Ignition Problem

[Simon Quested]

Hi Guys 

Thanks for the help !

Sorry I should have put this info in my first post.... the ignition unit 
and hall effect dizzy are from a ford seirra 2L. I have no idea what's 
inside the black box and as it works ok except for the idle miss I 
don't really want to spend another US$90 to change it just to find 
out that the problem isn't with the box....

> That looks distinctly like the primary voltage waveform of a
> dwell-limiting style module, driving the primary. You can see the low side
> driver pulling the -Coil (that's I presume your -ve signal)

Yep

> You should be able to also trace the
> secondary waveform with a couple winds of wire around the plug wires, and
> when one of these shorties get's really arrested all the way back to
> ground, you should notice a very crummy HV spike, I would think.

I'll have my car at work tomorrow I'll have a look then.

> If I had to GUESS, I'd say something is breaking down intermittently as
> the primary voltage fly's back as the field collapses, either the module's
> output driver transistor, OR the protection diode, OR, since this signal
> (don't ask me WHY, it should be well clipped I'd think before going
> anywhere else) goes to your EFI stuff, the receiver on that end should
> ALSO be suspect as breaking down and avalanching toward gnd.

After l loosened the strap on my pointy hat I remembered that I had 
this problem before I efi'ed the engine. so it wont be that....

> Say more about the construction of this gizmo.

I 'd love to but all I know about it isn't much =-(

> The "transistorized IGN",
> does it indeed have a separate module?

Yep, Its a black box (epoxyed with a big heat sink on the back) It 
has 6 wires 1 for power, 1 for gnd, 1 for tach, 1 to the -ve of coil and 
3 to the dizzy.

> The other thing I would ask is, has this setup EVER idled OK? If not, I'd
> kinda tend to suspect the breakdown occuring elsewhere than the IGN
> drivers, cuz they shouldn't be weak right outta the box. 

It was 2nd hand from a wrecker.....to buy the unit new from ford is 
big money....(same price as an msd 6al)

> If that EFI unit
> wasn't meant to see the peaks on a primary IGN coil

It was designed to connect to the -ve of the coil but the actual efi 
unit is at least 8 years old.

Thanks again Gar
 
Simon



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  Simon Quested (E-mail questeds at lincoln.ac.nz)
  Computer Technician, Silicon Graphics & Windows NT Support
  Computing and Educational Resources
  LINCOLN UNIVERSITY OF NEW ZEALAND
  Phone (64)(03) 3252811 Ext. 8087
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http://www.lincoln.ac.nz/ccb/techs/simon/default.htm
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Madness takes its toll. Please have exact change.
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