Playing with fuel senders, now speedo not working.

[Touring Whore]

I swapped the senders in my touring last night (though this didn't cure the faulty fuel gauge problem, just made it slightly different), and now my speedo isn't working (though the swingometer is). As I understand it, the sensor on the diff must be working for the swingomter to be working, so I'm thinking my problems must be related to the cluster. Does the SI board control the fuel gauge and the speedo, or is there anything else common to both gauges that I should be looking at, or is it more likely to just be coincidence that the speedo has stopped working, and is unrelated to my fuel gauge fault? For reference, the speedo needle doesn't move at all, the fuel gauge stays at 1/4 whilst driving, and goes to 1/2 or empty when stood. I'm not sure if the oddometer is working or not, but I'll check when I next take the car out.

Thanks in advance,

Guy

Edit: The swingometer and oddometer aren't working, so it looks like 2 unrelated problems. I'll have a look at the sensor wire from the diff once I've sorted the fuel gauge.

[Brianmoooore]

Speedo problems are most probably an internal break in the wiring near the diff. (Pull the individual wires gently - they shouldn't stretch.)
Is the fuel gauge problem one that's developed, or "always" been there?
Any chance your car could have been fitted with an instrument cluster from a "lesser" E30?

[Touring Whore]

I've just had the cluster out to tighten the nut at the back, but no difference - the gauge reads 1/4 full when diving (with a slight flicker/hunting at the needle), and empty when stationary (it should be virtually empty anyway, so empty when stationary may be the correct reading).

Brian - The fuel gauge problem has always been there. I did have one faulty sender, which I replaced, but it just adjusted the problem. It's possible the instrument cluster has been swapped (though it's a 316, I didn't think a lesser e30 existed!), is there any way of telling which cluster/ID plug I have got?

With the fuel gauge altering when moving, I'm thinking it may be a bad connection in the wiring somewhere? Something which is affected by movement must be a "mechanical" electrical fault?

[Touring Whore]

Right, I've got a bit more info on this. The needle is oscillating between half a tank and empty (empty being it's correct position). The needle position is dependant on the physical position of the car, as in it sits at 0 or half, then when the car moves a couple of inches it flicks to the other end, then a couple of inches further it flicks back. Moving at speed makes the needle "sit" at 1/4, though it is actually trying to oscillate between the two positions. A bit of guesswork makes me think it's somehow making and breaking the connection to one sender, so the two positions of the needle are either both senders connected and the needle showing empty (correct operation), then one sender gets removed from the circuit and goes open circuit, leaving the average (one good sender on empty and one open cct) as half a tank.

What I cannot understand is how the sender is making and breaking based on the car position on the road. I can stop and the needle will be at 1/2, and just nudge forwards to make it show 0, then nudge forward further and be back at 1/2.

Any thoughts anyone ?

[Brianmoooore]

Mmmmmmmm! Speedo not working and fuel gauge almost thinking it's a speedo!
Both signals pass through a plug and socket, which should be cable tied to the steel tube containing the fuel tank vents, under the carpet under the right hand side of the rear seats.
Could be worth checking out if the wiring here looks messed around with.