So this weekend I tested the white and black wire from the negative ignition coil to the pin 39 of the ECU

The big connector (40 pins) disconnected from the ECU the results are :
- On negative of the ignition coil => around 9V and the needle swings => ok
- Before the 6800 ohms resistor => around 9V and the needle swings => ok
- After the 6800 ohms resistor => around 9V and the needle swings => ok
- On pin 39 on the connector (not plug to the ECU) => around 9V and the needle swings => ok

So for me the pulses and wires are correct

With the big connector (40 pins) plug on the ECU the results are :

- On negative of the ignition coil => around 9V and the needle swings => ok
- Before the 6800 ohms resistor => around 9V and the needle swings => ok
- After the 6800 ohms resistor => around 2V and in didn’t see the needle swing
- On pin 39 on the connector (plug to the ECU) => around 2V and it is difficult to see the needle swing

And it is the same with 2 different ECU, I don’t know if it’s normal ???


I changed the throttle potentiometer :

For reminder the result from the original TPS :
ECU pin 20 and ground (throttle potentiometer)
=> closed 0.65V (handbooks said 0.085 to 0.545V) so seems ok
=> open 0.2V (handbooks said 4.2 to 4.9V) so seems NOT ok !



With the new TPS :

=> closed 1.1V (handbooks said 0.085 to 0.545V) so seems not ok
=> open 0.4V (handbooks said 4.2 to 4.9V) so seems NOT ok !

On pin 3 (yellow wire) it seems it’s the ECU output 5V for the TPS, maybe I have a problem with this wire ???
The resistors for both TPS are around 4000-6000 ohms => so OK

Please find below the electrical diagram for 1990 Range Rover.

If you have some ideas ?


19 is the TPS

 

I checked all the handbook for 1990 and they don't speak about anti-theft system.

 

OK. Definitely looks like a problem with TPS, so let's get that settled first. 5 V from the ECU is good and correct. Measure the voltage between G (green) ground, and R (red) signal. Don't just measure open and closed throttle, rather measure as the throttle is moved slowly from closed to open and back to closed. The voltage should move smoothly from low when closed (close to zero) to high value when open (close to 5).

If not, then we should check all the splices on the ground wire circuit path (wires RB), including the two temperature sensors (fuel rail temp and ECT) and the MAF. Make sure terminal 25 is well grounded, and the splices are solid and not corroded. If these grounds are bad, it will impact all four of those sensors. The voltage from battery ground to wire G should remain very close to zero, no matter the position of the throttle pot. If that voltage changes as the pot is moved, that indicates a poor ground path of wire RB.

As I write, it occurred to me that if the fuel rail temperature sensor shows high fuel temperature, then the ECM takes some response. If high ohms means high temp, then a loose splice or corrosion might appear to be high temp at the ECM. But I think most of the temperature sensors are negative coefficient, so low ohms means high temp. Just thinking out loud here. Focus on the TPS first.

 

Ok thank you very much for your answer, I will investigate around the TPS and let you know.

 

Can you post the list of components with numbers? Especially interested in relays 21 and 22. Thanks for posting the diagram.

 

It's in French...
23 : 8 injectors
22 : main injection relay
21 : relay for the fuel pump
20 : MAF
19 : TPS
18 : fuel temperature
17 : coolant temperature
1 : ECU

 

Tre bon! Make sure 12 V power is fed to relay 22 on wire N (brown) directly from the battery. Then make sure relay 22 is feeding 12 V power on wire NO (brown/orange) to the injectors when the key is turned on (switch 9). If relay 22 is not activating, could be a problem with the relay, or the ground wire UR (blue/red) circuit.

 

Sorry but this weekend I could not work on the Range.
Sunday when I arrived to work on it , I saw that last weekend I forget to disconnect the 12V battery and it was completely discharge (around 4V instead of 12 V).

But it was a clue, because I haven’t got this problem before the injection problem so it is link.
Something discharges the battery (ignition off), so maybe something on wires.

So I have to investigate on both with TPS.
I let you know.

 

I worked on the Range Rover this weekend.

When the TPS is disconnected, I have at the entrance between wire and ground :
Yellow wire (output n°3) : 0 V
Green wire : 2.7 V
Red wire : 0 V


When the TPS in connected between wire and ground :
Yellow wire (output n°3) : 2.2 V
Green wire : 2.4 V
Between Yellow and Green wires : 0.2 V


So I have no 5V at the entrance (Y wire) but I have around 2.5 V on the green wire.
Please find below a new electrical diagram I found on the WEB.

I found the point “312” nothing abnormal.
I check the connections on Fuel T° sensor, on coolant T° sensor, on Air flw sensor => I found nothing abnormal.

I am desperate and don’t know where I have to looking for !

 

It is not OK for splice S312 to have any voltage. Terminal 25 of Z132 should be very close to zero volts compared to battery negative (use a jumper wire going all the way to the battery). I assume the voltages you gathered are with the key ON. If there is voltage at S312, it could be Z132 is not grounded well, so check the main ground wire connections for Z132. Unscrew the ground bolts, remove any rust, and polish the terminals for good electrical continuity. You could even install a jumper wire between S312 and battery negative, then test voltages again.

I think it is a good idea to polish all the ground connection points (where ground wires connect to the chassis), especially the main ground near the battery. If the ground connections are rusty or corroded, that will cause lots of trouble and strange voltage readings.