[CA18DET Info 808 idea Dissy to DIS 101]

[tedscj at usa.net]

> 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          


Just to add more confusion,  I read a Chilton manual a while back that implied
that the signals were inverted.  The ign. module on a dizzy stays low and then
sends a high signal:
 _____[]______[]_____[]....
The DIS unit unit does the opposite:
_____  _____  _____
     []     []     [].....
I don't know if this is correct, or where they got thier info. but...

Also, I read in a post in the archives that using DIS code with a dizzy will
cause the car to run VERY BADLY,  which would lead me to believe that there is
more than just a few degrees difference between the two.

Also, I am running DIS on my car (originally used a dizzy)(also using a DIS
memcal, though).  And I am using a reluctor which is sensing some bolt heads
that I welded to one of my pulleys,  So DIS will work with reluctors.  The car
was running fine untill a couple of days ago when the ECM died, but I'm sure
that is unrelated.
Ted

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