Xflow fuel gauge and sender

[McBreadhead]

My 96 Xflow hasn't run for around 12 months and the fuel gauge has gone sleepy - it now barely registers despite adding 10 litres of fuel. It only moves from below the red zone marker to the first white mark immediately after the red zone finishes. 

Firstly how can I check the gauge itself is not faulty? It's out of the car at present. 

Secondly I've measured the resistance across the black and black/green wires to the gauge and get 186M Ohms without any power. From other threads I think the range is approx 0-250 so does that sound about right for a half full tank? Or should I connect power and measure it? Sorry my elec knowledge is useless.

Thirdly I suspect it's a seized sender part No TB 1114/034 which I think is a Smiths unit with 6 fixing screws. Can these be jogged back into life if I remove the screws and access the unit in the tank? Guess I'll need to replace the rubber seal if I do. 
 

Thanks in advance folks!

McB

[John Vine]

I'm not familiar with the XF fuel gauge or the float/sender, so my comments could be entirely wrong.

However, assuming the gauge is similar to the 1/4-sweep one used on later cars (up until about 2015?), the resistance range of the sender is likely to be something like 9 Ohms (full) to 203 Ohms (empty).  

You're measuring the sender resistance correctly -- no power required.  

To check the gauge, connect 12v and earth wires, and then short the sender terminal (the one with the black/green wire) to earth.  You should get a full-scale deflection. 

It does seem like your sender is faulty or the float arm is either stuck or dislodged in some way.  Is it set in the top of the tank?  If so, I imagine it's easy to remove so as to check its operation.  No doubt an XF owner will be along shortly to advise how to proceed? 

Without knowing where your fuel line exits the tank (I'm assuming you have an external pump?), it's difficult to know what the 186 Ohms reading indicates.  Later cars with an in-tank pump have a quantity of "unreachable" fuel below the level of the pickup (typically 6L in an S3).  I assume XFs have the same problem?  How much fuel was in the tank before you added the 10L?

JV

[McBreadhead]

John,

Thanks for your comments. 

Yes it's a Caerbont unit with 1/4 sweep.

Re testing the gauge, I assume I do this in situ and with power on?  I've got twinned green wires, one black and one green/black (plus the separate lighting circuit) so I am shorting the green/black to black?

Re the sender yes it's a top set device with separate high level feed to an external Facet fuel pump. In terms of quantity before I added the 10L I think the needle was showing just above the red. I'm not sure re unusable quantity however but it's an S3 chassis. Do you know if you can just buy new seals as I can see the old one is cracked around the edges?

[John Vine]

...so I am shorting the green/black to black?

Yes, and with the ignition on.  If it's easier, you could short to earth the black/green wire at the sender end.  Either way, you should see the needle sweep slowly across the gauge to max. 

Re wiring colours:

Green: 12v supply
Black: earth
Black/green: sender

The lighting wire is usually red/white.

If your sender is working correctly, 186 Ohms suggests that the float is close to the bottom of its range towards empty (assuming max = 200-ish).  Of course, with the angled tank bottom, the float won't necessarily indicate a true "empty".  What happens to the needle if you add another 5 or 10L?

Re a new seal, is it rubber or cork?  If cork, is this the one?

JV

[John Vine]

Or this cork/rubber composite perhaps?

JV

[jonsymons]

Hi McB - I have the same age XFlow and an equally infuriating fuel gauge/sender so spent a good while on this forum looking at historic posts. It was suggested that to test its not the gauge that is faulty you just remove the smaller of the two cables  - not the one with the white insulator (with it in the car) and the gauge should read Full. If it doesn't read full then its the gauge.

I've had the sender out several times and if you carefully bend the tabs back you can take the cover off the square 'resistor' and clean the little arm and wire windings and make sure they are connecting etc. That coupled with cleaning the contacts seem to be the only things you can try as its a very rudimentary/mechanical unit.

With it back together, you can then adjust the resistance range by carefully moving the small slotted screw (which adjusts the swing of the small arm) with it connected to a multimeter. I've read elsewhere these are 20 ohms empty and 265 ohms full (will try and find the post as there were a couple of options on the range) but I can't get that range working fully and need to have it back out to adjust again. You seem to be able to either have accuracy at the Full or Empty end, but not both. I'm aiming for the empty end accuracy.

I think you can still buy these senders (Redline) so replacement may be my next step - or give up and just dip the tank with a stick!

Let me know if you get it sorted as I'd be interested..

Jon

 

 

[jonsymons]

Can't find the link but I took a screengrab of the post last time I was looking:

 

[John Vine]

Re #7:

Linky

JV

[McBreadhead]

Wow great information guys thank you.
 

The gauge read fine with full deflection so I removed the sender from the tank and moved the float over its full range, cleaned the sender contacts and reassembled. And bingo gauge now working. I may renew the rubber seal for good measure. 
 

I spoke to Chris at Redline who likely has the part if anyone needs to renew. 
 

Thanks for your help. 

[John Vine]

Good result. Pleased you've fixed it.

JV