[xj] Fuel system problems

Symptoms below. All help appreciated.

– Both fuel tanks are drawing down simultaneously, regardless of the tank
chosen.

– When I pop the filler caps to refuel, one tank sucks air in and the
other blows vapors out. Which tank sucks and which tank blows depends on
which one I have selected using the switch on the dash.

bfh===
Burgess Howell
86VdP(Federal)

At 04:42 PM 10/9/99 -0500, you wrote:

Both fuel tanks are drawing down simultaneously, regardless of the tank
chosen.
– When I pop the filler caps to refuel, one tank sucks air in and the
other blows vapors out. Which tank sucks and which tank blows depends on
which one I have selected using the switch on the dash.

After much goofing around fixing ours, my advice is;
Replace the changeover valve with a normal T fitting.
The fuel system will then draw from an equalized tank system.
If you want to replace all 3 valves, go ahead, but after doing 2,
and spending $$, I am now going to install the T fitting.
If anyone says “but the handling…”, think about it;

  • Equalized tank volume will benifit handling in all situations
  • Fuel level senders in both tanks will read the same, if one fails
    just switch to the other, and don’t bother with the repair.
  • Fuel return valves can be replaced with high pressure metal line and hose
    clamps,
    or left until they fail, then replaced.
  • The chances of the t-fitting failing in the future are almost nil, so
    improved reliability.
  • If the dash switch fails, it can also be bypassed for more improved
    reliability.
  • Vapor recovery system may also be jammed. Try disconnecting the line from
    the tank
    vents before it connects to the 2 psi check valve. The tanks can then vent
    constantly.
    I have replaced the whole vapor recovery system with a GM fuel filter to
    prevent dirt from
    being sucked into the line, and the 2 psi valve mounted within one air
    cleaner.
    This way, no venting at rest, and when venting, fumes can be sucked into
    the engine
    and burned.

In the end, it is each owner’s preference, and personal choice on
modifications.

Kelly Spongberg
Rocky Mountain House, Alberta, Canada
1987 Jaguar XJ12 Vanden Plas
1998 Chevrolet K1500 Z71 Truck
1949 Ford F-1 pickup (someday project)
1997 Polaris Trail Boss Quad

At 04:42 PM 10/9/99 -0500, you wrote:
After much goofing around fixing ours, my advice is;
Replace the changeover valve with a normal T fitting.
The fuel system will then draw from an equalized tank system.
If you want to replace all 3 valves, go ahead, but after doing 2,
and spending $$, I am now going to install the T fitting.
If anyone says "but the handling…", think about it;

Handling reasons aside, there is a safety issue here. If one of your tanks should leak, with an equalized system, you have to spew gasoline everwhere to fix it. With the stock system, you have a back up. Example: If your car should develop a leak in the left tank while on a trip, you can feed off it until it is dry and then use only the right tank to get you where you are going - the left tank would pretty much be sealed off from the rest of the fuel system. Can’t do that with “equalizing” fuel tanks, as some Harley owners know…

With the stock system, there is a greater safety margin. So I spent the $125 to replace all the valves, they’ll be good for another 10 years, at least.

After much goofing around fixing ours, my advice is;
Replace the changeover valve with a normal T fitting.
The fuel system will then draw from an equalized tank system.
If you want to replace all 3 valves, go ahead, but after doing 2,
and spending $$, I am now going to install the T fitting.
If anyone says “but the handling…”, think about it;

What type and or source of the fitting??

  • Fuel return valves can be replaced with high pressure metal line and hose
    clamps,or left until they fail, then replaced.
  • Vapor recovery system may also be jammed. Try disconnecting the line
    from
    the tank vents before it connects to the 2 psi check valve. The tanks can
    then vent
    constantly.

I have replaced the whole vapor recovery system with a GM fuel filter to
prevent dirt from being sucked into the line, and the 2 psi valve mounted
within one air
cleaner. This way, no venting at rest, and when venting, fumes can be
sucked into
the engine and burned.

Kelly Spongberg

I’ve been having a similiar problem with right tank emptying into the left.
This problem seems to be INTERMITTENT. It seems to do it after the tanks
are filled, then continues for a period of time or may start again the next
day. I never top off the tank but stop pumping when the nozzle shuts off.

I’m getting tired of syphoning gas and listening for the return to the
proper tank. I’ve read ALL the threads on this problem and can now explain
proper functioning to my mechanic but why is it intermittent??? Cleaning
the contacts on the return valves was posted as a fix but what is the real
problem in my case?? When I push the change over switch I hear a clunk
from the boot, so I assume the change over valve is functioning. Since the
dash switch controls the whole system and the valve cycles and the gauge
selects R or L and even none when pushed in part way, I assume the switch
is ok.

Someone suggested adding Techtron to the tanks to clean the fuel system. I
added a bottle to each tank and ran both tanks for my ten mile one hour
drive home. There was no over filling but as I said the problem is
intermittent. I did notice the car running smoother but this might be the
plesebo effect.

Are the return valves behind a 4-5 inch round access panel at the rear of
each rear fender well?

The Jaguar is well engineered so I can’t imagine that a T fitting was not
considered. Is there any detriment to replacement with a T ???

Dr.Michael E. Rothman
'87 January build Series III USA
Princess Margaret

At 10:27 PM 10/09/1999 -0600, you wrote:

After much goofing around fixing ours, my advice is;
Replace the changeover valve with a normal T fitting.
The fuel system will then draw from an equalized tank system.
If you want to replace all 3 valves, go ahead, but after doing 2,
and spending $$, I am now going to install the T fitting.
If anyone says “but the handling…”, think about it;

<benefits snipped>

Kelly Spongberg
Rocky Mountain House, Alberta, Canada

I’m probably wrong, but one downside I could forsee would occur if: both
tanks nearly full and car parked with one side higher than the other –
fuel would transfer from high side to low side, and could overflow from
fill cap and/or vapor recovery system.

Just my WAG.

= = = = = = = = = = = = =
Mark Moburg (@Mark_Moburg)
Seattle, Washington

I agree with Spectre on this issue. Two weeks ago (see Holiday from Hell) I ruptured the LHS fuel tank in a prang. I would have lost both tanks if I had done this mod. It could be very expensive. As it was the car was driveable.

Evan-----Original Message-----
From: The Spongbergs [SMTP:kel-cel@ccinet.ab.ca]
Sent: Sunday, October 10, 1999 2:27 PM
To: BHowell
Cc: xj@jag-lovers.org
Subject: Re: [xj] Fuel system problems

At 04:42 PM 10/9/99 -0500, you wrote:

Both fuel tanks are drawing down simultaneously, regardless of the tank
chosen.
– When I pop the filler caps to refuel, one tank sucks air in and the
other blows vapors out. Which tank sucks and which tank blows depends on
which one I have selected using the switch on the dash.

After much goofing around fixing ours, my advice is;
Replace the changeover valve with a normal T fitting.
The fuel system will then draw from an equalized tank system.
If you want to replace all 3 valves, go ahead, but after doing 2,
and spending $$, I am now going to install the T fitting.
If anyone says “but the handling…”, think about it;

  • Equalized tank volume will benifit handling in all situations
  • Fuel level senders in both tanks will read the same, if one fails
    just switch to the other, and don’t bother with the repair.
  • Fuel return valves can be replaced with high pressure metal line and hose
    clamps,
    or left until they fail, then replaced.
  • The chances of the t-fitting failing in the future are almost nil, so
    improved reliability.
  • If the dash switch fails, it can also be bypassed for more improved
    reliability.
  • Vapor recovery system may also be jammed. Try disconnecting the line from
    the tank
    vents before it connects to the 2 psi check valve. The tanks can then vent
    constantly.
    I have replaced the whole vapor recovery system with a GM fuel filter to
    prevent dirt from
    being sucked into the line, and the 2 psi valve mounted within one air
    cleaner.
    This way, no venting at rest, and when venting, fumes can be sucked into
    the engine
    and burned.

In the end, it is each owner’s preference, and personal choice on
modifications.

Kelly Spongberg
Rocky Mountain House, Alberta, Canada
1987 Jaguar XJ12 Vanden Plas
1998 Chevrolet K1500 Z71 Truck
1949 Ford F-1 pickup (someday project)
1997 Polaris Trail Boss Quad

Why dual tanks and why not T-connect them?

The dual tank design goes back at least to the early 60’s and is a rather
good way to maximize fuel and storage capacity in a car with a full-size
spare. This is certainly clear when viewing the large boot of a Mark X or S
Type that the arrangement was effective. Few other car designers make use of
the fender space from the rear wheel to the back bumper. I had a Lincoln
that did and an amazing amount of material could be stuffed in the cubbies.
Anyway, good use of available space was most likely the primary reason for
the dual-tank design.

So, why not simply permanently connect the two? While colleagues have found
many applications for the opportunity created – my favorite was two
brothers who each had a tank to fill and use – I think that the simple
answer is that it would be very difficult to fill the off-side tank for a
couple reasons. First, air would be trapped above the fuel in the off-side
tank so you would need to open that cap anyway. OK, no big deal. Second, the
connecting tube would need to be large enough to handle at least half of the
fuel station pump flow rate. That would require a much larger capacity than
the standard hose. The side to side angle could also be a problem if the cap
seals were bad and would clearly have been a problem on 60’s Jags.

However, nothing is as effective as experimentation. If someone connects
his/her tanks, please let us know the consequences.

Steve Chatman

Excellent points, and we can add that free flow between the tanks would mean
no angle parking on some streets without excellent cap seals – San Francisco
comes to mind. {:o]

Alex
79xj6

Chatman wrote:>

Why dual tanks and why not T-connect them?

The dual tank design goes back at least to the early 60’s and is a rather
good way to maximize fuel and storage capacity in a car with a full-size
spare. This is certainly clear when viewing the large boot of a Mark X or S
Type that the arrangement was effective. Few other car designers make use of
the fender space from the rear wheel to the back bumper. I had a Lincoln
that did and an amazing amount of material could be stuffed in the cubbies.
Anyway, good use of available space was most likely the primary reason for
the dual-tank design.

So, why not simply permanently connect the two? While colleagues have found
many applications for the opportunity created – my favorite was two
brothers who each had a tank to fill and use – I think that the simple
answer is that it would be very difficult to fill the off-side tank for a
couple reasons. First, air would be trapped above the fuel in the off-side
tank so you would need to open that cap anyway. OK, no big deal. Second, the
connecting tube would need to be large enough to handle at least half of the
fuel station pump flow rate. That would require a much larger capacity than
the standard hose. The side to side angle could also be a problem if the cap
seals were bad and would clearly have been a problem on 60’s Jags.

However, nothing is as effective as experimentation. If someone connects
his/her tanks, please let us know the consequences.

Steve Chatman

Why dual tanks and why not T-connect them?
[snip]
…I think that the simple
answer is that it would be very difficult to fill the off-side tank for a
couple reasons.

The connecting tube between the tanks is small enough that flow from one to
the other during fueling is inconsequential.

Just fill them individually as would would with the normal setup.

As for the San Francisco parking situation, well, I certainly don’t have
anything like that to worry about. For those who do, perhaps a pair of
check valves between the tee and cocks?

And the rabbit goes 'round the tree once more…

bfhAt 04:34 PM 10/11/99, “Chatman” kchatman@mail.coin.missouri.edu wrote:

Burgess Howell
86VdP(Federal)

Solenoid valve open on ignition cycle would cure this one and anyway no one
in europe can afford to fill the beast to the brim our credit card limits
arnt that high1

PJ----- Original Message -----
From: Cannara cannara@attglobal.net
Cc: xjlovers xj@jag-lovers.org
Sent: 11 October 1999 17:20
Subject: Re: [xj] Fuel system problems

Excellent points, and we can add that free flow between the tanks would
mean
no angle parking on some streets without excellent cap seals – San
Francisco
comes to mind. {:o]

Alex
79xj6

Chatman wrote:

Why dual tanks and why not T-connect them?

The dual tank design goes back at least to the early 60’s and is a
rather

good way to maximize fuel and storage capacity in a car with a full-size
spare. This is certainly clear when viewing the large boot of a Mark X
or S

Type that the arrangement was effective. Few other car designers make
use of

the fender space from the rear wheel to the back bumper. I had a Lincoln
that did and an amazing amount of material could be stuffed in the
cubbies.

Anyway, good use of available space was most likely the primary reason
for

the dual-tank design.

So, why not simply permanently connect the two? While colleagues have
found

many applications for the opportunity created – my favorite was two
brothers who each had a tank to fill and use – I think that the simple
answer is that it would be very difficult to fill the off-side tank for
a

couple reasons. First, air would be trapped above the fuel in the
off-side

tank so you would need to open that cap anyway. OK, no big deal. Second,
the

connecting tube would need to be large enough to handle at least half of
the

fuel station pump flow rate. That would require a much larger capacity
than

the standard hose. The side to side angle could also be a problem if the
cap

seals were bad and would clearly have been a problem on 60’s Jags.

However, nothing is as effective as experimentation. If someone connects
his/her tanks, please let us know the consequences.

Steve Chatman

Solenoid valve open on ignition cycle would cure this one and anyway no one
in europe can afford to fill the beast to the brim our credit card limits
arnt that high1

PJ

Hm… that sounds familiar! Where have I seen an electrical fuel solenoid before? Oh, yes, the stock system had one…

So basically, in order to not slosh fuel when parking on a slope and to provide the same margin of safety, you need the following:

T fitting.
Left and right stopcocks.
Electrically operated solenoid to prevent fuel transfer between tanks.

To me, it looks like that’s an awful lot of trouble and expense to duplicate a single $40 electric valve that is readily available and easily installed.

And just remember, the more splices or junctions you have in your hose, the more leak possibilities there are. Personally, I don’t think I’ll ever perform this modification. I think it’s a crude “fix” for a problem that is easily solved. I believe that unless you install and properly configure it with all the above components, it is unsafe and could lead to damage to your Jaguar, or worse yet, you.

This is a bad idea! lets kill it
Dont piss about with fuel lines the OE fitments leak enough on their own.
PJ----- Original Message -----
From: spectre spectre@fok.com
To: Philip Jones <@Philip_Jones>
Cc: xj@jag-lovers.org
Sent: 13 October 1999 17:59
Subject: Re: [xj] Fuel system problems

Solenoid valve open on ignition cycle would cure this one and anyway no one
in europe can afford to fill the beast to the brim our credit card limits
arnt that high1

PJ

Hm… that sounds familiar! Where have I seen an electrical fuel solenoid
before? Oh, yes, the stock system had one…

So basically, in order to not slosh fuel when parking on a slope and to
provide the same margin of safety, you need the following:

T fitting.
Left and right stopcocks.
Electrically operated solenoid to prevent fuel transfer between tanks.

To me, it looks like that’s an awful lot of trouble and expense to duplicate
a single $40 electric valve that is readily available and easily installed.

And just remember, the more splices or junctions you have in your hose, the
more leak possibilities there are. Personally, I don’t think I’ll ever
perform this modification. I think it’s a crude “fix” for a problem that is
easily solved. I believe that unless you install and properly configure it
with all the above components, it is unsafe and could lead to damage to your
Jaguar, or worse yet, you.

I haven’t been reading the digest very close lately, so I am sorry if my problems have been discussed, but I need someone to point me in the right direction as this list did last year with my A/C problems. The A/C problems were fixed by a new compressor, dryer receiver and conversion to 134. A/C works great now. I can actually freeze people out of the car! The past year the car has run flawlessly. I replace a few parts here and there most as preventive measures.

Anyway, the current problem happened all at once, or in the last week or so and has rapidly deteriorated. First, I notice the gas tank whoosh, then fuel economy when down, then performance. It’s worse when the car is cold. Black smoke, chugging and engine is unable to rev. It stumbles and falls flat on its face. And yesterday at a very rough idle it stalled. Now the fuel usage has doubled and the power is about half, and even warm it isn’t running right. I’m sure the plugs are fouled. I plan to replace the plugs tonight and whatever else the list suggests. So, where do I start?

Dann Poindexter
Dayton Ohio Jaguar Owners

Dann, it could be the famed fuel-return valves (in rear fender wells) or
the pressure regulator on the fuel rail. First check that fuel is being
returned to the proper tank (the one selected) and that one only (look
into the gas cap, pushing the flap aside. If any fuel is going to the
unselected tank, one or both of the valves should be checked (left one
open only when power off, right one only when power on). Failure modes
can cause flooding and stalls. If all ok here, have someone check the
pressure regulator (you can do a quick check by pulling the vacuum hose
and sucking on the connector with another hose to see if the diaphragm
is ok).–
Alex
79xj6L SII
Menlo Park, Calif.

Dann Poindexter wrote:

I haven’t been reading the digest very close lately, so I am sorry if
my problems have been discussed, but I need someone to point me in the
right direction as this list did last year with my A/C problems. The
A/C problems were fixed by a new compressor, dryer receiver and
conversion to 134. A/C works great now. I can actually freeze people
out of the car! The past year the car has run flawlessly. I replace a
few parts here and there most as preventive measures.

Anyway, the current problem happened all at once, or in the last week
or so and has rapidly deteriorated. First, I notice the gas tank
whoosh, then fuel economy when down, then performance. It’s worse when
the car is cold. Black smoke, chugging and engine is unable to rev. It
stumbles and falls flat on its face. And yesterday at a very rough
idle it stalled. Now the fuel usage has doubled and the power is about
half, and even warm it isn’t running right. I’m sure the plugs are
fouled. I plan to replace the plugs tonight and whatever else the list
suggests. So, where do I start?

Dann Poindexter
Dayton Ohio Jaguar Owners

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