No tach signal 280zx dis. & GM 4pin HEI

[primer&rust]

Hello I have a 3.0 board built by DIY Auto setup for a VR trigger, 280zx distributor, Gm 4pin HEI and I can't seem to get a tach signal from the negative of the coil. I am trying to run fuel only with 029y4 and when I run the positive VR wire to the positive of the coil I do get a tach signal, it tries to start, has spark, and has RPM readings (between 70 RPM & 411 RPM) on the gauges but it does not start. When I run the negative VR wire to the negative side of the coil I get no spark at plugs or coil. I ran the 470 ohm 1/2 watt resistor between the wires on the modules firing side but this made little or no difference. When I try to start the car with the postive VR hooked into the coil + I do get the LED flashing. When I have the negative VR hooked into the coil it only flashes once and no spark. I am not running shielded wire to the coil, would this help at all as in Megatune it shows no RPM with the negative trigger. I have read so many post here and on the Megasquirt forum if anyone has an idea what might be helpful please let me know.

[primer&rust]

I found out the VR positive from the megasquirt is suppose to be connected to the negative trigger of the coil and the VR negative from the megasquirt is suppose to be grounded. Car idles but stumbles a little bit time for more prayer and tuning time. Hope this helps someone else out too.

[Matt Cramer]

The VR trigger circuit is not intended to be wired to the negative terminal of the coil. I'm not sure how long it will last when wired up this way, but it's better to switch to the optoisolator circuit if you're running off the coil.

[primer&rust]

From the Mega squirt website under the external wiring diagram for the v3.0 board "All MegaSquirt® installations must have an input (tach) signal to determine engine speed. This signal comes in on pin #24 of the DB37. A variable reluctor (VR) input (tach) sensor is shown (above) for the input. To use a Hall sensor, optical sensor, or points trigger, you connect the signal to the same input pin (DB37 #24) as the VR sensor. You must ground the VR other lead of the sensor as well, and pin #7 is shown for this (though pin #2 can also be used). However, pin 7 is not a 'dedicated' or specialized ground for the VR sensor, it just happens to be a ground (the next revision of the PCB will have a dedicated ground for the VR circuit on DB37 pin #2, so use pin #2 if you think you might upgrade at any point)." This is where I got the information and it seems to work.

[Zmanco]

There are two issues: which pin to use to connect to whatever tach signal you're using from the engine, and then how the MS board is configured to process the signal.

 

As Matt said, if you are taking the tach signal from the coil, then you need the board configured to use the opto-isolator input. It's been a while since I did this, but I believe at a minimum you have to move a jumper. There might be a wire that needs to be added too - I'll let Matt take it from there as he does this a lot more regularly than I do I know this is all documented on the MS website as well.

[primer&rust]

Alright so I can get the the car started and idling well but I can not hold a steady RPM when I rev the motor. If I stab the throttle and let off I can rev it to 5K RPM but if I try to hold RPM the engine stumbles and dies sometimes backfiring. I have played with the PWM settings( 1.2 opening time, 35% current limit, 1.5 time threshold for the stock injectors) and it idles well but that is about it. Could this be from pulling the tach signal from the coil negative instead of a VR trigger. When I tried to tee into the VR signal from between my ZX distributor and the GM HEI module I would get no spark or injection. I might have a weak VR signal because my tachometer inside the car never read RPM at idle. Is their a better distributor (280z) for a stronger VR trigger signal ( I know the ignition box was clear inside the car in the 280z) or should I just go ahead and install Ford EDIS. I believe I can pickup either one of these systems at a local wrecking yard. I'm trying to get the car up and running as it has been down 3 weeks so any input is appresiated. Thank You