Pin 34 and ground

Correct reading: 0V in Park and Neutral

4,5V-5,0V in R, D, 3, 2, 1

 

23. Road speed input (Speed Transducer)  

Jack up and slowly turn left rear wheel.

Connect multimeter between Pin 6 and ground.

Correct reading: 0-12V, changing 6 times per revolution of the wheel

 

24. Check Lambda sensors  

Take out the fuel pump relay

Connect multimeter between Pin 4 and 87A of the fuel pump relay socket. Correct reading 2,65-3,35 ohms

A reading between 5,3 and 6,7 ohms indicates one of the 2 Lambda sensors is shot