Westfield Megabusa Build Diary

01 Jun 2008
DASH2 sensor reading irregularities

The car has been out and about quite a bit now, and there is something strange going on with the sensors. I have checked the configuration and my maths over and over again and I still can't work out what the problem is.

I am one of the first DASH2 users, so I'm pretty much on my own when it comes to the configuration. I have managed to get the PDF files from VDO which document the resistance curves for each of the sensors, as well as their associated temperatures/pressures. Mark Walker has also send me the wiring diagram for the DASH2 loom, which shows that 910ohm resistors are used to create the potential divider circuits. I have everything I need, and I'm sure my spreadsheet to calculate voltages at the various points are correct too.

It turns out they are, and the DASH2 is dead accurate when everything is switched off. However, when I switch on the engine the values immediately jump up. 80c on the coolant temp will jump up to 95C just like that, and fuel level will also change!

It's a real head-scratcher, and Westfield say they have not seen anything like this before.

I have spoken to Race Technology about it too, and between us we think it sounds like an earthing problem. The more load you put on the car (e.g. engine running, main beam, fog lights, indicators, cooling fan etc), the higher the readings will go. There must be an earthing problem somewhere and current is being back-fed. I have followed the Westfield wiring instructions perfectly though.

I turn to the Westfield forum for help: http://boardroom.wscc.co.uk/cgi-bin/ikonboard.cgi?act=ST;f=3;t=63538