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

Laurence


10 Jun 2008
DASH2 problems continue

I have been in contact with Lorne at Race Technology about the sensors that change in value depending on battery load. Has has suggested a few different things.

I have tried changing the potential divider resistors from 910 ohm to 150 ohm which makes the problem better, but the problem is still there.

I have measured the resistance from the sensors with the engine running and not running and it doesn't change, yet it does change on the dash.

I am measuring the 5v reference feed and it's 4.96v which is right on the money. It's the same with the engine on or off! I just can't understand it, so I called up Westfield again who have asked for the unit back and they will send it to Race Technology for testing.

I have spent so long trying to get these sensor values right. These posts give only a very small summary of the work I have done checking and testing, and I'm getting frustrated with it. I'm not giving up though!

Laurence



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