Testing for a spark

[Steve P]

I'm in the process of setting the timing and not getting any ignition. So thought I would check for a spark at the plug. With the plug out and connected to its lead touching the plug to earth and turning over the ignition should produce a spark between the plug gap. No spark. But if the plug is lifted from the earth by 0.030"+ a spark is generated between the plug and the earth. Why might this be? Its the same for all 6 plugs.

 

P.S. All was fine before I reset the timing. I know, dont fix what isnt broken.

 

P.P.S. The distributor advance / retard micrometer. Should there be any play? Mine has about a 1mm axial play.

 

 

Thanks

 

Steve

[poolboy]

Do you have the LT wires to the coil connected to the proper terminals. Feed on the + and distributor on the - ?

[Steve P]

Yes the feed is on the (+) and the dizzy is connected to the (-) at the coil.

 

When the plug is connected to the lead the current should flow thru the plug oore. So if current there is current in the plug case I guess that could be an indication that the isolation is not functioning properly? But to have the same fault in all 6 plugs. I think something else is afoot.

 

Cheers

 

Steve

[SuzanneH]

Hi Steve,

are you checking each plug in its own plug lead or are you using the the same lead for all plugs?

 

 

Roger

[88V8]

Do you have 12V at the coil+

And a spark at the points?

And is the little furry wire in the dizzy OK, are you sure it's OK.

 

What else did you do in the process of setting the timing, other than swinging the dizzy?

 

Btw, if you have electronic ignition then sparking the plugs outside the engine is usually a no-no, as in likely to knacker the ignition module.

 

Ivor

 

PPS not a problem, the baseplate position is maintained by the advance springs

[Steve P]

Roger,

All the plugs were tested with their leads.

 

Ivor,

I will check the voltage at the coil this evening.

There is a spark at the points.

How does one check the little fury wire?

 

Points were set at the heel of the cam to 0.014"

Timing set static using a lamp in a circuit from coil LT (-) to battery (+). Advance / retard micrometer set to middle. Timing marks at 24deg BTDC lamp on. Turn crankshaft to 11deg BTDC adjust dizzy clockwise until lamp goes out.

Checked TDC for cylinder 1 and rotor arm is in the approx location of HT lead 1. Leads are in the correct position anticlockwise 1,5,3,6,2,4.

 

Cheers

 

Steve

[John L]

There used to be a tool, a bit like a divider, that you could adjust and see if the spark jumped across it, I thought it came from Gunson but I didnt see it there, but they do offer this now. http://www.gunson.co.uk/item.aspx?cat=0&item=4834

I'm sure there are other items that you can put between the plug and the lead to see if you get a spark.

John

[Steve P]

Ivor,

Regarding coil voltage you said "Do you have 12V at the coil+"

 

 

I put a meter across the coil and get 6.5V when the starter is engaged. Is that what you meant?

 

Cheers

 

Steve

[88V8]

Ivor,

Regarding coil voltage you said "Do you have 12V at the coil+"

 

 

I put a meter across the coil and get 6.5V when the starter is engaged. Is that what you meant?

 

Not quite.

If you crank the engine by hand with the ignition on and find the feed voltage to the coil oscillates between 12V and 8V as the points open & close, you've got a ballast ignition. Which is fine so long as you have a ballast coil to go with it.

In that case, across the LT terminals (with the coil not connected to anything) you should have about 1 ohm resistance.

 

On the other hand, if you crank the engine by hand and see a steady 12V feed, that's a standard coil and should show about 3 ohm resistance.

 

A standard coil with a ballast feed will give a weak spark, they need to be matched.

 

But.... 6.5V with the starter energised means the battery is knackered or flat and it's no wonder you get no spark. Charge it up and try again tomorrow.

 

Doesn't explain why your ignition retiming should have made it so.... unless the ignition was left on for ages in which case the coil might be cooked....

 

If it ain't broke, fix it until it is... hoho

 

Ivor

[rpurchon]

Not quite.

If you crank the engine by hand with the ignition on and find the feed voltage to the coil oscillates between 12V and 8V as the points open & close, you've got a ballast ignition. Which is fine so long as you have a ballast coil to go with it.

In that case, across the LT terminals (with the coil not connected to anything) you should have about 1 ohm resistance.

 

On the other hand, if you crank the engine by hand and see a steady 12V feed, that's a standard coil and should show about 3 ohm resistance.

 

A standard coil with a ballast feed will give a weak spark, they need to be matched.

 

But.... 6.5V with the starter energised means the battery is knackered or flat and it's no wonder you get no spark. Charge it up and try again tomorrow.

 

Doesn't explain why your ignition retiming should have made it so.... unless the ignition was left on for ages in which case the coil might be cooked....

 

If it ain't broke, fix it until it is... hoho

 

Ivor

 

take dizzy cap of.pull lead out from coil to dizzy cap and rest near engine flick points open with your finger nail.

you should get a spark from coil.if so coil is ok and wires to it and in dizzy are ok

 

try the same using plug lead and a plug.

 

if points are sparking = duff condensor.condensors just like to die.or they seem to on my car.

could be bad spring contact dizzy cap to rotor arm.or rotor arm duff.

richard

Edited November 10, 2010 by rpurchon

[RogerH]

Steve,

I'm getting confused now!!!

Measure your battery voltage. It should be 12Volts or a bit more. If less then it needs a serious charge.

With the ignition ON. Place the positive probe of the meter on the +ve of the coil and the negative probe to earth. It should read 12Volts.

Place the positive probe on the -ve of the coild and the negative probe to earth.

The reading should be either 0V (breaker shorted - closed) or 12V (breaker open circuit - open).

 

This is for a non-ballast system.

If you have a ballast resistor then you will get a lower reading (8Vish) at the +ve coil tag.

 

 

Roger

[Steve P]

Evening Roger & Ivor,

Across the batter = 12.6V

Coil + to earth = 12.4V hand crank engine = 6.5V continue to crank = 12.4V

Coil + to - resistance 2.6 ohm

LT to HT resistance = 7570 ohm

 

The fluctuation in voltage when hand cranking suggests a ballast system is fitted.

The LT resistance suggests a non ballast coil is fitted.

So it looks like a ballast coil should be obtained and fitted.

 

Please can you explain the difference between ballast and non ballast.

 

Just for info. This current coil has been fitted to since 2002.

 

rpurchon,

Thanks for your post however I found it difficult to understand your instructions so have not tried your suggestion yet.

 

 

Cheers

 

Steve

[rpurchon]

Evening Roger & Ivor,

Across the batter = 12.6V

Coil + to earth = 12.4V hand crank engine = 6.5V continue to crank = 12.4V

Coil + to - resistance 2.6 ohm

LT to HT resistance = 7570 ohm

 

The fluctuation in voltage when hand cranking suggests a ballast system is fitted.

The LT resistance suggests a non ballast coil is fitted.

So it looks like a ballast coil should be obtained and fitted.

 

Please can you explain the difference between ballast and non ballast.

 

Just for info. This current coil has been fitted to since 2002.

 

rpurchon,

Thanks for your post however I found it difficult to understand your instructions so have not tried your suggestion yet.

 

 

Cheers

 

Steve

 

the high tension lead that comes from coil to dizzy cap.place on engine.then open the points with your finger.

you should get a big spark from the end of the high tension lead.

yep a picture would definatley be worth 1000 words.

richard

[poolboy]

Steve, I'll try to explain a ballasted ignition.

First, it's purpose is to make a cold engine easier to start.

The coil for a ballasted ignition is designed to provide 20k volts when fed 8 volts.

But when the starter is engaged the coil is fed 12 volts and the coil can provide more than 20k volts.

That's a very simplistic explanation, but it illustrates the principle.

Edited November 11, 2010 by poolboy

[88V8]

Coil + to earth = 12.4V hand crank engine = 6.5V continue to crank = 12.4V

Coil + to - resistance 2.6 ohm

The fluctuation in voltage when hand cranking suggests a ballast system is fitted.

The LT resistance suggests a non ballast coil is fitted.

So it looks like a ballast coil should be obtained and fitted.

 

Just for info. This current coil has been fitted to since 2002.

 

 

Yes, you are correct, there is a mismatch.

The standard coil will work with a ballast feed, if all is perfect, although the spark is relatively weak and it doesn't take much to extinguish it. Perhaps as Peter says your condenser is fatigued.

 

When I bought the car in 07, I inherited the same setup as you, been on there since about 03 unbeknown to DPO who had replaced what was probably the correct coil with a standard one, but it worked because at the same time he was running larger plug gaps and as it was a 'sports' coil it was capable of producing higher voltage so in a blundering fashion this sort of balanced out. Was OK for a few months then started to give me problems with plug wetting on startup, probably after I renewed the plugs and set a standard gap. Would go onto 5 cylinders, change the plug away we go until the next cold start. Took me quite a while to track down the cause. Months in fact.

 

The ballast coil is designed to work at lower voltage. They vary, but usually in the region of 6-8V. I have a ballast on The Shed, I think it's about 4.5V.

 

There's a ballast resistor inline with the coil LT feed that drops the voltage to the required level for running. Like Poolboy explained, this is bypassed during starting by taking a 12V feed direct from the starter so that the 8V coil gets 12V and gives a correspondingly high output to facilitate cold starts. The other benefit of a ballast setup is that the 8V running voltage causes less erosion of the points, so with a points setup it's a good arrangement.

My ballast was 8V. You measure 6.5V so you need a coil to match. 6.5V seems to be quite a common value - FIAT, various Yanks - if you go to a good motor factor I'm sure you will find one.

 

Ivor

[Steve P]

Problem solved.

 

It turned out to be the plugs. All six of them.

 

I fitted a new coil and condenser and tested a plug for a spark. Again when the plug was earthed no spark at the plug gap, but lift the plug away from earth and a spark jumped from the plug to earth. Right back to where I started. I remembered that I had some old plugs somewhere so tested with an old plug. Bingo, it sparked. Tested 6 old plugs and all sparked. Tested the existing plugs again & all 6 no spark. Fitted the old plugs and it fired up first time.

 

It has been an interesting trouble shooting process. Thanks to all who took the effort and patience to help me find a solution.

 

Cheers

 

Steve

[Kiwifrog]

I had the same thing a couple of years ago with a TR4 all the plugs comitted harakiri at the same time drove me nuts for a day. Is there something with new plugs that causes this ???

 

Cheers

 

Alan,

[88V8]

It turned out to be the plugs. All six of them.

 

Well.

That was a good 'find'. I'd have been tearing my hair out.

What plugs were they?

 

Ivor

[Steve P]

Ivor,

The plugs that failed were NGK BP6ES.

 

The old plugs that I found and fitted are also NGK BP6ES. They have been in a drawer in the kitchen for more than 4 years.

 

I just would'nt have thought that all 6 plugs would fail to spark. But you live and learn.

 

Cheers

 

Steve