Re: Driving an HEI Module with other signals

["Programmer" <nwester@eidnet.org>]

1. Just one little warning about that 7 pin module, if you run anything
above stock compression and you have a knock sensor failure, it'll
advance timing to the point of no return.
2. The pattern from a GM pickup will always look more sawtoothed than an AC
pattern.
3. If you're going to run anything above 5500 RPM, I'd look into someone
elses HEI module.

Lyndon
-----Original Message-----
From: Mike Veldman <vmike@email.ceat.okstate.edu>
To: gmecm@diy-efi.org <gmecm@diy-efi.org>
Date: April 3, 2000 10:03 AM
Subject: Re: Driving an HEI Module with other signals


>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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