Driving an HEI Module with other signals

[Mike Veldman]

Well, I lost a week working out at Sandia, but fortunately it rained here
in Oklahoma saturday so I was able to play with ignitions.

I put an HEI in the machine and spun it up with a scope attached to the
pickup coil, a standard HEI coil for load with the other channel of the
scope on the coil leads, a surface gap plug in the pressure chamber at
150lbs pressure and the sun ignition scope on the plug lead.

The pickup coil measured around 1k ohms which is in GM spec.  The voltage
output from the pickup was a constant 2vpp throughout the tested RPM range.
 I ran it up to 6k.  The waveshape out of the pickup was a somewhat
distorted sine with the peak voltage occuring initially then tapering off
sloppily.  The output of the module was constant with no noticable phase
shift throughout the tested RPM range.  The spark voltage output measured
on the plug lead averaged 25kv.

I hooked the Hickok function generator on the EFI bench up in place of the
pickup, set to 2vpp.  Using the formula frequency=number of
cylinders/120xRPM I ran the pulses up to 4kc to simulate 6000 RPM.  The
module performed the same.

Next I set the pulse gen for 5vpp output, a more usable number.  The module
performed ok but became very hot at high RPM, so hot I was unable to touch
the distributor body (I hadn't thought to have a temp probe on it), anyway
hotter than at 2vpp measured with my hand wrapped around the body. The
average spark voltage fell off to 17kv.

Next test was to try a set of points, so I put my handy MOPAR point type
distributor back in the machine used a coil ballast resistor and a 2.7v
zener (close as I had to 2v) to bias the points, and hooked the circuit in
place of the pickup coil.  Point gap was set at .016, dwell ran a constant
42.  Ran the test with and without the condenser up to 6k RPM, the waveshap
with the condenser more closely resembled the pickup, but not exactly.
Seemed to work ok. average spark voltage around 20kv.

The last test run was on a 7 wire HEI module feeding the computer lead with
5vpp signal and with the biased points without the condenser and a 5.1v
zener.  Both worked well and consistantly up to 6k RPM with an average
spark of 25kv with the function gen and 20kv with the points.  

In all of the tests with the points there was a good deal of spiking on the
scope, this may have been false triggering the module.

These tests were run without any mechanical or vacuum advance.

I think if I were planning to try to run an HEI module from a source other
than the pickup coil I'd use the 7pin module designed for computer drive.

That's it for these tests for today, it was fun, thanks for the idea.
vmike

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