Well, it didn't take long. I inherited a very nice '93 XJS about 2 months ago. I've been "Sunday" driving it frequently, and have come to appreciate it's qualities. And everything worked. Until yesterday.


I was out joy riding when suddenly I noticed the low fuel warning light on. This surprised me because a) I actually could see it in the daylight with the top down, and b) I had just filled the tank about 10 miles back.


I also noticed that the fuel gauge showed zero fuel. Coincidentally, and possibly not related, the low engine coolant light was going on very intermittently.


Just before the drive, I had cleaned the trunk (boot). I took out the spare tire and floor carpet, removed a golf ball lost behind the tire by a previous owner, and vacuumed. Since this is the general area where the important bits are for the fuel quantity sensing system, perhaps I disturbed something?


From what I can gather from other posts about the system, it sounds like the most likely culprit is an anti-slosh module in the LH side panel. Or perhaps the fuel quantity sender itself. I'm hoping both are accessible from within the boot after removing the front carpet and side panel trim.


I've ordered a set of LED bulb replacements for the warning light cluster. So I'll wait until those arrive before I remove the cluster unit. From what I read, it sounds like there are contacts in that unit that will all need cleaning, and that I should add an extra ground jumper too.

 

http://www.jagrepair.com/images/Elec...Electrical.pdf


Have a look at page 31 of this 69 page PDF. It shows the sender and slosh module circuit. Remove the slosh module. Put a ohm meter on the 200 range between a good ground and the light green wire at the base of the antislosh module. If the in tank sender is good.... You should have resistance that varies as you bounce the car. To test the guage....ground the light green orange stripe wire. The guage should read full. Additionally you can put a jumper wire between the LG and LGO wires and you should have fuel level without the antislosh feature. If this is the case by elimination you can infer that the antislosh module is bad.

 

iscamerica,


Hi, and thanks for the quick response, suggestion and resources. I think it might be the fuel qty sender. I disconnected both wires and checked the resistance across the two connectors on the sender. It reads infinite resistance, open circuit. If the resistance goes up as the fuel quantity goes down, then an open circuit in the sender would give me the zero fuel on the gauge and low fuel light on.


I'm not certain if my care has the anti-slosh feature. What I have read in other posts is that it is in the left side of the boot (forward of the CD changer. But the harness from the sender goes to the right side of the boot (battery side) and then joins into a larger harness.


Am I correct in thinking that I should get some conductivity through the sensor? Having just topped off the tank, perhaps the float is very high, and is in a dead spot? It did come back to life very briefly a couple of times as I drove home. So perhaps tank sloshing was getting the float momentarily down into a conductive part of the variable resistance device. I'm assuming this is probably a wire wound type of variable resistance, and the float moves a wiper blade across the wires.


Thanks,
Greg

 

It should have an anti-slosh relay. Sounds like you've got it diag'd right to me. All your theories seem plausible. Chances are you can remove the sender and carefully expose the coil and clean it or perhaps tweak the arm position a bit. If it comes back to life when the sender drops a bit then leave it alone, it's just the nature / character of an older car. %2

 

I would think it has an anti-slosh unit too. That is what drives the low fuel warning light in addition to the qty guage. The schematic has the symbol for a transistor on the unit, so it has some active electronic circuits in it. My guess is that the unit just dampens the voltage fluctuations coming from the sensor due to sloshing. And that it trips the low fuel warning light on when the voltage drops below a set value.


Perhaps it is on the RH side. Maybe what I was reading about it being on the LH side was for UK vehicles? I wonder if the swap sides on a lot more than just the driver related cockpit items.


It's easy enough to get to the fuel sender connections, so I might do another test by putting a variable resistor across the two wires and see if I can change the indications. Do you know were I might get the resistance range for the sender, and if higher resistance equals less fuel?


Thanks again,
Greg

 

After sending my last response, I re-read your first advice. Am I correct in thinking that the tanks sender unit operates in a range from at or near zero to 200 ohms?


Thanks,
Greg

 

Page 11 suggests its on the Storage Compartment, left side.


I've looked for the resistance range but can not find it anywhere, its probably in the service manual in a diag procedure but I don't have it and I cant find it. Typically on cars this age its from 90 to 240 Ohms but that's just a guess.

 

The left side is definitely where it should be. The ABS ECU is there for sure, and I can see (barely) and feel what are probably the brake bulb fail and speed interface units. If it becomes apparent that the antislosh is the problem, I'll probe deeper for it (some how, it must be possible).


90 to 240 ohms should be good enough for my purposes. I just what to see if the gauge tracks the change in resistance, and if I can extinguish the low fuel warning.


Thanks,
Greg

 

I found this. See the last post. ...It suggests a German fellow hooked up a "scope" and tested it...typical.

https://translate.google.com/transla...opic%3D21441.0


It says..."The tank sensor delivers at full 17 ohms and 250 ohms at empty and linear intermediate values"

 

That confirms that higher resistance equals less fuel. So I'm pretty sure its the sender unit. It's probably on a dead spot. I'll drive it for awhile to see if it comes back to life. If it does, I'll let it be. If not, it seems like replacements are readily available.


Thanks for all your help and research.
Greg

 

It does seem to be a dead area of the sensor. After driving a short while, and jiggling the car, the gauge came back to normal reading and the low fuel light went out. But that only lasted about a minute, then it reverted to empty and low fuel light on. I drove around for awhile and it would intermittently show signs of life, but mostly not.


I ordered a new sender unit and gasket. If I'm going to go through all the work to drain the tank and remove the sender, I might as well replace it with new.


Thanks,
Greg

 

It was a defective fuel qty sending unit. I replaced it today, and the quantity gauged functions normally. And the low fuel qty light extinguished when I filled the tank after changing the sending unit.


Now, I'm off in search of the next Lucifer Electric problem. My "Sport" mode light (in the warning light cluster) is on dimly all the time.