Re: Idle / Ignition system

["drdhdmd" <doctorDHD@xxxx>]

Bill I think you missed my question or perhaps I wasn't clear 
enough. I know that the spark is produced when the points, or in the 
DMC-12's case, the ignition ECU "opens" the circuit and the magnetic 
field collapses... 

My questions are:

1)What is casuing the apparently large variation of this primary 
induced voltage as seen on the WS, white/slate wire of the coil from 
one firing to the next? 

2) Why does the tach jump when it sees this extra voltage?

3) Why does this happen only at RPMs less than 1400?

4) Is this normal DMC-12 operation?

5) What can I do to diagnose the problem.

Dave & 6530

--- In dmcnews@xxxxxxxxxxxxxxx, "content22207" <brobertson@xxxx> 
wrote:
> Actually what you're seeing is the ignition at work. Whenever the 
coil
> loses its ground (controlled by ignition module), high tension 
current
> builds up lightning fast, then is discharged to a spark plug as 
rotor
> passes its terminal. If the coil were grounded all the time, no
> current would ever build up.
> 
> Ignition module and tachometer take their signal from small wire
> (blue? I'm at work and can't remember color) that passes from
> distributor to compartment behind driver seat.
> 
> Take it easy grabbing ignition wires. While coil ground is only 12
> volts, HT wires can be as much as 100,000 on newer cars. Even stock
> DeLo is 18,000 or so (which I highly recommend bumping up at least 
to
> 40,000).
> 
> Bill Robertson
> #5939
> 
> >--- In dmcnews@xxxxxxxxxxxxxxx, doctorDHD@xxxx wrote:
> > OK, while playing around with the ignition / idle system of 6530 I
> noted 
> > something very interesting. As I previous stated, the tachometer
> makes small 
> > jumps upward, intermittently. I accidentally touched the wire 
that
> goes to the 
> > negative side of the ignition coil primary circuit (color WS) and
> noted that I 
> > was getting intermittent shocks. These shocks were at the same 
time
> that the 
> > tach jumped! When I connected a small neon bulb (i.e., an NE-2 
for you 
> > engineering types), the bulb would blink intermittently along with
> the jumping of the 
> > tach. (Hey I got fed up with getting jolted so I substituted the 
bulb 
> > instead.) Remember that the engine RPM is NOT jumping only the 
tach
> is. I suppose 
> > the tach is getting these voltage spikes and that is why it is
> jumping and maybe 
> > these spikes are affecting the idle ECU controller. The spike 
occur
> only at 
> > low RPM up to about 1400 rpm.
> > 
> > Does anyone have a clue as to what to do next?
> > 
> > Dave & 6530 thank you...
> > 
> > 
> > [Non-text portions of this message have been removed]