Disco coil advice please.

Obvious question, but have you checked that the battery isn't delivering 5v? Presumably it is turning over normally but won't fire?

If you unplug the coil LT lead and check the voltage from the lead do you get the same?

For what it costs (if they are not recent) I would swap the rotor arm and dizzy cap.

Thanks for the response, Tim. Battery voltage is 12.23 and turns the engine over as normal.

The #1 terminal (rt hand) has two wires and the #15 (left hand) terminal has three wires.

I am still trying to determine the source and destination of these five wires. The Haynes manual wiring diagrams do not seem to include the coil.

I did take your advice and buy a new distributor cap and rotor arm, which I have not yet fitted.

PJ

: > >My 1995 3.9 litre Disco will not start. : > >Haynes manual suggests that if there is no spark then turn on the : ignition : > >and check the voltage between the coil LT terminals and earth. : > >It should be almost battery voltage. : > >Mine is only 5volts on both terminals. : > >

: > >Has anyone experienced the above? : > >

: > >Many thanks for any feedback. : > >

: > >PJ : >

: > Obvious question, but have you checked that the battery isn't : > delivering 5v? Presumably it is turning over normally but won't fire? : >

: > If you unplug the coil LT lead and check the voltage from the lead do : > you get the same? : >

: > For what it costs (if they are not recent) I would swap the rotor arm : > and dizzy cap. : >

: >

: > -- : >

: > Tim Hobbs : >

: > '58 Series 2 88" aka "Stig" : > '67 Series 2a 109" aka "Ernie : > '77 101FC Ambulance aka "Burrt" : > '95 Discovery V8i aka "The Disco" : >

: > My Landies?

> Barcoding? > Tony Luckwill web archive at : Thanks for the response, Tim. Battery voltage is 12.23 and turns the engine : over as normal. : : The #1 terminal (rt hand) has two wires and the #15 (left hand) terminal has : three wires. : : I am still trying to determine the source and destination of these five : wires. The Haynes manual wiring diagrams do not seem to include the coil. : : I did take your advice and buy a new distributor cap and rotor arm, which I : have not yet fitted. : : PJ : :

Many thanks for the suggestion, Frank. My Disco does not have a contact set, although it has a distributor. It does have an amplifier near to the coil.

I am puzzled by the voltage between the LT terminals and earth. I expected the reading to be 12v and it is only between 5-6volts. I was hoping that some kind person with a petrol Disco would put a meter on their coil with the ignition switched on and tell me the voltage between the LT terminals and earth.

I have replaced the coil, distributor cap and rotor arm. I think the only other possibility is the amplifier.

PJ

Hint taken! But it won't be until tomorrow night I'm afraid.

Whereabouts are you. I think I have a spare amp somewhere...

I've just emailed some extracts from RAVE to you, which may (or may not) be helpful.

Cheers

Many thanks, Tim. I am in West Norfolk, by the way. This is undoubtedly quite a simple fault and I am determined not to let it beat me (with help from the more knowledgeable). The email address below, with obvious modification, does work.

PJ magister3AThotmail.com

You should have 12 volts on your LT side to produce a health 30kv on the HT side...

I think someone has already suggested it but have you unplugged the wires on the LT side and then measured the voltage drop to the earth... do you get 12 volts then? If yes, then your coil is probably knackered or an earthling / condenser(1) problem, if not the problem lies further up the +ve side of the circuit, or the earth side.

(1) never seen a failed condenser cause this problem - anyone else in the group?

Tom

on the LT side and then measured the voltage drop to the earth... do you get

12 volts then? If yes, then your coil is probably knackered or an earthling / condenser(1) problem, if not the problem lies further up the +ve side of the circuit, or the earth side.

Thank you for your response, Tom. I do appreciate that these are an unusual symptoms. I have replaced the coil, distributor cap and rotor arm. When the wires are removed from the +ve LT terminal they are 9.6v, 6v decreasing slowly to 0v and the third wire is 0v. The -ve terminal wires show 0.22v and 0v.

There is a condenser (suppressor?) behind the coil on the +ve side would this cause symptoms if faulty? I have checked the pickup coil resistance which is about 3000 ohms - which is within tolerance.

The only other relevant part is the amplifier. If it were faulty could it reduce the 12v input to 9.6v?

The engine died whilst I was driving along the A11. I am at the stage where I will consider ley lines, microwaves or nuclear radiation from the American bases as a cause. All the other electrics are working and the engine turns over normally.

Would it harm the coil if I ran an extra wire directly from the battery to the coil to ensure a 12v supply?

Tim Hobbs has been very helpful sending me diagnostic tests but the results (some are above) are not as one might expect.

I would appreciate any helpful suggestions from anyone or as a last resort details of a mobile auto electrician in West Norfolk.

PJ

Before doing this check that the coil is not a 6v coil with a ballast resister of some sort in line Most ignition systems run on either 6 or 9v this is because when you crank the engine over you get a voltage drop to about 9 - 10v if you run a 12v coil it's only getting 75% or so of it's required power so they put a 9v coil on with a ballast resister when you crank it over it by-passes the resister so the coil gets 9 -10v(100% of it's required power) when you release the key it goes via the ballast resister so still gets 9v (100%)

Andy

PJ - Halfords do the amps for £22 (which is a bit better than £100 plus VAT for LR genuine ones). I'd swap anything else that you haven't swapped too (e.g. condenser).

Thanks for that, Tim. It saved me some cash. It was £20.99 but I had to go and twist their arm as they are not on their computer but are in stock. It has not yet solved the problem. So it is not the coil, rotor arm, distributor cap or ignition unit. I am running out of bits associated with producing a spark. I will give up when I have replaced the rear light bulbs :-)

PJ

Coil HT lead?

I think there is a bit in the dizzy itself which can break - a little wire or summat, but I'm more than slightly hazy about that! And you don't want it to be that...

Thanks again for the input, Tim. I am very grateful for all your help. I am still very puzzled by the less than 12v input into the coil. The wire when not connected is 9v and only 6v when connected to the LT terminal.

PJ

Suggests that the coil (or something connected to it) is causing voltage drop. Did you try putting a battery straight to it? How much current is flowing through the coil if you put the meter in series between the LT lead and the LT terminal? Don't know what the right answer is, but shouldn't think it ought to be much.

Hi Tim,

I am most grateful for all your advice. I decided to jump in with both feet and put 12v into the coil. It started. I have a moving Disco again!! The bad news is I still don't know why I had a 9v supply to the coil.

I shall have to start doing some research on the ignition switch to coil wiring. The worst scenario I suppose is that the immobiliser is faulty and causing the low voltage.

PJ

On or around Sat, 24 Jan 2004 12:09:26 GMT, "PJ" enlightened us thusly:

bad connection somewhere between the battery and the coil... had this problem on a vehicle once, solved it by connecting coil supply to a relay. The proper solution is of course to track down the bad connection.

Thanks Austin. The input to the coil is only 9v disconnected and 6v when connected to the coil. When I connected the +ve from the battery to the coil, the Disco starts. The fault is the reduced coil input which comes, according to Haynes 13.51, from the immobiliser.

Hopefully with good weather tomorrow I will try to trace the black wire backwards from the coil to the immobiliser. I am not sure what the immobiliser looks like but I have been told that it is a black box and I found a one on the front O/S but that contained fuses.

I would have thought that if the immobiliser failed it would cut the coil supply completely not reduce it to 9v.

PJ

On or around Sat, 24 Jan 2004 22:17:45 GMT, "PJ" enlightened us thusly:

could be an internal fault in the immobiliser, I'd forgotten that you might have such an obnoxious item. but more likely really to be a bad connection. connections on vehicles have never been particularly proof against corrosion and other problems and they still aren't - 's got to do with cost of components - properly waterproof and durable connectors cost more.

yeah, it'll be a box somewhere. behind the glovebox, probably.

would tend to assume so. I think they normally do, along with cutting the fuel supply as well, if it's a decent one.