ignition coil, voltage? HELP .

[crofty1]

Hi everyone,
Where does the voltage for the coil come fron and via what if anything. I need to know the exact test points as i think i may have a dirty contact (high resistance), I am assuming that it should recieve the full battery voltage, which then goes on to the ignition module to get switched or am i wrong ??.

[red griff 500]

I think you'll find that 12V supply is applied to the LT positive side and the negative side is switched between 0 and 12V. The switching is done by the ignition amplifier module which in turn gets its signal from an inductive (or magnetic, not sure which) sensor in the dissy.

Steve

>> Edited by red griff 500 on Tuesday 29th March 12:35

[crofty1]

Cheers Steve,
Do you happen to know whether the 12v on the LT side comes straight from the battery via the ignition ?

[steve-v8s]

Never actually checked this on the Griff but often the coil supply is fed via a resistor which is shorted out when the starter is cranking. As a result you may find a reduced voltage across the coil. The idea being that as the starter drags the supply down whilst it is engaged, the shorted out resistor returns the supply to the normal level ensuring a good solid spark for starting.

[GreenV8S]

On mine there is no ballast resistor and the coil sees battery voltage.

[crofty1]

Cheers guys but i really need to know the actual circuit, so that i can trace it back. Just for info i am only getting about 4.5v when cranking, thats why i need to know exactly where it comes from and via what if anything.

[old64er]

crofty1 said:

Cheers guys but i really need to know the actual circuit, so that i can trace it back. Just for info i am only getting about 4.5v when cranking, thats why i need to know exactly where it comes from and via what if anything.

I know if the fuse to the ecu goes pop, then you dont get voltage to the coil,fuel pump or starter solenoid.

Does this mean it gets fed from the ECU ???

Sorry but thats as much help as i can be

[soddy]

As far as I am aware it is simply an igniition 12V feeding the positive coil terminal. The neagtive terminal does the switching via the amplifier or dizzy depending on which system you have. If you are concerned about the voltage drop or are getting no spark then just run an ignition live direct to the positive coil terminal and see if that helps. The fact that the voltage is dropping may be indicative of a fault with the coil itself, I am not really sure. I run engines on a dyno regularly and only ever use an ignition live for the coil so it should be perfectly safe to try.

[crofty1]

Actually sounds like pretty good idea running a live feed from the ignition, i'll try it over the weekend !.

Cheers everybody !!

[spend]

Rev counter barfed?

[crofty1]

What do you mean spend ?? Srry if i'm being dull !.