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Matt, Mechanical Engineer
Category: UK Car
Satisfied Customers: 21989
Experience:  BEng hons Mech engineering, in auto industry 22 years
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Landrover Range Rover: . Can you help me? I've a 93' Range

Customer Question

Hi. Can you help me? I've a 93' Range Rover Classic with the 3.9 litre engine. I am having a problem with my fuel pump in the fuel tank not powering up. Previously it would power up for 2 seconds and shut off then as it should. However, now I have no fuel pump operation but I read 5 volts on the middle of the three wires going to the pump. Inertia switch reads 0 volts. C4 fuse reads 12 volts. Pin 12 from ecu reads 1.8 volts. Ignition switch reads 12 volts. No obvious fuse blown. Line from fuel pump relay to inertia reads 5 ohms which seems high to me. The engine runs lpg also and that's all I can run on for the last few days. No problems before,,, on the way to work it worked perfect,,, as in started on petrol and clicked over to gas, but then when I went to move car in work it simply wouldn't start on petrol.
Submitted: 2 years ago.
Category: UK Car
Customer: replied 2 years ago.
Pin 12 now reads 11.8 volts with ignition on and off. I must have moved wires around! Also, the feed to the fuel pump briefly goes to 12 volts via multimeter when I turn ignition to start but immediately shoots back down in an instant.
Expert:  Matt replied 2 years ago.
If you haven't already then I'd suggest to replace the fuel pump relay and the ECU with new parts and also clean the relay socket connections on both as they are prone to corrosion
Customer: replied 2 years ago.
I cleaned both of the silver/metal relays under the seat. They both click. Is that not enough to show that the relay works? I'm happy to buy the two relays but they're clicking.
Expert:  Matt replied 2 years ago.
Hello I'm not sure what relays those are under the seat as my information shows the ecu and fuel pump relays are in the footwell
Customer: replied 2 years ago.
Two yellow ones in the foot well, they both click and I swapped both of them around. The 14CUX troubleshooting manual shows the two metal/silver ecu's under the FR seat. Why would I have both? Anyway they both click. Also the is 5 ohms of resistance between the middle pin (87) from the silver relay and the inertia switch.
Expert:  Matt replied 2 years ago.
OK the wiring on these old rangies can be a bit random but it sounds like your relays are fine the next possible candinate is the ECU itself I'm afraid as they are prone to issues as they age I can reccommend sending it to this repair firm as they are very reasonable
Customer: replied 2 years ago.
Is there any self tests I can do to check the ecu? All other parameters seem fine with it. Sending off the ecu seems like a last resort to me.
Customer: replied 2 years ago.
Also, would power from pin 16 not suggest that the ecu is working correctly. Pin 16 is the line to the fuel pump relay.
Customer: replied 2 years ago.
Pin 16 to ground is giving me 1.8 to 2.0 volts.
Expert:  Matt replied 2 years ago.
HelloOK the voltage measurements you've taken look like the earth / power supply to the pump is poor, I was concerned that the relay might not be switching over completlyI'd say the next step is to clean the pump wiring connections and ensure that its getting a full 12V and the fact that the p16 when earthed is only giving 2 v also indicateds the earthing is poor somewhere
Customer: replied 2 years ago.
I've already cleaned the connection for the pump from the LR area of vehicle. I get a consistent 5 volts reading there. 0 volts at the inertia switch though which doesn't make sense to me. Which earth would you reckon I should check to get pin 16 back up to 12 volts?
Expert:  Matt replied 2 years ago.
just under the relay box in the footwell is a m8 sized bolt that secures a bunch of wires to the car body - clean hear with some sandpaper and re-tighten the bolted joint
Customer: replied 2 years ago.
I cleaned the contacts, but with no success.
Expert:  Matt replied 2 years ago.
Hello Ok the next step is to try the earth under / by the main fusebox, again its a ring terminal bolted to the car body if this doesn't work then its time to get the meter out and start continuity testing all the fuel pump wiring between the relay and pump
Customer: replied 2 years ago.
I'll have a look at that tomorrow evening and get back to you with my findings.
Expert:  Matt replied 2 years ago.
good luck