CA18DET Info 808 idea Dissy to DIS 101

[Bruce Plecan]

-----Original Message-----
From: Geoff & Sue Richards <geoffsue at one.net.au>
To: diy_efi at efi332.eng.ohio-state.edu <diy_efi at efi332.eng.ohio-state.edu>
Date: Tuesday, November 17, 1998 4:42 AM
Subject: Re: CA18DET Info 808 idea



>>>well no nissan didnt use a 808 but I can give you a file that is a good
>>>thing for one ....but!......the delco dont like the cam/crank signal
>>>from the nissan.......but if you can overcome this problem then we can
>>>get things up and running without a problem...  :)
>>On some of the DIS to Dissy stuff they invert the signal so the timing
>>is wayyyy off, I'll bet that's it.
>>Bruce
>Hey Bruce
>if ya got time or the notion could ya explain this please
>Thanks
>Geoff


The following is not meant to be EE correct, but rather a working
explaination, for the ME, Mechanic types.  If any EE sees a violation
of the Prime Directive, please, feel to comment.
Like everything else the are numerous ways to do things, and I'm
sure there are exceptions to everything.  By and large this is how I
see things, are done with the gm ecms.
  On the DIS systems the sensors are Hall Effect Meaning they are
on or off.  On the Distributor systems they have a coil and reluctor
in the distributor.  This coil reluctor (cr) generates an A/C signal
The module shapes that into an on + off signal for the ecm/ign coil.
The reason for the / is that during crank the ecm is bypassed and
the module is firing the coil, without the ecm effecting the timing.
With a DIS, it to has a module but it's feed pulsating DC, so it
doesn't have to do that A/C to DC conversion.  But it has to synch
the coil firings.  Now, just to make things none interchangable or
help minimize tampering gm makes them just a touch different.
Like I said they both modules feed a pulsating DC to the ecm, and
it figures out when to fire the "ignition coil". 
5v_____            _____           _____            _____     
               I_____I          I_____I          I_____I           I_____
0v          A         B         A         B

In this little pattern make beleive that is what the ignition module
is feeding the ecm.  Notice at point A the voltage falls from 5 to
0,  and at B rises from 0 to 5v.  The program in the ecm/prom, 
can say OK, I'm gonna start the ignition event figuring at A or B.
One other little diddy, on the cr Distributor systems since it is 
an A/C voltage generating devise as you spin it faster it generates
a greater voltage, so the timing changes some.  On the dissy
type ecms/programs there is a correction for this.
    So if you take and try and run a dissy program with a DIS
car the timing will be way off.  If you even build a little inverter then
you will still be off by the advance correction in the program.  So
the proper way to do such things is find out the 2 (may actually 
be more) items to change in the program to get things right.
Or if you go the inverter route, BE WELL aware that the advance is
all wrong due to the correction.
Cheers
Bruce          With the winter coming on Doc and his pals are getting
                    the kitchen ready for hunting season, just nothing like
                    hunting from the kitchen.   Since the tornado went thru
                    saves opening windows, but it does get breezy..
                    Wonder if ya can buy replaement glass?.