Ed Maher wrote this in a reply to another post about choosing a LB9 or anL69."If the exact shape of the advance curveconcerns you, you can run a regular distributor and still keep closed loop control on the carb by running the tach signal into the dist. reference to the ECM". Can anybody tell me how exactly to do this? Is there or caould there be a tech article written for doing it (ED)? I really like my CCCS setup, but I would love to have more control over my timing. Thanks!

Mark

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1986 IROC LG4 "Bone Stock" (for now)

 

Well, unfortunately i ran out of CCCS cars before i really felt like trying this, so i don't know if there are any snags that need to be worked around.
AFAIK, the tach signal is a square wave, 1 pulse per cylinder firing. AFAIK, the distributor reference is 1 pulse per cylinder firing. I do now know the voltage levels off-hand, but the tach signal may be 12V, and the dist. ref. may be expecting 5V. If thats the case, a simple voltage divider w/ 2 resistors will fix that.
Other than that, the ECM will have no idea that you aren't using it's timing signal.

So theres your tech article...someone needs to verify the tach and dist. reference voltage levels and simply hook it up. Yes it is that simple.
Actually, this will work on any of our cars, even TPI. None of our ECM do any real investigation into if it has control of the timing. But if you have an EFI car, kludging a timing curve still leaves you nowhere with the fuel cure so you might as welll burn PROMs and do it right.

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Ed Maher - Moderator @ The TPI & Carb Boards
92 Z28 Convertible - Quasar blue / Tan top
305 TPI A4 2.73 - 14.7 @ 93.6
Stock except ported plenum and dual cats
-=ICON Motorsports=-

- Definitely prototypes, high powered mutants of some kind. Too weird to live, too cool to die