Mechanics

FUEL PUMP??

1984 Jaguar XJ6

Engine Performance problem
1984 Jaguar XJ6 6 cyl Two Wheel Drive 98000 miles

XJ 6 started running rough, hesitation at times. It did stop running and has not started since. Fuel pump tests good. Has spark. We have got as far as finding that when you go to start the car, fuel pump comes on for a split second then shuts itself down. Causes? Thinking maybe the fuel pump relay or fuel pump diode unit is bad. Inertia switch also but not thinking so. Any and all help would be appreciated. Thanks.
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Cliffgriswell
September 28, 2008.



Could be the thermo time switch, and or cold start injector, both are listed below.
FUEL INJECTION SYSTEM - LUCAS/BOSCH AFC -1984 Jaguar XJ6
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ARTICLE BEGINNING
DESCRIPTION
The Lucas-Bosch Air Flow Controlled (AFC) fuel injection system is an electronically controlled system operated by incoming air flow. The AFC fuel injection system also contains a feedback system which measures oxygen content of exhaust gases and maintains the air/fuel ratio at about 14.7: 1.
The system consists of an electric fuel pump, fuel pressure regulator, fuel injectors, Electronic Control Unit (ECU), air flow meter, air temperature sensor, throttle switch, coolant temperature sensor, oxygen sensor, 3-way catalytic converter, and electrical relays. In addition, all models are equipped with a cold start system to aid in cold engine starts. The cold start system consists of an auxiliary air valve, cold start injector, and thermo time switch.
Air conditioned vehicles are equipped with a fuel cooler. Fuel return lines are routed through a cooler which is part of the air conditioning refrigerant system.
Fig. 1: Jaguar AFC Fuel Injection System
OPERATION
ELECTRICAL RELAYS
The main relay, diode unit, and fuel pump relay are located on the firewall next to the battery. When ignition is turned on, the main relay is activate. This connects the battery circuit to the ballast resistors and injectors. The main relay also allows current to flow to the control unit and the fuel pump switch on the air flow meter.
Relays are located in engine compartment, near battery. When engine is cranked for starting, the diode unit is activated. This energizes the auxiliary air valve, cold start system, and fuel pump.
ELECTRIC FUEL PUMP
The electric fuel pump provides fuel under pressure to the fuel pressure regulator. Power for operation during cranking mode is provided from starter relay via the diode unit. After the engine has started, control of the fuel pump is by a fuel pump circuit in the air flow meter.
The first movement of air flow meter air measuring flap (about 5 °) closes the fuel pump contacts and provides power to fuel pump after engine has started. With engine stopped, no air flow is present, measuring flap closes and fuel pump contacts are opened to cut power to fuel pump. This method of circuitry reduces the risk of fire in a collision. The fuel pump is a sealed unit; no service required.
FUEL PRESSURE REGULATOR
The pressure regulator consists of a sealed, spring loaded diaphragm with a connection for intake

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manifold vacuum. Fuel is provided to fuel injectors under 36 psi (2.5 kg/cm2 ) pressure.
A connection for intake manifold vacuum provides a constant pressure differential which ensures that the amount of fuel injected is solely dependent upon injector " OPEN" time. Fuel in excess of fuel pressure or pressure differential is returned to fuel tank. No service of pressure regulator is required.
FUEL INJECTORS
A fuel rail links the fuel pressure regulator with the fuel injectors. Each cylinder is provided with a solenoid-operated injector which sprays fuel toward back of each intake valve. Each injector is energized through the ignition coil and grounded through the ECU to complete the circuit.
Each injector is linked to a resistor to reduce operating voltage to 3 volts and to protect injectors from power surges. Resistors are located in a single unit mounted on right side of firewall.
The ECU controls the length of time each injector is open. The " OPEN" time of the injector governs the amount of fuel delivered. The injectors deliver 1/2 the amount of fuel required each crankshaft revolution.
ELECTRONIC CONTROL UNIT (ECU)
All components of the control system are electrically connected to the ECU. See Fig. 2. The ECU is a pre-programmed computer which receives and interprets data from various sensors to calculate the amount of fuel required by the engine to maintain efficiency with minimum exhaust emissions.
Fig. 2: Electronic Control Unit (ECU) Unit located at front of luggage compartment.
Impulses from the oxygen sensor informs the ECU of oxygen content of exhaust gases and the ECU constantly adjusts the air/fuel ratio by controlling the injector " OPEN" time.
The ECU provides fuel enrichment whenever engine is cranked, regardless of engine temperature. This is activated by a direct electrical connection from the starter circuit to the ECU. The ECU is a sealed unit; no service is required. It is located in the trunk against the front bulkhead.
AIR FLOW METER
All engine air is drawn through the air flow meter. The meter is basically a tunnel with similarly shaped measuring flap and dampening flap (offset 90 ° on same casting).
The measuring flap swings on an axis in air stream against reverse pressure of a spiral spring and is connected to a potentiometer. The potentiometer transmits an electrical signal proportionate to the angular displacement of the measuring flap to inform the ECU of engine load. See Fig. 3.
In addition to monitoring air flow, the meter also controls fuel pump operation and idling. At idle, the measuring flap is almost closed due to spiral spring pressure. An idle air by-pass receives air from main air flow through a small hole, the size of which is controlled by the idle mixture screw. This adjustable air by-pass influences CO levels at low engine speeds.

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FUEL INJECTION SYSTEM - LUCAS/BOSCH AFC -1984 Jaguar XJ6
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AIR TEMPERATURE SENSOR
The air temperature sensor is an integral component of the air flow meter which converts the temperature of incoming air into electrical signals. These electrical signals are received by the ECU and processed to adjust the amount of fuel injected by the injectors. The air temperature sensor is a non-serviceable device.
Fig. 3: Lucas-Bosch AFC Air Flow Meter
THROTTLE SWITCH
A contact type throttle switch is installed on throttle chamber. The throttle switch sends information on throttle position to ECU. On the contact switch, signals are sent when throttle is at idle or full throttle positions. See Fig. 4.
COOLANT TEMPERATURE SENSOR
This sensor provides ECU with temperature information relating to warm-up enrichment operation. During warm-up period after a cold engine start, additional fuel is required to maintain engine performance. As coolant temperature increases, the ECU decreases fuel enrichment until engine reaches normal operating temperature.
Fig. 4: Contact Type Throttle Switch
COLD START SYSTEM
The cold start system provides additional air and fuel during cold engine starts. The cold start system consists of an auxiliary air valve which provides additional air, cold start injector which delivers additional fuel, and a thermo time switch which controls operation of the cold start system.
The thermo time switch has a bi-metallic contact surrounded by a heating coil which is energized during engine cranking. This switch limits cold start system to 8 seconds under extreme cold engine starts in relation to engine coolant temperature. When coolant temperature is above 95 °F (35 °C), bi-metallic contact breaks ground circuit of cold start injector and cold start enrichment is by-passed.
The auxiliary air valve provides additional air during cold engine starts and warm-up period. The valve consists of an electrically heated bi-metallic strip, movable disc and air by-pass channel.
The heater coil on the bi-metallic strip is energized by the fuel pump relay. Control of the valve is based upon engine temperature. The air by-pass channel is open when engine is cold and gradually closes as temperature rises. At predetermined temperatures, air by-pass channel is blocked and additional air flow stops. See Fig. 5.
Fig. 5: Auxiliary Air Valve
ADJUSTMENTS

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HOT (SLOW) IDLE RPM
See the appropriate article in the TUNE-UP section.
IDLE MIXTURE
See the appropriate article in the TUNE-UP section.
THROTTLE VALVE
1. Remove air intake hose and elbow to expose throttle valve. Loosen throttle valve lock nut on stop screw and loosen stop screw. Ensure throttle valve closes fully. 2. Insert a.002" (.05 mm) feeler gauge between throttle valve and throttle housing bore. See Fig. 6. With feeler gauge in position, adjust stop screw so it just touches stop arm. Tighten lock nut. Press stop arm against stop screw and remove feeler gauge. 3. Seal threads of adjusting screws and lock nuts with paint spots. Install hose and elbow. Check operation of throttle linkage and adjust if required by ensuring outer cable is secured in bracket so inner cable is under light tension, but not enough to move operating lever. Tighten lock nuts.
Fig. 6: Adjusting Jaguar Throttle Valve Clearance
Fig. 7: Fuel Injection Wiring Diagram (XJ6)
TESTING

NOTE: The fuel injection system maintains constant fuel pressure in fuel lines and components. Be sure to relieve pressure before attempting to open system. Do not allow fuel to flow onto engine or electrical parts, or allow an open flame in area while testing fuel system or components.

ELECTRONIC CONTROL UNIT (ECU)
Do not attempt to test ECU, permanent damage could result. It is possible to check plug wires for continuity. The ECU should only be judged faulty after compression is checked, ignition system has been tested and found problem-free, and all other fuel injection components have been thoroughly tested (including wiring).
FUEL PRESSURE
1. Depressurize fuel system by removing fuel pump relay and cranking engine for a few seconds. Turn ignition switch off and connect fuel pump relay. 2. Disconnect fuel rail at cold start injector and connect fuel pressure gauge. Disconnect negative lead from ignition coil and turn ignition switch on. Pressure reading should be 35.5-37 psi (2.5-

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2.6 kg/cm2 ). 3. Slow pressure drop is permissible; sudden pressure drop requires check of entire fuel system for leaks. After testing fuel pressure, depressurize fuel system, remove test equipment and reconnect fuel lines and ignition coil negative lead. 4. Operate fuel change-over switch on dash and recheck reading. Reading from both fuel tanks should agree. On all models, if pressure reading is not to specifications, replace fuel pressure regulator.
AIR TEMPERATURE SENSOR
Disconnect negative battery cable and air flow meter connector. Connect ohmmeter leads to terminals 6 and 27 on potentiometer connector. If readings are not as specified, replace air flow meter. See Temperature/Resistance Relationship chart.
TEMPERATURE/RESISTANCE RELATIONSHIP Temperature °F ( °C) 32 (0) 68 (20) 104 (40) 140 (60)

Ohms 5000 2500 1180 600
AUXILIARY AIR VALVE
1. Remove auxiliary air valve connector and connect an ohmmeter to both terminals. Resistance should read approximately 33 ohms. If not, continue testing as follows: 2. Remove auxiliary air valve from inlet manifold and immerse mounting plate in cold water, avoiding contact of terminals and by-pass channel with water. 3. The movable plate should fully expose by-pass channel. Gradually heat water. As temperature increases, channel should become blocked. If valve does not respond as outlined, replace auxiliary air valve.
THERMO TIME SWITCH
1. Using a thermometer, check engine coolant temperature. Compare coolant temperature with value stamped on thermo time switch body. Connect an ohmmeter between terminal " W" on switch and ground. 2. If coolant temperature is higher than switch value, a very high resistance denoting an open circuit should be obtained. 3. If coolant temperature is lower than switch value, a very low resistance denoting a closed circuit should be obtained. If switch does not respond as outlined, replace thermo time switch. 4. If switch passes resistance test, allow coolant temperature to cool below stamped value on switch. With ohmmeter connected, connect battery power via an isolating switch to terminal " G". 5. Using a stop watch, check delay time as ohmmeter changes between high and low resistance. Delay period should be as specified. See Coolant/Delay Time Relationship chart. If not,

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replace thermo time switch.
COOLANT/DELAY TIME RELATIONSHIP
Temperature: °F ( °C) 32 (0) 50 (10) 95 (35)
Delay: Seconds 4.5 3.5 0
COLD START INJECTOR
1. Engine must be cold to perform this test. Remove electrical connector from cold start injector and connect voltmeter across connector terminals. Crank engine. Battery voltage should be present. 2. Release fuel system pressure and remove cold start injector with fuel lines attached. Reconnect electrical connector and place injector in container. 3. As cold engine is cranked, fuel spray should be observed until thermo time switch cuts off relay. When engine is warm, no fuel spray should occur during cranking. If injector does not respond as outlined, replace cold start injector.
COOLANT TEMPERATURE SENSOR
1. Disconnect battery ground cable and electrical connector from sensor. Connect an ohmmeter between sensor terminals. Reading should be as specified. See Temperature/Resistance Relationship chart. 2. Disconnect ohmmeter and check resistance between each terminal and sensor body. A very high resistance denoting an open circuit should be obtained. If sensor does not respond as outlined, replace coolant temperature sensor.
TEMPERATURE/RESISTANCE RELATIONSHIP Temperature °F ( °C) 32 (0) 68 (20) 104 (40) 140 (60) 176 (80)

Ohms 5900 2500 1180 600 325
THROTTLE SWITCH
Disconnect battery ground cable and throttle switch electrical connector. Connect a powered test lamp between terminals 3 and 18 of throttle switch. Open throttle. Test lamp should glow when throttle nears wide open position. If not, replace throttle switch.
REMOVAL & INSTALLATION

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AIR FLOW METER
Removal & Installation
Disconnect battery ground cable. Disconnect rubber hose from both sides of air flow meter. Remove bolts securing meter to bracket. Move air flow meter upward, unplug electrical connector and remove air flow meter. To install, reverse removal procedure.
ELECTRONIC CONTROL UNIT (ECU)

Removal & Installation
Disconnect battery ground cable. ECU is located at forward end of luggage compartment. Remove ECU cover, retaining band and cable clamp clip. Unclip end cover and lift out ECU. Disconnect pin connector and remove ECU. To install, reverse removal procedure. Ensure pin connector is installed squarely and securely.
COLD START INJECTOR

Removal & Installation
Disconnect battery ground cable and remove electrical connector from injector. Relieve fuel line pressure. Remove injector retaining screws and remove injector. To install, reverse removal procedure.
AUXILIARY AIR VALVE

CAUTION: Auxiliary air valve removal should be done only when engine is cold. Removal of valve requires having replacement valve ready for immediate installation or draining cooling system below level of valve.

Removal
Disconnect battery ground cable. Disconnect air hoses and electrical connector from auxiliary air valve. Remove coolant system cap. Remove valve retaining bolts and air valve.
Installation
Clean all gasket material from mating surfaces without damaging seating area. To install, coat new gasket with non-hardening sealing compound and reverse removal procedure.
COOLANT TEMPERATURE SENSOR

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CAUTION: Coolant temperature sensor removal should be done only when engine is cold. Removal of sensor requires having replacement sensor ready for immediate installation or draining cooling system below level of sensor.

Removal & Installation
Disconnect battery ground cable. Drain coolant and unplug sensor electrical connector. Loosen and remove sensor. To install, reverse removal procedure. Use sealing compound on sensor threads. Replace sealing washers, if equipped.
THERMO TIME SWITCH

CAUTION: Thermo time switch removal should be done only when engine is cold. Removal of switch requires having replacement switch ready for immediate installation or draining cooling system below level of switch.

Removal & Installation
Disconnect battery ground cable. Drain coolant and disconnect switch electrical connector. Loosen and remove switch. To install, reverse removal procedure. Use sealing compound on switch threads. Replace sealing washers, if equipped.
FUEL PRESSURE REGULATOR

CAUTION: Fuel system pressure must be relieved before removing fuel pressure regulator.
Removal & Installation
Disconnect battery ground cable. Disconnect fuel lines and vacuum line at regulator. Remove pressure regulator (separating from bracket, if installed). To install, reverse removal procedure.
FUEL INJECTORS

CAUTION: Fuel system pressure must be relieved before removing fuel injectors.

Removal
1. Disconnect battery ground cable. Unplug electrical connectors at injectors. Remove screws attaching fuel rail to intake manifold. Release clips holding fuel supply and return rails.

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2. Remove manifold pressure pipe. Remove nuts and washers from injector clamps. Lift off fuel rail with injectors, loosen injector clamps and remove injectors from fuel rail. Remove and discard " O" rings if equipped.
Installation
To install, reverse removal procedure. Ensure electrical connectors are properly installed on injectors before installing fuel rail assembly to manifold. New " O" rings should be installed on injectors, if equipped.

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Merlin2021
Sep 28, 2008.