Rev Counter Calibration

[Aidan]

diesel tach won't work with petrol engine you need the petrol dash and clocks
all post 85MY vans have the w circuit connected to the dash for the buzzer of doom circuit, only it's split in the dash circuit if there's a rev counter fitted
bod circuits for petrol and diesel are different because of the different tacho feed signals

[wackiki]

So it's the foil/bod that is specific to the Petrol/diesel? if so is there a mod to alter them?

[wackiki]

also why did vw use two systems on one model, when the alternator signal is being used in the dash on both models. seams a little strange?
Does anyone know of different part numbers for the dashes? Seams it could be a calibration issue. My rev counter is working, it just isn't calibrated properly. Maybe a couple of resistors need changed for a lower value?
Or it's as though it needs a faster signal, an amplified signal or a signal from an alternate place.

[AngeloEvs]

If I were fitting a Diesel dash with Revcounter that has the correct DOPS (Buzzer of doom PCB)in the speedo I would disconnect the Ignition coil feed at the coil and link it across to the 'W' connection on the Alternator. This wire from the coil supplies the RPM signal (from the coil) to all post 86 Petrol vans whether they have a Tacho or not as it is a fundamental requirement for the Buzzer of doom. The Multiconnector pin connections at the dash are identical on both post 86 Petrol and Diesel other than pin 14 is left blank on a petrol as it is used for the glow plug LED on Diesel vans. You do not have to remove the Glow plug LED as it will not function on a petrol van anyway. I would not run an additional wire but simply divert the current Coil signal for the BOD to the W on the Alternator. In a nutshell, Petrol take a feed from the coil for both Tacho and BOD, Diesel take the feed from the Alternator for both Tacho and BOD and both versions arrive at the Multiconnector at the same pin location - you only need to change the RPM source - the wire is already there but currently
fitted to the coil.

[kevtherev]

also why did vw use two systems on one model, when the alternator signal is being used in the dash on both models. seams a little strange?

No coil for diesel... petrol came first

[wackiki]

Cool I gave it a go but don't appear to have a w terminal, so I'm going to wait for the 90amp one I ordered last week on flea bay.

[billy739]

petrol alternator will not have a w terminal.

the oil circuit needs a rpm signal petrol or diesel.

in diesels its from the alternator w terminal . petrols use the coil negative.

its possible to mod the tacho to be ok with the coil wire, but i dont know the specs.

alternatively i can swap a petrol tacho and circuit board with ya

[wackiki]

Thanks Billy that's great. What i'll do is see if my new alternator has the w terminal, if not i'll PM you.