[s-cars] coil diagnosing

[Rich Assarabowski]

Paul:

The only way to test them is with an insulation resistance tester often
called a "Megger" (brand name).  Basically you're looking for a low
resistance path to ground (insulation breakdown) which occurs when you apply
high voltage.  You can't do it with an plain old ohmmeter since an ohmmeter
only applies 9V from it's internal battery instead of the 1000's of volts
you need for insulation to break down.  The dielectric testers apply a high
voltage and they measure resistance to ground at these conditions.  

Shops which repair electric motors or alternators use these.  Too bad, I had
one of them available in my previous work place...  You might try taking the
cover with all 5 coil packs to a shop (there's an automotive electrical
place on Main St. in E. Hartford) and see if they're willing to do it.  You
have to be careful in how they test it, as you can also ***damage***
insulation if you don't do it right :(   Without knowing the voltage rating
of these coils it's a bit of a risk...

Only other way is trial and error one by one (ugh!).  The bad one I pulled
out in mine looked no different than all the others, the shorts are all
internal.  Oh, and it checks out fine with an ohmmeter.  FWIW mine was the
#5 coil.  It was easy to find since it was missing at idle (I used the "pull
the injector" trick).

-- Rich A.
   '92 & '93 S4

>Isn't there an impedance or conductivity or whatever test to try as well?
Can someone handhold me here?  I promise to 
>call you in the morning...
>
>Also of note, or maybe not...  all 5 coils had a slight bluish char on one
side, and #4 had it on both sides.  Does this >mean anything?  I know many
here seem to report #4 failure being most prevalent.  149,997 on them.