Cutting out

[Triumphcrazy]

Hi guys , Can anyone tell me what voltage readings are correct for mk2 stag with ballast wire ? , I have read that to test for a ballast system is to disconnect the + wires on coil and measure voltage with multimeter ignition on , this I have done which indicates around 12 volts , if I crank ignition it drops to around 9v is this correct ? , I have checked the starter motor and the white/yellow cable small terminal has been disconnected for some time obviously by a previous owner , the coil fitted shows 3ohms when measured suggesting its a non ballast coil which I assume why the starter wire was disconnected ?, this set up/ coil has been reliable for a number of years until recently , if I reinstate the terminal and connect this wire what voltage readings should I expect repeating the test ?
the car runs ok from cold increase the revs to around 2500 for period , the return to fast idle it the faulters and cuts out , the coil is very hot and she will not restart until cooled ? any ideas Lloyd ?

[flying farmer]

The coil should not be getting hot. I would try reconnecting the white/yellow wire.

Is yours a mk1 with the separate ballast resistor, or a mk2 with the pink/white wire wound into the loom?

Assuming it is supposed to be a ballasted coil, when running the voltage across the coil should be about 8 volts when fed from the ballast resistor. When cranking it gets fed the 9 volts you are seeing with the coil disconnected. It is possible the ballast was faulty so the previous owner disconnected it to cure an ignition problem, but it has been gradually cooking the coil.

Neil

[Triumphcrazy]

Hi Neil , Its a mk 2 with ballast wire , the coil fitted seems to be a non ballast with 3ohms measured across it ? , ill try connecting the starter wire up and fit a ballast coil as intended and see if any difference to running , obviously I don't know if the ballast wire has burnt out ? Thanks Lloyd

[Mike Stevens]

I would have thought that a 3 ohm coil is more likely to be a 12V (non-ballasted) type. When you measured the coil resistance, did you check the meter reading beforehand with the leads shorted (which should give 0 ohms)? If the reading was not zero, you probably need to subtract this from the coil reading. This is a common problem with multimeters as they are really intended to read much higher resistances where the odd 1-2 ohms offset doesn't matter.

Another way to check is to measure the current into the coil with 12V across it. A 12V coil should be about 4A, a ballasted coil (without the ballast resistor) 6-8A.

There's nothing wrong with using a 12V coil without the ballast - you just don't get that spark 'boost' on start which is probably not a great issue in the UK anyway.

Cheers,
Mike.

[Triumphcrazy]

I have refitted the starter wire and replaced coil with a lumenition ms4 ballast type , if I run at 2-3k revs for prolonged period she the begins to faulter/backfire/unburnt fuel in exhaust etc ? she will then either idle or cut out after short time , the coil is vey hot , replace with a cold coil she will restart and the process repeated with same symptom voltage between 6-7 volts when running ?

[Ian Durrant]

I have refitted the starter wire and replaced coil with a lumenition ms4 ballast type , if I run at 2-3k revs for prolonged period she the begins to faulter/backfire/unburnt fuel in exhaust etc ? she will then either idle or cut out after short time , the coil is vey hot , replace with a cold coil she will restart and the process repeated with same symptom voltage between 6-7 volts when running ?

The ballast wire hasn't been bypassed has it?

Are you running points?

Kind regards
Ian

[marshman]

I have refitted the starter wire and replaced coil with a lumenition ms4 ballast type , if I run at 2-3k revs for prolonged period she the begins to faulter/backfire/unburnt fuel in exhaust etc ? she will then either idle or cut out after short time , the coil is vey hot , replace with a cold coil she will restart and the process repeated with same symptom voltage between 6-7 volts when running ?

How and where did you measure the voltage? As I have explained in another thread some time ago when the engine is running you no longer have a nice easy to measure DC voltage on the coil. Any voltmeter, apart from an old analogue moving iron (quite rare!) meter, will not give an accurate reading. The pictures below show the "horrific" waveforms present on the both sides of the coil. The first is at the coil terminal connected to the ballast and the second on the terminal going to the points (it will be similar if you have one of the new fangled electronic ignition thingies) These waveforms and the voltage and current measurements were taken this evening on my Stag which still runs the twin points and has a standard (non flame throwing, non mega boosted) ballasted coil with the original ballast resistor fitted.


waveform_ballast_side.jpg

Ballast side - 0V at bottom, 2V/div, volts switching between about 5.9 and 14v

waveform_coil_side.jpg

This is the "mess" on the points side. When the points close it goes down to 0V, When they open the volts shoot all over the place, the top of the screen is 40V.

The actual voltages and current I measured with the engine on a fast idle (approx 1000rpm) are as follows:

VOLTAGE
Measurement Location	Engine Running or Not	Measured Volts	Battery Volts
Coil - Ballast Side	Engine Running 1000 rpm	10.3V	14.25V
Coil - Points Side	Engine Running 1000 rpm	7.25V	14.25V
Coil -Ballast Side	Engine NOT Running, Ignition ON, Points Closed	5.6V	13.20V
Coil - Points Side	Engine NOT Running, Ignition ON, Points Closed	12.4V	13.20V
CURRENT
Measurement Location	Engine Running or Not	Measured Current	Battery Volts
Inline with wire from Ballast to Coil	Engine Running 1000 rpm	1.8A	14.25V
Inline with wire from Ballast to Coil	Engine NOT Running, Ignition ON, Points Closed	3.0A	13.20V
All measurements made on Digital Multimeter (DMM)

With electronic ignition I am not sure if you can just turn the ignition on (with out the engine running)and measure the volts on the coil (ballast end) to see if you have approximately 6V. This would show the ballast is in circuit and working correctly. - Just thought you could briefly earth the "points" side of the coil and measure the voltage on the ballast side, if all is well then it should be around 6v.

Gpoing by the number of ignition problems posted on here that seem to be traced back to some part of the Lumention ignition circuit I would suspect a problem with that if you have replaced the coil and the ballast resistor wire checks out.

Roger

[Triumphcrazy]

Its on lumenition Ian which is new , the ballast wire appears intact , I was now thinking of bypassing and fitting a non ballast coil with a feed from fusebox side to see if any difference to running ?