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Disco starting problem / weird electrics


Redhand
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I have a 1993 Disco 200tdi, It has a factory fitted immobiliser, and there are no aftermarket alarms immobilisers etc fitted It is absolutely Bog Standard. with no additional electrical items added. It has developed a problem the symptoms are.

Will only drive when the hazard lights are switched on.

If left for a while it will start occasionally. But will switch itself off as soon as you start to move or touch any switches etc.

Won't switch off if the hazards are on. even if you're stood outside the vehicle with the keys in your hand. I've removed the fuse for the hazards and this stops the indicators flashing but means if you drive it you've no indicators

I have disconnected all the wiring to the column switch gear and it doesn't make the slightest difference to the starting of the vehicle Once it dies you have to plug the connector with the hazard wiring in before it will restart. So I'm asuming it's the immobiliser and not the switch gear.

Anyone heard of this happening before and how did you cure it... It has been suggested that the crash sensor has activated/failed. and that the cure is to hold the bonnet switch down while holding the key in the preheat glowplug position. This confused me as surely this happens everytime you start the vehicle anyway (the bonnet doing the job of holding the pluger switch down)

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Hi Redhand,

I think maybe that it would be worth you searching this forum for the word 'spider'?

Here's a good one to start with:

linky

Rog

I thought the spider problem was restricted to 300tdi's... All the posts I've read on the spiders have all been 300tdi's

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So that's the spider ruled out. Anyone else have any ideas what it might be..

I suspect that it might be a short circuit in the wiring loom somewhere and / or a loose connection.

I would perhaps try removing the wire from the fuel valve solenoid and running a separate wire and switch from the battery +ve to the fuel solenoid. This will at least allow you to start the engine and stop it without resort to pulling fuses.

Note that short circuits can cause electrical fires!

HTH

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......

Will only drive when the hazard lights are switched on.

.....

You may want to elaborate on this a bit.

When you switch on the ignition do the dash lights come on?

If the dash lights don't come on when you switch on the ignition, do they come on if you engage the hazards?

What happens when you turn the ignition key further, to the start position? The starter engages and the engine rotates but doesn't start? Or what does it do?

Given the facts so far, my suspicion would be the ignition switch or something else (connectors/wires) on the +12V line between the battery and the fuel valve solenoid.

On the other hand the hazards trick that you play there raises some questions.

So I would disconnect the alarm (both connectors) so I can rule it out and see what happens (providing that I ground pin 86 from the starter relay).

Then disconnect the glow plug timer relay. Now I would have the most basic starter circuit and it would be very easy to trace the fault.

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You may want to elaborate on this a bit.

When you switch on the ignition do the dash lights come on?

If the dash lights don't come on when you switch on the ignition, do they come on if you engage the hazards?

What happens when you turn the ignition key further, to the start position? The starter engages and the engine rotates but doesn't start? Or what does it do?

Given the facts so far, my suspicion would be the ignition switch or something else (connectors/wires) on the +12V line between the battery and the fuel valve solenoid.

On the other hand the hazards trick that you play there raises some questions.

So I would disconnect the alarm (both connectors) so I can rule it out and see what happens (providing that I ground pin 86 from the starter relay).

Then disconnect the glow plug timer relay. Now I would have the most basic starter circuit and it would be very easy to trace the fault.

No dash lights unless Hazards are on.

Yes they come on when you engage the Hazards

Nothing happens unless the Hazards are engaged.

I'm assuming that the Alarm is the black box above the fuse box behind the drivers side dash? If so I have disconnected it and it made no difference. Not tried playing with the starter relay. Only relay I can see is in the engine bay near the washer bottle. I have removed all the wires going to the switch cluster and it made absolutely no difference at all.

It will start normally if left alone for an hour or so. but the fault returns as soon as you attempt to drive away.

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Here's the Starting electrical Diagram for a 1993MY Discovery 200Tdi (the second pic is the same as the 1st but with some ref points so that will be easier for me to explain):

post-1725-1219964473_thumb.jpg

post-1725-1219962644_thumb.jpg

First step would be for you to make sure the fuel shut off solenoid ST9 gets power (+12V) after ignition on.

That is to make sure you have +12V in all red points I marked in the diagram (3 & 4 - tested with ignition on).

My guess is that at least in point 4 you don't get +12V unless the hazards is on. But forget about hazards for now. Leave it off and you will deal with it later.

If you disconnect the alarm ECU you shouldn't be able to start the engine (but the dash should get illuminated and the cut off solenoid should get energized). Starter relay ST6 won't be grounded at pin 86 (left "on air" if Alarm ECU is missing) so no current through the coil when you will switch the ignition key to the START position => starter motor won't be engaged. So if you want to rule out the alarm, you need to ground pin 86 of the starter relay. But leave it in place for the moment.

Yes, the alarm ECU is under the dash on the right side, it has 2 connectors (one of them with 6 pins in line and the other with 16 pins - 2 rows x 8 pins each row) and it looks about like this:

post-1725-1219964715_thumb.jpg

It seems that it gets power through the hazards, possibly a short circuit of some kind, but the current isn't strong enough.

You should attempt to do the tests when you can't start the vehicle normally and with hazards off.

In case you do the test with a multimeter and nothing shows up (that is if you get +12V in all four points with ignition on), you may want to do the tests with a test lamp or something else that needs more than 3A to work (a headlight bulb, for example).

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Update that didn't last long. Now there's nothing at all even with the Hazards on?????? :blink::( Back to the drawing board.

Tried all the tests above ^^^ nothing no voltage at any of the points marked regardless of whether the immobiliser was unplugged or not. Got a live supply to the ignition switch but that goes as soon as you turn the key.

Refitted old switch and it's back to the way it was before. Will work but only with Hazards on. I'm going to try and source another switch and see if that helps. If not I'm resorting to petrol and a matches..

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