I've just bought a new fuel level sender to the fuel tank

I tested it out the car by connecting the wires and slowly manually moving the float arm from empty to full whilst watching the dashboard gauge.

It appears to max out at 3/4 full on the gauge - that's the sender unit pinned at max height/full tank.

I've tested the gauge by grounding out the gauge wire at the sender and the gauge does go to the full mark when you do that.

just wondering if this is normal for a replacement sender unit to not get the gauge to the full mark - is it normal for the fuel gauge to just not be very accurate, or perhaps the new sender is somehow faulty?

 

All I can do is commiserate. I've had this exact problem with several sending units over the years, on several Jags. The parts are simply not being made to exact spec, I reckon. Fortunately they've all been accurate at the lower end of the scale....where it matters most.

Cheers
DD

 

Yeah I think you're right. I thought maybe I should complain to the supplier and return it, otherwise I'm part of the problem of people accepting sub par parts...
but then I don't want to be hanging around for weeks with an unuseable car & how would I even find a supplier using a different manufacturer ? ..Is there even more than one manufacturer now?

I noticed when fitting it that the locking ring was easier to install aswell, so clearly the metal base of it isn't quite as thick as the OEM one. Hoping it doesn't leak.

 

I respectfully disagree guys! This happened to me twice, and each time it was a matter of cleaning up the guage cluster connections, as here:
https://www.jaguarforums.com/forum/x...ng-fix-267848/

 

For the facelift, the sensor is simply a voltmeter. The lower voltage, the higher the tank. Ground is full, 12v is empty.

I would think the older ones operate the same way. Should be easy to test , off the car, with a power source and a multimeter?

 

Do you own an ohm meter?

I prefer the analog ones, not digital, for most automotive stuff.

Simply ohm the sender in and out of the tank, if it reads 0 ohms (or real close to zero), with the float at max height,( assuming the float can reach max height while in the tank), also, it isn't the sender.

https://www.homedepot.com/p/Gardner-...-318/202867892

Doug

 

Interesting findings on the gauge cluster connections Greg.
What i'm thinking though is that when I ground out the terminal at the sensor, the gauge does move to the full position, so to me that sounds like it rules out any connection issues anywhere else in the wiring/cluster?

I do have a multi meter - does anyone know the range of values the sensor should read?
AZdoug, When the gauge is on max/full, how close exactly to 0 ohms should it be?

 

You should have zero, or near zero ohms across the tank sender terminals when the tank is full. I don't think a reading of a couple ohms would make the gauge not read full, 10 or more ohms, yes, i could see a variance.

You should the same reading when the sender float is lifted to max extension, out of the tank.

Is you get 0 ohms outside the tank, and some ohm ohm level with the tank full, from the float, the sender float is hitting something that keeps it from full rise.

Doug

 

Quote:

What i'm thinking though is that when I ground out the terminal at the sensor, the gauge does move to the full position, so to me that sounds like it rules out any connection issues anywhere else in the wiring/cluster?

I agree

Quote:

the sender float is hitting something that keeps it from full rise.

Worth checking, for sure.

I can't remember (if I ever knew) what the innards of an XJS tank look like but tanks often have a snaggle of internal pipes and baffles that the float could get hung up on.

Cheers
DD

Cheers
DD

 

If the sender is hitting something, preventing it from going all the way up, your tank has partially collapsed. Your rochester valve probably needs to be replaced, or cleaned. Basically the suction from the fuel pump has created enough negative pressure to slightly collapse the tank. You can restore it by removing that back panel (removing the spare tire) and using the exhaust hose to repressurize it. Don't go past 10psi. It won't take much to pop it back in place, but too much, and you'll need to have the tank replaced, or the seams repaired. Expensive.

The hard pipe connecting the rochester valve to the fuel tank exhaust might be bad too? You can test that by sending pressurized air down that path. Have the front drivers side tire off so you can disconnect the rochester valve and check for air flow?

Either way, all tests run through the fuel tank which requires access from the back. It's really not that bad to get to.