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1987 XJ-S V12 Coupe. Just replaced the fuel sending with the correct part # today, DAC5500.
I wired it up before mounting it in the tank. It works as expected, near/at the bottom of the float range, the Low Fuel light is triggered. By varying the float level with my hand, I can watch the fuel gage go up and down as expected. So I have the two signal wires connected correctly.
So
It works like this.
It doesn't work like this.
I mount it in the tank. Nada, nothing.
I take it back out and test it again...works fine. Put it back in the tank, nothing. If I let it sit just slightly out of the tank (see photos) it works, or I should say it at least triggers the low fuel light, which is probably all it should do since the tank is close to empty. As soon as I seat it (even without tightening, or even installing, the locking ring) it quits again.
The ground wire shows zero resistance to ground. But just to do something, I jumpered it to another, closer, ground location. No difference, behavior is as before.
In the photos it looks like the sealing gasket isn't there, but it is. It seals fine and there are no leaks.
Actually, at least in my case, it can't be mounted upside down. There is a tab that fits into a slot on the tank that won't let the device seal if it's not installed right-side-up. Of course, depending on which knock-off sender one has (mine is a Eurospare, I wasn't going to part with +$150 for the OEM part), it's probably possible to do so.
I did confirm that the float was past the baffle plate, so that wasn't the issue either.
Anyway, a happy ending may be in site. I finally just got frustrated with it, installed it, put the retaining ring on and decided to mess with it some other day. Went to the gas station and filled it up...still nothing. Made a few stops on the way home, and after starting it at one of those stops it suddenly decides to work, or at least it's now showing the tank is full.
Actually, at least in my case, it can't be mounted upside down. There is a tab that fits into a slot on the tank that won't let the device seal if it's not installed right-side-up. Of course, depending on which knock-off sender one has (mine is a Eurospare, I wasn't going to part with +$150 for the OEM part), it's probably possible to do so.
I did confirm that the float was past the baffle plate, so that wasn't the issue either.
Anyway, a happy ending may be in site. I finally just got frustrated with it, installed it, put the retaining ring on and decided to mess with it some other day. Went to the gas station and filled it up...still nothing. Made a few stops on the way home, and after starting it at one of those stops it suddenly decides to work, or at least it's now showing the tank is full.
Who knows!
Thanks,
John
John, Strangely enough that is exactly what happened to me. I installed the new one and it didnt work and 2 x small trips later she fired up!
Seems to work ok now reliably but is far from accurate. It is now at least a rough guide of how thirsty the V12 actually is haha
When you say it doesn't work when mounted, what DOESN'T it do, read, report...? What does it report? Are you saying the needle on the dash just bottoms out? Dead?
It grounds through the tank so sometimes the retaining ring needs to be nice and clean to make contact. In your first photo the mechanism is probably sitting on the edge of the tank and grounding.
If that's the case,,, for a more accurate reading, maybe I'll direct ground mine... Hmm, is it the usual to use the actual tank, a tank holding 20gallons of gas,,, for grounding? Im intrigued,,, I have an electrical schematic and tomorrow, I am going to check to see what the 3 wires are all about.
It grounds through the tank so sometimes the retaining ring needs to be nice and clean to make contact. In your first photo the mechanism is probably sitting on the edge of the tank and grounding.
It does not ground through the tank JB. The ground tab on the sender goes to a dedicated earth via the loom. In fact, the locking ring rubber seal might even insulate the sender from the tank.
It does not ground through the tank JB. The ground tab on the sender goes to a dedicated earth via the loom. In fact, the locking ring rubber seal might even insulate the sender from the tank.
Older Jags do ground through the tank, my 1966 S Type and 1990 Daimler Limo do. It only has the signal wire in the loom, no ground. The lock ring provides a good ground path to the sender, as it presses tight against both the tank and sender.
Older Jags do ground through the tank, my 1966 S Type and 1990 Daimler Limo do. It only has the signal wire in the loom, no ground. The lock ring provides a good ground path to the sender, as it presses tight against both the tank and sender.
I am sure that may be so, JB, but the XJS does not. In the photos the earth tab on the sender is clearly visible, it is connected to the white clip, and it has its own dedicated earth wire in the loom.
What it doesn't (or didn't do) was anything. As soon as it was pressed up against the gasket the needle would go to the bottom and stay there. When power was applied (the switch to ignition) there would be a just-detectable "jump" of the needle, and that was it.
I did try a dedicated ground (other than the ground connection on the wiring harness)...connected the ground tab on the sender to part of the body in the boot. It made no difference.
While it is "working" now, it's not dampening. The needle will still swing at times.
I think I mentioned before that I originally installed the part number for the convertible. While it didn't work anywhere below half a tank, it also dampened. I may fool around to removing the arm from the coupe version and see if I can install it on the convertible version. More work than should be required, but we all go through that drill!
08-31-2018, 01:09 PM
Fuel sender mystery
