Hi,
I was wondering where I would find the sending unit for my gas gauge? Also how hard will it be to get to it? Is it the usually the sending unit, gauge or something else that the causes inaccurate readings? I have only owned the car for a few days and have not seem any pattern with the gauge reading (like it reads correctly or reads empty). The prior owner just told me that the gauge does not work.
Thanks,
Jomo

 

The sending unit in the fuel tank.You access it from the top of the tank. The tank either has to be totally removed, or maybe just pulled out a bit. I have never done it so don't know how easy/hard it is.

 

Jomo,

The tank doesn't have to be removed to get to the sender unit on your convertible.

However before you take the sender out, check the anti-slosh module which is a known failure point. Remove the module, and bridge terminals 3 & 5 of the holder and see if that cures it. First of all buy the parts & service manual from the shop at Jaguar Heritage if you're going to run an XJS.

Good luck

Paul

 

It was too easy, but my fuel gauge seemed to have a mind of its own. I did the cluster disassemble/clean/reassemble thing, helped the volt meter the most, but no change in the fuel gauge. Took the spare out, pulled the cover out, saw the connections on the fuel tank right in front of me. Simply pulled the wire, grounded it just long enough to see that the fuel gauge worked properly a few times, plugged it back in, and it seems to work perfectly now. Bad connection? I love dielectric grease on these cars.

 

All they had were Owners Manuals, not service manuals. I tried searching their web site for them and came up with nothing.

 

There may be something wrong with their website. I bought a DVD that has the full range of XJS manuals and publications.


Go to the HOME page, and then click the SHOP button on the top right. Then on the left under Categories, click on Technical Publications. The selection "Technical Publications DVD-NEW RANGE" is where I found it. It has the same green cover as those currently displayed. I bought it about in June this year. I doubt that they have discontinued it because publishing a DVD is very cheap, and the selling price was about $100 US as I recall.

 

NtaFord,

They seem to have stopped producing a number of the old-type DVDs for the XJS, see here:

Jaguar Heritage. Technical Publication DVDs

and, at the moment they seemed to have run out of stock of the new-type DVDs for the XJS, see here:

Jaguar Heritage. DVD's

I would give them a call or email and ask when they expect to have stock back in for the new DVDs.

Good luck

Paul

 

Hi,
I ran some tests and here is what I found out. When I grounded the green wire from the sending unit the gauge read full. I then put a 100 ohm resister across both wires to the sending unit. I felt that should be low enough to get the gauge near or at full. The gauge barely went to 1/4. I then put a 470 ohm across the two wires and got an empty reading. I thought maybe about halfway it should have been. What might be the problem as this gauge while driving is all over the place.
I looked for the anti-slosh module in the area behind (towards the front of the car) the CD Changer and all I saw was a relay and a big silver module about the size of a radio. Is it this silver device?? If I remove the anti-slosh module can I drive the car?
Thanks,
Jomo

 

Jomo,

First of all, you can drive the car with the anti-sloh module disconnected, you just don't get any fuel gauge reading or low fuel light.

The A-S module is like a slightly large relay, it's black and it sits on a relay mount bar just behind the boot strut mount panel on the left. It's a bit difficult to see but use a torch and it's quite feasible to remove with the boot strut in situ. If you absolutely can't find it, then disconnect the strut, prop the boot open and remove that black small strut mount panel, then you'll see it.

In order to test whether it's causing the problem, pull off the module, then use a small peice of wire and bridge terminals 3 & 5 of the module plug-on loom. This then gives direct voltage from the tank sender unit direct to the gauge. If the gauge reading is now right, you've discovered the problem. Leaving it disconnected and terminal-bridged like that will give you a gauge that might vary a bit with corners and acceleration (the purpose of the module is to smooth out these fluctuations) and the low fuel light won't work as it's driven off the module only.

Good luck

Paul

 

Paul,
I pulled out the module and opened it up. It looks like a mess in there with broken lines in the cb and cold soder. So I will be replacing this module. I do have two questions. Usually the numbers for the pins are on the module/relay itself but mine has no numbers on it. So I was hoping that you could please inform me which pins you call 3 and 5. How about we agree on something let's suppose you are holding the module in front of you with the pins facing you in a way that down the center are 3 pins with the 1st 2 being horizontal and the last one vertical with one pin on the the left side and one one on the right side which are both vertical. Last question is where are good places to get parts for my car? I took your advice and ordered a manual.
Thanks,
Jomo

 

Jomo,

Sockets 3 & 5 are the middle horizontal one and the vertical one above it. Just put a small bridge wire between them.

Hope that makes sense.

Good luck

Paul

 

Paul,
I jumped a wire across those two terminals and the gauge did not move at all with the ignition on, it just sat there on empty. Then I started the car and that changed! It seems to be working now. My tank was full and it reads full and actually went down a little during an outing. I did not see the gauge fluctuate at all during the drive! Thanks for your time. I truly appreciate it (unlike that student who wants to buy an xjs with a bad motor!)
Thanks,
Jomo

 

Hi Jomo,

I'm really quite confused by that. Are you sure you've successfully bridged the correct sockets on the wiring plug? The reason I'm confused is that you mentioned before that the gauge did read something when the module was connected. And we know that thee gauge can deflect fully when given full voltage as you've tried.

The A-S module only smooths the voltage. I've only ever seen a defective module cause the gauge to read low as the capacitors leak the voltage when they fail. By bridging terminals 3 & 5 on the wiring plug, you're just sending the voltage from the sender direct to the gauge. So if the gauge moves at all with the module connected, it must move at least that much with the module disconnected and the voltage passed straight through with a bridging wire. So you see why I'm confused!

The input voltage from the tank sensor comes in on terminal 5 (the middle horizontal one) and goes out to the gauge on terminal 3 (the top vertical one). With the bridge wire in place, try measuring the voltage at each end of the wire whilst it's connected to help confirm it's firmly in place.

Paul

 

Paul,
We are all trying to learn from this forum so please do not be upset by question. If based on what I said in this post you did not think that bypassing the A-S module would help then why did you ask me to bypass it? Were you trying to gather more information?
Tonight I drove the car again and the gauge did fluctuate a bit-about 1/8 of a tank from time to time. It really seems to be working correctly. As I went up and down steep hills the gauge adjusted correctly.
I will describe the best that I can about how the gauge has been working for the 2-3 weeks that I have owned the car. Sometimes it was reading correctly and other times it was reading around empty. It fluctuated every time I drove the car. It never read more than what I felt was in the tank.
If you need me to try to explain anything further or have any questions for me then please ask as I do appreciate the time you are spending on this.
I will certainly update this post as I use up the tank of gas.
Thanks,
Jomo

 

Hi Jomo,

Perhaps I didn't make myself clear in the last post. The reason that I was surprised was because I fully expected your gauge to read correctly with the car at rest when the A-S module was removed and the plug bridged at Terminals 3-5.

If you have fuel in the tank, then bypassing the A-S module from the circuit should give you a correct reading (if it is the A-S module that is at fault). Because that didn't happen, I think you must have 2 faults.

If you bridged the plug correctly and the gauge then didn't read properly at rest, then the fault must lie either with the sender, the wiring or the gauge. However, because you can deflect the gauge fully just by grounding the sender then that would imply the gauge is ok, and one of the the problems is an intermittent fault with the sender or the wiring.

However, because you've implied (I think?) that (when it's working) the gauge varies when you go up steep hills with the A-S in place, that seems to imply that the A-S module is also at fault. By smoothing the voltage when there are small changes in the sender position (such as when the fuel level moves when you go up hills) the A-S module prevents the gauge from fluctuating. You also mentioned that the A-S circuitry looks dodgy anyway.

My conclusion would be:

- gauge reads empty with A-S plug bridged probably = faulty sender or wiring
- gauge fluctuates up hills probably = faulty A-S module

The simplest things to check would be:

- Try removing the A-S module and bridging it with a different bit of wire. If the gauge is reading today with the module in place, then it must read ok with the module removed and the bridging properly in place. If it now works, then drive around for a while with the module removed and bridged and confirm that the gauge always reads (although it will vary a bit on hills and bends).

- Check the sender connections for good continuity
- Pull the instrument cluster (3 screws + 2 screws) and carefully check the wiring plugs and earth screws. These facelift clusters are notorious for bad earths.

If none of this works and the gauge reads zero with the A-S removed and bridged, then I think you have to start looking at a possible sender replacement.

The priority is to get the gauge working (but recognise it will fluctuate a bit) with the A-S plug bridged. Once that is stable, put the A-S module back and see if you get problems. If that then happens, you replace the A-S module.

I do hope that helps. Let us know how you get on.

Paul

 

Paul,
I need to clarify a couple of things. I did put the bridge wire in yesterday and have not removed it. Yesterday during a second outing with the car (and w/o the A-S module) the gauge did fluctuate while I went up and down hills which is what I would expect w/o the module in place. With the ignition key in my hand, ie not in the ignition, I bridged terminals 3 and 5. I then inserted the ignition key and turn it all the way (just before the starter position) and the gauge did no move at all. I thought that there must be a 2nd problem as that module is clearly fried. Then I fired up the car and the gauge instantly moved to just under full which was where it should have been.
I understand that I have only driven the car about 20 miles since bypassing the module but so far all is good. I am thinking that everything is working correctly with my bypassing the A-S module.
Jomo

 

Jomo,

OK, now I understand. Sorry, I thought you were driving around today with the A-S module back in place.

Taking things one at a time: If the gauge now behaves itself as we would expect, ie accurate at standstill / steady speed and minor fluctuations on bends / inclines, that implies that sender, gauge and wiring is all ok.

I'm not sure why the gauge didn't work without starting the engine. The circuits are wired to operate the fuel gauge with key in Ignition Position II. However, it is possible that there is a slight lag before the gauge starts to read. I guess the other reason could be that the sender float has developed a leak and sinks to the bottom when it's left for a while. However, if that were the case, I don't think it would suddenly recover just because the engine started. Let's ignore that one for now.

Overall, I think you're probably in not too bad a position. You clearly need a new A-S module or could you fix the existing one? As I mentioned, we have seen not just dry joints but also leaking capacitors on failed modules. If you're handy with electronics, you could give yourself a little challenge and fix it or else buy a new one.

After that, I think there's every chance that your gauge could be back to normal.

Do remember that with the A-S removed and the gauge hot-bridged, then you won't have a low fuel warning light operating. The light is driven only off one of the pins of the A-S module.

Good luck

Paul

 

Paul,
Thanks for reminding me about the low fuel indicator not working w/o the A-S module. I will test every thing on the circuit board and try to fix it. I drove the car today and the gauge was reading perfectly. It even moves now when I turn the key.
Thanks,
Jomo

 

Hi,
I replaced the Anti-Sloth module today and all is looking good. The only change that I see (and should see!) is that when I go around bends or on inclines the gauge does not fluctuate at all as compared to when I bypassed the A-S module.
Since I just purchased the car and really have no idea how many miles I could go on a tankful I really wanted this gauge to be working correctly-and now it is! Thanks to all that helped me on this problem.
Jomo

 

I could sure use one of those here in North Idaho!