9V at coil only !!!

[e635815]

Hello folks,

Here is my issue on a 2000 Chimaera 500.
The battery is fine and fully charged (reads 12,8 volts after a night on charge).
The starter motor is new (and I mean litteraly new: I've installed it yesterday) and cranks the engine just fine.
But it won't start at all...
And this is what I have found:
With ignition on, I can measure 12,xxV at the coil. When I crank the engine, voltage drops to 9V. And this isn't enough to generate a spark anymore.

Does someone have a clue why voltage is droping and what can be done against it?
Thanks
Philippe

[darkcat]

could it be a bad earth to th chassis??

apparently very common, im sure someone can tell you where the negative is atached...

[blitzracing]

9 volts is correct, as its a ballasted coil, it will be 12 volts when the ignition amp is open circuit,(Like points do) which it is when the engine is not turning. The ignition amp only goes short circuit (like closing the points) when the magnetic rotor lines up with the pickup and is moving. At this point the voltage will drop to around 9 volts. You can check the coil by unplugging the ignition amp, and putting a wire from the -ve side of the coil and touching it on the chassis. You should ge a spark that can jump about 1.5 cm from the king lead to ground.

Edited by blitzracing on Sunday 28th March 17:56

[e635815]

I don't think 9V is right for the coil. When I unplug the main lead from the dizzy cap and approach it to the engine, I get no spark when cranking said engine.
It should spark 8 times per rev, shouldn't it?
What I can see is only one or two sparks at the very start of the cranking and then nothing...

[blitzracing]

It works like this. In normal operation, without the engine turning you will see 12 volts on the positive side of the coil (and the negative for that matter). This is because there is no voltage drop across the ballast wire to the coil as no current is being drawn as the coil is not being switched on by the ignition amp. When the engine starts to turn on the starter motor, the ballast wire is by passed so the coil gets the full voltages from the battery, but this may well be as low as 9 volts if the starter is drawing several hundered amps at the same time. The coil is designed to run at around 10 volts to give a full spark. Once the car has started, the supply to the coil is once more ballasted so the voltage is limited again. Do the check I mentioned previouly, you should see 12 volts with the coil un grounded and about 9-10 volts when you ground the negative side with the wire. You should also get a good spark when you disconnect the wire from ground. If you dont the coil is knackered, if you do suspect the ignition amp or trigger.