Engine Controls - System/component Tests Mercury Capri III

INTRODUCTION

Before testing separate components or systems, perform procedures in BASIC TESTING article in the ENGINE PERFORMANCE Section. Since many computer-controlled and monitored components set a trouble code if they malfunction, also perform procedures in TESTS W/CODES article in the ENGINE PERFORMANCE Section.

Note. Testing individual components does not isolate shorts or opens. Perform all voltage tests with a Digital Volt-Ohmmeter (DVOM) with minimum 10-megohm input impedance, unless stated otherwise in test procedure. Use ohmmeter and Breakout Box (BOB) (007-00033) to isolate wiring harness shorts or opens.

Wastegate Actuator

Disconnect air hose from wastegate actuator. Apply 7.0-8.6 psi (.5-.6 kg/cm 2 ) regulated air pressure to wastegate inlet fitting. Replace turbocharger if wastegate actuator rod does not move.

Ground Circuits

Turn ignition off. Connect BOB, leaving ECA disconnected. Measure resistance between each specified BOB pin and ground. See ECA GROUND CIRCUIT RESISTANCE table. Repair indicated ECA ground circuit if resistance is greater than 5 ohms.

ECA GROUND CIRCUIT RESISTANCE

Power Circuits

Turn ignition off. Connect BOB, leaving ECA disconnected. Turn ignition on. Repair indicated ECA power circuit if battery voltage does not appear on specified BOB pin. See ECA POWER CIRCUIT RESISTANCE table.

ECA POWER CIRCUIT RESISTANCE

ENGINE SENSORS & SWITCHES

Inspect each component and all related wiring for any looseness or damage. Make all resistance and voltage measurements using Breakout Box (BOB) unless specified otherwise.

BAROMETRIC PRESSURE (BP) SENSOR (CAPRI)

Connect BOB. Remove dust cover from BP sensor, located on passenger side cowl. Turn ignition on. Connect vacuum pump to BP sensor. Measure voltage between pins BP and SIGRTN on BOB while applying vacuum to BP sensor. See BAROMETRIC PRESSURE SENSOR OUTPUT VOLTAGE table. Replace BP sensor if voltage is not as specified.

Barometric Pressure (BP) Sensor (Festiva)

This unit is incorporated into ECA, and cannot be checked or serviced separately. If a Code 14 is set and cannot be cleared, replace ECA.

BAROMETRIC PRESSURE SENSOR OUTPUT VOLTAGE

BRAKE ON-OFF (BOO) SWITCH

Unplug connector from BOO switch at brake pedal. Connect ohmmeter to switch terminals. With pedal released, ohmmeter should indicate no continuity. Ohmmeter should indicate continuity with pedal pressed.

CLUTCH ENGAGE SWITCH (CES)

Unplug connector from CES switch at clutch pedal. Connect ohmmeter to switch terminals. With pedal released, ohmmeter should indicate continuity. Ohmmeter should indicate no continuity with pedal pressed.

CRANKSHAFT POSITION SENSOR (CPS) (FESTIVA)

Unplug 3-wire connector from distributor. Measure resistance between CPS terminal on distributor (Yellow/Blue wire) and ground. Replace CPS if resistance is not 210-250 ohms.

CYLINDER IDENTIFICATION (CID) SENSOR (CAPRI)

Turn ignition off. Connect BOB, leaving ECA connected. Turn ignition on, but DO NOT start engine. Measure voltage at BOB test pin No. 34 (Yellow wire). Voltage should be less than one volt or more than 10 volts. Start engine and run at idle. Voltage should be 3-5 volts. Replace CID sensor if voltage is not as specified.

ENGINE COOLANT TEMPERATURE (ECT) SENSOR

1. Remove ECT sensor. ECT sensor is threaded into top of lower intake manifold on Festiva, and on underside of intake manifold on Capri. Place ECT sensor and thermometer into container of coolant.
2. Connect ohmmeter to coolant temperature sensor terminals. Cool and heat container. Measure resistance at specified temperatures. See «ENGINE COOLANT TEMPERATURE SENSOR RESISTANCE»(/mercury/capri/iii-1990-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. Replace ECT sensor if resistance is not within specification.

ENGINE COOLANT TEMPERATURE SENSOR RESISTANCE

EXHAUST GAS OXYGEN (EGO) SENSOR

With engine at normal operating temperature, unplug connector from EGO sensor in exhaust manifold. Measure voltage between EGO sensor terminal and ground. Voltage should increase with increasing engine speed, and decrease with decreasing engine speed. Voltage at idle should fluctuate within a range of .2-.8 volt.

Note. A steady voltage of more than .55 volt indicates a continuously rich condition. A steady voltage of less than .55 volt indicates a continuously lean condition.

IDLE SWITCH (CAPRI)

Unplug connector from throttle position sensor on throttle body. Connect ohmmeter to switch terminals IDL and ground (Green/Orange and Blue/Yellow wires on mating connector). Resistance must be less than 5 ohms with throttle in idle position, and more than 10,000 ohms at WOT position.

KNOCK SENSOR (CAPRI TURBO)

Disconnect vacuum hose at distributor. Connect timing light. Start engine. Determine and record ignition timing. Tap intake plenum with a plastic mallet. Knock sensor is okay if timing retards. If timing does not retard, check associated circuitry and components. See TIMING CONTROL SYSTEMS under IGNITION SYSTEM.

NEUTRAL GEAR SWITCH (M/T)

1. Unplug neutral gear switch connector, located near transmission. Place transmission in Neutral. Resistance across switch should be infinite.
2. Place transmission in any other gear. Resistance across switch terminals should be zero ohms. If necessary, replace switch.

POWER STEERING PRESSURE SWITCH

1. Start and idle engine. Remove connector from switch, located at steering gear. Connect ohmmeter to switch terminals. Turn steering wheel from side to side while observing ohmmeter.
2. Replace power steering switch if continuity does not exist with front wheels turned, or if continuity exists with wheels straight ahead.

THROTTLE POSITION SENSOR (CAPRI)

Unplug connector from throttle position sensor, located on VAF meter. Connect ohmmeter to sensor terminals TP and SIGRTN (Orange and Blue/Yellow wires on mating connector). Measure resistance at each throttle opening specified in THROTTLE POSITION SENSOR RESISTANCE table. Replace sensor if resistance is not within specification.

THROTTLE POSITION SENSOR RESISTANCE

THROTTLE POSITION (TP) SWITCH (FESTIVA)

1. Ensure idle speed and ignition timing are adjusted to specification. Stop engine. Disconnect negative battery cable. CAUTION: DO NOT tamper with throttle stop screw at throttle lever. Doing so may result in damage to throttle body.
2. Unplug TP switch connector at throttle body. Insert appropriate feeler gauge between throttle stop screw and stop lever. Check for continuity between specified terminals on TP switch connector. See ADJUSTMENTS article in the ENGINE PERFORMANCE Section and «THROTTLE POSITION SWITCH CONTINUITY»(/mercury/capri/iii-1990-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table.

THROTTLE POSITION SWITCH CONTINUITY

VANE AIRFLOW (VAF) METER

1. Check all wiring, harnesses, connectors, and components for evidence of damage, overheating, shorting, or looseness. If any defect exists, repair as necessary.
2. Inspect vane airflow meter for damage. Ensure measuring plate moves smoothly. Turn ignition off. Install BOB. Turn ignition on. Measure voltage between BOB test pins VAF and ground on Festiva, or between VAF and SIGRTN on Capri. Voltage must be as specified in «VANE AIRFLOW METER VOLTAGE»(/mercury/capri/iii-1990-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table.

VANE AIRFLOW METER VOLTAGE

VANE AIR TEMPERATURE (VAT) SENSOR

1. Unplug connector from VAF meter. On Festiva, connect ohmmeter to terminals VAT and ground (Green/Black and Black wires on mating connector). On Capri, connect ohmmeter to VAF meter terminals VAT and SIGRTN (Brown and Blue/Yellow wires on mating connector).
2. Measure intake air temperature. Measure resistance between specified terminals. See «VANE AIR TEMPERATURE RESISTANCE»(/mercury/capri/iii-1990-1995/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. Replace VAF if resistance is not as specified.

VANE AIR TEMPERATURE RESISTANCE

WIDE OPEN THROTTLE SWITCH (FESTIVA)

This switch is part of the throttle position switch. See THROTTLE POSITION (TP) SWITCH (FESTIVA) .

Ignition Module

See IGNITION SYSTEM .

A/C Clutch Relay

See MISCELLANEOUS CONTROLS .

Cooling Fan Relay

See MISCELLANEOUS CONTROLS .

Canister Purge Control Solenoid

See FUEL EVAPORATION .

Fuel Pressure Regulator Control Solenoid

See FUEL DELIVERY under FUEL SYSTEM.

Idle Speed Control (ISC) Solenoid

This solenoid is part of the Idle Speed Control By-Pass Air (ISC-BPA) valve. See IDLE CONTROL SYSTEM.

Fuel Pressure Regulator

1. Measure fuel pressure. See FUEL PRESSURE in BASIC TESTING article in the ENGINE PERFORMANCE Section. Stop engine. With fuel pressure tester still installed, measure fuel pressure after 5 minutes. If fuel pressure is greater than 21 psi (1.5 kg/cm 2 ) after 5 minutes, go to next step. Replace fuel pressure regulator if fuel pressure does not remain higher than 21 psi (1.5 kg/cm 2 ).
2. Remove fuel pressure regulator. Inspect "O" ring, gasket, and mounting surfaces for defects. Connect vacuum tester to fuel return tube, and apply 20 in. Hg vacuum. Replace fuel pressure regulator if vacuum drops by more than 10 in. Hg in 10 seconds. Reinstall fuel pressure regulator.
3. Again measure fuel pressure. If regulated fuel pressure is higher than specification, check for engine vacuum leaks, damage to fuel pressure regulator housing, or a restricted fuel return line. Replace fuel pressure regulator if no problems are found.

Fuel Pressure Regulator Control Solenoid (Capri)

1. Locate PRESSURE CONTROL (PRC) solenoid on cowl panel, next to canister purge solenoid. Unplug PRC connector. Remove both vacuum lines. Plug one vacuum port. Apply vacuum to remaining port. Replace PRC solenoid if it does not hold vacuum.
2. Connect 12-volt power to PRC terminals. If vacuum drops to zero, PRC solenoid is okay. Replace PRC solenoid if vacuum does not drop to zero.

Fuel Injectors

1. Using stethoscope, listen for normal clicking sound at each injector during idle and acceleration. If no clicking sound occurs, remove electrical connector from injector.
2. Measure resistance between injector terminals. Replace injector if resistance is not 12-16 ohms. If injector resistance is okay, check for 12 volts at each injector connector. Repair or replace connector as necessary.

Idle Speed Control By-Pass Air (ISC-BPA) Valve

1. Remove ISC-BPA valve from engine. Connect a hose from a hot water tap to coolant inlet nipple on ISC-BPA valve. Blow through valve air port. Note resistance to airflow.
2. Supply hot water at 130°F (56°C) minimum to ISC-BPA valve, and allow time for valve to respond. Blow through valve again. If resistance to airflow does not increase when valve is hot, replace ISC-BPA valve.
3. Apply 12 volts to solenoid terminals. If solenoid does not click, replace ISC-BPA valve.

IGNITION SYSTEM

Note. For basic ignition checks, see BASIC TESTING article in the ENGINE PERFORMANCE Section.

Advance Components (Capri)

Ignition advance is controlled by a centrifugal advance mechanism within the distributor, and by a vacuum advance mechanism. If centrifugal advance is not within specification, service distributor. Replace vacuum advance unit if vacuum advance is not within specification. See IGNITION TIMING table. Also see IGNITION TIMING in ADJUSTMENTS article in the ENGINE PERFORMANCE Section.

Advance Components (Festiva)

Ignition timing advance is controlled by the ECA.

IGNITION TIMING

Retard Components (Capri Turbo)

Positive pressure to the vacuum advance cylinder on the distributor retards ignition timing. The ECA also retards ignition timing when it receives a signal from Knock Sensor (KS) and related circuitry.

1. Disconnect and plug hoses at distributor. Connect timing light. Start engine. Determine and record ignition timing. Tap intake plenum with plastic mallet while monitoring ignition timing. If timing retards, Knock Control (KC) circuitry is okay. If timing does not retard, go to next step.
2. Unplug KC sensor service connector, located near ECA. Tap intake plenum with plastic mallet while observing ignition timing. If timing does not retard, go to step 4). If timing retards, go to next step.
3. Reconnect KC service connector. Tap intake plenum with plastic mallet while monitoring ignition timing. If ignition timing retards, replace knock controller. If ignition timing does not retard, go to next step.
4. Unplug KC service connector. Temporarily install known good knock sensor. Tap intake plenum with plastic mallet while monitoring ignition timing. If ignition timing retards, replace knock sensor. If ignition timing does not retard, go to next step.
5. Turn ignition off. Connect BOB. Ensure vehicle power (VPWR) and ground wires to knock sensor are okay. Check all knock sensor wiring for shorts or opens. If wiring is okay, replace knock sensor.

1. Disconnect vacuum hoses from solenoid. (Scheme 21) Blow through port "A". No air should flow from port "B".
2. Disconnect 2-wire connector from solenoid. Connect 12 volts to one terminal. Ground the other terminal of solenoid. Blow through port "A". Air should flow through port "B". Replace canister purge control solenoid if performance is not as specified.

Scheme 21

Carbon Canister

1. Start and warm engine to operating temperature. Stop engine. Remove carbon canister. On Festiva, carbon canister is located under brake booster. On Capri, carbon canister is located on right side of engine compartment, near cowl panel.
2. Inspect carbon canister for presence of liquid fuel, as evidenced by odor or weight. Blow into air vent, and check for air exiting from fuel vapor inlet. Replace carbon canister if it contains fuel, or if air does not pass freely through it.

POSITIVE CRANKCASE VENTILATION (PCV)

1. Remove PCV valve from valve cover. Disconnect it from PCV hose. Shake valve vigorously to verify plunger is free to move. Replace PCV valve if plunger is not free.
2. Idle engine until it is warm. Remove fresh air hose at inlet end. Plug nipple immediately to prevent stalling. Verify presence of vacuum at inlet end of hose. If vacuum is not present, replace PCV valve, or service hoses or loose oil dipstick.

Dashpot

Disconnect PCV valve. Remove resonance chamber. Push dashpot rod inward, then release it. Replace dashpot if rod does not go inward slowly and return quickly.

MISCELLANEOUS CONTROLS

Note. Although some of the controlled devices listed here are not technically engine performance components, they can affect driveability if they malfunction.

Remove relay from its socket near left headlight, in front of battery. Connect ohmmeter to contact terminals (Blue/Red and Black/White wires on mating connector). Ohmmeter should indicate continuity. Supply 12 volts to remaining terminals (Green/Yellow and Yellow wires on mating connector). Ohmmeter should indicate no continuity. Replace A/C clutch relay if operation is not as specified.

Cooling Fan

Unplug connector from cooling fan. Apply 12 volts to one terminal of fan connector. Ground remaining fan connector terminal. Replace fan if it does not run.

Cooling Fan Control Relay

Remove relay from its socket near left headlight. Connect ohmmeter to contact terminals. Wire colors are Yellow/Red and Black on mating connector on Festiva; Yellow/Green and Black on Capri. Ohmmeter should indicate continuity. Supply 12 volts to remaining relay terminals. Ohmmeter should indicate no continuity. Replace cooling fan control clutch relay if operation is not as specified.

See also:
• ECA GROUND CIRCUIT RESISTANCE
• THROTTLE POSITION (TP) SWITCH (FESTIVA)
• IGNITION SYSTEM
• MISCELLANEOUS CONTROLS