Disco 1 No 12 volts at pump

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Jonah1962

Jonah1962

Member
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Location
Walsall
Hi all could anyone shed any light on this prob, 300 tdi disco Finally got it running. Had problems with the imobiliser/alarm I've done the spider bypass, had the alarm/ key fob re programed all good, but can't get 12 volts to the pump solanoid when cranking over It's there when running. Only way I can start it is 12 volts via battery through a switch???. Thanks for any advice
 
He means the ignition switch is maybe wired wrong.
On a fender you would go to the back of the ignition switch and find the terminal which stays live while cranking and running but goes dead with the key off, and wire the solenoid to that.
 
Jonah1962 said:
Hi all could anyone shed any light on this prob, 300 tdi disco Finally got it running. Had problems with the imobiliser/alarm I've done the spider bypass, had the alarm/ key fob re programed all good, but can't get 12 volts to the pump solanoid when cranking over It's there when running. Only way I can start it is 12 volts via battery through a switch???. Thanks for any advice
Click to expand...

Ok... if your 'spider' was bypassed correctly then there shouldn't be any issues.

But as it stands you will require a switched supply to your pump from the ignition, picked up from the switch tails where they enter the front of the fuse board,, it maybe the yellow, maybe the white wire.... I can't confirm as I'm a long way from my vehicle at the moment so use your volt meter to check the correct wire there's only 3.

I had to install an additional wire, my engine would crank but not fire, I use petrol so the wire was the coil, but the immobiliser principle is the same as diesel.
 
discool said:
Ok... if your 'spider' was bypassed correctly then there shouldn't be any issues.

But as it stands you will require a switched supply to your pump from the ignition, picked up from the switch tails where they enter the front of the fuse board,, it maybe the yellow, maybe the white wire.... I can't confirm as I'm a long way from my vehicle at the moment so use your volt meter to check the correct wire there's only 3.

I had to install an additional wire, my engine would crank but not fire, I use petrol so the wire was the coil, but the immobiliser principle is the same as diesel.
Click to expand...
Thanks discool, as far as I'm aware the bypass plug is workin, as before I put it in I had no power to the glow plug relay an no power at the solinoid wire. Once it's running its fine I can flick the switch off just the cranking problem. Think that's the only way to sort it like u say straight from ignition.
 
Ok u require the 12v supply that's on position two from the switch
Although the immobiliser meets the insurance spec and its approval it still quite simple item, one circuit to prevent starting plus another to cut fuel supply with both petrol or diesel.
Either circuit can fail and the simplest way to repair is to "overlay" a wire direct, therefore no need to touch the spider.
The failure of the glow plugs can possibly affect the starting of a Tdi but they have nothing to do with the immobiliser, relay failure is A known issue, I believe.
 
discool I've soldered a wire from ignition position two wire where it enters
Fuse board, I've got 12 volts at pump solinoid wire ,glow plug relay working.
Still won't fire up, tested the wire while cranking over only 9 volts, I'm guessing
This isn't enough to open the solinoid. Put a direct 12 volt feed from battery to soliniod it fires up, take the feed off while its runing, fine 12 volts at solinoid wire??. The
Only thing I can think of is something is draining power while cranking over.
I've done a drain test with multimeter through the negative lead an battery
An it's only showin 0.001. If I take out the 100amp alternator fuse this shows
No draw 0.000. I'm baffled back to the 12 volt switch lol.
 
Last edited:
Hmmm...there is a simple work around for this using the ign switch to operate a relay feeding the solenoid direct from the battery.
But you shouldn't need to do that.
What voltage are you getting at the ignition switch terminal whilst cranking?
 
There will be a some voltage drop taken by the starter motor when cranking.
Based on my vehicle, the second position of the switch supplies the yellow wire, this enters the fuse board in a three way connector with the the other two wires.
Perhaps the solenoid need a higher current supplying it, what is the load? something to check maybe, but then what do I know I've never seen one.:)
Its my understanding that the spider bypass takes care of every thing, it appears not :(
 
Jonah1962 said:
discool I've soldered a wire from ignition position two wire where it enters
Fuse board, I've got 12 volts at pump solinoid wire ,glow plug relay working.
Still won't fire up, tested the wire while cranking over only 9 volts, I'm guessing
This isn't enough to open the solinoid. Put a direct 12 volt feed from battery to soliniod it fires up, take the feed off while its runing, fine 12 volts at solinoid wire??. The
Only thing I can think of is something is draining power while cranking over.
I've done a drain test with multimeter through the negative lead an battery
An it's only showin 0.001. If I take out the 100amp alternator fuse this shows
No draw 0.000. I'm baffled back to the 12 volt switch lol.
Click to expand...
I know this is not a proper fix, but, try using a relay in the fuel solenoid circuit, use the original supply wire to the fuel solenoid as the relay activation wire and supply the solenoid through the relay direct via a fused supply from the battery. I think that as the ignition switches get older they wear inside on the contacts and this can lead to voltage drop problems, I have had to fit a relay in the supply to the starter solenoid on my Disco 1 because the ign switch start contacts just stopped doing their job, I've had no problems starting it up since this mod.
 
Gazbo said:
I know this is not a proper fix, but, try using a relay in the fuel solenoid circuit, use the original supply wire to the fuel solenoid as the relay activation wire and supply the solenoid through the relay direct via a fused supply from the battery. I think that as the ignition switches get older they wear inside on the contacts and this can lead to voltage drop problems, I have had to fit a relay in the supply to the starter solenoid on my Disco 1 because the ign switch start contacts just stopped doing their job, I've had no problems starting it up since this mod.
Click to expand...
Tis wot I said ^^^^:D
 
Flossie/ discool thanks for the replys.
I've tested the voltage at the ign while cranking an it drops to 9 volts on both yellow and white wires. I fired it up tested again running 14 volts. Looks like the relays the way to go :mad:
 
Gazbo said:
I know this is not a proper fix, but, try using a relay in the fuel solenoid circuit, use the original supply wire to the fuel solenoid as the relay activation wire and supply the solenoid through the relay direct via a fused supply from the battery. I think that as the ignition switches get older they wear inside on the contacts and this can lead to voltage drop problems, I have had to fit a relay in the supply to the starter solenoid on my Disco 1 because the ign switch start contacts just stopped doing their job, I've had no problems starting it up since this mod.
Click to expand...
Gazebo
Thanks for that, think I'm gettin somewhere now u mentioned that.
Sometimes I turn the key and nothing as if the battery's flat, then others times it starts first time. I know the spiders working as if I disconnect it I've got nothin.
Do u think a new ignition would sort it.
 
Jonah1962 said:
Gazebo
Thanks for that, think I'm gettin somewhere now u mentioned that.
Sometimes I turn the key and nothing as if the battery's flat, then others times it starts first time. I know the spiders working as if I disconnect it I've got nothin.
Do u think a new ignition would sort it.
Click to expand...
I think this problem can afflict a lot of older vehicles particularly depending on how they have been used i.e. lots of miles about the city, stop start/on, off etc, vs lots of long distance miles, so my thinking would be yes, but is it practical? A new swtch may be expensive and may be a bit of a chore to fit, not too sure having never done it.
I do know that the relay idea does work as a relatively cheap and easy solution and have used it to solve voltage drop problems in several old cars, I have previously owned a string of old 6 volt VW Beetles in years gone by, a different version of the same problem, but, the relays activation coil current draw is extremely low and it takes a large percentage of your switching current problems away, I know I said it is not a proper fix but it is what I do to overcome the issue, a "purist" would require a new switch to keep things as original, I just want things to work.............. your choice?.
 
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