HEI advance/retard

[steve ravet]

> Date: Thu, 2 Dec 1999 18:32:58 -0600
> From: "Ken Kelly" <ken73 at houston.rr.com>
> Subject: ECU's and HEI
> 
> Out of curiosity, I've been trying to think of ways to manage an engine by
> building my own ECU. Obviously, this is an arduous task, but one I'm not
> afraid to embark on.
> 
> I started off by figuring out the inputs and outputs and determined that I
> could do it with a few of the new high-speed BASIC Stamps from Parallax, but
> lately I'm beginning to wonder if it can't be done (easier) with an analog
> system - i.e. transistors/diodes/resistors/capacitors and have pots for
> tuning? I believe this is the way Holley does most of their systems aside
> from their 4D and 4Di systems.
> 
> My main big question, however, is HOW do the HEI electronic systems work?
> How does the computer adjust retard and advance? Is it a signal varied by
> voltage, frequency, or what? I'm at a total loss for this concept. The other
> parts of the engine I have figured out (injectors, MAP, TPS, O2, etc.) but I
> can't quite see how the timing works on the electronic versions of the HEI.
> (I see it has a seperate 4 wire interface?)

I once saw a diagram that showed how the timing relationship worked. 
Basically the pickup in the distributor tells the ECM where the rotor
is, the ECM sends a signal back that says fire the coil now.  the time
difference between the two is the advance.  There are plenty of details
like are the edges positive or negative that I don't know.  Bruce or
Shannen probably do.

I was hoping the diagram was on the ftp site, but I don't see it there
as .jpg, .bmp, or .pdf.  It someone remembers what I was talking about
and can supply a pointer to it that'd be great.  It looked like a scope
display of the timing signals, and was annotated with labels and arrows.

oh yeah, if you want to roll your own and like motorola assembly then
look at the efi332 list (efi332.eng.ohio-state.edu/efi332)

--steve


-- 
Steve Ravet
steve.ravet at arm.com
Advanced Risc Machines, Inc.
www.arm.com