Ign Advance on MR-2

[lance]

The 4AG engines use a trap door MAF and throttle position sensor for spark
timing.  The distributor generates Ne and Ge signals.  You are correct the
advance is entirely under the ECU's control, and there is no crank position
sensor per se.  Interestingly, the throttle position sensor can be
completely nonfunctional and the engine still runs without any SOTP
notification or MIL indicating that something is wrong.  If you forget to
reconnect it, the connector will get chewed up by the left drive axle.  Ask
me how I know.

Lance

-----Original Message-----
From: owner-diy_efi at diy-efi.org [mailto:owner-diy_efi at diy-efi.org]On
Behalf Of Les Newell
Sent: Saturday, August 11, 2001 02:46
To: diy_efi at diy-efi.org
Subject: Re: Ign Advance on MR-2


Hi Mike,
The ECU generates the advance/retard. The wheel with four teeth is to tell
the ECU when a piston is at TDC and the wheel with one tooth is to tell the
ECU when piston 1 is at TDC. From this information the ECU always knows the
crank position. There is probably a vacuum sensor attached to the manifold
somewhere. From this information and possibly data from other sensors the
ECU can work out the optimum timing.

Les


> Hi all.
>
> I'm still learning, so be gentle... <grin>
>
> I've got an '87 MR-2 and I'm trying to figure out how it effects timing
> advancement.  It has 2 wheels in the distributor, one with 4 teeth, the
> other with 1.  The single-toothed wheel is probably used to run the tach
and
> is slightly offset from the cooresponding tooth on the 4-tooth wheel.
>
> Now the teeth on the 4-tooth wheel pass by what looks like a magnetic
pickup
> and I presume that this gives the ECM the baseline timing.  However, it
also
> passes by what looks like a small magnet which is attached to the pickup.
>
> There are no vacuum lines, so it is not doing vacuum advance.  The only
> moving part is the shaft on which the two wheels move.
>
> So, my question is: How does this mechanism manage to advance the spark?
>
> Thanx for any input.
> Mike Diehl.
>
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