<VV> RE: Engine miss with rapid tach movement

[Larry Forman]

Hi Dan,
Just in case this does not solve it, it is time for some diagnostic tools 
to help isolate the problem.  One approach would be to take a dwell/tach 
meter and connect it in the dwell mode and run long cables up front so you 
can observe what is happening when the miss happens.  Another idea is to 
take a DVM and measure the voltage on the negative side of the coil, and 
observe the miss.  Then try the grounded side of the points, if you see the 
negative part varying incorrectly.  A third measurement point would be the 
positive terminal of the ignition coil.  The idea is to fault isolate so 
that you can determine if the points ground is intermittent, or maybe the 
negative coil/points lead grounding to the distributor intermittently, or 
something in the positive voltage supply side to the coil through the 
ballast resistor.  By taking measurements and relating those to the miss 
happening that might help fault isolate.

Regards,

Larry

At 09:21 PM 5/11/2004 -0700, Dan & Synde wrote:
>Well, now I'm really stumped!  I did find that when I put the distributer
>drive gear on that I failed to line up the mark on the gear with the rotor
>mark, It was 180* out.  Funny thing is, it ran the same when I lined it up.
>Here's what I swapped out and the problem still exists:
>Points, points wire, condenser, cap, rotor, coil.  I tried jumping the coil
>(+) directly to the battery momentarily to rule out the wiring harness, made
>no difference.  The miss is intermittant and it occurs at random.  Sometimes
>it is barely noticable and all but goes away.  It is accompanied by the tach
>needle moving, sometimes as much as 400-600 rpm but the engine itself isn't
>changing speed that rapidly.  It doesn't seem like this would be on the
>output side of the coil but since I already tried the cap and rotor, I may
>try plugs and plug wires.  If that doesn't fix it, then maybe the
>distributer itself is not as good as I think it is.
>
>Stumped
>
>Dan Kling
>1961 Greenbrier Deluxe, 4spd, 3.89
>1963 Spyder, 4spd, 3.55 Saginaw (engine in the works)