SPA Dash interference

[3Dee]

Been wrestling with an annoying problem with my SPA dash and the fuel level indicator.

The indicator gets all upset when I operate the fuel switch to flick over to the other tank in that it freezes! ie, will not show the other tanks level - stays the same.

If you cycle the ignition after changeover, the dash reinitialises and shows the correct level.

I have sought help for SPA and Marky about this, and the conclusing is some sort of interferance going on with the changeover valve circuit which of course is on the same switch a-la- standard ultima.

I have proved this by disconnecting the valve switch connections, then the dash operates as expected, showing the correct levels on switchover.

SPA suspect EMI spike problems (very odd if so as the factory don't appear to have this problem, but then they do use an analogue type fuel gauge), others suggest running the + feed for the valve from other than the ign as currently both are from the ign.

The switch is mounted just below the dash so proximity might also be an issue.

Any electronics wizards out there?
Can you guys out there suggest solutions, any observations...

...driving me nuts as this prevents me completing the dash.

[spatz]

you could try a higher value resistor 10k-100k to ground for the dash input (aka switch output)
They will not alter the measure too much as the tank level resitance is around 50 ohms but will connect the dash input to ground
through the resistor no matter what you do with the switch.

[3Dee]

Hi Spatz,

Sounds intriguing!

Could you elaborate a little more for an old numpty like me!
Connect what to what, and how... You know what I mean!

...and what is the theory behind this?

[spatz]

just try a 10k or 100k resistor from your dash input to ground, this will then always load the dash circuitry with a small current no matter if you switch or not.
Your readings might be off by 2% but give it a try. it might fix the issue

[3Dee]

That is very interesting!

I remember suggesting this to SPA, but there was no comment. Thank you for putting this back on the table!

I will try this!

cheers

K

[Storer]

I can't remember if the tank switch over switch has a dead centre position.

It may be that a switch that cuts the feed to the dash (as if you power it down) and then powers it up again from the second tank will solve the problem.
i.e. a 3 position switch - position one = d/s tank - position two = off - position three = n/s tank.


Paul

[3Dee]

Hi Paul,

Yes it does have 3 positions.

I will have a go with the resistors... sounds strangely logical!