Engine Controls - System & Component Testing Land Rover Discovery I

INTRODUCTION

Note. For system and component testing information not covered in this article, see corresponding system or component fault code definition under TROUBLE CODE IDENTIFICATION CHART in appropriate SELF-DIAGNOSTICS article. Perform appropriate fault code test.

Note. Testing individual components does not isolate shorts or opens. Perform all voltage tests using a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in test procedure. Use ohmmeter to isolate wiring harness shorts or opens.

Before testing separate components or systems, follow proper workflow. If a no start condition exists, proceed to appropriate BASIC DIAGNOSTIC PROCEDURES article. If a driveability condition exists, proceed to appropriate TROUBLE SHOOTING - NO CODES article for diagnosis by symptom (i.e., ROUGH IDLE, ENGINE STALLS, etc.).

Power Circuits

Release Engine Control Module (ECM) connector retaining clip and remove connector from ECM. Access is gained by removing front seat base trim of right hand front seat. Remove connector shroud and maneuver it along harness until there is enough clearance to enable meter probes to be inserted into back of plug. There are six pin numbers (1, 13, 14, 27, 28 and 40) molded onto rear of plug as shown in illustration. (Scheme 43) Pin wire colors are identified in ENGINE CONTROL MODULE CONNECTOR TERMINAL IDENTIFICATION table.

To test Powertrain Control Module (PCM) power circuits (Scheme 42) After completing test, retest vehicle to ensure faults have been rectified. If faults still persist, recheck using Lucas diagnostic equipment.

Scheme 42

Scheme 43

ENGINE CONTROL MODULE CONNECTOR TERMINAL IDENTIFICATION

ENGINE COOLANT TEMPERATURE SENSOR CIRCUIT

1. Turn ignition switch to OFF position. Access Engine Control Module (ECM), located behind right fascia. (Scheme 44) Disconnect ECM connector. Check resistance between ECM harness connector terminals No. 7 (Green/Blue wire) and 25 (Red/Black wire). (Scheme 43) Engine Coolant Temperature (ECT) sensor circuit resistance should be as specified. See «FUEL & COOLANT TEMPERATURE SENSOR RESISTANCE»(/land-rover/discovery/i-1989-1998/remont/testing-diagnostics/#engine-controls-system-component-testing) table. If resistance is not as specified, go to next step. If resistance is as specified, ECT sensor circuit is okay.
2. Check for short or open in Green/Blue wire between ECM terminal No. 7 and ECT sensor. If wire is okay, check for short or open in Red/Black wire between ECM terminal No. 25 and ECT sensor.

FUEL & COOLANT TEMPERATURE SENSOR RESISTANCE

Scheme 44

FUEL TEMPERATURE SENSOR CIRCUIT

1. Turn ignition switch to OFF position. Access Engine Control Module (ECM), located behind right fascia. (Scheme 44) Disconnect ECM connector. Check resistance between ECM harness connector terminals No. 32 (Gray/White wire) and 25 (Red/Black wire). (Scheme 43) Fuel Temperature (FT) sensor circuit resistance should be as specified. See «FUEL & COOLANT TEMPERATURE SENSOR RESISTANCE»(/land-rover/discovery/i-1989-1998/remont/testing-diagnostics/#engine-controls-system-component-testing) table. If resistance is not as specified, go to next step. If resistance is as specified, FT sensor circuit is okay.
2. Check for short or open in Gray/White wire between ECM terminal No. 32 and FT sensor. If wire is okay, check for short or open in Red/Black wire between ECM terminal No. 25 and FT sensor.

HEATED OXYGEN SENSOR CIRCUIT

1. Start and run engine until it reaches normal operating temperature. Access Engine Control Module (ECM), located behind right fascia. (Scheme 44) Backprobing, measure voltage between ECM connector terminals No. 23 (Blue wire) and 4 (Black wire) for left Heated Oxygen Sensor (HO2S), or terminals No. 24 (Blue wire) and 4 (Black wire) for right HO2S. (Scheme 43) Voltage should be fluctuating between 0.5-1.0 volts. If voltage is as specified, HO2S is okay. If voltage is not as specified, go to next step.
2. If voltage is steady around 0.5 volts, check for vacuum leaks, faulty of contaminated injectors or low fuel pressure. If voltage is steady around 1.0 volts, check for high fuel pressure, leaking injectors or saturated carbon canister. Repair as necessary. If no problem is found, check for short or open in Blue wire between ECM and HO2S or Black wire between HO2S and ground. If wires are okay, replace HO2S.

HEATED OXYGEN SENSOR HEATER CIRCUIT

1. Turn ignition switch to OFF position. Disconnect Heated Oxygen Sensor (HO2S) connectors. Remove fuel pump relay located behind right footwell trim panel. (Scheme 45) Connect a jumper wire between fuel pump relay connector terminals No. 30 (Purple/White wire) and 87a (White/Orange wire). Check for battery voltage at HO2S harness connector terminal No. 1 (White/Orange wire). If battery voltage is not present, go to next step. If battery voltage is present, check for malfunctioning fuel pump relay.
2. Check for blown fuse No. 6 (15-amp) located in engine compartment fuse box, at right front of engine compartment. (Scheme 46) If fuse is okay, check for short or open in Purple/White wire between fuse No. 6 (15-amp) and fuel pump relay. If wire is okay, check for short or open in White/Orange wire between fuel pump relay and HO2S. If problem is not found, go to next step.
3. Access Engine Control Module (ECM), located behind right fascia. (Scheme 44) Disconnect ECM connector. Measure resistance between fuel pump relay connector terminal No. 87a (White/Orange wire) and ECM harness connector terminal No. 4 (Black wire). (Scheme 43) Resistance should be 2.5-6.0 ohms. If resistance is not as specified, go to next step. If resistance is as specified, HO2S heater circuit is okay.
4. Check for short or open in Black wire between HO2S and ground terminal E103. Ground terminal E103 is located at left rear of engine compartment. (Scheme 47) If wire is okay, check for short or open in Black wire between ECM connector terminal No. 4 and ground terminal E103.

Scheme 45

Scheme 46

Scheme 47

MASS AIR FLOW SENSOR CIRCUIT

1. Access Engine Control Module (ECM), located behind right fascia. (Scheme 44) Backprobing, measure voltage at ECM connector terminal No. 35 (Blue/Green wire). (Scheme 43) If measurement is not 0.2-0.7 volts, go to next step. If measurement is 0.2-0.7 volts, Mass Air Flow (MAF) sensor is okay.
2. Check for short or open in Brown/Orange wire between MAF sensor and engine control load relay. Engine control load relay is located behind right footwell trim panel. (Scheme 45) If wire is okay, check for short or open in Blue/Green wire between MAF sensor and ECM. If wire is okay, check for short or open in Red/Black wire between MAF sensor and ECM terminal No. 25.

FUEL SYSTEMS

FUEL SYSTEM PRESSURE RELEASE

Note. Fuel at low pressure will remain in system. To remove low pressure fuel, place absorbent cloth around fuel pipe fitting during disconnection.

1. Remove fuel pump relay. Fuel pump relay is located behind right footwell trim panel. (Scheme 45) Start and run engine.
2. When sufficient fuel has been used to cause fuel line pressure to drop, injectors will become inoperative, resulting in engine stall. Switch off ignition. Disconnect battery negative lead.

Scheme 48

1. Release fuel pressure. See «FUEL SYSTEM PRESSURE RELEASE»(/land-rover/discovery/i-1989-1998/remont/testing-diagnostics/#engine-controls-system-component-testing__fuel-system-pressure-release). Connect pressure gauge on outlet from fuel filter, located on chassis under right rear wheel arch. (Scheme 48)
2. Reconnect battery and turn ignition to ON position, while observing pressure gauge. Pressure should be 34-38 psi (2.39-2.67 kg/cm 2 ). Maximum allowable pressure drop is 10 psi (0.7 kg/cm 2 ) per minute.
3. If pressure is low, ensure filter is not blocked and pump is operating correctly, recheck pressure. If pressure is still low replace pressure regulator. Start vehicle and check for leaks.

FUEL CONTROL

Note. Before removing any of injectors, remove and examine spark plugs, check for consistent plug color. A leaking injector will result in appropriate spark plug being "sooted up." Following test may only be carried out using suitable injector test equipment.

Fuel Injector Leakage

Leak test with injectors closed but pressurize to 36 psi (2.54 kg/cm 2 ). No injector should leak more than 2 drops of fuel per minute.

Fuel Injector Volume

Perform fuel delivery test with injector open and pressurize system to 36 psi (2.54 kg/cm 2 ). Fuel delivery from each injector at 64-72°F (18-22°C) should be 9.8-10.7 Inch 3 (160-175 cm 3 ) per minute using cleaning fluid, or 11.0-11.9 Inch 3 (180-195 cm 3 ) per minute using gasoline.

IGNITION SYSTEM TEST

1. Inspect battery cables and connections to ensure they, are clean and tight. Check battery state of charge.
2. Inspect all primary ignition system connections to ensure that they are clean and tight. Check that secondary ignition wires are correctly positioned and not shorting to ground against any engine components. Wiring harness and individual wires should be firmly fastened to prevent chaffing.
3. Check air gap between pick-up limb and reluctor teeth, using a non-ferrous gauge. Air gap should be.008-.014" (.20-.35 mm). (Scheme 49) Air gap is set initially at factory and will only require adjusting if tampered with or when pickup module is replaced.

Scheme 49

SECONDARY IGNITION WIRE TEST

Disconnect secondary ignition coil wire from distributor cap and hold it approximately 0.25" (6 mm) from engine block, using suitable insulated pliers. (Scheme 50) Crank engine. If sparking is present, check for faulty distributor cap, rotor arm and wires. Also check for incorrect ignition timing. If all components are okay, go to ROTOR ARM TEST. If no spark or weak spark is present, go to PRIMARY IGNITION SYSTEM VOLTAGE TEST.

Scheme 50

Scheme 51

Scheme 52

1. Turn ignition switch to ON position. Measure voltage between 4 circuits indicated in illustration. (Scheme 51) Measurement for V1 should be more than 12 volts. Measurement for V2 should be no more than 1 volt below voltage measured at V1. Measurement for V3 should be no more than 1 volt below voltage measured at V1. Measurement for V4 should be 0.0-0.1 volt.
2. If all measurements are as specified, go to «AMPLIFIER TEST»(/land-rover/discovery/i-1989-1998/remont/testing-diagnostics/#engine-controls-system-component-testing__amplifier-test). If measurements are not as specified, isolate fault using illustration. (Scheme 52) If coil and amplifier are suspected, disconnect wire at ignition coil negative terminal and measure voltage at V3. If voltage is still incorrect, install new ignition coil. If voltage is correct, check for short or open in Blue wire between ignition coil and amplifier. If wire is okay install new amplifier. If engine will not start go to «AMPLIFIER TEST»(/land-rover/discovery/i-1989-1998/remont/testing-diagnostics/#engine-controls-system-component-testing__amplifier-test).

AMPLIFIER TEST

Connect voltmeter between battery positive terminal and ignition coil negative terminal, voltmeter should register zero volts. (Scheme 53) Switch ignition ON, voltmeter should still register zero volts. Crank engine, voltage should increase when cranking, in which case proceed to SECONDARY IGNITION COIL WIRE TEST. If there is no increase in voltage during cranking, proceed to PICK-UP COIL RESISTANCE TEST.

Scheme 53

PICK-UP COIL RESISTANCE TEST

Remove amplifier. Check resistance between pick-up terminals in body of distributor. (Scheme 54) Reading should be 2000-5000 ohms. If reading is as specified, check all connections between pick-up and amplifier. If connections are okay, install new amplifier. If engine still does not start, go to SECONDARY IGNITION COIL WIRE TEST. If reading is not as specified, install new pick-up and attempt to start engine. If engine still does not start, go to SECONDARY IGNITION COIL WIRE TEST.

Scheme 54

SECONDARY IGNITION COIL WIRE TEST

Replace secondary ignition coil wire with known good wire. Hold distributor end of secondary ignition coil wire approximately 0.25" (6 mm) from engine block, using suitable insulated pliers. (Scheme 55) Crank engine. If weak or no sparking is present, install new coil and repeat test. If sparking is present, repeat test with original secondary ignition coil wire. If sparking is present, go to ROTOR ARM TEST. If weak or no sparking is present, install a new secondary ignition coil wire. If engine still does not start, go to ROTOR ARM TEST.

Scheme 55

ROTOR ARM TEST

Remove distributor cap. Disconnect secondary ignition coil wire from distributor cap and hold it about 0.13" (3 mm) above rotor arm electrode, using suitable insulated pliers. Crank engine. (Scheme 56) There should be no sparking between rotor arm and secondary ignition coil wire. If there is no sparking, go to VISUAL CHECK. If sparking occurs, install new rotor arm. If engine still does not start, go to VISUAL CHECK.

Scheme 56

VISUAL CHECK

Ensure distributor cap and top of ignition coil are clean, dry and have no tracking marks. Ensure that secondary ignition wire insulation is not cracked, chafed or missing. Check for faulty secondary ignition wire. Ensure park plugs are clean, dry and set to correct gap. Ensure that pick-up and reluctor leads are not fouled. Ensure that rotor arm and distributor cap are not cracked or show signs of tracking marks.

Valve Air Flow Check

1. Attach a 9.75-10.25 CUBIC INCH vacuum tank to colored side of valve.
2. Expose Black side to atmospheric pressure.
3. Observe vacuum drop. Time required for vacuum to drop from minus 20 In Hg to minus 2 In Hg should be .5 second maximum.
4. To check vacuum recovery air flow, attach a 22.25-23.25 CUBIC INCH vacuum tank to Black side of valve.
5. Expose colored side to atmospheric pressure.
6. Observe vacuum drop. Time required for vacuum to drop from 16 In. Hg to 8 In. Hg will be 4-6 minutes. If delay valve does not comply with any of test results, replace unit.

External Leakage Check

1. Seal colored side of valve and attach a short flexible pipe to other end.
2. Submerge valve in water and orally blow through valve.
3. If any external leakage is noticeable, fit a new valve. If delay valve does not comply with any of test results, replace unit.

Equipment Required For Testing

1. Nitrogen cylinder (compressed air may be used to pressure system when there has NEVER been fuel present in fuel or evaporative control systems).
2. Water manometer (0-30 In. of water or more).
3. Test pipes and "T" fitting.

Test Procedure

1. Unless there has NEVER been any fuel in system, ensure there are at least 2 gallons of fuel in fuel tank. Disconnect pipe to vapor separator at adsorption canister. Connect pipe to nitrogen cylinder and water manometer using "T" fitting. Pressurize system to 26.5-27.5 In. of water, allow reading to stabilize, then turn off nitrogen supply.
2. Measure pressure drop within a period of 2.5 minutes. If drop is greater than 2.5 In. of water, system has failed test. Note that a fully sealed system will show a slight increase in pressure. Should system fail test, maintain pressure in system and apply a soap solution around all joints and connections until bubbles appear to reveal source of leak. Repair leak as necessary. Repeat test. Remove test equipment and reconnect pipe to adsorption canister.

A/C CONDENSER FAN CONTROL MODULE CIRCUIT

1. Start engine. Turn on A/C. Check for condenser fans operation. If A/C condenser fans are not working, go to next step. If A/C condenser fans are working, A/C condenser fan control module circuit is okay.
2. Check for a blown fuse F3 (30-amp), located in fascia fuse box, behind left side of fascia. (Scheme 57) If fuse is okay, check for a blowen fuse F7 (20-amp), located in engine compartment fuse box, right front of engine compartment. (Scheme 46) If fuse is okay, backprobing, measure voltage at condenser fan relay terminal No. 86 (Black/Purple wire). Condenser fan relay is located behind right side of fascia on bracket. (Scheme 58) If 12 volts are present but condenser cooling fans are not working, go to next step. If 12 volts are not present, check for short or open in wiring harness between A/C switch and condenser fan relay.
3. Remove condenser fan relay. Connect a fused jumper wire between condenser fan relay connector terminals No. 30 and 87 (Black/Brown wire). If fans are now working, replace condenser fan relay. If fans still do not work, check for short or open in wiring harness between battery and condenser fan relay. If wiring harness is okay, go to next step.
4. Backprobing, apply 12 volts to A/C condenser fan control module connector terminal No. 5 (Black/Green wire) for at least 2 seconds within 6 seconds of switching engine off. Condenser fans should run for 9-10 minutes and turn off. If fans do not work, disconnect A/C condenser fan control module connector. Backprobing, connect a fused jumper wire between A/C condenser fan control module connector terminals No. 4 (Black/Brown wire) and 8 (Green/White wire). If fans work, install a new A/C condenser fan control module. If fans do not work, check wire harness for short of open.

Scheme 57

Scheme 58

Automatic Gear Selector Switch Circuit

Note. Automatic gear selector switch will also be referred to as transmission range selector switch.

For automatic gear selector switch circuit testing (Scheme 59)and (Scheme 60).

Scheme 59

Scheme 60

See also:
• ENGINE CONTROL MODULE CONNECTOR TERMINAL IDENTIFICATION
• FUEL SYSTEM PRESSURE RELEASE
• ROTOR ARM TEST
• AMPLIFIER TEST
• SECONDARY IGNITION COIL WIRE TEST
• PICK-UP COIL RESISTANCE TEST
• VISUAL CHECK