Car Ignition Project - Adding Crank Trigger to L98 Engine - Using GM Vortec Parts -April '03

After making several hundred power tests, I wondered if the stock HEI distributor caused misfire or

inaccurate spark timing to the engine. I decided to experiment with a crank trigger system, to see if it gave

a more stable timing reference. The objective was to reduce observed 'spark scatter' in the data logs.

Result: The completed trigger works; has been tested up to 6,000 RPM; and reduced measured 'scatter'

in subsequent testing. No direct delta power measurements were made for the trigger change alone.

 Aftermarket triggers I reviewed for the project were costly & looked difficult to fit. Further research found these parts from the Vortec V8 truck engines ~'96. They were relatively inexpensive, mount internaly, and are readily available from any GM parts store.


 The Vortec crank position sensor signal was not a direct plug-in to the stock HEI module.

After some bench testing with the trusty O-Scope, I came up with a circuit to get the 4X crank reference pulse into the 727 ECM.


 After completing bench tests I went ahead and installed the parts in the Corvette.



 Nothing ever goes quite the way you expect. But with a little fitting and persuasion, all the parts went in and hooked up. A bit of creative cursing & it began to make sparks right where it was supposed to. It's been working very well after 6 months of in-car testing to date.

Acknowledgments: Parts & tech help were sourced from Superior Chevrolet.

Matt Sandine provided data amalysis of before & after 'spark scatter'.

Copyright 2003 DrJ all rights reserved. Home