Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSJAGUAR1991XJ-6 L6-4.0LREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSDESCRIPTION AND OPERATIONENGINE MANAGEMENT SYSTEM
1991 Jaguar XJ-6 L6-4.0L
Engine Management System
1991 Jaguar XJ-6 L6-4.0LSECTION Engine Management System
Overview
The AJ6 4.0 Litre EMS is an integrated engine management system, controlled through a digital Electronic Control Module (ECM) containing a microprocessor.
The system maintains optimum performance over the engine operating range by precisely controlling fuel injection, ignition timing and emission control functions. In addition, the ECM provides various interface outputs and incorporates an on-board diagnostic function.
Function And Control - Summary:
- Fuel delivery (fuel pump)
- Evaporative emission control (canister purge)
- Fuel injection
- Cold start
- Warm-up
- Exhaust emission
- Oxygen sensor feedback
- Overrun fuel cut-off
- RPM limitation (engine overspeed)
- Wide-open-throttle fuel cut-off
- Ignition timing
- Idle speed control
- Air injection
- Exhaust gas recirculation
- Adaptive idle fuel metering (1993 MY ON)
- On-Board Diagnostics (OBD)
- "Limp home" capability
- Vehicle systems interfaces
- Serial communication (IS0)
Typical AJ6 4.0 Litre EMS
EMS Components Installed on Engine
EMS Components Installed on Vehicle
The AJ6 4.0 Litre EMS is an integrated engine management system, controlled through a digital Electronic Control Module (ECM) containing a microprocessor.
The system maintains optimum performance over the engine operating range by precisely controlling fuel injection, ignition timing and emission control functions. In addition, the ECM provides various interface outputs and incorporates an on-board diagnostic function.
Function And Control - Summary:
- Fuel delivery (fuel pump)
- Evaporative emission control (canister purge)
- Fuel injection
- Cold start
- Warm-up
- Exhaust emission
- Oxygen sensor feedback
- Overrun fuel cut-off
- RPM limitation (engine overspeed)
- Wide-open-throttle fuel cut-off
- Ignition timing
- Idle speed control
- Air injection
- Exhaust gas recirculation
- Adaptive idle fuel metering (1993 MY ON)
- On-Board Diagnostics (OBD)
- "Limp home" capability
- Vehicle systems interfaces
- Serial communication (IS0)
Typical AJ6 4.0 Litre EMS
Components Locations:
EMS Components Installed on Engine
Components Locations:
EMS Components Installed on Vehicle
RENDER: 1.0x
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.