Need Help getting Mk2 vw tach working

[Psi4gti]

Here's the breakdown, i had connected the VEMS's tach output straight to the tach, the car ran for a few months and do keep in mind that i barely drive it, then all of the sudden the signal started getting weak and the tach needle dropped dead never to come up again.
Sent the Unit to Jason at VEMS US and he fixed the output, got an MSD tach adaptor, forgot the number but it was powered, had ground and a "signal in" and "signal out". Hooked it up and it ran ok for a couple of weeks or months, then same thing, needle starts acting funny, eventually dropping and never getting up again.

I got this inline gadget from Kevin Black, switched the tach output to pin 34 out of the 36 pin plug and nothing, can't tell you what the gadget has in there so can't really tell. I eventually cut that gadget out because it's not working in this setup.
I reached out to Jason at VEMSUSA again and sent me another gizmo that resembles the old MSD adaptor that i had, powered, ground, "signal in" and "signal out" to tach. I hooked it up and nothing, swap another 3 tachs and none work.
Took the car to my friend's house and used his oscilloscope, he told me that the pin 34 was putting out a "dirty" signal and wasn't good or strong. I then went to the software and swapped Tach outputs from 34 back to pin 4, test the output and then said that the signal coming out of "Low Current output o (0.2A) Grounding, EC36 Pin 4 was good but the signal out of the gadget wasnt.

Is there anything i can look for? Do i need to change any configuration in the software? Seems like the Tach output is working, no?

Thanks in advance and i know that i can swap a newer style cluster in there but I want to use the old cluster.

[GintsK]

Old tach probably want high voltage spike. So if you have not spare IGBT in VEMS, solder it in free IGN output. And configure this as tach output.
Then you can experiment with various inductances: relay coil, injector coil... up to coil from old ignition. Circuit is similar to Ignition.

Gints

[koabi]

http://www.vems.hu/wiki/index.php?page=MembersPage%2FKoabiBrooks%2FQuestions

see the 2007-02-03 question - hope that helps

[Psi4gti]

I was thinking with a friend and decided to first make sure that everything will work on my end by getting a coil signal from a car with a coil then grounding both cars to complete the circuit. If that works then it must be the adapter, I don't know what's inside of the gizmo i purchased but did a couple of searches and looks like the MSD 8920 may work.

 

[Psi4gti]

Got an idea after talking to a friend, used my next door neighbor's 1971 VW Beetle to test my cluster first, found the main cluster power, ground and tach signal. Hooked them all up including tach signal to the negative of the Beetle's coil. Tach worked flawlessly so bad tach theory is out the door.

Moved onto my gti and tested for continuity, tach signal has continuity, then power and ground, all check out ok.

This leaves me with a possibly dirty or bad signal from the VEMS or an adapter that doesn't work.

I will report what i find.

[Psi4gti]

Problem solved, tach and adapter were fine, it was a bad signal from the P259 as per Jason@VEMS US, signal was coming out but voltage was dropping to 2.5 or so causing it not to work, put it all back in and is working flawlessly.

Big up to Jason@VEMS who's been very helpful.