I filled my "new to me" 2010 XK convertible for the first time and within several miles of driving, the fuel gauge went from showing full to showing half full (or half empty for you pessisimists). It would intermittently show full but mostly hung around half full, and showed only half the range. Is this a known issue? I have five months left on original warranty so I can get it taken care of, but I wanted to be informed when I take it in for service in case it's not happening on that day.

 

Took a look at the workshop manual. Very interesting: there are two fuel level sensors in the 5.0 model tanks:

I guess it averages the two readings - so if one says 100% and the other says 0%, you get 50%. That would suggest that one of the sensors has an intermittent fault - might be the sensor, might be the wiring leading back to the AJB (the fuse box between the back seats). Wiring comes out of the tank to a connector on the mounting flange. The sensor wires are white/red (left) & white/blue (right).

 

Thanks Ngarara. That makes sense given the behavior I've seen. I'll have them check that out.

 

Seems, and only 'seems', that one could disconnect a connector and read the resistance of each circuit with the tank full. It would be obvious which 'float' is failing IF it is one of the floats and not some other thing.

 

Did you drive on any roads like this:

 

Only in the Southern Hemisphere...

 

Even simpler: with a full tank, disconnect one, and see if your fuel gauge settles at 50% (in which case, you disconnected the faulty one) or keeps flicking between 0% and 50% (in which case you disconnected the good one)

 

That's where I should go! My XKR has been in the garage for more than a month because of the winter here in Canada. If I go down under my gas will leak out! I can't win.

 

Ok... So expanding on the fuel-related theme, I don't know if this is related to the faulty gauge reading, but tonight I got a message to "check fuel filler cap". I checked it. It's there. It's on correctly. I checked again. And again. Yet the message persists. Checked again just for the hell of it. Message still there. I swear I wasn't driving upside down through the Australian outback. Any ideas?

 

According to the workshop manual, that message appears if there's an air leak in the fuel system - basically, the Tank Leakage Detection system (part of the emissions-control measures) knows that the fuel system is open to the atmosphere somewhere. Usually that is because the cap is not fitted properly, or the seal on it is dirty or damaged, but there might be a leak somewhere else. Alternatively, the detection system itself is blocked or faulty.

If the cap is clean and the seal is undamaged, it would probably pay to take the car to a Jag dealer/specialist to get the diagnostic codes read - that should pinpoint the problem.

 

The fuel cap alert is telling you there is not a vacuum in the return line to your gas tank which in most cases is the fuel cap not properly sealed. This could also be caused by a leak in the return line.


I had this problem on my truck when the return line rusted out and triggered a similar alert (and I thought you might have been driving down under). The return line should be 1 continuous line, only with an engine and tank connection--no sections. Maybe the fuel fill sensor and fuel cap sensor are sharing data and some way through a module. I think you're getting close to solving this.

 

Although it would require a "smoke test" to determine if/where there would be a leak I would replace the gas cap or it's gasket/seal 1st. This would take it out of the equation . If you still have a warranty then have the dealer do it. Reset the MIL and see if it comes up again.

 

In ref to the fuel sender problem. To disconnect one or more of the wires to the fuel sender unit, from the connector CA070, would mean you'd have to depin one or more of the three wires in that connector. Easier to just ohm it out from CA070 than depin one or more wires in it.

Fuel caps can be checked out for integrity by a emissions shop . On cars without OBDII, in Texas at least, they remove the cap and put it on a gas cap checker which pulls a vacuum on it to see if it's any good or not. Takes but a ??? three minutes to do.

If the cap is good..........tough. I had a 2000 Sorry A__ van that had the vent hose for the filler pipe disconnected on top of the 2000 Sorry A__'s van's fuel tank. Tank had to come down to tighten up the vent hose. Fuel feed and retuen lines had to be disconnected to do the fuel tank removal. I'm sure you local Jaguar Dealer won't charge you very much to fix it. Just your other arm and leg.

I've not a clue why they show connector CA070 twice in the picture attached.

 

To close the loop on this, I took it to the dealer, still under original warranty, and they replaced the fuel tank. Very glad it was still under warranty.

 

Ouch! Seems a bit drastic.

 

It did seem a bit drastic. The service manager initially mentioned the senders but later notified me that they had to replace the tank after they diagnosed it. It was on their dime, so I didn't question it.

 

It's nice to have it fixed but I always wonder what other issues are created when something this major is done (if changing the gas tank is major).

 

It's reasonably major, in that you have to disconnect the driveshaft and remove the rear subframe (including the rear suspension and wheel hubs) to remove the tank. But they would have had to do that anyway to get at the faulty fuel-level sender inside the tank.

However, looking at the workshop manual, there's no instructions for removing & replacing the left-hand sender, which is on the opposite side of the tank from the fuel pump and filter (which is the only significant hole in the tank). You can pull out the pump and replace the RH sender attached to it, but for the LH sender, replacing the whole tank is probably the only easy way.

 

Good assumption.

 

Holly crapoly. That looks like an expensive procedure just for a fuel tank. I'm sure glad you had it covered under warranty and I thought it was because you were driving down under.