11 - Fuel system ( ,
11.1 - Collapsing Fuel Tank Warning ( ,
The injection pumps used on these cars has enough power to suck the tank in on itself in the event of a venting problem.
There are the more usual vent problems caused by stuffed check valve, carbon canister, or such. There is also the vent line under the car which can be plugged solid with dried out fuel. What appears to happen is the owners fill the car to the top of the neck, which puts the fuel level above the fuel separator in the vent system. So raw fuel runs in to the vent line and evaporates leaving the sludge behind.
11.2 - Overview of the Fuel Injection System ( ,
The engine management system is controlled by the ECU and maintains optimum engine performance by metering the fuel into each cylinder's inlet tract and adjusting the ignition timing angle at the sparking plugs. It correlates data received from a number of sensors located on and around the engine to provide optimum ignition timing and fuel metering parameters relative to engine load and speed. The EM system also controls three features which may have a direct bearing on starting problems:-
1 Fuel pump - to prevent fuel flooding and/or spillage when the engine is stationary with the ignition switch in position 'II'.
2 Cold start control - to ensure there is sufficient fuel in the inlet manifold to create a combustible air/fuel mixture.
3 Idle speed control - to compensate for varying engine temperature and load conditions.
The system also incorporates a 'limp home" facility allowing continued engine operation following certain sensor failures, the specific failure being indicated on the instrument pack.
Fuel is delivered to solenoid operated injectors by the pump operating (via a variable pressure regulator) at virtually constant pressure so that the quantity of fuel injected for a given duration of injector ‘on’ (open) time is constant.
Injector operation is by means of an electrical pulse which actuates a solenoid valve in the injector body. The duration of the pulse is determined by the ECU on intake air and engine speed information from the FLOWMETER and CRANKSHAFT SPEED SENSOR.
Correction factors are applied by the ECU to provide two functions which may cause starting problems:-
1 - Cranking enrichment during starting.
2 - Temperature enrichment during starting and warm-up.
Cranking enrichment occurs when the starter motor is activated by INCREASING THE INJECTOR OPERATING FREQUENCY FROM ONE PULSE TO THREE PULSES PER CRANKSHAFT REVOLUTION and is implemented by the ECU in response to an input from the STARTER SOLENOID. This cranking enrichment is only effective up to 600 rev/min.
Temperature enrichment occurs during starting (and warm up) by increasing the injector 'on' time and is implemented by the ECU in response to an input from the COOLANT TEMPERATURE SENSOR. This is the square topped sensor in the thermostat housing. After-start enrichment is provided to supply added fuel during warm up by the ECU which increases the injector 'on' time and decreases the amount of additional fuel supplied.
The ECU interfaces with input/output devices as follows:-
1 FUEL INJECTORS: solenoid actuated
2 IGNITION AMPLIFIER: generates high energy electrical pulses for distribution to the sparking plugs.
3 AIR FLOWMETER: a hot wire sensing device to monitor which inlet manifold air flow for optimum fuel and ignition control.
4 IDLE SPEED CONTROL VALVE: stepper motor driven device controlling the volume of air to maintain correct idle speed.
5 CRANKSHAFT SENSOR: provides engine speed and crankshaft position information to ECU for precise ignition timing and fueling control.
6 THROTTLE POTENTIOMETER: interprets the throttle position.
7 FUEL PUMP RELAY: controls fuel pump!
8 COOLANT TEMPERATURE SENSOR: thermal device which monitors coolant temperature to induce cold starting and warm-up enrichment.
9 SUPPLEMENTARY AIR VALVE: a solenoid actuated device to provide additional air during cold starting.
Other relevant system devices and signals are as follows:-
1 Ignition 'on' sensing: an input taken from contact 87 of the ignition 'on' relay which, in addition to applying power to the ignition coil, energises the main and fuel pump relays through the ECU. A timer is also initiated which, through the fuel pump relay, permits fuel pump operation for approximately 0.5 seconds to ensure the fuel rail is pressurised prior to cranking.
2 Cranking sensing: an input which induces cranking enrichment when the starter solenoid is activated.
The start routine is as follows:-
When the Ignition is switched 'On' power is applied to the various devices through contacts L14-87/30 of the main relay which is energised, via contacts B 17-87/30 of the ignition 'on' relay, when the vehicle ignition switch is in position '11', i.e. when 0 Volts is applied to B 17-85 of the ignition 'on' relay.
Power to the ECU at L3-1 and L2-10 generates a system reset which causes an initialization routine and starts the fuel pump to pressurise the fuel rail prior to cranking. The fuel pump is activated via contacts L5-87/30 of the fuel pump relay which is energised by an output from the ECU at L12-7.
Following the initialization routine, sensor scanning begins to determine engine conditions and to obtain appropriate ignition timing and fuel metering parameters. In addition, the following primary functions are performed:-
1 The stepper motor of the idle speed control valve is driven, via L12-15/16 and L12-18/19, to set the valve at a position suitable for engine starting. Rapid valve positioning is achieved for all conditions by extending or retracting its stem from a mid-travel position restored each time the ignition switch is set to "off'.
2 The solenoid of the supplementary air valve is actuated, via L12-20, to open the valve at temperatures below - 1O° C. (If you're 14 hours from a Jaguar Dealer, it's either extremely hot or extremely cold)
3 Fuel pump operation is terminated, i.e. the output at L12-7 is removed, after approximately 0.5 seconds to eliminate possible fuel flooding should an injector be stuck in the open position.
4 The exhaust system air pump and solenoid vacuum valve (if fitted) are activated by the air pump relay which is energised, via L12-2, at temperatures between 15° C and 45° C.
When the engine cranks fuel pump operation is reinstated and any fault number displayed on the instrument pack fascia is deleted, provided the ECU detects crankshaft sensor input at L13-13 and 14.
As the engine rotates on the starter motor, fuel is introduced into the air flow of the inlet manifold by the fuel injectors which are actuated by the ECU under control of the crankshaft sensor input. Injector triggering occurs, through L12-12, 13 and 25, three times per crankshaft revolution with appropriate correction factors imposed. The ignition amplifier is also actuated at the correct times, through L12-1, to fire the sparking plugs.
When the engine fires, cranking enrichment stops at 600 rev/min, injector pulses occur once per rev, and both warm-up and after-start enrichment occur. In addition, any extra manifold air is delivered by the supplementary air valve which is driven in response to coolant temperature, throttle potentiometer and crankshaft sensor inputs.
Fuel and ignition requirements are calculated at each sensor scanning to maintain optimum engine efficiency. If a sensor failure is detected, a signal is sent to the instrument pack to indicate the failure. The nature of the fault is also stored in ECU memory and is output as a fault number the next time the ignition switch is set to position.
11.3 - Fuel Pump ( ,
One thing that might help isolate some of the problems of no start/ cold start, would be to remove the fuel pump relay and jumper pins 30 and 87 in the socket. This should run the pump all the time. Then see if the car starts. Don’t run it to long that way, but as a test of the no start/ no cold start troubles, it may prove useful.
11.4 - Fuel Injectors ( ,
Remove connector from each injector. You should be able to measure about 3 ohms between pins on each injector and open circuit to body.
They are held in by the fuel rail. There are O rings on both ends that are a snug fit (twist and PULL).
Undo the fuel lines...on my car there was no pressure after sitting overnight. Obviously, do this job with the engine cold, no smoking, playing with matches or using candles for light. Put lots of rags under the connection points and use 2 spanners, one to hold things still and the other to turn the nuts.
Undo all the electrical connections to the injectors and cut any wire ties. Then undo the clamps(plastic) holding the fuel hose to the rail.
Undo the 3 or 4 bolts holding the rail to the inlet manifold. Then you can rock it back and forth while pulling it out. Then there are clips holding the injectors to the rail and the snug O rings again.
11.5 - Fuel Non-Return Valve ( ,
How to replace the non-return valve on the fuel pump. Always take standard safety precautions when dealing with petrol.
Car may take a few turns of the engine to start. This is more noticeable when the engine is warm.
No fuel pressure left in the fuel rail when the engine is off.
Jaguar part is about $37 and fits into the fuel pump. The fuel pump is located on the rear chassis.
Relieve fuel pressure (in case the old one is not totally shot!)
Jack rear left hand side. Put car on axle stands. Remove left hand wheel.
You should be able to follow fuel line back to the fuel filter (just forward of the wheel arch) and then to the fuel pump which is behind wheel arch.
Get new valve ready with new copper washer on smaller end. Place container to catch petrol below pump.
Original valves required 17mm spanner. Fuel hose requires 19mm spanner. New valve required 19mm spanner.
There is a hex bolt or similar fitting off to the side of the fuel line where it enters the pump. You can use this to hold the pump and stop it turning in its bracket.
Loosen fuel line. Holding the non return valve to prevent it rotating. Undo enough to get it loose then do it up again finger tight to stem the fuel flow (if any). Now hold pump body and loosen the non return valve.
No go back and remove fuel hose. You will still have to hold valve or it will probably unscrew instead.
Don't worry if you see something fall out of the end. You can place pipe up on spring and it won't push out too much petrol. However, valve end will by now be spewing petrol all over the place. Plug end. Hopefully, because you have already loosened it you will be able to unscrew the valve by hand (it's a bit tight to get your hand in so a "dry run" may be in order)
As soon as it's out, drop it and pick up the new one to stem the flow of petrol. The new one WILL stop the petrol coming out as soon as you have a couple of turns made.
Tighten up valve, holding pump body to stop rotation. Then re-attach fuel hose etc.
The purpose of loosening the valve is so that you don't have to spend time trying to undo the valve with fuel leaking out.
The bits that might fall out of the valve is a spring and ball which form the old non-return valve.
11.6 - Replacing Fuel Lines ( ,
Buy hose, about 6 ft of 5/16 or 7.9mm, and fuel injection hose clamps.
Let car cool, then undo the coolant recovery tank mounts and move it aside.
Remove the air inlet parts(air flow sensor, elbow, bellows to throttle body along with the heated air tube(that black thing with the wires to it). This gives room to work.
Undo the clamps holding the fuel lines to the rail, the clamp on the cruse control bellows, the plastic clamps under the cruse control bellows and the clip and holder at the bottom where the hoses mount to the hard lines going to the back of the car.
Make a note of which hose goes where, e.g. the hose that goes to the back of the rail goes to the top hard line and the hose from the front of the rail goes to the bottom hard line.
One hose at a time, grind a grove in the metal rings with a dremmel tool or a grinding bit in a drill, then cut the rings with a medium size set of wire cutters. Then cut the hose using care not to get the metal parts under the hose. BEWARE of the fact that the hoses have a rubber insert in the hardline end that will fall out.
Cut the new hose to the same length as the old one then put the clamps on, then put the hose on the metal ends and tighten the clamps.
Put everything back together using the original clamps.
turn key on for 10 seconds, off, on, off then start the car and check for leaks.
11.7 - Throttle Position Sensor ( ,
Throttle pot has two identical pots. One for gearbox and other for engine ecu.
One end of each pot is grounded by ECU (about 0V) and other end is supplied with 5V from ECU. Middle should be somewhere between 0V and 5V.
However, the idle setting should be 0.6Volts with 2thou gap on throttle body to butterfly.
It can be adjusted by loosening screws. Pot should move smoothly from 0.6V up to about 4.5V (full throttle).
Some correct settings are:
88 MY is .24 V to .40 V
89 MY is .31 V to .36 V
90 MY and later is .57V to .62 V at closed throttle
11.8 - Purge Valve ( ,
Fuel code 89, purge valve.
It's supposed to put a vacuum to the charcoal canister to suck out all those nasty gas fumes that build up in the tank and go into the canister instead of the air.
It's on the drivers side, above the charcoal canister behind the headlight.
The ECM looks at the O 2 sensor for a change when the purge valve is open, no change = check engine.
Purge drive circuit probably means connection or valve malfunction.
The valve can easily be checked by switching ignition on and off. It makes a very loud click. You can also check with 12V directly across terminals which is easier if you haven't got a friend. i.e. two wires to battery but be careful with dangling wires etc.
You can checked valve operation by blowing down the tube off the manifold.
11.9 - Air Flow Meter ( John Pring & Dana Haydel,
The mass airflow sensor is a metering device designed to determine the actual “mass” of air entering the engine. It is not a volumetric flow device and it does not require external air density compensation for proper operation. The engine must receive a mass airflow signal to account for changes in air density caused by temperature and altitude. A simple volumetric flow rate signal would be insufficient.
The meter itself, is between the air filter and the inlet manifold (looks like an aluminum tube with a rectangular box on top and a cable harness connecting to it). It is considered a very reliable component typically being trouble-free, and like the engine management computer, should never be condemned without thorough investigation. It performs it primary function of metering the mass of air drawn into the engine using two thermal sensors. These sensors are located within a bypass channel in the MAF sensor. One sensor is termed the “compensating coil” and is unheated while the other sensor is called the “sensing coil” and is electrically heated by the sensor circuitry. The amount of sensing coil current needed to keep the differential temperature between these two sensors constant is directly proportional to engine load (mass air flow).
The compensating coil is always at ambient temperature while the sensing coil is always attempting to create a fixed differential temperature as it is cooled by the air stream. In order to clean the sensing coil, the temperature flashes to 1000 degrees C for one second, four seconds after the ignition is switched off. The engine management computer is monitoring a voltage drop within the MAF sensor electronic circuitry, which is directly related to the current flowing through the sensing coil. This design is factory setup and calibrated. It is non-adjustable for the owner.
Early XJ40s incorporate a manual idle trim adjustment which is a 10 turn, 0-1000 ohm potentiometer built in to the air flow meter for minor idle fuel adjustment, but it works independently of the thermal sensors. Later models have adaptive idle fuel metering and no adjustment or input from the owner is necessary. These MAF internal adjustments, whether manual or automatic, are designed for emissions adjustment. The total available trim for either the manual or automatic idle fuel adjustment is only +/-10% of the nominal injector pulse duration at idle. Manual trimming is not recommended unless the owner has access to an emissions analyzer.
Located on the left side of the MAF sensor is the six pin, rectangular electrical connector. This connector can be problematic. It cannot be over-emphasized that the engine management system utilizes low voltage control signals. These signals are subject to faults and high resistance joints caused by corrosion. To overcome this known problem, later models of XJ40s were equipped with gold plated connections. The connector is held in with wire clip. If you push up on the wire clip from underneath, the connector can be removed from the sensor.
Electrical conductivity problems may be resolved by simple cleaning of the connector pins using a quality electronic component cleaner. It may be necessary to bend each male connector pins (in the MAF sensor housing) slightly to insure good connectivity. Pin layout is according to the figure below. Pin 36 is towards the front of the car. Pin identifiers may change from model to model, but the basic function remains the same.
Typical readings on certain conditions:
36 & 6 : Grounds
7 : ECU Ground
8 : Empty Connector
9 : 12 VDC Supply
12 : ECU Supply 5.0 VDC
Ignition on MAF disconnected (no start) Ignition on MAF connected (no start) MAF connected engine running @ idle (~750RPMs)
7 <1V (leakage) 7 >1V (leakage) 7 ~1.2V to 1.4V
9 Battery voltage 9 Battery voltage or slightly less 9 >Battery voltage due to alternator operating
12 ~ 5V 12 ~1.85V 12 ~1.8 to 2.5V
Battery voltages on pin 9 that deviates significantly from the chart need to be investigated further and repairs made.
Note: Should the battery be disconnected the engine management will need to re-learn the base idle. This “re-learning” is automatically achieved by operating the engine at normal coolant temperature and driving for a distance > 50 yards. The engine may stall at idle once or twice until the adjustment values are accepted and stored within the ECU RAM.
Pin 7 readings < 1.2V can produce poor running conditions and if lower possibly no start. A voltage of <0.2V or > 4.5V is will generate a diagnostic test code (DTC 12). Refer to Fault Code List for other diagnostic help with this fault.
Pin 12 reading will typically increase towards 5V as engine revolutions are increased. This reference voltage is from the ECU.
Bench Test (Circuit Checks) for MAF Sensor:
1) Remove the electrical connector from the MAF sensor.
2) Connect a 12VDC power source (battery) to Pin 9 (+) which is normal 12 VDC supply to the MAF sensor and Pin 36 (-) which is normal ground for the MAF sensor. Ensure the power supply positive is connected to Pin 9 and the negative is connected to Pin 36. Do not reverse power supply polarity.
3) Connect a quality digital multi-meter setup to monitor voltage to Pin 7 (+) and Pin 6 (-). Ensure multi-meter positive test lead is to Pin 7 and negative test lead is to Pin 6. If multi-meter polarity is reversed, voltages will indicate negative but the absolute values will be correct.
Test 1 : Air meter stationary with no flow
Test 2 : With a blast of air in the direction of flow
on MAF disconnected (no start)
on MAF connected (no start)
|MAF connected |
engine running @ idle (~750RPMs)
|7 <1V |
|7 >1V |
|7 ~1.2V to |
|9 Battery |
|9 Battery |
voltage or slightly less
|9 >Battery |
voltage due to alternator operating
|12 ~ 5V|
|12 ~1.8 to |
on pin 9 that deviates significantly from the chart need to be investigated
further and repairs made.
Note: Should the
battery be disconnected the engine management will need to re-learn
the base idle. This re-learning is automatically achieved
by operating the engine at normal coolant temperature and driving
for a distance > 50 yards. The engine may stall at idle once or
twice until the adjustment values are accepted and stored within the
Pin 7 readings
< 1.2V can produce poor running conditions and if lower possibly
no start. A voltage of <0.2V or > 4.5V is will generate a diagnostic
test code (DTC 12). Refer to Fault Code List for other diagnostic
help with this fault.
Pin 12 reading
will typically increase towards 5V as engine revolutions are increased.
This reference voltage is from the ECU.
(Circuit Checks) for MAF Sensor:
1) Remove the
electrical connector from the MAF sensor.
2) Connect a 12VDC
power source (battery) to Pin 9 (+) which is normal 12 VDC supply
to the MAF sensor and Pin 36 (-) which is normal ground for the MAF
sensor. Ensure the power supply positive is connected to Pin 9 and
the negative is connected to Pin 36. Do not reverse power supply polarity.
3) Connect a quality
digital multi-meter setup to monitor voltage to Pin 7 (+) and Pin
6 (-). Ensure multi-meter positive test lead is to Pin 7 and negative
test lead is to Pin 6. If multi-meter polarity is reversed, voltages
will indicate negative but the absolute values will be correct.
1 : Air meter stationary with no flow
2 : With a blast of air in the direction of flow
to 1.5V then returns to Test 1
Drifted Module inoperative. Sensors(s) detached
voltage as in Test 1