anyone in phoenix with megasquirt who could test

[mobythevan]

I went to the FAQ section and looked at the old install guide I wrote years ago.  I believe you want the dizzy wire pulled up to 12 volts.  Using 5 volts will lead to problems I think because of the variations of different diodes that end up in the tach circuit.  These potentially drop the voltage too much to trigger the ECU.  But, only make one change at a time.  So finish verifying that the stim works and that you see the voltage toggling on the dizzy wire.  Then if you do not see a good steady tach signal, change your pullup to 12 volts.

[JIM73240Z]

I am so sick of looking over the build instructions.  everything is there.  I reflashed to a msII code and tried that just to make sure.  even less stuff coming through and still no tach signal.  I have one more thing to do and send it over to a guy in town who looked at it last and said it look alright and have him go through it without me standing there.  if he cant get this thing going I am ordering a haltec.  I hate doing it since I spent so much already but damn.

 

jimbo

[Matt Cramer]

If you want to check the opto input circuit yourself, here's a simple test: With the Megasquirt powered up, apply 12 volts to pin 24 or TachSelect, and check the voltage on the TSEL jumper with a voltmeter. You should read zero volts. Next, ground pin 24 so it has no volts on the input circuit, and check TSEL's voltage again. You should see 5 volts there. Let me know what you find.

[JIM73240Z]

so now the computer works with the stim all day.  major accomplishment.  I have 5v at the dizzy on the signal wire (GB) and 12v on the power (BW).  still no tach signal.  I have the power coming from the positive side of the coil and the 5v coming from there as well. any thoughts.  I may swap out the relay board because it seems I am 2 for 2 on soldering my boards.

 

jimbo 

[mobythevan]

I have the power coming from the positive side of the coil and the 5v coming from there as well. any thoughts. 

 

That doesn't sound correct.  I must not be reading it right.  You can't have 12 volt power coming from the coil positive and 5 volts also coming from the coil positive.

[JIM73240Z]

no.  one wire is a full 12v.  another has the resistor that brings it down to 5v.  I was just going for a convenient power source.

 

jimbo

Edited April 1, 2014 by JIM73240Z

[mobythevan]

Your resistor should be like this:

 

        12 volts

             |

             |

         1k Res    

             |

             |

GB--------------------------MS optical trigger input

 

Is that how you have it wired up?  The resistor does not actually drop the voltage to 5 volts.  You would need a voltage divider circuit to accomplish that.  You do not want to drop the voltage to 5 volts.  So pullup resistor to 12 volts as shown on GB and then connect GB to MS trigger input and you should be golden.  Let me know if that ascii schematic does not make sense.

 

EDIT:

Dizzy side ------------ Harness Side
Red (12v) B/W
White (MS trigger) G/B
Green (not used) G/Y
Black (gnd) Black

 

B/W is connected to 12 volts and Black is connected to ground, these two power up the optical circuit inside the dizzy.  Then every time the slot passes I believe the GB wire becomes connected to ground through the optical coupler in the dizzy.  By having the pullup to 12 volts, the signal on the GB wire will go from 12 volts to ground as the slots pass by and back to 12 volts.  This creates a nice 12 volt square wave to trigger the MS computer.  You may know all of this already, I am not trying to talk down to you.  I like reiterating this for everyone's benefit, including my own.  

[JIM73240Z]

no problem at all.  I hate electricity.  the only way I can picture it is if it is water going through pipes. 

 

I have my 12v coming in and reading at 12v per my voltmeter.  then I have another 12v wire with the 1k resistor soldered in the wire, then continues to the shielded wire, connects to that and goes to the dizzy.  it has 5v per my volt meter and backed up by everything that I can find.  I hope that helps

 

thanks moby

 

jimbo

[mobythevan]

If it is possible for you to disconnect your GB wire from MS and then measure it with the voltmeter while turning the dizzy very slowly, you should see the voltmeter go between 12 volts and ground as the slots pass.  Not sure if that is easy to do with things installed.  Once you connect the GB wire to MS it is possible that you have a voltage divider because of resistors that are populated on the mainboard tach circuit.  I cannot remember off hand.  However, try the experiment if you can and that would verify the dizzy and pullup circuit are operating as expected.  I think you did this earlier in the thread.  

[JIM73240Z]

I took out the dizzy so that I can get to the wires.  I took off the ign wire from the relay so that I can see a voltage drop when I turn the dizzy.  nothing.  stays 12v.  I do not have the plug for the 83 zx turbo dizzy.  so I have 3 wires with female spade connectors for the 4 male spades that are in there.  I have the 83 zx fsm and the 82 zx fsm and they say nothing for the cas.  except for the 82 which has a diagram of the round plug that went to the cas not to the dizzy.  don't have that either.  looking at the plug in the bottom of the dizzy, there is an indentation for the plug to go in only one way.  with that said and orientated at 12 o'clock, which wire goes where.  to top it off, I had the gw(+) at 12v solid and the gb (signal with 1k resister) at a solid 5v.  today it is at 12v.  not sure what happened, did the resistor blow and I nee to put in another one.  this is a pita project.

 

jimbo

[JIM73240Z]

ok.  moby told me to take the dizzy out and SLOWLY turn by hand to see if the v drops.  at first nothing mattered so in a fit I ordered a new cas in fear of my frustration and moving wire to spade since nothing was working.  put in the new cas.  no change.  went to a datsun shop I found here on the surface of the sun and he showed me the connector to verify my connections.  wired per the directions, nothing.  put back in the old cas, nothing.  I have a spare cas I guess.  this is all from my digital multi meter.  so I broke out my old analog needle multi meter and noticed a drop from 5v to 4.75-4.5 v.  not the result I was expecting.  I thought it grounded.  any ideas?

 

jimbo

[NewZed]

I can't really follow what your expectations are but the attached pictures might help show what the CAS output should be.  Two of the wires should show a voltage pulse, from zero to probably ~5 volts.  One of the wires will pulse rapidly as you turn the distributor because it's seeing 360 slits per revolution, the other will sit at zero, I believe, and only change state six times per revolution.

 

So, if it were me, I might fabricate a narrow blade-shaped probe that I could slip in beside each wire in the connector while it's plugged in, to measure voltage.  With the key on and no CAS movement, you'll probably get a 5 (that's your power supply to the CAS from the ECU), and maybe a 5, and a dead one.  Stick the probe in the two that aren't constant 5, and spin.  

 

I might be way off, but that seems to what the pictures and text say.  Added the "And so forth" picture just for the humor.

Edited May 27, 2014 by NewZed

[JIM73240Z]

correct.  one should change a lot over the course of rotation and one should be every 60 degrees.  when I rotate, I see the 5v and when the diode passes the 60 degree slot it drops to 4.5 v not to 0.  so I am wondering if there is something else I am missing.

 

jimbo