Jaguar XJ40 Fuel Pump Problems
On the XJ40 a silent fuel pump is more often its relays or wiring than the pump itself: the pump relay is switched through the oxygen sensor heater relay, and either can fail while looking new. I'd listen for the half-second prime at key-on, then bridge the pump relay in the boot before buying a pump.
How bad is it · Garage, carefully
Expect it to stop without warning; not at all if it smells of petrol
A failing pump, relay or plug can cut the engine on the move and leave it unwilling to restart. A fuel leak at the rear is a fire risk, so fix it before driving.
Which one applies to yours depends on your symptoms, your model year and what has already been done to it.
Likely causes, most common first
Read the check cost before the odds: a free check that rules a cause out beats a likely guess that costs money.
The relay chain that switches the pump
The pump relay doesn't switch on its own: the engine management main relay feeds the oxygen sensor heater relay, and that relay energises the fuel pump relay. Any of the three can corrode, close slowly or sit loose in its socket. A relay can look new and still be bad.
No half-second whirr from the rear at key-on, or the pump only wakes up seconds after the engine fires. A code 44 can come with it.
With a helper, feel the management relay click in the engine bay, then the pump relay in the boot near the right rear light. Bridge pins 30 and 87 in the pump relay base: if the pump runs, work back through the heater relay. The oxygen sensor heater relay is the one with the yellow base on the right-hand bulkhead; swapping it with its neighbour is the quickest test.
New relays, ideally sealed Bosch ones in place of the light blue Hella originals, or a cleaned socket — contact cleaner in the heater relay socket can be the whole cure. On a 1994 car, for example, the pump relay is built into a module in the boot (DBC10422), and reflowing the solder joints on its board is worth trying.
Wiring, the pump plug or a ground in the boot
The pump's power plug can melt around a terminal, and the feed to the tank collects old alarm splices, a blown fusible link on top of the tank or a dead ground in the boot. A burnt suppression capacitor between the pump wires can short the feed. The two-pin plug above the battery, under the boot trim, can arc and burn at one terminal, so the pump gets power one day and not the next. On the in-tank cars from 1991 the wiring beyond the connector in the evaporative flange on top of the tank breaks down and overheats; Jaguar issued a bulletin replacing the pump, its module and the flange for it.
The relay works, yet there's no 12 V at the pump plug; or a wire bridging the relay base gets hot within seconds. A sudden no-start that turns into starting only some of the time fits a burnt terminal.
Measure at the pump plug before buying anything. If a jumper heats up, follow the pump wires behind the boot front-wall carpet to the plastic cover and look for a short. Clean the boot grounds. Running the pump on a lead straight from the battery splits the pump from its feed in a minute. A loose plug in the right-hand fuse box can also cut the pump. On an in-tank car measure at the flange connector on top of the tank as well as in the boot — a good reading in the boot proves nothing about the last few inches.
Repair broken wires and the plug, with a high-temperature connector if it has melted; cut out a burnt capacitor; replace a blown fusible link with an inline fuse. Cut out a burnt plug and join the wires with screw-type connectors. On refitting, make sure each small terminal has really gone into its partner rather than resting on top of the tab.
A worn pump
Depending on the year, the pump is an external Bosch unit by the tank or sits inside it. Either kind wears at the commutator: it gets louder, then stops on a dead spot, and a knock can bring it back for a while.
A whine that grows louder over days; it cuts out and a tap on the pump gets it going; 12 V at the plug but no sound.
With voltage proven at the plug, have someone crank while you hit the tank with a rubber mallet or a wooden handle. If it fires, the pump is on its way out.
A new pump with a filter and intake sock. On in-tank cars check that the new pump's outlet fits the canister lid before the tank comes out — many listed pumps don't; a Walbro-made unit such as Carter P72222 does.
Stalls in hot traffic on the external-pump cars
Hot fuel from the return reaches the pump inlet almost directly. A tired external pump on hot fuel cavitates and the engine starves. Jaguar's TSB 19-22 added a second pump to 1988–1990 cars.
Dies after long stop-and-go driving in the heat with half a tank or less, gurgling in the tank, and restarts after cooling down or adding fuel.
Keep the tank above half in hot weather and see if it stops. A loosened filler cap tests the tank vent at the same time.
A new genuine Bosch pump, for example 69568, rated 120 litres/hour at 3 bar. Cheap aftermarket pumps have died within a year here; the second-pump kit is rarely needed.
A blocked tank vent: the pump pulls against vacuum
As fuel is used, air has to get into the tank through the evaporative system. If a vent hose or the canister line is blocked, the tank goes into vacuum and the pump labours, surges or starves, and wears out early.
Pump surging or droning at idle when hot; pumps that die again and again; Fuel Fail 44 now and then.
Run with the filler cap a quarter turn loose for a few days. If the noise or stalling goes, look at the evap canister hoses and vent lines. On the early cars the two small rubber vent hoses on the boot bulkhead near the differential clog with varnish or dirt: clear them with a length of wire.
Replace a perished evap canister hose with properly fitting tubing — a poor fit can make it worse. A loose cap is a test, not a fix: tighten it before rain.
Inside the tank: a loose pipe, a cracked canister or a blocked strainer
The in-tank pump sits in a plastic canister. A feed pipe can come off the pump, or the canister well can crack and let pressure blow out the bushing the pump outlet plugs into. Sludge from old fuel blocks the strainer.
The pump runs but little or nothing reaches the filter or the rail; power fades and it stalls; a new pump spits air. Black rust in the fuel rail that sticks to a magnet means water has been in the system.
Pump running, open the feed at the filter. Weak, frothy or no flow with a healthy pump means the problem is in the tank.
Reconnect or replace the hose with proper high-pressure fuel hose, not clear tube. A cracked canister needs a used cap, as new ones aren't sold separately. After bad fuel, clean the tank and blow out the lines. With rust in the rail, assume the injectors have taken some too and have them cleaned and flow-tested along with the tank.
Petrol smell or a drip at the rear
The usual leak points are the copper washers at the fuel filter banjo, the seal between the check valve and the external pump, the feed and return hoses at the boot floor above the differential, and a drain plug in the bottom of the tank that can vibrate loose.
Petrol smell in the garage; a wet patch on the rear subframe or behind the tank, sometimes visible from one angle only.
Look from underneath with a torch at the filter, the pump outlet, the hose unions and the tank bottom. Don't drive it with an active leak.
O-ring washers in place of copper at the banjo (CBC6460 and CBC6461), a new bonded seal at the pump outlet, or a tightened tank plug.
Long cranking hot or cold: pressure bleeding away after shutdown
A check valve in the pump outlet holds pressure in the rail after you switch off. When it leaks, fuel drains back and the next start needs several key cycles. A leaking pressure regulator gives the same symptom through the return. On the cars with the external pump, that non-return valve sits on the pump's outlet side (JLM1854). On the in-tank cars the non-return valve is built into the swirl canister around the pump, which is no longer sold new.
Starts only after switching the key on and off a few times to run the pump; worse when hot or after standing for days. It can show cold too: four or five turns before it fires after a night's standing, yet instant restarts an hour later.
Fit a gauge at the rail end and cycle the ignition without starting. If the pressure collapses at once, the pump's check valve is the first suspect; the regulator is the other. A quick test without a gauge: switch the key on several times, then start. If it fires at once, lost pressure is your answer. Clamp the return line with the rail at about 38–40 psi: if it still drops fast, the leak is on the pump side. Pull the regulator's vacuum pipe — petrol in it means a holed diaphragm.
A new non-return valve cured a 1994 4.0 that needed two or three turns to start hot; it was fitted at the tank, but an inline one-way valve (JLM1854) between the tank and the filter is the usual cheaper route. An extra non-return valve in the feed line ahead of the regulator, instead of dropping the tank to reach the original. A new regulator can shorten the cranking without curing it, for example from four or five turns to two or three; a non-return valve in the return line in the engine bay also helps hold the rail.
A noisy pump: a clogged fuel filter
A filter that has never been changed makes the pump push against a restriction, and it buzzes louder.
A buzz or whine from the rear that a new pump didn't cure, or that started after a fill-up. A whine on an in-tank car can also be a cracked plastic pump casing; a hum when the tank is low in hot weather often goes after filling up.
Change the filter first, before the pump.
Worth trying: a new filter, and a different filling station if it started after a fill-up. Cleaning the strainer sock on the pump inlet removed most of one pump's noise.
A put-put noise inside the car at idle: the fuel line dampers
Pressure pulses from the injectors are meant to be soaked up by dampers in the feed line. When the feed hose hardens with age, the pulses travel into the body and sound like a pump fault.
A ticking or put-put that changes with revs, heard inside the car but not outside, with the engine running normally.
Rest a hand on the fuel rail and the feed line at idle: you can feel the pulses. The pump itself hums steadily rather than ticking with the revs.
Worth trying: a new feed hose — Jaguar's bulletin replaces the feed hose only, not the return. On some cars the damper is part of the rail.
The order to check them in
The point of the order is money: each step either rules a cause out or makes the next one worth doing. Green is free, amber costs a little, red is the one to arrive at last.
Key to II: listen for the prime
A half-second whirr from the rear means the relays and the pump are alive. After that the pump runs only while the engine turns.
freeCheck the inertia switch
On right-hand-drive cars it's in the driver's footwell below the bonnet release.
freeBridge pins 30 and 87 in the pump relay base
The relay is in the boot near the right rear light. Pump runs: look at the relay chain. Silent: the wiring or the pump. A jumper that heats up means a short.
freeMeasure at the pump plug; clean the boot grounds
12 V at the plug and no sound: knock the tank while someone cranks.
freeChange the filter and put a gauge on the rail
Pressure that won't build, or falls straight back after the key is off, tells you where to look next.
a filter and a borrowed gaugeOnly then drop the tank
Drain it first. Turn the line clips 90 degrees rather than pulling them off; unions can seize solid. It's easier than cutting an access hole in the shelf.
a pump, or the labourWhat it usually isn't
Don't spend money here first:
If none of this finds it:
On jagaux.com
- Jaguar XJ40 Cranks But Won't StartIf the pump primes but it still won't fire: rotor, crank sensor, grounds.
- Jaguar XJ40 Rough Idle and StallingIf it runs but idles rough or stalls at junctions.
- XJ6 (XJ40) fuse boxes and relaysWhere the relays and fuse boxes sit; other years from the same page.
- Jaguar VIN decoderConfirm your exact model year, engine and factory options before ordering parts — free.
Ratings, fuse numbers and torque figures vary by model year and market. Read the legend on your own car before pulling anything, and use the figures in the manual for your car, not the ones in a video.
Check your VIN: exactly which car you have and which bulletins apply to it.