[xj40] Fuel pump question - Do I need to replace it?

My vehicle is a 1994 XJ6 with 130,000 miles originally sold
in California.

I have been chasing down some issues relating to a failed
smog test, and I was wondering about the fuel pump. I may
ask about the failed smog test in the future, but for this
post I’m interested in the fuel pump. As far as I know I
have no pump related operating issues. I can run the engine
at high RPM and wide open and it goes great. It seems the
consensus on here that the pumps can fail after 100,000
miles. I was going to check the pressure and volume.
Unfortunately my pressure check setup has the wrong fittings
so I couldn’t check the pressure. The only thing that I
could do was to check the volume. I disconnected the fuel
input to the injection rail and directed it to a gas can. I
then jumpered the fuel pump relay so the fuel pump would
run. Only about 1 liter of fuel came out and then it
started pumping air and gurgling. I had fuel in the tank,
but it was only at about 1/4 tank. I reconnected the fuel
line and after about 1 minute of fuel pump running time, I
was able to start the engine. Everything seemed fine and
the car drove normally. I tried the volume test again and
the very same thing happened.

Does this indicate a problem with the pump? I have never
seen this in any other vehicle. I have always been able to
run a fuel pump with no back pressure and it would pump out
the entire tank if given enough time. It seems like this
pump needs the back pressure to pump fuel.

I can get the Walbro pump locally for around $85 US. My
‘‘non-return valve’’ doesn’t work either. Is the non-return
valve replaceable without buying the entire fuel pump
assembly for the insane price? If the internal non-return
valve is not available, can I put a check valve in the fuel
supply line to the engine. What part number would I use and
where can I get one.

Thanks,
Carl–
Carl Leonard
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In reply to a message from Carl Leonard sent Mon 26 Mar 2007:

Carl,

A fuel pressure test would answer your question, both in
terms of flow rate and check-valve operation.

You should get around 2 litres per minute from the pump. I
emptied a near-full tank by that method when I needed to
change the fuel level sender unit.

Other than a failing fuel pump, three other possibilities
spring to mind - a clogged filter sock on the pump intake,
or a split feed pipe between the pump module (cannister) and
the tank outlet (inside the tank) or a failed (blue) seal
between the actual pump and the check-valve in the module
outlet.

In any of these circumstances, you should be able to
determine if they are the problem by listening to the sound
of the pump motor. Does the pump motor run continuosly, loud
and strong (ear to open filler neck), despite the flow rate
dropping as you describe? If so, that suggests that the pump
itself is OK and getting continuous power but is being
starved of fuel or is pumping it straight out in to the tank
instead of down the feed line.

If the sound of the pump motor trails off as the flow rate
drops, then you have a pump problem or an intermittent power
supply problem to the pump (oxy sensor heater relay on the
firewall OK?).

The check-valve in the pump outlet is unlikely to be the
cause of a flow-rate problem. It is a simple spring & ball
device and I guess the failure mode would normally be ‘stuck
open’. Others have fitted an independant check-valve outside
of the tank - IIRC, the archives contain details of make and
model - but I don’t think that is going to solve your
flow-rate problem.–
The original message included these comments:

run. Only about 1 liter of fuel came out and then it
started pumping air and gurgling. I had fuel in the tank,
but it was only at about 1/4 tank. I reconnected the fuel
line and after about 1 minute of fuel pump running time, I
was able to start the engine. Everything seemed fine and
the car drove normally. I tried the volume test again and
the very same thing happened.
Does this indicate a problem with the pump? I have never


Bryan N, '91 Sovereign 4.0 L, RHD
Cambridge, United Kingdom
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In addition to Bryan’s excellent response, I would also suggest a fuel
pressure gauge, as that’s about the only parameter not measured (and assumed
correct) by the EFI. I got a small 0-60 gauge for about $10 from
www.McMaster.com and also bought a tee and 8mm/ 5/16 hose nipples to splice
it in the fuel supply line near the throttle position sensor. I installed a
check valve there as well; also from McM.

Our '93 suffered the dreaded blue donut rupture last year at 120K miles,
leaving us stranded on the interstate. Studying the fuel pump module, I can
indeed conceive it could run dry with no back pressure, and a partially
clogged sock.
rdr

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The blue donut is a small rubber seal/isolator that holds the output end of
the fuel pump inside the plastic fuel module in the gas tank. When it
tears from old age, it leaks all the fuel pressure and the engine won’t run.
If you had some raw material, you could carve one with a dremel tool or
something. The Jaguar fix is a new module with fuel pump inside, for $800+.

The other weak link in the late XJ-40 is the six relays along the firewall.
They should be replaced with new black ones. Our local electronics store
has them for $5 each, or you can get them from Jaguar for $50 each. While
you have them out, test the tension of each contact in the sockets with a
1/4" spade (FastOn) terminal from a hardware or electronics store. It will
be the terminal that matches the relay terminals. If contacts have low
tension, they can be probed with a dental pick or something to close their
gap and restore proper tension. I also run a tie wrap around the groups of
them, to minimize vibration.

Failure of the relays/contacts will give false failures on the VCM that will
send you on a wild goose chase to fix things that aren’t bad. It happened
to me with FF 46,47 and 89. It can also cause the tranny to go into limp
home mode, and the aircon to not work.

Our most expensive fix has been the Japanese aircon compressor that threw a
rod.

I’m copying this to the Forum, as others may have the same questions.

Yes, I read your post on Jagforum. What is the dreaded blue donut? I have
a 1993 Jag Xj6 4.0 I-g Vanden Plas with 105000. What other problems have
you had and what is to be expected. So far I have had minor issues.

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