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Determining rising vs falling edge on Mopar dizzy
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Author:  Sam Powell [ Fri Nov 05, 2010 4:59 am ]
Post subject:  Determining rising vs falling edge on Mopar dizzy
I think I am slowly coming up from "Special needs" to "remedial" in the EFI department. :wink: I am getting ready to switch over from the square wave tach signal of the MSD box to the sine wave out put of the Mopar dizzy as a first step in getting timing control switched over to the ECU.

Does anybody know the orientation of the Mopar dizzy, and the designed read in their ignition box? One lead is white, and one is black, which would suggest that the black one goes to ground and the other to the ECU pick up contact on the terminal strip.

I finally understand the terms rising edge vs falling edge in ignition trigger design,but don't have the equipment to determine it, which would be an oscilloscope. With a sign wave, the voltage crosses from + to - twice in a cycle and one edge is sharp and clear, and one edge is not so well defined. Apparently it is the one on the front edge is that is better defined. You would think that after a full cycle it would not make any difference, but somehow the circuit knows, and reversing the leads on the dizzy changes the profile so that if the rising edge was the sharp one before, the sharp edge now becomes the falling edge with the leads reversed. And, you must select which edge you wish to sample in the tuning soft ware. It is a simple choice of rising edge vs falling edge. It will run if the wrong one is selected, but not as well. And the timing will not be reliable.

The mega manual says to watch the timing and see if it advances correctly when the engine is revved, and if it is stable at idle. . If the timing is unstable, or backwards from the table, then swap the leads from the dizzy.

However, I plan on having the timing curved locked out, which is an option used for setting the timing. And, I intend to leave it that way until I get a locked distributor, and simply stick with the mechanical curve for the time being. Like I said this is the first step towards getting switched over to ECU timing control. If I can get it running with this distributor and dizzy, then I will know the wiring is good,and swapping in the locked distributor will leave only one variable to trouble shoot if it does not start.

When I switched to the ACcel ECU a few years back, I changed the ECU, wiring and distributor all at the same time. I initially could not get it to start at all, and had too many variable to trouble shoot. The ignition pick up was always suspect. Initially the laptop gauges showed no RPM, which indicated there was no read from the dizzy. But I did not know if tht was my wiring, the ECU or the dizzy. So, I want to avoid that nightmare again if at all possible. Change one thing at a time!

So to repeat the question, does anybody know the orientation of the Mopar dizzy, and the designed read in their ignition box? One lead is white, and one is black, which would suggest that the black one goes to ground and the other to the ECU pick up contact on the terminal strip. Does anyone know if this is the case? Is the white lead the signal, and black one ground, and should I be selecting rising edge in the laptop tuning software? The conventional wisdom is, if it does not run well, switch the leads. I would like something better if possible.

Sam
Author:  emsvitil [ Fri Nov 05, 2010 3:08 pm ]
Post subject: 
Does this help any?

http://www.diyautotune.com/tech_article ... engine.htm
Author:  emsvitil [ Fri Nov 05, 2010 4:01 pm ]
Post subject: 
http://www.megamanual.com/ms2/pickups.htm
Author:  Sam Powell [ Fri Nov 05, 2010 7:07 pm ]
Post subject: 
Thanks E. That first Article I do not have. That is a big help. I had the second one printed out already. It is a help to know which wire on the Mopar pick up is positive.

I think I am about to give this a try. I work tomorrow. Maybe Sunday afternoon.

Sam
Author:  Sam Powell [ Sat Nov 06, 2010 5:33 am ]
Post subject: 
I have read and re-read and re-read the section on VR pickup with MS II and I still lack clarity surrounding the diagram in the manual that shows the sine wave dropping through zero on the rapid, or quick side, and yet calls this "rising edge". It seems backwards to me. Why isn't that falling edge. This diagram is a few screens down from the top of the link in E's second posting. http://www.megamanual.com/ms2/pickups.htm

And, it shows the opposite where the sine wave is rising rapidly and falling slowly, and the diagram calls this the "falling edge".

I am kind of bewlidered by this. And more importantly, I still am left unsure of whether to chose falling edge or rising edge when I wire the Mopar pickup leads with + going to the tach pick up.

It says in the first article that E linked to chose falling edge, but this is with the pick up leads being wired through a GM HEI module. And there is no direct connection from the Mopar leads to the MS relay board. I am using an MSD box, and my coil trigger wire will go to the white wire on the MSD. I don't know if the HEI module changes anything.

I feel like I am back in college. I can just imagine the students in the room raising their hands and saying, "I don't get it", and having the teacher clear it all up up with a few comments. And then the light bulbs going on. I need a teacher right now. Thanks if you are out there.

Sam
Author:  Sam Powell [ Sat Nov 06, 2010 12:34 pm ]
Post subject: 
The Mega Manual shows wiring for the MSD box to requires an HEI module, presumably to convert the sine wave to a square wave. However, this is version 2.2, and I have the version 3.57 board, which I think has the circuit built in for this function. So, again I am a little confused. TMI at this point. A little confused he says? :wink: One of the confusing things about the Mega manual now is that there have been so many versions of MEga Squirt put out there that you have to be very careful about the information you read, and make certain it is for what you are using.

So, does anybody out there know if the MS II 3.57 has the circuit for the Mopar pick up built into it? When I asked Matt for info about hooking this up, he did mention the need for an HEI module. So, I assume it is not needed. But, if I don't hear from some one here who knows for sure, I will probably wait another couple of days to hook things up and try it.

Sam
Author:  emsvitil [ Sat Nov 06, 2010 6:46 pm ]
Post subject: 
I think I'd go with this from the 2nd link:
Quote:
2.

(Easiest) Go ahead and set the delay tooth, trigger edge and trigger offset under the assumption that the zero crossing trigger will occur when the centers of the sensor and tooth are aligned and this will be what the ECU sees. Then check with a timing light, and if things are not right (i.e. if the timing is off by a long ways, timing changes with engine speed beyond what the timing table dictates, and the timing is 'jittery', you can reverse the polarity on the VR sensor wires (see above), or the change the trigger edge using the software input.
Author:  Sam Powell [ Sat Nov 06, 2010 7:35 pm ]
Post subject: 
Yeah, I think you are right. I know the timing is currently set at 10 BTDC initial. If I read this right, if things are wired correctly, it should still set at 10 BTDC with the timing locked out in the software. And, (if I am reading it right), if I am picking up the wrong edge, the timing will change a fair amount. I may not be able to see the error in the timing until I unlock the timing map, and let the timing float with the map.

For all I know I do not currently have the ideal orientation of the pick up wires with regard to the MSD. It ran when I hooked it up, and I never tried it the other way to see if it got better or worse.

Sam
Author:  Sam Powell [ Sun Nov 07, 2010 2:34 pm ]
Post subject: 
Well, I wired things the way Matt told me to, which is pin s-5 to the white wire on the MSD, and the pickup wires to the Tach tap on the relay box and ground. NO SPARK. It will not start. When I hook it back up the original way,it starts and runs. This would be with the tach output from the MSD to the tach connection on the relay box, and with the dist. pickup wires to the purple and orange wires on the MSD.

I chose all the settings in the hardware the way Matt said to do it. One of two things could be wrong. Or maybe both could be.

1. For some reason the ECU is not reading the VR output. I have chosen Basic Trigger for the pick up, since none of the others seem to make any sense.

2. The white wire on the MSD box is not reliable for some reason. Maybe that circuit is corrupted in some way.

I will send an SOS to Matt, and come up with plan B. I did not think to see if the laptop dash was showing a crank RPM, which is a vital piece of info. I will have to rewire it, and look at that.

My suspicions lie with the MSD box right now. Any ideas? Has anyone had an MSD box to south in just this way, leaving the rest of the circuits OK?

It is possible to wire this up with a GM HEI module as well. This project is on hold as well. So far it works great when I wire it just like the MS I but it fails every step beyond that. The thing that is frustrating is that there are now so many options as far as codes go. You must ignore about 3/4ths of what the Manual says since it is not for the specific code variation you might be using.

Back to special needs class. I think I will go watch a football game, or maybe practice the piano.

Sam
Author:  emsvitil [ Sun Nov 07, 2010 3:49 pm ]
Post subject: 
Doesn't sound like you're using the correct wires (I'm assuming a 6A)

White:
This wire is used to connect to the points, electronic ignition amplifier output or to the Yellow wire of an MSD Timing Accessory. When this wire is used, the Magnetic Pickup connector is not used.

Orange:
Connects to the positive (+) terminal of the coil.
This is the only wire that makes electrical contact with the coil positive
terminal.

Black (small):
Connects to the negative (-) terminal of the coil.
This is the only wire that makes electrical contact with the coil negative
terminal.

Violet
and Green
(Magnetic
Pickup
Connector:
These wires are routed together in one harness to form the Magnetic Pickup
connector. The connector plugs directly into an MSD Distributor or Crank
Trigger. It will also connect to factory magnetic pickups or other aftermarket
pickups. The Violet wire is positive (+) and the Green is negative (-). When
these wires are used, the White wire is not.

Red(small):
Connects to a switched 12 volt source. Such as the ignition key or switch.


TACH output is a spade terminal on the box..........
Author:  emsvitil [ Sun Nov 07, 2010 3:50 pm ]
Post subject: 
http://static.summitracing.com/global/i ... m28645.pdf
Author:  Sam Powell [ Mon Nov 08, 2010 4:50 am ]
Post subject: 
E, when you control timing with the ECU, the VR signal gets routed through the ECU and the white wire on the box is then fed by a signal from the ECU. The wiring as I described is wired correctly according to the Manual, except, they do not have the latest version in there. My ECU which is called msextra version 3.57 is new. In the older MS II's they used an HEI module to convert the VR signal to a square wave between the ECU and the distributor.

Since Matt told me to hook the VR output directly to the ECU , I am assuming that there is a circuit built into 3.57 to do the square wave conversion. However, I made no choice to change the pick up style in the tuning software. If this conversion circuit is indeed in the 3.57, it seems I would have to chose it somewhere, but I could find no such choice. There are about 6 things you must make choices on concerning ignition trigger, and I might have any one of them wrong. Although I selected different things as I was cranking to see if I could perhaps stumble upon something that was right.

Now here is a crazy idea. The 3.57 also is supposed to have a built in coil driver, although they warn you against hooking this up wrong as you can burn something out if you do so. (It seems to me all it has to do is make and break ground for the negative coil terminal). However, back to the point, if the MSD box converts the VR pickup to a square wave via the tach signal, which is what the ECU reads in the working configuratiion, why could you not, at least temporarily, leave the MSD box in as the VR/square wave signal conversion box and run the coil directly from the ECU as is shown in this article? http://www.diyautotune.com/tech_article ... 1-nova.htm


IN this way the ECU would see its square wave which it clearly sees now, and responds to reliably. Can you hook up an MSD box, and fire it without a coil hooked up to it without burning it out? Eventually I would replace the MSD box with another square wave conversion of some kind. A GM HEI would be the easiest perhaps.

There is more diagnostic to do here now with what I have. I am off to the garage to wire it back up the way it would not work, and check the laptop tach to see if the ECU is seeing a signal at all. I should have done this last night. Football and piano seemed the easier route to go then.


Sam
Author:  emsvitil [ Mon Nov 08, 2010 1:38 pm ]
Post subject: 
I'm not sure the TACH out from the MSD is a square wave.

I think all it was designed to do was drive a tach, so it might be any shape...........
Author:  Sam Powell [ Mon Nov 08, 2010 7:16 pm ]
Post subject: 
How can we find out what the tach output is on the MSD bax? Something made me think it was a square wave. Whatever it is, the ECU reads it fine, and the ECU does not pick up the VR signal at all. When the VR is wired directly to the ECU there is no tach read on the lap top during crank. When I wire the tach output from the MSD to the ECU it reads just fine, and runs fine.

This is a bit of a mystery. Does anybody know if the MSD tach signal is a square wave? In the GM conversion article linked above, they take the tach lead off the HEI to trigger the ECU. Then fire the coil directly. So it seems I could use an HEI module instead of an MSD, or in addition to as the Megamanual shows for the older MS II.

Another bit of info: The communication cable between the ECU and the relay box was build for MS I and may not have all the needed wires in it. I am looking into that now. But it seems if the ECU picks up the tach output form the MSD, it should pick up the VR from the distributor also.

Sam
Author:  Matt Cramer [ Tue Nov 09, 2010 8:46 am ]
Post subject: 
The tach output on the MSD box is a 12 volt square wave. I've sent you an email about checking the MS box.
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