Disco 1 3.9 v8 no power to fuel pump

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Jbfenn

Jbfenn

Member
Posts
13
Location
West sussex
Had my 1997 d1 for a couple of weeks and I’m trying to get the bugger to run. (Cold weather is slowing me down a lot tho). I don’t seem to be getting any power to the fuel pump. I’ve checked the voltage from the purple/white wire to the ground and there’s nothing.
I get power to the fuse in the engine bay, the relay works fine, and the inertia switch isn’t the problem. The engine cranks over fine but the fuel pump just won’t run. What else could it be?
 
I had similar experience on mine, a 90 with a 3.5V8 and auto. Does yours have an in-tank full pump or an external in-line one? If the former, as on mine, the plastic cap that plugs onto the top of the pump assembly was loose with a poor connection - it wouldn't start the other day and after tweaking the cap and refitting is ok now. Worth a look....
ESR2242.jpg
 
Jbfenn said:
Had my 1997 d1 for a couple of weeks and I’m trying to get the bugger to run. (Cold weather is slowing me down a lot tho). I don’t seem to be getting any power to the fuel pump. I’ve checked the voltage from the purple/white wire to the ground and there’s nothing.
I get power to the fuse in the engine bay, the relay works fine, and the inertia switch isn’t the problem. The engine cranks over fine but the fuel pump just won’t run. What else could it be?
Click to expand...
It could be an iffy ‘immobiliser’ if you also find that there isn’t a spark at the plugs.
 
I’ve checked and replaced the fuel pump relay, not yet checked the other one. (Guessing it’s the other metal capped Bosch one).
Fuel pump is in the tank but I’ve not checked the other connectors on it, have heard there are two underneath the car (between inertia switch and pump) but not sure exactly where they are.
I’ve got spark but have heard the immobiliser can fail on either spark, fuel or both. Is there an easy way to get to the spider rather than ripping the whole dash out?
 
The only thing underneath the vehicle is the fuel filter on the chassis behind the offside rear wheel. As u have stated that your vehicles engine cranks and here is also a spark there’s no need to touch the immobiliser.

There’s no easy way to access the ‘spider’ but if it was faulty then simple overlay of two single wires below the dash would isolate the immobiliser function, therefore no need to touch the ‘spider’.
 
discool said:
The only thing underneath the vehicle is the fuel filter on the chassis behind the offside rear wheel. As u have stated that your vehicles engine cranks and here is also a spark there’s no need to touch the immobiliser.

There’s no easy way to access the ‘spider’ but if it was faulty then simple overlay of two single wires below the dash would isolate the immobiliser function, therefore no need to touch the ‘spider’.
Click to expand...
Are there no wiring connectors under the car? I heard there was one by the muffler.
 
Jbfenn said:
Are there no wiring connectors under the car? I heard there was one by the muffler.
Click to expand...
I’m not aware of any external wiring that’s under the floor from the front to the rear of the vehicle, it’s above the headliner or under the carpet, not that I’ve ever had the need to find out.
For the 12v supply to the fuel pump it starts at fuse 6 in the engine bay fuse box, then on to the relay in the drivers footwell (the center relay on the top row of five relays), then via a black wire from the relay which then changes to the white/purple wire and onwards to the pump.
The fuel pump relay switching is controlled by the the EFI ECU as and when required.
 
discool said:
I’m not aware of any external wiring that’s under the floor from the front to the rear of the vehicle, it’s above the headliner or under the carpet, not that I’ve ever had the need to find out.
For the 12v supply to the fuel pump it starts at fuse 6 in the engine bay fuse box, then on to the relay in the drivers footwell (the center relay on the top row of five relays), then via a black wire from the relay which then changes to the white/purple wire and onwards to the pump.
The fuel pump relay switching is controlled by the the EFI ECU as and when required.
Click to expand...
I know there’s power to the relay, But after that what is there that could fail between the relay and the pump, other than loose wiring.
Am I correct in saying the fuel gauge shares the same wiring as the pump? Just confused as to why the gauge still works if it’s a wiring issue somewhere.
 
I suspect that the supplies for the pump and the fuel gauge are together in the same loom i.e. a single cable although may then be combined in to another loom for other services.

How are you checking for voltage at the pump? you may or not know that it’s only at the pump for a few seconds to enable priming (ECU controlled) after the ignition switch is turned to position two, but returns when the engine is turned over via another instruction from the ECU.
So other than removing the relay and bridging the relative wiring to give you a permanent 12v and check that it arrives at the pump terminal, you could just check the continuity of the white/purple wire from the pump to the relay with your multimeter.
 
discool said:
I suspect that the supplies for the pump and the fuel gauge are together in the same loom i.e. a single cable although may then be combined in to another loom for other services.

How are you checking for voltage at the pump? you may or not know that it’s only at the pump for a few seconds to enable priming (ECU controlled) after the ignition switch is turned to position two, but returns when the engine is turned over via another instruction from the ECU.
So other than removing the relay and bridging the relative wiring to give you a permanent 12v and check that it arrives at the pump terminal, you could just check the continuity of the white/purple wire from the pump to the relay with your multimeter.
Click to expand...
I’m checking voltage between the purple/ white wire(live) and the ground. Get the gf to turn key to position 2 while I’m checking the voltage, the immobiliser light goes off but no power to the pump.
Then crank the car over, get spark but no power to pump.
Guessing it wouldn’t be a bad ECUs as everything else works and the car cranks over.
What order does the wiring go in?
Is it:
Battery > fuse > inertia switch > ECU > relay > pump?
 
:cool:
Jbfenn said:
What order does the wiring go in?
Is it:
Battery > fuse > inertia switch > ECU > relay > pump?
Click to expand...
Battery > fuse > relay contacts > pump > inertia switch > earth connection.

The relay contact closes to supply the 12v to the pump.
Fuse #3 in the dash Satellite fuse box 1 supplies the relay via white/green to the relay coil, plus it’s the fuse for the ECU. Relay coil to ECU (relay control wire from the ECU) is blue/purple.




Now off to see the fire works :cool:
 
discool said:
Well done in finding where the problem was. So just for future reference for owners looking at this tre

ad where exactly was it?

Easiest way of doing it is checking you have voltage right after the inertia switch, if you do then the only thing between there and the pump is wire. Then you follow the wire underneath until you find the fault. Mine was just above the rear axle where the wire had rubbed on the body and shorted out.


Sent from my iPad on a train
Click to expand...
 
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