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MG Midget and Sprite Technical - Midget No Spark

Hi all, hoping for much needed help!! 1977 1500 midget, I have removed the engine to do clutch work, refitted and now I have a loss of spark. It has lumenition fitted, and I have a free white with black trace wire with a spade terminal on the end. I seem to remember something being joined in to the wire as well, but i cannot find anything to connect to it, but no spark.

Any hints most welcome!!

Regards

Gary
G Miller

White/black is the normal colour for the points/coil (and rev counter) connection - it has the make & brake voltage; what you might call the 'output' of your elec ign system.

Put a bulb on it; other end of bulb to +ve (assuming lumnition is switch earth), and it should switch on/off as you crank the engine.

(BTW - my experience with Luminition is on the whole negative; I've replaced several units on friends cars over the years with points when unit has gone u/s - often the LED under the dissy cap)

A
Anthony Cutler

I've just done the same to another classic, out with the old Luminition back to points & it fired up 1st time.
The Aldon units are much better.
Brad (Sprite IV 1380)

Hi Anthony,

thanks for your help.

If this is O/P for ign, where should it connect to? The lumienition has 3 wires - red black and blue, all connected.

Thanks

Gary
G Miller

how about a picture Gary?

the white/black wire ought to connect the coil negative terminal to the switching system, whichever car its on and whichever system is on it ISTR, so it should originate at the coil (or meet there for later cars with pulse counting tachos, does your tacho pulse when cranking the engine?)

The power to the coil is normally a white ignition fed supply, the black trace on the "spare" wire indicates it should be travelling to earth (via the points, lumenition or other electronic ignition) after passing through the coil.

Black is the "normal" earth colour for Lucas based systems.

A picture might help us help you
bill sdgpm

There should be 6 wires in total to the lumenition box.

One group of red/black/blue goes to the optronic sensor in the Dizzy

On mine I then have a Red (+ve feed), Black (Earth) and Purple. The purple goes to the -Ve side of the coil. I use the existing live feed (White) to the coil (+ve) to feed the above red feed. And then there is a white with black trace from the -ve side of the coil (i.e. same side as purple) to the rev counter.

Mine was ex-ebay and I actually won 2 in close succession at bargain prices. So I have them cabled with identical multiplugs. If I suspect its playing up - it takes 30 secs to try the spare. Only had to do it once in anger and it was the coil that failed not the ignition. (On the autoroute outside Calais!)




Dean Smith ('73 RWA)

Hi All,

Thanks for all you help, I have an update! Turning it over with the distributor cap off, you can hear clicking of the luminition. There is a spark from the HT Lead from the coil when checked by holding it onto an earth on the engine. I have removed a spark plug and put it on a lead onto an earth (Through a lifting eye) and there is no spark! There is only a spark when I turn the ignition key off slightly (across the plug). When the withe an black wire is attached to earth, there is no spark when the key is turned off or on.

I can remember removing a wire from it that was just twisted around it, but i cannot think for the life of me what it was, and cannot see it! This is the problem. It was running perfectly before i took the engine out to do the clutch parts.

Please help me!!
G Miller

The picture shows the wire here, and the lumenition inside the dissy. The wire was taped in with the wires for the alternator.


G Miller

The white and black shouldn't be held to earth. It should only be from the Coil -VE to Rev counter and also from coil -VE to distributor for a standard points based system - it is the making and breaking of this connection to earth (via points in a standard setup or lumenition in yours) that sets ups the field in the coil that drives the high voltage spark. So if you hold it to earth - you never get the make and break cycle and you will never get a spark. (You can create a quite effective anti-theft device by having a hidden switch for the white/black to earth under the dash - when activated you simply dont get a spark and you're average opportunistic scrote will assume the car wont start and move on). So it may be that loose white & black was the original (now redundant) connection to the Distributor and can be ignored. You should definitely have at least 1 white/black on the -ve side of the coil to drive your rev counter.

If you're getting a good spark direct from the coil then that strongly suggests your low tension side (i.e. lumention etc is all OK). You should see the rev counter flicker when you turn the car over (do you ?)

If the spark isn't making its way to the plugs then check ..
The graphite bush is still in the distributor cap. Mine drops out quite easily and causes the exact symptoms you have.
You have a good earth for the engine - is the earth strap back on and in good condition.
DO you have a spare rotor arm to test ?
Have you cleaned up the rotor arm and the contacts in the dizzy cap ?

Dean Smith ('73 RWA)

Hi Gary,

On my 1500 there are 2 white/black wires on the - side of the coil, one of these would connect up to the wire coming from the points, as you don't have points it should be spare, but it is still connected to the coil,i think the other white/black goes to the rev counter. Sorry its not much help regarding the lack of a spark. Are the connections in the connector clean? i seem to recall that you should have a power supply to the Lumenition unit with an earth, are these good ?

HTH
Alan
A Pritchett

Thanks for all your assistance, I will get some new HT leads (Found main HT kin lead from Cap to coil u/s)Cap & Rotor and see what happens.

Its probably one of those things, I assumed that as it was running when it came out it must be something i have done.

It would appear the Black & White goes know-where and maybe a red herring.

I am moving house and need to get it MOT'ed, hence the desparation in my words :-)

Thanks all, any other ideas let me know, i will keep posted if fixed.

Regards

Gary
G Miller

Hi All,

I managed to get 2 sparks back!! I now need to get 4 spark plugs, then its on to the next thing!! I have some more questions if anyone can help would be much appreciated!!

Firing order is 1342, when timing marks are lined up on the bottom pulley it can be firing on 1 or 4, is it firing when one valve is opening and one is shutting?

Also, I am not sure if i am getting fuel through, i have removed a pipe from the carburettor and it appears to be coming out, but the amount i have turned it over you would think that the plugs would be wet, but they are not. If you look at the fuel pump from the passenger side wing, the pipe at the top is connected to the tank, the port closest to the engine is going to the carb, is his correct?


Cheers Gaz
G Miller

Not sure of the firing order for the 1500 (I have only lived with A Series) anyway that aside the engine fires when both valves are closed. One valve opening and one valve closing is the opposite to the firing stroke.

The pump should only be able to pump 1 way so if fuel is being pumped out then it is piped correctly

Robert (Bob) Midget Turbo

Ok thanks rob, I will have to check the bowls to make sure they are full and the floats arent stuck, plus Ive got my leads on back to front!!

Its a long time since ive done this!! Usually working on Diesels.....

Thanks

Gaz
G Miller

Hi All,

Just to let you know, got 4 sparks, got the right firing order (Thanks Rob) and all running!!

Thanks for all your help, much appreciated!

Gaz
G Miller

This thread was discussed between 05/03/2010 and 10/03/2010

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