8V Ignition Fault Diagnosing

[M@tt 77]

Last night i popped round Colins(Leet205) to have a look at his non starting 8v

 

Now its years since i've looked at a 8v so am pretty rusty on them, however we were getting fuel but no spark. He'd replaced the dizzy cap and rotor and ignition amplifier on but still no joy

 

My understanding of how the 8v ignition side of things work is this (hopefully some one can confirm or correct me )

 

The small pickup on the dizzy housing sends a signal to the ignition amplifier. The ignition amplifier then boosts this signal and inturn tells the coil when to fire and then obvoiously the coil sends voltage to the dizzy through the king lead and the appropriate sparkplug will fire caused by the rotor arm position within the dizzy cap.

 

so the things we checked were

 

• the ignition pickup lead was ok from the dizzy housing ie no broken wires
  
• the wire continuity between the ignitoin amplifier and the coil was OK
  
• there were the appropriate 12v at the ignition amp and the coil
  
• we tried connecting a spark plug direct to the king lead from the coil but still got no spark.
  
• we tried a spark plug touching the coil terminal incase the kinglead was fubared - still no spark
  

 

i've got a draper automotive multimeter and one of the features on it is dwell/rpm which bacically means you connect one of the probes to the negative side of the coil and the other to the negative terminal of the battery and it will report the engines RPM. Now when we connected this up and tried cranking the engine over we were getting about 180rpm reading which sounds about right but this inturn would indicate that the dizzy pick up and ignition amp appear to be working fine and its probably a knackered coil, as this signal will initially come from the dizzy pick up and then be boosted by the ignition amplifier. So as we were able to get this signal it appears the coil is getting it ok but just not firing

 

does that sound reasonable?

 

I've got a spare coil (condition unknown) he's going to try tonight so finger crossed it will sort it but just would appreciate anyone confirming/dismissing my understanding

[Anthony 1,003]

Sounds about right to me - if you're getting a negative pulse to the coil, and fuel is being injected, then that would suggest that the dizzy pickup and ignition amp are working. Try another coil on it and hopefully it should spring into life

[M@tt 77]

nice one cheers Anthony

[Leet205 48]

Cheers guys

[Leet205 48]

It was the coil!

[M@tt 77]

love it when a plan comes together