efi Megasquirt EDIS ignition - got the Tach working!

[AustrianVespaGuy]

I was starting to get frustrated trying to get my tach working with the new EDIS system, (no success from IDM pin 2, CTO pin 11, or diode circuit) and I finally came across this on an Opel forum, an it works pretty well! I had to up the resistor from the 100K to 1M, and it actually only works up to ~4500RPM, but I'm still better off than I was before. Not sure what the pic of the modification on the back of the tach is all about, but I figured I'd post it together, since I found them together. Hope this helps someone!
-Carl

Edited July 1, 2014 by AustrianVespaGuy

[ClayW]

How did your tach work before? Or did it work at all?

I have a similar EDIS problem that I haven't been able to fix. My tach, wired without the resistor only goes to 3000 before it dies.

Maybe a higher value than 1M? Worth a shot!

[JohnC]

You can also take the 100k ohm resistor and use it to provide a bit of leakage around one of the 1N4004's. This is how it's working on my car. (courtesy of Tim Skwiot)

[AustrianVespaGuy]

I've played with this some and settled at ~400K ohms being the best. Now it works up to ~5500, but the needle twitches every now and then at idle. At 220K it worked all the way up, but would bounce all over the place down at idle, so this is my best compromise. Haven't tried leaking at a 4004 yet though, that will be my next experiment.

-Carl

[JohnC]

I'll send you a diagram. No need to experiment. Tim S provided a solution that works, and is being used by several '02 megasquirters.

[johnhup]

I'll send you a diagram. No need to experiment. Tim S provided a solution that works, and is being used by several '02 megasquirters.

John, could you please post it here? I still havent hooked mine up yet. I've been having similar problems to what is being mentioned in this thread. I dont understand how to 'leak' around one of the 4004's

[AustrianVespaGuy]

Here it is, I'm going to try this here this evening, but I can't seem to wrap my head around why this will help, but that's ok, I'll just give it a go. BTW, I'm assuming that's still a Zener in there after the 4004s, right? It just looks like another 4004 in backwards, but I'm assuming that's just a simplified symbol and is still supposed to be the Zener.

-Carl

[JohnC]

Here it is, I'm going to try this here this evening, but I can't seem to wrap my head around why this will help, but that's ok, I'll just give it a go. BTW, I'm assuming that's still a Zener in there after the 4004s, right? It just looks like another 4004 in backwards, but I'm assuming that's just a simplified symbol and is still supposed to be the Zener.

-Carl

Yes, it's exactly the same as what you originally posted. The only difference is the bypass resistor. I didn't label the diodes.

[AustrianVespaGuy]

OK, I FINALLY really got the tach working across the whole RPM band! Here's a brief history of my ordeal with this thing:

Original MSQ diode circuit only got to 2000 RPM, then went dead.

Added Tim's 100K resistor 'leak' around one coil diode: tach died at 2500 RPM.

100K resistor to ground after Zener caused tach needle to 'bounce' all over the place.

220K resistor to ground worked fairly well, but still bounced at low RPM.

320K resistance worked up until ~4500RPM.

100K voltage divider instead of Zener did not work at all.

So just for the heck of it, I tried using TJFs 100K voltage divider AFTER the original MS circuit INCLUDING the Zener diode and now, finally, it all works properly! Seriously no idea why, but there you have it. My schematic is below, hopefully it will help some more of you.

-Carl

[JHG762002]

OK, I FINALLY really got the tach working across the whole RPM band! Here's a brief history of my ordeal with this thing:

Original MSQ diode circuit only got to 2000 RPM, then went dead.

Added Tim's 100K resistor 'leak' around one coil diode: tach died at 2500 RPM.

100K resistor to ground after Zener caused tach needle to 'bounce' all over the place.

220K resistor to ground worked fairly well, but still bounced at low RPM.

320K resistance worked up until ~4500RPM.

100K voltage divider instead of Zener did not work at all.

So just for the heck of it, I tried using TJFs 100K voltage divider AFTER the original MS circuit INCLUDING the Zener diode and now, finally, it all works properly! Seriously no idea why, but there you have it. My schematic is below, hopefully it will help some more of you.

-Carl

I originally wired my tach up using the 100k leak and the zener, but it would only read to 2500rpm, just as stated above. So this afternoon I decided to redo the wiring using Carl's fix. Rather than start by cutting it all out I decided to temporarily splice in the 100k resistor ground after the zener and see if it helped. It did, in fact it solved the problem completely. The tach needle doesn't bounce and runs smoothly to 7k.

So here is yet another fix. I guess there's no rhyme or reason.

[TJF]

Glad you got yours working. I wonder why there are 5 different solutions to what seems to be the same problem, but on a given car some solutions don't work, while on another car it solves the problem.

[JHG762002]

It may in part be the year of the car, mine is a 76 and has the original cluster as far as I know. I'm not sure if enough 02's of varying years have been done to be able to draw any conclusions though.