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[WillCJ]

So, car I just bought came with a warning from the PO that the tank is empty when it reads 1/4 full, so out with the tank to see if the float is stuck, but when I run a wire to the sender and try it out, it reads 1/4 full on full down stoke, no visible reason, except the sender has ZJ printed on it, so maybe wrong fuel pump/sender combo?
Well I am not going to replace the whole thing, but prob can't get just the sender?
I was thinking someone might have a bad pump with good sender for an XJ, if that is the problem?

[Dave69]

the sender is not matched to the fuel gauge, the reading is normally measured on resistance of the sender and matched to the fuel gauge, the ZJ sender fitted to another model might have different resistance readings hence your reading error.

you can drop a variable resistor pot into the sensing wire and retune an empty reading. plenty of diagrams on google for wiring

[Jonny Jeep]

My 97 TJ used to to that. There was a recall for the fuel sender. Might be worth contacting your local dealership to see if it affects your XJ, in which case it's a free replacement. resistance should be 20 ohms full, 220 ohms empty.

[Brynjaminjones]

Hmmmm, interesting. Is it at exactly a quarter that the light comes on? My fuel light comes on when it gets to a little below a quarter - after driving about 5 miles the needle will often then go right to empty. I always thought it was just a Jeep character flaw, but now you've got me wondering if it's not as empty as it says it is! I've driven quite a long way with the gauge off the scale and never had so much as a splutter!

[WillCJ]

Hmmmm, interesting. Is it at exactly a quarter that the light comes on? My fuel light comes on when it gets to a little below a quarter - after driving about 5 miles the needle will often then go right to empty. I always thought it was just a Jeep character flaw, but now you've got me wondering if it's not as empty as it says it is! I've driven quite a long way with the gauge off the scale and never had so much as a splutter!

No Light, just reads 1/4 full when actually empty, so I am topping up when 1/2 tank to be sure.

[Brynjaminjones]

Ahhh sorry, I misread your original post! 

[Dave69]

just been looking at fuel gauges for yj and cj and the major opinion is that the gauge are somewhat vague.

[WillCJ]

Thanks to all for replies so far, I checked with the local dealer, no recall on my Jeep.
I checked resistance empty (sender back in tank) and  read 18 ohms, but may have to re-test/think that, as opposite to suggested readings? certainley goes to below empty when un-plugged.
I know Cj gauges are a bit wacky, have after-market on in mine (and temp gauge) so can rely on that.
I looked at a sender/pump unit on the Bay, and close up it also had ZJ printed on it, so may be that is correct.
I am swapping in a petrol/LPG tank combo in at moment so full space in rear, so tank still out for a couple of days, not got a variable resistor to try yet.

[Jonny Jeep]

Low resistance should indicate full as a bad connection would drop the indication to empty so you don't think you have more fuel than you actually have.

I have ZJ marked on mine to so that's normal.

[WillCJ]

Low resistance should indicate full as a bad connection would drop the indication to empty so you don't think you have more fuel than you actually have.

I have ZJ marked on mine to so that's normal.

Thanks for adding the ZJ markings bit, confirms correct sender, prob mis-reading my multimeter, and didn't check which way the figure should be, so will check it again.
Cheers.

[WillCJ]

Low resistance should indicate full as a bad connection would drop the indication to empty so you don't think you have more fuel than you actually have.

I have ZJ marked on mine to so that's normal.

I re-checked the resistance at empty with my auto-ranging multimeter, and it reads 189 ohms, so making sense, a bit low as expected. thanks for the figures.

[WillCJ]

Just to bring this up to date, and from the information already given, I bought a 30ohm resistor from Maplins, shunted it in to the sender wire and , while I had the sender out, worked the arm again and got the result I wanted, 'full' when at the top 'half' (or just below) when at half travel, 1/4 at 1/4 travel and low fuel light comes on, and right down to 'empty' when arm fully down, all in all I class that as a good result!
Cheers all for the input.

[Mike Pavelin]