Rotary Engines (was "SDS EM-2??????")

[Andrew Ghali]

On Sun, 12 Jul 1998 15:55:04 -0400, "Bruce Plecan" <nacelp at bright.net> wrote:
>
>>>I'm thinking in particular about the ECU of an 87 RX-7, but there
>>>must be huge numbers of cars out there with similar, L-Jet derived
>>>EFI systems that would be in the same boat.
>
>Trouble is the lack of players.  Before I began 101 I asked several
>times for what to pick on.  Had like 2 votes for ford, and zero for
>Bosch, Magdklafmf Marelli, Mazda, Toyota, Nissan.  The winner
>was gm that had a couple dozen votes.
>    If I was working on an EFI engine, I'd look at all my options.
>Forgive me since it's been since 84 that I did much rx7 work,
>but how many degrees of crankshaft revolution is there between
>rotor ignition firing,  are the injectors for an independent runner
>manifold.  Do they still use 2 plugs per rotor, one several degrees late?.
>    Based on those answers I'd look for a easy to replace/explore
>ecm, and use that.

Bruce:

Sorry it'ts taken so long to get back to you, I put this on the back burner
while things went non-linear on the list.  Now to answer your questions,
not necessarily in any particular order.  When you started work on Programming
1O1, I was new on the list, and I realized that the rotary contingent was a
small, quiet minority.  I hoped to learn from your _method_ how to eventually
attack Mazda's Nippondenso ECU box.  So instead of voting, I was content to
let the people who knew what they were doing choose what they saw as best
and follow along.

About the rotary engine, please forgive me if I am insulting you with too
basic information.  Most Mazda rotaries (i.e. almost all) have 2 rotors
(13B or the earlier 12A) not counting triple rotor Japan-only and racing
engines (20B and 20G), or even the few 4 rotor beasts you won't find on a
street.  According to my documentation, you get one rotation of a rotor per
3 turns of the eccentric shaft (piston engine fans read: crankshaft) with
3 faces per rotor, which give you 120 deg between pulses per rotor or 180
deg per turn of the e-shaft.  Due to the long, narrow cumbustion geometry,
there are two plugs per rotor - the leading and trailing plugs.  The trailing
plugs are above the leading plugs; roughly at 2 o'clock while the leading
plugs are at 4 o'clock.  Trailing plugs are fired by individual ignition
coils (in the 13B-REW of the 3rd gen twin turbo) or ignitors (earlier 13B),
while the leading plugs are tied to a single coil or ignitor as waste fire.
Timing at idle is fixed at 5 deg ATDC leading and 20 deg ATDC trailing, while
at crank it is fixed at 5 deg BTDC (both?), and variable everywhere else.

The fuel system seems to be on of the greatest variables between differnt
motor versions; the following is relevant directly to the 13B-REW and
partially to earlier 13B's.  Fuel is delivered through two fuel injectors per
rotor; the primary injects almost right into the intake port and runs alone
at low RPM.  At around 3K, the secondary injectors come online further up
in the intake runners.  During deceleration, fuel is cut to the rear rotor
or both, depending on TPS and RPM.  At overboost, fuel is cut to the rear
rotor.

The 13B-REW is an incredibly complex engine, as you would readily notice from
the Rx-7 mailing list.  Almost daily people report puzzling problems that
Mazda dealers can rarely fathom without resorting to pulling the engine.
As many people have found out: you don't want some grease monkey that can't
even diagnose a problem properly to be replacing your engine.  There are 16
major solenoid valves on the motor, some on/off, some PWM in addition to the
3 seperately timed ignition signals (4 would be better, no?) and 4 seperate
fuel injector signals.  The Service Highlights manual lists 12 zones of
operation based on throttle/MAP vs. RPM.  I doubt that there are any stock
ECU's that could even support the I/O requirements for the 13B-REW, much
less have any code that could be used directly.  Please correct me if I am
mistaken.  I wish it were not so; if you look at the pricing for after-
market ECU's, the rotaries are by far the most expensive (probably partly
due to the rarity of the engines)!

For my '87, which is non-turbo, I'd just like to understand its modes of
operation.  Someday, I'll think about putting a turbo engine into it but
that's a long way away.

Andrew