22 replies to this topic

[RWDwanted]

We have just got a new mini. We brought the car as a non runner the guy said that the engine was temperamental. Well the plugs are getting wet and after testing to see if there was any spark it turns out there isn't. I have taken the lead from the coil off the distributor and still no spark. So is it defiantly the coil or how can i test to see what is faulty?

The engine is not original, after doing a search of the engine number it is a A+ 998cc.

[bmcecosse]

Very unlikely to be the coil - they are very reliable. Look at points/condenser/rotor arm/dizzy cap/ HT leads pretty much in that order. AFTER - checking there is a voltage getting to the coil - and a lead going from the other terminal on the coil over to the dizzy.

[RWDwanted]

According to the haynes manual if you remove the lead from the middle of the distributor cap and hold it close to the block and turn the engine over it should generate a spark. i have tried this and it did not produce a spark, although that doesn't rule out there being a problem with the distributor. Does the above test not mean that there is a problem before the distributor?

[cowboy]

Very unlikely to be the coil - they are very reliable. Look at points/condenser/rotor arm/dizzy cap/ HT leads pretty much in that order. AFTER - checking there is a voltage getting to the coil - and a lead going from the other terminal on the coil over to the dizzy.

this is partially wrong advice, with some good points added to it. if the ignition has been left on for a considerable lentgh of time then the coil can become damaged and stop working.

if you have no spark from your coil, then you need to check the low tension side of your ignition system.

just a quick reminder of how the ignition system works, the low tension side is built up of the coil, points, condensor, the points create an open circuit in the system creating the HT spark.
the HT side is made up of the coil output, king lead to the dizzy, rotor arm in the dizzy, spark plug leads, and then of course the spark plugs.

when the points inside the dizzy are closed the circuit is closed, a charge is then built up in the coil, and as soon as the points open the spark will travel from the coil along the king lead, into and then through the dizzy to the spark plugs, if the points do not open or stay open, then the circuit will not create the spark in the coil.

a simple test which i teach is to get a test lamp, ( a bulb with 2 wires on it) connect one end to a good earth point on the engine.
dosconnect the lead going into the dizzy.
turn the ignition on, and then see if you have power at the + side of the coil. if you don't then you have an open circuit in the wire from the ignition switch to the coil.
if the light comes on, then check the output - side of the coil. if the light fails to come on then the coil needs to be replaced.
then check the wire from the coil the the dizzy, where you disconnected it. again if the light fails to come on then you have an open circuit in that wire, change it.
if you have power at this lead then the fault is in the dizzy.
check the points are opening, check that the points have not been fitted wrong,(the wires going onto the points could be touching the base plate, this will create an earth before it should)

hope this helps

[dklawson]

Both Roy and Cowboy have given you good advice. I agree with Roy that the coil is unlikely to have failed. Yes, they do fail but people often blame them prematurely without diagnosing the system fully. You are likely to hear people say things like "Oh yeah, my coil went bad. I replaced it along with my points, plugs, condenser, cap and rotor and it fired right up". When you shotgun the repairs by replacing everything at once you can't determine which component really was at fault.

Cowboy has given you some good advice on how to troubleshoot this. If you want to read about this, I have a similar document that will hopefully give you some additional information. The PDF in the link below is my attempt to explain how the ignition works and then take you step by step through some tests to find what's wrong. If you have a good understanding of how the ignition system works, finding faults is a lot easier.
http://home.mindspri...tsIgnitions.pdf

[RWDwanted]

Thanks a lot for the advice guys.

[Gooders]

Both Roy and Cowboy have given you good advice. I agree with Roy that the coil is unlikely to have failed. Yes, they do fail but people often blame them prematurely without diagnosing the system fully. You are likely to hear people say things like "Oh yeah, my coil went bad. I replaced it along with my points, plugs, condenser, cap and rotor and it fired right up". When you shotgun the repairs by replacing everything at once you can't determine which component really was at fault.

Cowboy has given you some good advice on how to troubleshoot this. If you want to read about this, I have a similar document that will hopefully give you some additional information. The PDF in the link below is my attempt to explain how the ignition works and then take you step by step through some tests to find what's wrong. If you have a good understanding of how the ignition system works, finding faults is a lot easier.
http://home.mindspri...tsIgnitions.pdf

This guide is very useful, however does the same apply to my mini, which is possitivly earthed?

Cheers

[dklawson]

For a positive earth car, the significant changes are the low tension connections to the coil. Other than that the ignition system works the same.

On positive earth cars the original coils were marked SW and CB (for ignition switch and contact breaker). The coil SW terminal received the power from the ignition switch and the CB terminal received the white/black wire that goes off to the distributor. When you have such an old coil connected to a car which has been converted to negative earth, these two connections are supposed to be swapped (SW gets the white/black and CB gets white from the switch on negative earth).

[Gooders]

Ahh rite ok, so if i need to get a new coil i would simply reconect without switching wires?

[RWDwanted]

Right i got round to trying to find the problem with the lack of spark.

I have checked the coil primary resistance and that read 1.3 ohms, and the secondary resistance is 5.2 K omhs

Do you think these readings look ok, looking at the document above they seem a little low?

[Dan]

You haven't said what Mini the engine is in. Does it use ballasted ignition? What colours are the wires on the coil?

[RWDwanted]

The car is an 82 but the engine has been replaced as far as i can tell the engine is a post 85 engine. As far as i can tell it is not a ballast ignition and the wire run from the fusebox to the coil is white but doesn't look original.

[Dan]

You've got a ballasted coil in a non ballasted car, it's quite likely to be damaged even though it still shows 1.3 ohms. In any event, you need a non ballasted coil even if this one is working. I would suggest fitting new points and condensor along with a non-ballasted coil.

The age of the engine isn't really relevant to what type of coil is fitted. The ignition wiring in this case in non ballasted and so the ignition system must be run as non ballasted whatever the engine had originally, unless you want to add a ballast system. If there is only one wire to the coil + terminal and it's plain white delivering 12v, it's non ballasted ignition (unless it's a Lucas electronic dizzy).

[RWDwanted]

I thought that ballasted coils ran off 8v the coil that is fitted now is a Ducellier coil and has 12v stamped on it. The person we got the car from seemed to bodge things together, and swap parts. As the coil doesn't fit in the clamp that is meant to hold it in place it is very possible that he has fitted a ballasted coil to a non ballasted ignition. So as few as replacing the coil do i need to identify the distributor to by the correct coil or will a non ballasted coil work with and distributor?

[Lloydc]

Very helpful topic, I'm experiencing the same problem now in my 1980 Mini 1000.

I've followed the haynes and used Cowboy's trouble shooting guide and from it, can conclude that there is a problem with the dizzy.

However, the points are opening and closing as they should and they're well shielded cables nowhere near the baseplate.

Really struggling for ideas so here's my cry for help!

 

 

Chris