New Fuel Sender - erratic out put on gauge

[ManicGTI]

I had a new tank fitted a year or so ago, with all new lines, crossover etc and thought it would be sensible to fit a new sender at the same time.  It has behaved strangely ever since fitment, often not registering any fuel for  a while after filling it, then randomly going to max, I don't expect it to be totally linear, but it's so wildly wrong that It's essentially useless.  Once I get under half a tank it could read anything from in the red to almost 1/2 (on the flat, not hill dependant).  Some time it can take 15 off mins before it registers full after a refill.

I carry a 5l can and end up refilling and finding i've still got 15-20l in the tank (2WD DJ 60l tank?).  

I'm running SLV dash repair kit, am happy gauge itself is working fine.

I thought I'd float it on here before I start dropping tank and replacing sender (which I really don't want to do) in case there's something simple I can check/test/sort - or maybe I need a reality check - are they all like this?

Aannoyingly the sender in the old tank worked far better!

[AngeloEvs]

The fuel gauge reading will change as you go up or down gradients, turn left or right, etc, it’s a well known issue with the T3 but yours sounds more sensitive than it should be. I think there two sender types for the T3 depending on year of manufacture (according to the Bentley Manual) as the VW gauge calibration test uses different values of resistance for each type. Might be worth checking which type of sender you fitted.

A Visual inspection of the wiring to the sender and the SLV wiring to the fuel gauge is a starting point. I would also check the voltage regulator is providing a stable 10v to the gauge under driving conditions. I am not familiar with the SLV product and how the regulator is mounted but regulator connection problems can cause its output voltage to swing from 0v to the full Charge voltage of around 14v and would cause the problems you are experiencing - worth eliminating. You would need to attach two fly wires, one to chassis 0v the other to the regulator output connection on the gauge and connect to a multimeter reading D.C. volts and monitor while tapping the regulator itself.

The only way to test the new sender is to isolate it and measure its resistance under driving conditions or by taking measurements on the flat and on gradients by jacking one end up or using ramps. You will need to interrupt the wiring to the sender and attach a multimeter reading resistance. A reading of around 100 ohms is approx 1/3 full.

[davidoft1]

Check the wiring connections, corrosion can cause miss readings , check the dash plug is clean they can throw up some crazy faults

[Aidan]

SLV ? do you mean SHC ?

[ManicGTI]

Thanks guys!

Yes sorry, was a typo on SLV, I meant the SHC (SlaughterHouse Customs) dash repair kit.

[R0B]

I would be checking the solder pins if it's an SHC one. Here's an example taken from the temp gauge thread above this one.