Very strange issue with tacho output ??????????

[rossi46numberone]

Hi everybody,
I'm back with my VW Golf running for one week all day long with my Vems 3.6,and I think i'm on the right way :D.
Now I'm on the fine tune step and going to connect all the peripheral device.
My questions today is about a very strange Tacho issue:
I've wired the Tacho output on EC36 pin 3 with a pull up resistors,when I check it with DVM, I have exactly the same signal as the original Bosch ECU give out: positive 7 volt average and +/- 30Hz at idle,frequency increasing with Rpm.
Do I miss something?
Does the ecu give ground to the dashboard/tacho by a specific wire on the original ecu harness?
Ps:when I swap the ecu and put back the Bosch motronic  the tacho work very well....
Any suggestions :'(

Michele 

[boostd audi]

i tapped into the tach signal in wire that normally would come from the stock wiring..  instead of the feed wire coming from stock harness into fuse block i connect pin 4 with 1k pullup to the wire going into the fuse block.  i can pin it out on the CE2 block if you need me too as well, however i will have to go out and lookin my car i do not remember which plug it is. i believe it a G1 or G2 plug.

[rossi46numberone]

Do you have Audi A3??

[boostd audi]

no its wired like that in the VW

[rossi46numberone]

I've tried to wire directly the Vems p259 output to the T10 orange connector and still doesn't work....
Now i'll try to by-pass all the harness and try on the 32 pin blue dashboard  connector.....
Michele.

[boostd audi]

it is on a G1 or G2 plug, (clear plugs)

i will get pin tomorrow when i can look at the bentley diagrams.

[boostd audi]

well did the pin i gave you work?

i have pullup internal on my pin4 so i just run a wire right to the pin i emailed you on the fuse block..

like that i alost every vw

[andreNL]

I have a tacho problem to,
When engine starts it shows rpm nicely but after 10sec tacho dies.
Voltage is 12v pullup through a 510ohm resistor on the P259 tacho output
When tacho dies voltage droppes to 6.6v engine kees running nicely?????
Any ideas anyone?
cheers andré

[boostd audi]

i changed resistor to a 1k and most newer ecu's come with a 1k in it now..

it is aleast easy to try.