Discovery Starter Motor won't Turn - Hugo {P}
An hour after picking up my K reg Discovery 2.5 TDiS, I tried to start it and couldn't

However, it will bump start.

Inside the drivers side wing there is a 30 amp fuse, which has blown. The vendor did everything reasonable to get the problem sorted by taking it up to her garage, so I have no beef with her. Both she and the garage thought that the problem was over.

In addition the starter motor was removed, stripped down and cleaned up.

The blowing of this fuse means that the starter motor won't turn - but what could be causing the fuse to go?

The most likely explanation is a short circuit possibly in the battery, relay, solenoid circuit, but where is this short circuit occurring? I assume the current going throught the starter switch and powering up the relay is usually much lower than 30 amps - or am I wrong?

In daylight tomorrow, I intend to look for the obvious, such as chafed wires on bodywork, black marks on the ignition switch etc, however, are their any Disco nuts here who have known of similar problems? Where this fuse had not been fitted, does anyone know where the burning smell may have come from in their experience? 30 amps is a lot of current.

Any help would be greatly appreciated.

Hugo
Discovery Starter Motor won\'t Turn - M.M
Hugo,

OK the earliest (1992ish) Discos didn\'t have any fuses in the starting circuit. Just main power from the battery to the starter solenoid......and the aux circuit to trigger the starter from the ign switch feeding to the starter relay which in turn energised the starter solenoid.

Of course there is the added complication of the glowplug and diesel stop solenoid circuits which are closely associated.

Then we have the later (1995on?) vehicles which were very similar but with the addition of a fuseable link in the feed to the starter relay but the starter solenoid was still a separate unfused supply from the battery. Now this fuseable link is like a massive fuse and I reckon it should be a 60A or 100A capacity.

I have a feeling that there was something in between around 1994 but still with a heavy link and not a fuse.

So....

Has someone replaced a 60A fuseable link with a 30A fuse by mistake? Has someone added a 30A fuse to a circuit that should have a direct feed? In either case perhaps the 30A fuse just copes sometimes and blows on other occasions.

Has someone wired in the glowplugs as well through this fuse by mistake. In fact tell us what the operation of the glowplugs is...do they appear to heat?

To be honest this would be a doddle to diagnose with the vehicle in front of you but hard online!

You really need to find out what this fuse feeds. Does it look original or a crude addition? What is the wiring colour?

I would eliminate the starter as faulty early on by powering its solenoid directly from the battery for a test start.

This fault sounds to have very little to do with Disco unreliability and lots to do with mechanics who can\'t diagnose in a logical way!!

Don\'t forget to ask Mark for my mail address if this is going to get involved.

M.M

[He asked and I provided. Yesterday, I think. M. ]





Discovery Starter Motor won't Turn - Aprilia
The main feed to the starter/solenoid is unfused (it will run 300A+ on a cold morning!).
The circuit that is giving you the trouble is the control feed to the starter relay winding - this current passes through the ignition switch and is a very modest current (1A or less). This current only flows when the ign. switch is in the 'cranking' position. There is also a glowplug circuit, but this operates when the switch is in the 'ign on' position and does not, I think, involve the 30A fuse.

Since the 30A fuse blows when you try to crank the engine then the fault has to be a short circuit somewhere 'downstream' of the fuse. Most likely culprit is, of course, the relay itself - the winding could have gone s/c. Failing that you will have to trace the wire from the fuse to relay and look for damage.

HTH
Discovery Starter Motor won't Turn - M.M
Aprilia's comment "There is also a glowplug circuit, but this operates when the switch is in the 'ign on' position and does not, I think, involve the 30A fuse" highlights something I was tryting to get at but perhaps got buried in the detail of my post....

I wonder if the fuse that goes is actually blowing when you operate the starter...or might it blow during the glowplug heat period...and then in turn then prevent the starter operating.

To clarify the setups...

The earliest versions should have direct feeds from the battery to glowplug unit and starter relay.

The middling period (yours?) might have one fuseable link that feeds ign switch circuit, the glowplug unit and the starter relay.

The later (1995ish) vehicles have a separate fuseable link for the glowplug control unit and one for the starter relay.

But all of that is with the proviso that LRs are like a big kit car and it is common to find features from the *wrong* year on them due to things owners have done in the past.

M.M


Discovery Starter Motor won't Turn - Aprilia
Yes, I think we need to know at which point the fuse blows. Is it during cranking only, or does it blow in the 'ign on' position?
Discovery Starter Motor won't Turn - Hugo {P}
Thanks guys for the suggestions.

I think it blows when I try and start it. I heard a distinctive 'pop' when I tried to turn it, and the mechanic also claimes that he observed it blowing when he tried to turn the key.

I've got a few spare fuses, I'll give it another shot later to confirm.

Hugo
Discovery Starter Motor won't Turn - Aprilia
Try it again and then pull the relay out and give it another try. If it doesn't blow with the relay removed then you've discovered that the relay is faulty. If it *does* blow with the relay removed then you've discovered a short in the wiring or in the relay base socket.
Discovery Starter Motor won't Turn - Hugo {P}
Thanks Aprilla

I'll confirm it's the starting that's doing it and no the glow plugs.

Assuming this is correct then I'll do what Aprilla suggests and remove the starter relay and turn the key.

Thanks again guys!

Hugo
Discovery Starter Motor won't Turn - Hugo {P}
Thanks Aprilla
I'll confirm it's the starting that's doing it and no the
glow plugs.
Assuming this is correct then I'll do what Aprilla suggests and
remove the starter relay and turn the key.


Well, looking at what Aprilla has said, the diagram in the manual confirms this.

A brown lead goes directly from the battery to the starter solenoid, the ignition switch and the starter relay (amongst other things on the fusebox).

Hence this brown lead acts as a common live for all 3 items.

If we are looking at a short curcuit, then either one of these 3 items could be at fault.

Starter solenoid - easy to find, below heat shield attached to the starter motor.

Ignition switch - easy to find - steering column obviously

Starter relay - where is it? Mr Haynes OBE tells me it is behind the side panel of the passenger footwell, with a black wiring connector (I assume this is the connecting block that the relay sits in). I cannot find a black wiring connector anywhere in this area.

So tomorrow, I shall confirm the solenoid one way or the other by disconnecting it and testing for a voltage drop across the fuse terminals.

I guess if there is no voltage drop then that pretty much puts the solenoid in the frame.

Next question is, how am I going to test the ignition switch?

Question after that is - where is that relay?

Hugo
Discovery Starter Motor won't Turn - M.M
Hugo,

So where does your blowing fuse come in the brown wire? Is it close to the battery so everything (obviously not the main heavy lead to the starter itself) in the starting system runs through the fuse?

As far as I was aware for every model year variation one thing was the same.... the feed to the starter solenoid was separate and unfused.

Did you say ages ago you thought this fuse was a DIY addition?

Oh the starter relay can be either passenger or drivers side footwell, I'd have guessed yours would be drivers side near/below the main fuses/relays.

M.M
Discovery Starter Motor won't Turn - Hugo {P}
Hi MM

I think I am thinking along the same lines as you.

Yes, I do think the fuse is a DIY addition, why it was added I don't know.

As far as I can work out, when I turn the starter the fuse blows and I cannot start it again.

However, the power to the ignition switch still remains on, lights on dash bear this out.

I know that mine is a 93 model year, from the chssis number. However, haynes have cunningly labelled their starter wiring diagrams 'Pre 1993 model year' and 'Post 1993 Model year'. As if I was not confused enough!

The main difference between them is that the Post 1993 MY incorporates an Alarm ECU and a Fused Connection to the Brown wire going to the ignition switch and starter relay only, not the starter solenoid. S here are in effect two common lives. The Pre 1993 MY has just one live going to all 3 components, which is not via a fused link.

As the lights on the dash remain on and there is power to a load of relays (can hear and feel them all clicking away when I turn the key to 'start') I suspect I have a separate feed to the ignition switch that is not via that lashed up fuse.

Hence I beieve the "Post 1993 MY" applies to my vehicle, though the LR dealership say that the Alarm was not a standard part until 1994. (LA model year label in the VIN, whereas mine is a KA). However their parts depot said that this was an optinal extra available at the time, and it seems that one is fitted, since the lights flash 3 times when it is locked.

I am starting to think that the DIY fuse addition is ill conceived. Tomorrow, after a job interview, I shall disconnect the high current wire from the solenoid and fully turn the key, measuring the voltage drop across the empty fuse carrier.

Why would this fuse carrier have been introduced? Is it to protect a sensitive component in the starter curcuit, such as the relay? If so it may be in the wrong place.

Furthermore, why has it only just started causing problems? I fully believe the lady when she told me she had no trouble starting it before I decided to buy it. In addition, the mechanic who replaced the previous fuse carrier reports that the old fuse carrier was being arced across even with the fuse there when the key was turned to start (and it started), which makes me think there was a hell of a current going across it.

If I can establish that this wire with the fused carrier only serves the Starter solenoid, electric windows and central locking, and a few other normally fused services, then I am tempted to remove it and re make a closed connection. As you say, this wire to the solenoid should not be fused and all the other services I know it takes out are fused via the fuse box inside the car.

What do you think?

Hugo
Discovery Starter Motor won't Turn - M.M
Hugo,

Interesting.

A question you haven't quite answered is in which feed is this fuse located? Is it cut into the brown feed very near to the Battery?

M.M
Discovery Starter Motor won't Turn - Hugo {P}
MM

Yes, the fuse is cut into the brown feed near the battery but above the off side wing.

Hugo
Discovery Starter Motor won't Turn - Hugo {P}
Just an update,

I had my local mechanic take a look at it.

At first he was sure it was the glow plugs that were at fault, but after I showed him their operation without blowing said fuse, he ditched that idea.

It started several times this morning on one fuse, so the problem seems to have temporarily gone away at least.

I also know that there is an in line fusable link to this wire, which has not shown any signs of trouble - yet...

He suggested that the wire should be able to carry 50 to 60 amps without issue.

In the end he suggested shorting the fuse out, as neither he or I could identify any good reason for it being in there.

The fuseable link should provide adequate protection I would have thought.

Just to be on the safe side I may make sure that the terminals on the solenoid valve are properly insulated. That is the only place I can think where the 300 odd amps could possibly bridge to this smaller supply.

I suspect I may be looking at a replacement solenoid soon though.

The vehicle is going in for its service next week. I could probably do it myself but a service record needs to be kept I feel.

MM and Apprila - thanks for all the useful correspondance.

All the best

Hugo
Discovery Starter Motor won't Turn - M.M
Hugo,

If, as it seems, this fuse has been added in addition to the larger fuseable link then it seems just daft. In my first post I said I thought this supply capacity ought to be up to perhaps 60A or 100A.

Once I had proved there wasn't any good reason to have this additional fuse I too would have bridged it. I was thinking of advising you to piggyback it up to a 60A rating to see what happened then.

Obviously at a distance I was being cautious with the advice...not wanting a premature engine loom fire!

Fingers crossed.

Other service info soon.

M.M
Discovery Starter Motor won't Turn - Hugo {P}
MM,

Where can I get a 60 amp fuse with carrier?

The highest I've seen that fit in these carriers is the 30 Amps.

To be honest, I agree with you, this would be my preference.

Hugo
Discovery Starter Motor won't Turn - Aprilia
For fuse carriers try somewhere that sells boat bits - if there is canal near you there is likely to be someone selling bits and pieces for narrowboats etc. They usually have a good selection of 12 electical bits and pieces. An local autoelectrician may also be able to help out, or a scrappy if you're feeling brave!
Discovery Starter Motor won't Turn - AndyT
You could try Halfords, or any auto-electrical factor.

I know that the Vauxhall Corsa and Seat Ibiza use a maxi type fuse (both fitted at the bulkhead) for their glow plugs of around 70-80amps, so perhaps try a dealer or scrap yard.
Discovery Starter Motor won't Turn - Hugo {P}
Thanks Guys.

I'd better try an auto electrician.

Hugo
 

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