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If fuel gauge is not working, easy way to tell how much fuel is in each tank?

XJ6 & XJ12 Series I, II & III 1968-1992

If fuel gauge is not working, easy way to tell how much fuel is in each tank?

 
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Old 01-08-2012, 09:32 AM
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Default If fuel gauge is not working, easy way to tell how much fuel is in each tank?

My fuel gauge isn't working--I suspect the floaters have filled with gas and have now sunk to the bottom. Is there any way to tell how much fuel is in each tank? Perhaps by knocking on it or something?
 
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Old 01-08-2012, 09:48 AM
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If draining or pumping the tanks isn't in the cards (pumping them would be very easy) then you have a couple choices.

1) Run 'em dry. Bad choice. The pump will suck up muck from the bottom of the tanks.

2) Fill each tank and drive long enough to ensure the tanks are about only 1/4 full.

Each tank is 12.5 gallons. City driving should yield about 12 mpg. That's 150 miles per tank. Drive about 120 miles on each tank. The fuel level should then be wayyyyyy below the fuel sender openings....which are actually rather high on the tanks.

Others may chime in with more ideas

Cheers
DD
 
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Old 01-08-2012, 03:31 PM
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A piece of wooden broom handle down the fuel filler hole maybe ?

In the early 60s, my friend had an MG TF sports car, and that was the ONLY way to check - no fuel gauge was fitted !!
 
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Old 01-08-2012, 07:39 PM
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Hahaha...

Doug, could you expand on the "pumping" option? I am thinking of buying a transfer pump to pump the fuel into gas tanks for disposal.

Multi-Use Transfer Pump

I would really like to remove the drain plug on the fuel tank, but I just can't do it where the car is at now--or anywhere within "driving" distance (the car can barely make it around my parking lot!)--and risk spilling lots of fuel. It's parked right underneath a 7 story apartment building and a lot of people would be pissed!

Do you know if the XJ6 has some sort of anti-siphoning valve/trap?
 
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Old 01-08-2012, 07:41 PM
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Also, any idea how to tell which fuel tank the car is drawing off of right now?
 
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Old 01-08-2012, 07:51 PM
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Pumping out the gas:

Collect enough gas cans or buckets or whatever.

Remove rubber fuel hose from the rear of the fuel rail. It will need to be extended to reach your gas cans. Fashion or buy some sort of coupling/pipe/joiner so you can add some additional fuel hose to the existing fuel hose for added length

Locate the fuel pump relay. It's on the firewall. It's the one that has, among others, white/green wires. Unplug the relay from the socket. Set the realay aside.

Using a jumper wire apply 12v to the terminal(s) inside the socket that are associated with the white/green wire(s). You hear the fuel pump run. Be ready for quite a strong flow of fuel into you gas cans.

Cheers
DD
 
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Old 01-08-2012, 08:26 PM
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Fantastic! I should cancel that order that I just placed for a fuel tank siphon, then!
 
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Old 01-08-2012, 08:53 PM
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Does the fuel tank switcher work with the engine off? How do I drain the second tank in this fashion?
 
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Old 01-08-2012, 10:54 PM
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Well, I purchased the Jaguar Service Repair Manual. Hopefully that will stop me from asking stupid assinine questions!
 
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Old 01-09-2012, 01:03 AM
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Originally Posted by amcdonal86 View Post
Does the fuel tank switcher work with the engine off?

The key must be on, not the engine.



How do I drain the second tank in this fashion?


Just use the dashboard switch to switch other tank and pump it out

Cheers
DD
 
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Old 01-09-2012, 10:50 PM
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I see the line going on the back of the fuel rail. Do you happen to know what the I.D. of this hose is so I can buy a similar one to hook it up to and extend it for the purposes of draining the fuel? Also what sort of fitting should I use?
 
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Old 01-09-2012, 10:51 PM
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Originally Posted by Doug View Post
Using a jumper wire apply 12v to the terminal(s) inside the socket that are associated with the white/green wire(s). You hear the fuel pump run. Be ready for quite a strong flow of fuel into you gas cans.
So i'm planning to literally just run some speaker wire from each terminal of the battery to the white/green wires (one each). Is this correct?
 
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Old 01-09-2012, 11:22 PM
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Originally Posted by amcdonal86 View Post
I see the line going on the back of the fuel rail. Do you happen to know what the I.D. of this hose is so I can buy a similar one to hook it up to and extend it for the purposes of draining the fuel? Also what sort of fitting should I use?


3/8" ID fuel hose

Just get a two-ended nipple or a piece of 3/" tube of some sort to join the two 3/8" hoses together. There won't be any pressure to deal with. Just lots of flow.

Cheers
DD
 
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Old 01-09-2012, 11:26 PM
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Originally Posted by amcdonal86 View Post
So i'm planning to literally just run some speaker wire from each terminal of the battery to the white/green wires (one each). Is this correct?
No.

One wire from the "+" post of the battery to the wire/green wire in the fuel pump relay connector.

You probably have two white/green wires in the connector. Only one goes directly to the fuel pump. Try both. If you get the wrong one, nothing will happen. When you've got the right one you'll hear the pump and fuel will be gushing !

Cheers
DD
 
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Old 01-10-2012, 07:46 AM
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Originally Posted by Doug View Post
No.

One wire from the "+" post of the battery to the wire/green wire in the fuel pump relay connector.

You probably have two white/green wires in the connector. Only one goes directly to the fuel pump. Try both. If you get the wrong one, nothing will happen. When you've got the right one you'll hear the pump and fuel will be gushing !

Cheers
DD
Haha, thanks. Good thing I asked! I really appreciate your help!
 
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Old 01-12-2012, 07:16 PM
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Well I finally figured out how much fuel is in at least one of the tanks. Last time I was in the car a couple days ago, I sat in the drivers seat with the engine off, keys OUT of the ignition and pressed the changeover switch, and then immediately pushed it back to its original position. Out of curiosity, before I left the car, I opened the gas cap on the right and noticed a "whoosh" sound. Cool, the engine must've been using the right gas tank last time I ran the engine, right? Well two nights later I come back and open the right gas cap. Again I hear a whoosh, but this time it is immediately followed by old gasoline rushing out of the cap. It kept pouring and pouring, until finally I opened the other gas cap and it stopped. Now the right tank is full to the brim! Have no idea how much is in the left tank... what is going on here???
 
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Old 01-12-2012, 08:46 PM
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'87 XJ6 fuel tank overflow - Jaguar & Land Rover Enthusiast Forums

This thread in the link seems to describe EXACTLY my problem.

"
Recently I noticed that my Jag seemed to be cutting out a little. That was soon followed by a strong smell of gas and loss of power. I switched tanks and got far enough to pull off the road and it then died. All of this happened in the distance of about 4 blocks at speeds under 35mph. When trying to diagnose the problem I opened both fuel caps. When I opened the passenger side cap, fuel began to bubble up out of the filler neck and down the fender. It doesn't seem to matter which tank I have selected to run off of or whether the engine is running or not. I don't think it matters if the key is in the ignition or not. I had just driven about 15 miles on the highway prior to this. I find no evidence of fuel spilling out around either of the front tires. I filled up with fuel last night and I don't think I had run off the passenger tank at all since the fillup so it was probably still pretty full when this happened. Hope someone can help. Thanks....Art"

A Jag Tech explains what happened, and why it's happening:

"When you select the right fuel tank, the changeover valve in the trunk shuttles so that the fuel pump draws fuel from that tank. The pump is designed to provide more fuel than the engine will ever need just so it always has plenty. The pressure regulator maintains the right amount in the fuel rail and the excess goes into the return line. The return line runs back to about the differential where it splits off to each tank. Since you have the right tank selected, the right side return valve is open and the left one is closed. This makes the system, in effect, a one tank system just like any other car. When that tank gets low on fuel you press the button on the dash and the changeover valve shuttles the other way, the right side return valve closes and the left one opens. The universe is in harmony. Sometimes this works fine electrically but the seals in the return valves don't seal. This causes fuel to be drawn from one tank and returned to both. Since the tank not selected is full, trying to add more fuel is a bad thing. That is when the fuel flows through the vapor line into the canister causing the problem you are experiencing."

How likely do you think this is what I'm experiencing? Will I need to replace the charcoal canister?
 
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Old 01-12-2012, 10:01 PM
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The overflow can and does occur as described above. I might add that any info from Phil Prince is good as gold. He stopped doing the Jaguar/forum/internet stuff many years ago, though. Swell guy.

The whoosh sound is usually caused by a plugged/faulty pressure valve up there by the charcoal cannister. Replace it, disconnect it, or drill thru it. It's the one on the horizontal vapor line running to the cannister, behind the right front wheel.

Cheers
DD
 
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Old 01-12-2012, 10:18 PM
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Would that cause the symptoms I have? (Stumbling stalling under acceleration/revving the engine above idle?) I'm thinking for diagnostic purposes of just disconnecting the charcoal canister. Also, until I can troubleshoot the fuel system fully, I'm thinking of just replacing the changeover valve with a brass Y or T-fitting. Are the hoses in the trunk just 3/8" ID like the ones under the hood?
 
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Old 01-12-2012, 11:41 PM
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The hoses in the trunk that go from the tank to the switching valve to the pump are 7/16. I have seen a car in the junkyard that had a T-fitting in place of the switching valve, I don't know how well that works. There is some risk in one tank emptying into the other if the car was ever parked with one side significantly higher than the other, but most of the time it probably works fine. As Doug said the valve near the charcoal canister is important because it is the venting for the tank and must flow freely or tank collapse is a real risk as the fuel is used. The valves that block return flow behind each rear wheel also need to be considered, and possibly replaced with straight tube.

Your fuel senders may have seized. It is possible to remove them and clean them carefully, scraping off the scale that builds up, then opening them and cleaning off the resistor wire that is coiled inside, and ensuring good contact and freedom of movement is restored.
 
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