110 fuel tank level gauge and sender

[Troll Hunter]

Hi, All,

This week obviously isn't my week.  I've had fuel tank level problems for a long time, relying on my trip meter reading to refuel.  In my rebuild I decided to tackle them.  I initially suspected the tank sender unit, so I bought a new one, STC1492, since it was originally a petrol V8 although now a 300Tdi.  This is the sender that fits in the left hand side of the tank, with the three vertical electrical connections, the top one for the tank contents gauge indication, the middle one to earth, and the bottom one to the low fuel warning light.  I think I've got that right!  Still the same problem, so it must be the gauge.  Bought a new gauge, PRC7313, again still the same problem. 

So yesterday I spent several hours with a bench set-up of a 12 volt battery, the two senders, the two gauges, and a multi-meter.  Both sender units behaved the same: holding the float arm up to simulate a full fuel tank the resistance across the sender was ~ 0.4 ohms.  At the low tank level the resistance was ~0.8 ohms.  On both units the low level warning circuit only came on at a very low tank level, quite correctly, and the resistance was ~0.4 ohms.  Raising the float arm and the circuit went open.  The resistance over each of the gauges was also <1 ohm.

When I powered the circuit, on both senders the float position had no impact on the gauge reading - both gauges read Full at all float positions!  So, where is my problem?  Do I have a problem, other than suffering from Blue Box disease?  What resistances should I expect over these senders? Should I be buying LR original items?

Please help a guy with no hair to pull out!  Many thanks in advance, and all advice will be very much appreciated.

Mike

[miketomcat]

I can't help with the problem because I have the exact same issue. The only difference being we have twin tanks and when I switch to the under seat tank it all works as it should.

Mike

[ianmayco68]

Total guess here but i seem to remember reading somewhere that there’s a resistor of some sort in the circuit , might be total rubbish and I might be mixing it up with something else but who knows .

[pete3000]

STC1492 sender doesn't come back as anything for me, PRC8463 is the diesel part number?. The resistances measured don't sound right, have you got the ohms range on 200 ohms or e.g 20Mohms. I've just pulled my 300tdi setup out so i'll go and measure the old sender vs gauge positions.

[pete3000]

Right, my sender is PRC8463, connections as follows

 

Stud/bolt = earth/0v to chassis earth via short black wire, pushed on via bullet style female.

White plastic terminal also stamped as T on sender face = gauge reading back to gauge PRC3107 terminal 1

Red plastic terminal also stamped as W on sender face (warning?)

 

clipped ohm meter to stud, and white. Measured full position top of travel, 7-10 ohms, mid way ish 150 ohms and empty 350 ohms (linear scale?)

with clip still on stud measured resistance to red W, open circuit till 25mm from end of dip tube then 0.1  ohms for low fuel light.

 

PRC3107 Gauge wiring,

terminal 1 from sender white T

terminal 2 green from 12v ign switched feed

earth/ov black from gauge earths

 

 

[western]

I think STC1492 should of been STC1482 which is a sender for 110 with petrol engines upto VIN JA915411 with low level warning light facility according to the 110 parts book.

[Troll Hunter]

Yes, thank you, western, it should be STC1482. Damned finger trouble again!  And my 110 CSW was originally a V8, hence the sender variant.  Do you recommend that I change to PRC8463, particularly if I need to renew the sender?

ianmayco68, there isn't any resistance shown on the LR wiring diagram, and there was none when I stripped the wiring.

Pete3000, many thanks for the resistance readings on your sender and for the wiring details, and yes, I was on the 200 ohm range.  It appears that, yet again, I'm suffering from Blue Box disease.  Unfortunately, because of my location, it costs more to return faulty items than to just suck it up😠.  I'll just end up buying yet another sender, and this time will fork out for a genuine product (ouch!).  

Mike

[western]

Yes I would try the PRC8463 sender unit. 

[pete3000]

Yes I'd swap to the PRC8463, stick a meter across it before fitting to confirm readings above, your gauge should be ok as the PRC7313, is the newer number of my PRC3107. Good luck.

Pete

[Troll Hunter]

Thank you both for your latest responses.  I'll get the PRC8463, but with the hols and the dreaded lurgie-19 it'll probably take a couple of weeks before I get it.  I'll update then.  All the best for Christmas and 2021.

Mike

[western]

your welcome, get well soon &have a great christmas as far as possible