the ignition live goes to one side of the coil but when i test the other side of the coil (the one with the green wire from the ecu) it also gives out an ignition live, even when i crank the engine. is this right or is my coil fooked?

 

it earths via the plugs (hence the spark)

 

ahh right, so the coil is ok?

 

Yes.

The side of the coil marked up -VE should flash with a test lamp attached to it (wire still connected to the coil) when you crank the engine over. If it doesn't, it's not being triggered and is more than likely to be distributor or wiring related.

When it flashes off, the coil has been earthed (for a breif second) causing a collapse of the field within the coil creating the spark.

 

fezzie2 sorry i never answered this for ya i have a habit of reading PM's and not responding for a while

 

As daz c says.
The coil is just that a coil of wrapped around another coil of wire wire.
It will of course be positve until it receives the opposing current on other end negative, this then generates a strong magnetically induced current in seconday(inner windings HT), when the negative is taken away by ignition circuit the filed induced voltage seeks a path to earth through the leads/plugs, all happens very quickly.
The ration of turns of primary and secondary coils dictates the voltage output as input voltage fixed 12v.
tabetha

 

Other end is the constant +12V (black wire) and the other is the ignition live (green wire). At crank speed (~200rpm) a spark is given each 300ms. When you compare this with a common coil dwell time of ~5ms, you would see that at average the ignition live is only a few tenths of a volt short of the battery voltage.

tabetha, the coil ratio is not that important as it first seems. Remember that several tens of kilovolts are easily acchieved even with common coil ratios of less than 100.

 

if u have enough primary voltage!

 

Remembe that the primary is always operated by only 12V. How much voltage can be seen momentarily when the 12V circuit is broken depends on the primary coil inductance and it's resistance as the primary winding will exhibit a voltage of U=L*di/dt.

 

The green wire isn't ignition live. The black wire is ignition live. The reason why you will find voltage on the green wire is because it's not been earthed yet.

 

Pardon my english, live was a badly chosen word. I meant the green one anyhow whatever you call it. My point was that at cranking speed it's earthed for such a small amount of time each time that a multimeter won't read anything.