5VDC For Timing When Running...Later Version Maybe?

[69 1/2 Six Pack Bee]

I know I am going to have to run a relay for a 5-volt supply for timing control when using my HEI. Are later rev's of the code going to make it possible to pull this source from the CPU instead of an external source?

Thanx,
Bud

[Bernard Fife]

Bud,

You don't HAVE to use a relay with the HEI, you will soon be able to use the 'trigger return' cranking timing mode instead.

This instructs MS-II to fire the coil based entirely on the input from the module, and not do any calculations, etc., essentially mimicing the HEI modules bypass mode. (This is useful because the crankshaft speed itself is quite variable during cranking, so that the predictions of a 'next cylinder' algorithm can be quite wrong.)

There were some issues in the code that prevented the easy use of this previously (the code switched from the falling edge of the input signal to trigger on the rising edge). This is what the HEI module does in 'limp mode' in order to provide rpm dependent timing, but isn't especially useful for our needs. However Al has sorted this in the beta version of the 2.1 code (not yet released), and once it is tested it should be a good substitute for the 'bypass' mode of the HEI module.

Lance.

[WopOnTour]

Hi Lance
Catching up on some old threads and came across this one
Why is having different code for bypass control neccessary?
(By different I mean from what MSnS-E already uses by triggering a 5V output when rpm>400- mimicing the native GM logic)
Are you trying to allow the MS to control timing during cranking??
AFAIK this would be impossible with a GM module as the EST circuit is automatically attenuated to ground (within the module) whenever Bypass is less than 5V and allowing internal switching within the module itself to trigger the coil/s directly based on the raw VR input.

I guess I would like to understand why base timing in bypass mode (cranking) isnt "good enough" and neccesitates a code change. The MSnS-E code changes that James Cortina made last spring (at my request) to initiate the 5V on the bypass circuit using LED19 output function flawlessly IMO.
Am I missing something??

Regards
WopOnTour

[Bernard Fife]

Am I missing something??

Yes, I think so.

Lance.

[WopOnTour]

Errr I mean LED19
So the MSII is capable of controlling timing somehow during cranking then? (rpm<400)
How can this be?

The EST circuit is shunted through a resistance to ground when in Bypass mode (0V on Bypass) so any timing signal on the EST cicuit would have no affect

The only diagram I have handy to support this is for the DIS IGN on the Northstar engine, but pretty much any OBD1 module would look the same if you scoped Bypass and EST
What am I missing if you dont mind?
WOT

[Bernard Fife]

WOT,

The original poster was asking about not using the bypass relay (or another bypass signal). If you leave 5 Volts on the bypass pin at all times, then MS-II has control over the timing, even during cranking. By having it send a 'trigger return' output to the module, you get essentially the same timing as you would in bypass mode, but without the relay and without using up a processor output.

Lance.

[WopOnTour]

WOT,

The original poster was asking about not using the bypass relay (or another bypass signal). If you leave 5 Volts on the bypass pin at all times, then MS-II has control over the timing, even during cranking. By having it send a 'trigger return' output to the module, you get essentially the same timing as you would in bypass mode, but without the relay and without using up a processor output.

Lance.

Thanks Lance
Would you send this trigger return on the EST circuit, or the Bypass??
I assume you mean on EST so that when below an RPM threshold basically EST will have no effect because there will be no trigger signal (return only) and then the module will trigger in it's bypass state. But you will still need to keep 5V on the bypass don't you? This will work even while maintaining 5V on the bypass? That's great, so like you said the goal was to eliminate the need for a seperate "switching" bypass output? That's sweet
It was this statement that got me in right field

This instructs MS-II to fire the coil based entirely on the input from the module, and not do any calculations, etc., essentially mimicing the HEI modules bypass mode. Lance.

Because I couldnt see how the MSII would be able to fire anything with the module in bypass mode, but if the module has already switched (5V on Bypass) basically the return mode will just trigger the module at the fixed rising edge resulting in essentially base timing. Does this sound correct?Normally in bypass mode there will be a small amount of advance that occurs (from within the module) as RPM increases , will the trigger return technique you decribe do this as well? or will it be fixed timing?
Thanks for the clarification
WOT

[jsmcortina]

Lance is saying that the MS2 code will have full control of the HEI7 module. The "bypass" pin will always be set so that the CPU has control.

The EST signal sent back will mimic the REF signal. This should result in the same behaviour as if the bypass pin were used, but saving the extra wiring.

Why didn't GM do that?

James

[WopOnTour]

Why didn't GM do that?

That's a good question- guess they had tons of outputs to spare?
I was always under the impression the engine wouldnt even start if there was a short to voltage on the bypass circuit during cranking.In fact the "CRANKS BUT WONT START" diagnostic charts in the GM manuals of that era, had you disconnect the "set timing" (bypass) connector to insure the ignition was 100% IC module controlled. But this may have been due to some failsafe funtion when the DTC42 is set when the incorrect voltage state is detected on the bypass. Of course no GM module, No DTC.

Ingenious really to eliminate it
I'll definately be messing with that on my DIS>MS mockups
Thanks to both of you for the clarification
WopOnTour

[WopOnTour]

Lance is saying that the MS2 code will have full control of the HEI7 module. The "bypass" pin will always be set so that the CPU has control. James

James and Lance, can this return code work for the PCB Rev3 boards and MSnS-E as well?If not I presuming I will still need to use the LED circuits for Bypass and Ignition Control for GM DIS? (Just about to do my first Rev3 board and want to make sure I have all my asumptions straight)

I'm a bit confused how the Rev 3 board affects the MSnS-E options. I did a search of all YOUR posts and didnt come up with anyhing that explains how the LED17 and LED19 mods have been implemented for the Rev 3.

Do they still work as with 2.2? Although the LED numbering is different that shouldnt make any difference correct?
LeD17 is now LeD14 and LeD19 is now LeD16
AND
Instead of X11(25) and X12(27) they are now shown in the silkscreen as IAC1A and IAC1B.

Certainly the X/IAC pads would work, but should I consider using, or advising others to use the SPARES instead? Since IAC terminals are there for MS2 , future upgrading would be easier if the IAC terminals were left unused IMO. So assuming I used the spares for LED14 and LED16, are there any existing conventions or general recommendations on WHICH of the spare terminals to use for these?

I guess I'm asking if the spares have already been spoken for in other MSnS-E mods, and if so which? OR is it the wild west and users can just go ahead and use any of the unused DB37 terminals for whatever they wish.

What is your opinions
Thanks
WopOnTour