The largest and best supported Jaguar cars enthusiast site on the Internet!

Serving Enthusiasts since 1993
The Jag-lovers Web

Currently with 3,166 members

Fuel Pump

Fuel Pump

Thank you to all who responded my question reg. interim use of the fuelpump
from my MK II. The MK II pump is an aftermarked pump (plastic-body)- made
in New Zealand. To day I took my 120 50 miles with that pump. No problem.
But I have to get a set of warmer (?) sparkplugs and adjust the
I'll restore my long-bodied SU(!) pump, and try to get a transistor,
according the article I got from J.Spence.
- Martin Jacobsen
  120 DHC 53

Re fuel pumps in general, I had several SU units rebuilt but they were
still a headache; after a year or so the reliability was poor. Maybe just
bad luck, but... Haven't tried the "transistorizing" fix but instead bought
a non-original replacement unit from XK's Unlimited (this was for the Mk
II) and have been delighted. It was cheap, works great, was a perfect fit
with no mods, and even "clicks" like an SU. So far so good. The XK's sales
guy claims they have no complaints on these. I don't thik it was more than
$40 USD; not bad for a quick and effective fix.
- Dick Rowley
'54 XK 120 FHC SE; '62 Mk II

I have an XK-150 roadster (1958) and a fuel pump that hates me. All fuel
pumps hate me.
1. The pump is new as of Aug. Less than 25 miles on it.
2. The pump is getting power.
3. The pump is getting gas.
4. The pump does not go when
turned on.
5. If you hit it and I am about to really haul off and hit it real hard, it
will make a very light sound that stops immediately.
When I checked the gas there was some water in it. I am going to try and
clean this out today.
Any suggestions beyound: get a new fuel pump?
- Ron. W

Ron- Get a used one. They don't work just as well as your new one.
- James Warren

If it is the fuel pump replace it, but replace it with a non SU. If you
want the part number of the Carter I am using let me know. It works fine.
L J Haithcock
'59 XK-150S OTS

Check the ground....hook power cables directly to its post and its body
from the battery.
- Bob Wright

I had the same problem with my fuel pump. Turned out to be an intermittent
fuel pump problem and when it wasn't, it was an intermittent wire from the
fuse panel through the chassie to the pump. Finally strung a new wire and
replaced the pump with a nice solid state one made in New Zealand. Now it
clicks like mad at every flick of the switch. Good Luck
Aloha, Rob XK-140 FHC

Thanks, I went right down stairs and tried to see if opening the fuel line
would prevent back pressure.. Failure. The line was dry. Turned on the
car..........No clicks. Tried to start ....... no gas to the
SUs. Line still dry.

What is the next step?
- Ron

Take the end cap off and separate the points. If you get a spark, they are
getting power...... if not, sort that out first. Then try the points bit
again to see if that starts the solenoid off doing its tickety tick thing
which means that you have a pumping action.
- Dick Clements

I assume we're talking about the original type SU rectangular body pump.
New last August and you got 25 miles out of it, and then nothing. Installed
correctly, inlet on the bottom and outlet on top? When was the 25 miles,
last year? Sitting unused for a few months since?  Then I will submit my
guess that the one-way check valve discs in the pump body are stuck closed.
Believe it or not, tapping the body with a small hammer just might break
them loose. If not, they are accessable through the top 6 bolt cover. Be
prepared for sudden flow from the tank, in fact if you have a section of
rubber hose between the tank and pump put a C-clamp on it to shut off the
flow. Here's where the shutoff valve we once discussed on this list would
be useful.
If that's not it, then clean the filters in the tank drain plug and the
pump lower cover, and any others you may have. Good luck and keep us
- Rob Reilly

A mild click after a 'smart' swipe with a knock-off hammer might indicate
corroded contact points (under the cap on the round end, where the wire
connects). Undo the nuts on the electrical contact bolt and remove the cap.
Take a points file or a small piece of emery cloth/paper and clean the
points nce or twice, then reassemble and try again. Your new pump is
exhibiting the characteristics of an old pump with worn, corroded contact
points; his may be due to long storage since manufacture!

If not, keep pluggin'! Something has to explain the phenomina!
- Larry Schear
  Twin Cam, Inc.

Check to see if the pump has a good ground. Run a seperate ground wire from
a screw on the pump to the chassis.
Dennis Murphy
Geneva, IL
1952 XK120
1990 XJ-S

Power to the pump...but what about "from?" Try a direct ground from the
battery (jumper cable).
- James Warren
update 9/98...
Would whoever is knowledgeable about the fuel pump transistor change, please
again describe for us newbies?
     I could use the info on the flex radiator fan also if someone would also
respond on this. Am I better off putting an electric fan on front and rear of
radiator and removing mechanical fan?  Central Florida weather.
Steve McDonald

I have to dig the fuel pump info out. There are 2 different circuits
depending on the polarity of the car.
For what it's worth, I try to always install the electric fan on the
inside of the radiator and removing the driven fan. That cuts down on
noise and seems to add to engine rersponsiveness. Probably a function of
noise. Also less wear and tear on the belt and water pump.
George Badger


Both positive and negative ground conversions are documented on the web
site at System
The positive ground version I tested the negative ground version I did not.

Dick White

After my fuel pump giving up the ghost a number of times ( always at the
worst possible time and at the worst possible place ) I have replaced it
with an electronic S U fuel pump conversion kit . It fits inside the
existing cap and is easy to fit. It can be obtained from Autoflux in the UK
( Phone 01579 320459 ) at 45 Pounds.

Roger Herrick

Thanks for the tips re the fuel pumps.  I had a friend who was
transistorising his pumps (3.8 150 S) here recently and sent him a print
out of the web site article, so I hope he makes it work and translates the
article into Aus for me (i.e. local suppliers of the necessary parts etc).
 In the meantime, I will keep thumping as required - the 120 has jammed
brakes too - damn!
Regards, John Elmgreen

The necessary electronic parts for the fuel pump are available at Dick
Smith Electronics in Australia and New Zealand.

The transistor and diode are as specified in the Website article and the
transistors are catalogue number MJE2955T (PNP) for negative earth and
MJE3055T (NPN) for positivr earth. Total cost about $5.00.
Regards, Michael Standley

Michael S:  Thanks for the tips re the transistor / fuel pump parts in
Sydney.  I will pass the details on to Ian Hutchinson (XK150 S DHC 3.8).
Regards, John Elmgreen
One of the things I have learned the hard way over the last couple of years
is read the manual thoroughly before starting a task. After I rebuilt my
fuel pump, I noticed in the manual that I was supposed to flex the diaphram
to the end of the solenoid travel before clamping its perimeter in place. I
think my pump is now ticking more often than it should (about once every 5
seconds at idle). Has anyone else made this mistake? If so, how much
difference does it really make in the stroke volume (ticking rate)? I'm
thinking about taking it apart and putting it back together right but I
don't know whether it will be worth the trouble. What is the normal range
of ticking rate at idle? - Bruce Cunningham

Bruce: I would say that as long as your pump is ticking in a consistent manner
and the engine isn't starved for fuel at high RPM, that you need not take
it apart again. I have made that same mistake of not stretching the
diaphragm and when I did it in combination with some rather stiff diaphragm
material, the ticking was rapid and  intermittent; I had to do it over.
Your "idle tick rate" sounds average to me, particularly since my own pumps
do some periodic ticking even when the engine isn't running. (I guess some
fuel is leaking back to the inlet side since it's not overflowing from the
carbs.) Any cardiologists out there want to give an acceptable "tick rate"
for a 45 to 50 year old Jaguar? ( rest, ... at idle,  ...after
exercise, ...etc.) EKG?  :-) - Regards, Dick Cavicke

According to my calculations, the actual stroke volume for my fuel pump is
about 0.11 oz. of petrol per tick under normal running conditions. Does
anyone know whether there is any kind of specification for this? - Bruce

hello bruce,  met you and the mrs at stratton mtn and again at british
invasion in all the weather.. i'll see what i come up with regarding the
fuel pump, i also think i'd need to know the frequency of the pumps
activity at various times . what say?? regards ( dove grey 120) - bernard

Glenn`s Repair Manual gives a value of 1 pint (0.57 litre) per minute. - Mike.

Is the pint per minute spec with no pressure? - Bruce Cunningham

If you have any questions or comments send e-mail to:
Main Page Back to the Library


Please help support the move to the new site, and DONATE what you can.
A big Thank You to those who have donated already!



Go to our Homepage
Improve your Jag-lovers experience with the Mozilla FireFox Browser!

  View the latest posts from our Forums via an RSS Feed!

Jag-loversTM Ltd / JagWEBTM 1993 - 2023
All rights reserved. Jag-lovers is supported by JagWEBTM
For Terms of Use and General Rules see our Disclaimer
Use of the Jag-lovers logo or trademark name on sites other than Jag-lovers itself in a manner implying endorsement of commercial activities whatsoever is prohibited. Sections of this Web Site may publish members and visitors comments, opinion and photographs/images - Jag-lovers Ltd does not assume or have any responsibility or any liability for members comments or opinions, nor does it claim ownership or copyright of any material that belongs to the original poster including images. The word 'Jaguar' and the leaping cat device, whether used separately or in combination, are registered trademarks and are the property of Jaguar Cars, England. Some images may also be Jaguar Cars. Mirroring or downloading of this site or the publication of material or any extracts therefrom in original or altered form from these pages onto other sites (including reproduction by any other Jaguar enthusiast sites) without express permission violates Jag-lovers Ltd copyright and is prohibited
Go to our Homepage
Your Browser is: CCBot/2.0 (, IP Address logged as on 24th Sep 2023 04:49:21