[xj40] Fuel pump wiring

Jeffrey_Slocum · February 15, 2003, 3:38pm

Hi Bryan

Well I got the tank reinstalled last evening , my new connector didn’t
seem to be working for the fuel pump. I jumped the fuel pump relay and
have found that I don’t have 12V at the connector in the boot.I have
checked the jumper to ground where the fuel pump relay goes and have 12V
supplied to the plug in the boot. I did have 12v there when i checked
before starting all this work to resolve the bad connector inside the
tank. Is there a fuse in the line somewhere? There doesn’t seem to be
one in the haynes manual on the 92 diagram. what else could cause me to
lose the 12v at the connector. Any help or direction would be greatly
appreciated.

Jeffery G Slocum
92 Majestic
98,000

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !

Bryan_N · February 15, 2003, 4:12pm

In reply to a message from Jeffrey Slocum sent Sat 15 Feb 2003:

Jeffery,

Left-Hand fuse box, fuse C8 (White / Natural 25 Amp) - ‘Fuel pump
control and lambda sensor’ ???–
Bryan N ('91 Sovereign)
Cambridge, United Kingdom
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !

C_Knotts · March 25, 2004, 2:16pm

I have intermittently had problems with getting the car to start.
As it kept getting worse and I read more about the fuel pump
problems I suspected the pump was at fault. I tested the pump and
it works fine. I tested the relay and found no problem there. I am
not an expert at electrical testing but assumed it to be something
in the wires going from the power source to the pump. I installed a
wire with an in-line fuse which runs directly from the battery to
the pump and have been using that since ~November of 2003 since I
rarely drive the car. I just pull the fuse when I want to shut it
off. With warmer weather approaching I would like to fix this
problem for real. Can anyone help me? Specifically I would like
information on the location/how the wires are ran from the pump to
the relay and ultimately the battery. Can someone provide me this
information. I do have the Haynes manual and the JDHT CD ROM from
this site.

Thanks much,
Chris Knotts–
'89 XJ40
Columbus, OH, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !

Bryan_N · March 25, 2004, 4:35pm

In reply to a message from C Knotts sent Thu 25 Mar 2004:

Chris,

On your car with the external pump, I recall that problems have
been reported with a connector or wiring under the floor below the
rear seat.

You will need to remove the rear seat squab and under the
insulation pad you will see a couple of wires disappearing through
a grommet in a hole in the floor. There’s a blue wire with a red
tracer and a black wire going to a connector under the floor.Check
that you have 12 volts on the blue/red wire when you try to start
the engine. If so, you should check the cleanliness of the
connector and the continuity of the wiring from the connector
through to the pump.

On the fuel pump relay, you should have 12 volts on terminal 30
(Brown wire) direct from the battery and if you jump terminals 30
and 87 the pump should run.–
The original message included these comments:

I have intermittently had problems with getting the car to start.
problem for real. Can anyone help me? Specifically I would like
information on the location/how the wires are ran from the pump to
the relay and ultimately the battery. Can someone provide me this

–
Bryan N ('91 Sovereign 4.0 L)
Cambridge, United Kingdom
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !

C_Knotts · March 25, 2004, 5:12pm

In reply to a message from Bryan N sent Thu 25 Mar 2004:

Thanks for the tip; I will give it a look. So, the wires enter the
inside under the seat? From there where do they go… at what point
do they exit the car again?

I am not the most knowledgeable when it comes to electronics
testing. I do have a small, digital voltmeter from Radio Shack…
will that do the job? You say to test these certain points while I
crank the engine is that correct? I also couldn’t explain what a
relay does if someone asked me… and help you can offer is much
appreciated.

Thanks again!
Chris–
The original message included these comments:

Chris,
On your car with the external pump, I recall that problems have
been reported with a connector or wiring under the floor below the
rear seat.
You will need to remove the rear seat squab and under the
insulation pad you will see a couple of wires disappearing through
a grommet in a hole in the floor. There’s a blue wire with a red
tracer and a black wire going to a connector under the floor.Check
that you have 12 volts on the blue/red wire when you try to start
the engine. If so, you should check the cleanliness of the
connector and the continuity of the wiring from the connector

–
'89 XJ40
Columbus, OH, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !

Bryan_N · March 25, 2004, 7:17pm

In reply to a message from C Knotts sent Thu 25 Mar 2004:

Chris,

You said you had the JDHT CD-Rom?

From the index, select XJ6 Service Manual Volume 5. That shows the
wiring harness for the 1990 cars which still had the external fuel
pump so it is identical (or very similar) to your car.

Scroll through to page 82 of 108 ‘Fuel Pump Link Harness Connector
Location’. You will see connector LS10, the one I described to you
in my earlier post with the two wires going to the fuel pump, one
Blue/red, the other Black. Set your DMM to 20 Volts DC and measure
the voltage coming to that connector from the harness in the car
as you crank the engine. (I guess you also get the half-second
priming burst when you first turn on the ignition without engaging
the starter but that is so short you may not read it).

Now scroll back to page 14 of 108 - ‘Bulkhead harness LB (LHD)
(ABS) Connector Location’. You will see down by the left hand ‘A’
pillar connector LS3, a black 9-way socket. Pin 5 of that connector
has the Blue/red feed to the fuel pump which links through the side
harness to connector LS10 under the rear seat squab. You can check
that you have 12 volts on that too as you crank the engine. Pin 2
on connector LS3 (Black wire) is ground.

Look also on the right side of that picture to the under dash area
on the passenger side where you will see connector LB15, a yellow
relay base. That is the fuel pump relay. The Pink/brown wire from
the engine ECU to terminal 85 and the White/brown wire from
terminal 86 back to the ECU (and the MAF controller) provide the
switching signal to pull in the relay which is fed by 12 volts on
the Brown wire to terminal 30 on the relay and provides power from
terminal 87 of the relay via the Blue/red wire to the pump.

So, as I said in my earlier post, if you remove the fuel pump relay
from its base and short out terminal 30 (Brown wire) to terminal 87
(Blue/red wire), if the wiring downstream of the relay to the pump
is OK, you should hear the pump running.–
The original message included these comments:

Thanks for the tip; I will give it a look. So, the wires enter the
inside under the seat? From there where do they go… at what point
do they exit the car again?
I am not the most knowledgeable when it comes to electronics
testing. I do have a small, digital voltmeter from Radio Shack…
will that do the job? You say to test these certain points while I
crank the engine is that correct? I also couldn’t explain what a
relay does if someone asked me… and help you can offer is much
appreciated.
Chris

–
Bryan N ('91 Sovereign 4.0 L)
Cambridge, United Kingdom
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !

Dave_Ryding · March 26, 2004, 12:03am

In reply to a message from C Knotts sent Thu 25 Mar 2004:

I, too have experienced the same problem, especially with a cold
engine. (idle for any more than 2 hours). My Jag. mechanic has
tried replacing relays etc. tested fuel pressure, but cannot
determine the source of the problem. The only thing that works for
me has been to turn the ignition to the start position (without
cranking) several times in succession. Eventually you can hear the
fuel pump do the job that it is intended to do, and the car will
start. This has been VERY frustrating and continues to be so. By
the way, it is my understanding that the fuel pump is internal. I
own a '93 Sovereign.–
The original message included these comments:

I have intermittently had problems with getting the car to start.
problems I suspected the pump was at fault. I tested the pump and
it works fine. I tested the relay and found no problem there. I am

–
Dave Ryding
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !

Bryan_N · March 26, 2004, 7:08am

In reply to a message from Dave Ryding sent Fri 26 Mar 2004:

Dave,

When I had that problem on my car (also with an in-tank fuel pump
unlike Chris’s car which still has the external pump), the problem
was the fuel pressure regulator. Heres a procedure I wrote to check
out the system after finding, like you, that it would only start
after cycling the ignition on and off a few times to take advantage
of the half-second priming bursts.

XJ40 Fuel Pressure Test

[To identify faulty Fuel Pressure Regulator or Fuel Pump Check
Valve]

Install fuel pressure test gauge in feed line at inlet to fuel
rail. [Example of suitable test gauge - http://www.jag-
lovers.org ]
Conduct the fuel pressure tests as described in Haynes Chapter
4, Section 3. If the readings conform to those quoted in the
Specifications at the beginning of Chapter 4, you need proceed no
further. However, if the �Hold� pressure of 21 psi cannot be
maintained, read on.
Prepare a suitable clamping device to close off the flexible
fuel feed and return lines with protection for the rubber hoses
(small Molegrips � locking pliers � with cardboard in the jaws to
protect the hose work well).
Have an assistant cycle the ignition key ON-OFF a few times
without engaging the starter to ensure the fuel rail is fully
primed and immediately after the last operation of the key, quickly
clamp the fuel feed line upstream of the fuel rail / fuel pressure
gauge.
Note the reading on the pressure gauge. It should read something
over 21 psi, falling back quickly to 21 psi and holding there for
an extended period.
If the pressure falls below 21 psi and drops to near zero within
a minute or two, the Fuel Pressure Regulator is leaking fuel back
to the tank via the return line and should be replaced.
Remove the clamp from the fuel feed line.
Conduct a similar test, but this time, immediately after the
last key operation, quickly clamp the fuel return line downstream
of the Fuel Pressure Regulator.
Note the reading on the gauge, which, depending on how quick you
were with the clamp, should be somewhere between 21 and 60 psi, but
the actual reading is not important.
If the pressure drops rapidly to near zero within a minute or
two, the check-valve (non-return valve) in the outlet from the fuel
pump is defective, allowing fuel to return to the tank via the feed
line.
On the external pumps, it is a relatively simple matter to
change the check-valve which simply screws in to the outlet of the
fuel pump. On the in-tank immersed pumps it�s a PITA because the
fuel tank has to be removed to gain access to the pump itself � but
the check-valve is such a simple device it should be capable of
being cleaned up and rendered serviceable. (Important because it
does not appear to be available as a spare part from a dealer).–
The original message included these comments:

In reply to a message from C Knotts sent Thu 25 Mar 2004:
I, too have experienced the same problem, especially with a cold
engine. (idle for any more than 2 hours). My Jag. mechanic has
tried replacing relays etc. tested fuel pressure, but cannot
determine the source of the problem. The only thing that works for
me has been to turn the ignition to the start position (without
cranking) several times in succession. Eventually you can hear the
fuel pump do the job that it is intended to do, and the car will
start. This has been VERY frustrating and continues to be so. By
the way, it is my understanding that the fuel pump is internal. I
own a '93 Sovereign.

–
Bryan N ('91 Sovereign 4.0 L)
Cambridge, United Kingdom
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !

Dave_Ryding · March 26, 2004, 12:53pm

In reply to a message from Bryan N sent Fri 26 Mar 2004:

Thanks, Bryan, I’ll have to have a go. Typically though it’ll be a
PITA.–
Dave Ryding
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !

D_and_P_Lokensgard · March 29, 2004, 12:29am

Thanks so much for looking up the wiring connections for the fuel pump
circuit, Bryan! It was very timely for me - the Majestic has been
exhibiting intermittent non-start condition, which I had traced to the fuel
pump or power circuit to it. I replaced the relay, cleaned and tightened
the relay socket connections, and still had the problem. With the help of
you diagram, I found that I had 12 volts at the connector under the rear
seat when the circuit was energized, but if the pump was plugged in the
voltage dropped to zero. Aha, a high-resistance connection, but where?
With the help of your post I located connector from the bulkhead harness to
the left side harness, and the poor connection was there - after cleaning
the contact surfaces, the voltage drop with the pump on was eliminated. I
also cleaned the bulkhead power connection next to the battery for good
measure, and coated it with Vaseline. All seems fine now.

Thanks again,

Dave Lokensgard
'96 XJR
'90 Vanden Plas Majestic (DAVZCAT)
'55 XK140 OTS
Poway, California

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !

Bryan_N · March 29, 2004, 8:05pm

In reply to a message from Lokensgard sent Mon 29 Mar 2004:

Dave,

Pleased to hear it helped. It’s good to get feedback on problems
solved, particularly since as a result of a silly back injury, I
was virtually immobile for a week and could find no better way of
passing the time (since I couldn’t even clean my two dirty cars)
than trying to unravel the complexities of the Jag Service Manual
wiring diagrams and harness locators! [I can hear the chorus already - ‘get a life!’ :-)]

I wonder if it helped the original posters, Chris and the other
Dave too. Hopefully we’ll get their feedback in time, successful or
not - it’s nice to know.–
The original message included these comments:

Thanks so much for looking up the wiring connections for the fuel pump
circuit, Bryan! It was very timely for me - the Majestic has been
exhibiting intermittent non-start condition, which I had traced to the fuel
Dave Lokensgard
'90 Vanden Plas Majestic (DAVZCAT)

–
Bryan N ('91 Sovereign 4.0 L)
Cambridge, United Kingdom
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !

Ian_Booth · March 18, 2023, 11:41pm

Thanks for the post Bryan - my fuel pump has started to not work from time to time and I am looking to trace the wiring - your post is a perfect guide.
I thought it was lack of spark but ruled that out today. I changed the pump a year or so ago so dont think its that - will see. Hoping for easy fix as its stranded on a NYC street!