Fuel gauge going crazy-please help
 

Hey there guys

My car was sitting for 3 months and when I have started driving it again, the fuel gauge is going up and down like crazy all the way to empty and then back to full. My anti slosh module is relatively new (2 years), but it's getting very hot. Should I get another module and see if it works? Or did the sender in the fuel tank go bad from the car sitting? Any other possibilities?

If anyone has any experience with this failure mode, or knows how to fix the anti slosh module, please let me know. Keep in mind I mentioned the anti slosh module is getting very hot

Thanks

I'm no expert, but it doesn't sound like a sender issue at all to me. you can check that by holding the orange/green Sending unit wire to a ground while running the car. I really doubt that's it though. I'd check the anti slosh module, make sure each post on it is getting the right voltage and go from there. I'm sure others will weigh in with better info as well.

Check the condition of all the wiring joints and earth contacts.

Don't change anything unless you know it's the cause of the problem.

First of all, determine if it's the A/S module. Pull off the module. Use a short piece of wire to bridge the sender input voltage terminal and output gauge voltage terminals of the module holder. If the gauge now reads correctly the fault is your module.

If it still fluctuates, bridge the wires off the sender unit. If the gauge now deflects to full, it indicates the gauge is working. So, it's either the sender or the wiring connections. Don't discount the earth connection of the instrument cluster either.

Good luck

Paul

I had a sender intermittently fail once. It would get hot and read empty, then read more accurately when cool the following morning. Mechanic could not figure it out. My theory was that my exhaust pipe was cooking it. It eventually completely failed, making it easier to diagnose.

A little late with this post and link, although I did post on another thread.
The following link is at least on point and gives an option to by-pass the slosh module.
Jaguar Enthusiast Vol 30 No.5
I hope this helps.

Gerry T.

I have the same issue. Its been going on for years. I checked with a multimeter and the ohms are correct. I have concluded that the sender is sticking. Given the price and the fact that it is generally only when below a half tank, I just left it. Eventually I will replace the sender.

Hoodun, the below is pasted in from another thread hereabouts.

Remove the light green/ornage wire from the fuel tank sending unit. Turn the ignition 'on'. Now touch the wire to a ground. The fuel gauge should move to 'Full". If it does, the gauge itself and wiring are OK and the problem must be the sending unit.

If it doesn't move to 'Full" then the gauge itself is faulty or there's a problem other than the sending unit

Cheers
DD
__________________
Doug Dwyer
Pacific Northwest USA
1988 Series III VDP V12
1985 Series III XJ6

Yes, the sender was expensive but in my case solved the problem. My previous post on this thread would be a go-to solution (slosh module) if the new sender had not worked out. Somewhere on this forum, I posted a report describing how I tried cleaning up the contact strips on the sender using a pencil eraser but it did not work. I thought afterwards that perhaps there was not enough pressure on the two contact strips, by the contacts themselves. It would be tricky to adjust them though.

HTH
Gerry T.

Hey guys, sorry I haven't updated on this. My daily driver X type got rear ended and I have been super busy at work....

I still haven't determined the reason for the fluctuation. I am goingto try some of the suggestions here and see what I come up with.

It seems that after my XJS came back from the paint shop I now have a list of things that need to be tended to, so I shall be posting a lot of other topics too.

Thanks guys

Hard lines about the X-type, Mark. At least not your fault.
I do hope that my info is accurate for you, because I just noted that your XJS is a convertible, so I do not know for sure that the sender is in the rear middle of the fuel tank like it is on coupes.
Keep us updated as and when...

Gerry T.

Thanks Gerryxjs, the article you posted was spot on!!! Problem solved.

I just want to add here that this is pin5 and pin3. If you have a resistor lying around use a low value (10-30 ohm) instead of the wire. If not, then do not worry about it. Its not worth running to the store to get a resistor for, just use the wire.

The Needle Would Start Its Crazy Dance
http://www.rockauto.com/Newsletter/images/RAmech.gif
The fuel gauge in my 1992 Dodge B250 van should have been reading about ¾ full, but instead the needle was swinging wildly to different spots between the ¾ and empty marks. Every few seconds, the needle would start its crazy dance. The needle was moving even when the van was sitting still at stoplights. It was hard to concentrate on driving while the big gauge in the center of the dash needed an exorcist.

It is an older vehicle and the problem came on suddenly. My first assumption was that the fuel gauge sending unit in the fuel tank had worn out. The sending unit is an arm with a float on one end and a variable resistor on the other. When the fuel tank is full, the float rises up and moves the variable resistor to its low resistance (impedance) end. Low resistance means more electrical current gets back to the gauge in the dash and the needle moves up to the full mark. As the fuel level falls in the tank, the float moves the variable resistor towards the high resistance end, less current makes it to the gauge and the needle moves towards the empty mark. An electromechanical system that is bound to wear out eventually.
http://www.rockauto.com/Newsletter/i...mStory9315.jpg
The sending unit is an arm with a float on one end and a variable resistor(circled)on the other
Luckily, I remembered an old Goss’ Garage segment from an episode of MotorWeek (RockAuto is a sponsor of MotorWeek). Pat Goss said sulfur could become too concentrated in old gasoline as more volatile chemicals evaporate away. Sulfur tarnishes the silver-based contacts on the variable resistor, creating random spots of high resistance that lead to random movements of the fuel gauge needle. The recommended solution was to pour a bottle of fuel system cleaner in the gas tank. The right cleaner in the tank would remove the corrosion and the fuel gauge would start working again.

I am skeptical of potions, but nothing is easier than pouring a little bottle into the fuel tank, so I gave it a try. A typical grocery/variety store has a dizzying selection of bottles labeled “Fuel System Cleaner.” I chose the first bottle I found that had printed on the label, “Removes deposits from the fuel sending unit, which can cause erratic fuel gauge readings.” The top ingredient listed on the label was kerosene.
http://www.rockauto.com/Newsletter/i...tory9315_2.jpg
The bottle of fuel system cleaner worked! There was an almost immediate reduction in the crazy swinging, but it took a couple of weeks before movement of the fuel gauge needle was back to normal. I avoided replacing the fuel pump/sending unit module (found under Fuel/Air in the RockAuto catalog) unnecessarily and perhaps inadvertently installing new parts in a fuel tank still full of bad gasoline.

Tom Taylor,
RockAuto.com

I read this today on the Rockauto newsletter.

Interesting. I have noticed that the problem would go away at random times. I never thought to corollate it with fuel cleaner I put in the tank. I will definitely try this. I used that same max life cleaner and I actually think it may have solved my issue. ...this could be purely psychological but I will know soon enough.