Ign Advance on MR-2

[Chris Conlon]

At 01:15 AM 8/12/01 -0600, Diehl, Jeffrey wrote:

>We're thinking that as the tooth approaches the magnet, it induces a current
>which gets larger as the tooth approaches and smaller as it passes, forming
>(perhapse) a sin wave pattern.  

The reluctor is a very basic and common sort of device. There's lots
of information on it and circuits for it, even in the archives. Go to:

http:///www.national.com/design

and search for the LM1815 for a quick start. There was also a
Motorola part... the MC3334 perhaps, that accepted reluctor signals.

Faking a reluctor signal is not hard. A pulse wave of the proper
width, fed into a properly chosen transformer, is all you need.


>Now, if the ECU fires a spark plug when this current exceeds a fixed
>voltage, we could advance/retard the ignition timing by adding a bias
>voltage into this equation.  The fact that the pickup only has two wires

Don't go there. The ECU is looking for a zero crossing, since that's
the only signal event that occurs at a precise point with respect
to the bump passing the reluctor. Also the pulse is so short at
higher rpms that, even if it did work this way, you'd only get a few
microseconds of adjustability. Not nearly enough.

If you want to know *for sure* the relationship to TDC you pretty
much have to crank the engine over carefully by hand with the dizzy
half apart, and see what crosses where, when. Most likely you'll
find that the NE pulses are X degrees before TDC, and the G pulse
is some degrees before one of the NE pulses. This lets the ECU
start counting when it sees the NE pulse, then delay for some
calculated time, then fire that cylinder.

I'd be *very* surprised if the 87NA ECU is full analog. Have you
opened it up? The later ECUs apparently use some kind of 8051
derivative, and I bet yours does too.

Really I think the first place to start is with circuits that deal
with reluctor signals. I think that understanding how they are
typically used will clear up what the ECU is doing, and how. Try
searching the major semiconductor makers for relevant parts. MSD
even makes a box (can't find the p/n) that takes reluctor signals
and outputs Hall-effect style pulses, which may be helpful when
it comes time to actually fake out the ECU.


   Chris C.

----------------------------------------------------------------------------
To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org