Engine Controls - System/component Tests - Carbureted Jeep Wrangler I

INTRODUCTION

Before testing, separate components or systems, it is highly recommended that all procedures listed in BASIC TESTING article be performed.

Note. Testing of individual components does not isolate possible shorts or opens in the control harness of electronically controlled systems. Use an ohmmeter to isolate shorts or opens in harness. All voltage tests should be performed with a Digital Volt Ohmmeter (DVOM) with a minimum 10-megohm input impedance (unless specifically stated differently in testing procedures).

GROUND CIRCUITS

1. Using an ohmmeter, check for continuity to ground by backprobing MCU terminals No. 17, 20 and 60. (Scheme 82) Resistance should be zero ohms. If not, repair open to ground.
2. Using a DVOM, touch negative lead of voltmeter to a good ground. Using positive lead of voltmeter backprobe each ground terminal. With vehicle running, voltmeter should indicate less than 1 volt. If voltmeter reading is greater than 1 volt, check for open, corrosion or loose connection on ground lead.

POWER CIRCUITS

1. Using a voltmeter, turn ignition on and check for voltage between MCU terminals No. 1 and 57. If battery voltage is not present, check IGN/LPS fuse. If fuse is okay, check for an open wires between fuse box and control unit.
2. Connect a voltmeter between ground and MCU terminal No. 58. Turn ignition switch to the START position. Battery voltage should be present between control unit terminal No. 58 and ground. If voltage is not present, check for an open in Green wire between MCU and ignition switch, or check for a defective ignition switch.

COOLANT TEMPERATURE SWITCH

Switch is located at rear of cylinder head. Disconnect switch connector. When coolant temperature is less than 135°F (57°C), switch is open. At higher temperatures, switch should have continuity to ground.

HIGH ALTITUDE JUMPER

At altitudes over 4000 feet, ensure the altitude jumper wire is connected (grounding terminal No. 11 at MCU and terminal No. 3 of diagnostic connector) and all other high altitude changes are performed. A high altitude kit is available from manufacturer and must be used in addition to connecting high altitude jumper.

KNOCK SENSOR

See IGNITION SYSTEM in this article. Also (Scheme 95)and (Scheme 96).

OXYGEN SENSOR

Perform OXYGEN SENSOR & CLOSED LOOP TEST. (Scheme 96)

THERMAL ELECTRIC SWITCH

Switch is also referred to as the Thermo Electric Switch (TES). Switch is located in air cleaner housing. Disconnect switch connector. When temperature at switch is greater than 65°F (18°C), continuity should exist across switch terminals. At temperatures less than this, no continuity should exist.

VACUUM SWITCH ASSEMBLY

The 4" and 10" vacuum switches are located together in a bracket located at the rear center of engine compartment. The 4" switch is Natural in color, while the 10" switch is Green in color. Switches are normally closed (vacuum less than calibration). To test switches, perform OPEN LOOP SWITCH TEST. (Scheme 89)

WIDE OPEN THROTTLE (WOT) SWITCH

Disconnect WOT switch connector. Switch is located on throttle linkage of carburetor, behind electric choke housing. With accelerator pedal fully depressed, continuity should exist across WOT switch terminals. Continuity should not exist with accelerator pedal released (more than 15 degrees less than WOT).

COMPUTERIZED ENGINE CONTROL SYSTEM

The CEC system should be considered a source of trouble for engine performance, fuel economy and exhaust emission complaints ONLY after normal tests that would apply to a vehicle not equipped with the system have been performed.

Before performing any diagnostic test, other engine associated components and systems that can affect air/fuel mixture, combustion efficiency or exhaust gas composition should be tested for malfunctions.These include

1. Basic carburetor adjustments
2. Mechanical engine operation (i.e., spark plugs, valves and rings)
3. Ignition system
4. Loose vacuum hoses and fittings

DIAGNOSTIC TESTS

Fuel feedback system incorporates a diagnostic connector which provides for systematic evaluation of each component that could cause a malfunction. (Scheme 83)

An electronic Fuel Feedback Tester (ET-501) is available to aid in diagnosis. When tester is not available, there are several tests for each system.

To perform a complete system diagnosis, test No. 1 should be performed first and succeeding tests in sequence, thereafter. These tests will provide a thorough system diagnosis.

The steps in each test will provide a systematic evaluation of each component that could cause a malfunction. After completing a repair, repeat the test to ensure malfunction has been eliminated. The equipment required for tests is a tachometer, a hand vacuum pump, a digital volt-ohmmeter (DVOM) with minimum 10-megohm input impedance, and jumper wires. For terminal identification during testing (Scheme 82)and (Scheme 83).

Scheme 82

Scheme 83

Scheme 84

Scheme 85

Scheme 86

Scheme 87

Scheme 88

Scheme 89

Scheme 90

Scheme 91

Scheme 92

Scheme 93

Scheme 94

Scheme 95

Note. For additional oxygen sensor information, see TITANIA OXYGEN SENSOR TESTING article.

Scheme 96

Note. For additional oxygen sensor information, see TITANIA OXYGEN SENSOR TESTING article.

Scheme 97

Scheme 98

Scheme 99

Scheme 100

Scheme 101

Scheme 102

Scheme 103

Scheme 104

Scheme 105

FUEL DELIVERY

Note. For fuel system pressure testing, see BASIC TESTING article.

FUEL CONTROL

For fuel control testing on 4.2L, see OPEN LOOP and CLOSED LOOP tests. (Scheme 89)- (Scheme 94) and (Scheme 96) - (Scheme 97). Fuel control on 5.9L engine is regulated through mechanical adjustments. See ADJUSTMENTS article.

IDLE SPEED

On 4.2L engine, idle speed is controlled by MCU through the stepper motor, sole-vac throttle positioner, and idle relay. (Scheme 102)- (Scheme 104). Idle speed on 5.9L is controlled by mechanical adjustments. See ADJUSTMENTS article.

Note. For basic ignition checks, see BASIC TESTING article.

IGNITION COIL TEST

Ignition coil can be tested on any conventional coil tester or with an ohmmeter. A coil tester is preferable because it can be used to detect faults that are impossible to detect with an ohmmeter.

PRIMARY WINDING RESISTANCE TEST

1. Remove the connectors from the positive and negative terminals of ignition coil. Set ohmmeter to low scale and zero pointer.
2. Connect ohmmeter to coil negative and positive terminals. Resistance should be 1.13-1.23 ohms at 75°F (24°C). If coil temperature is above 200°F (93°C), 1.5 ohms is acceptable.

SECONDARY WINDING RESISTANCE TEST

1. Remove high voltage ignition wire from high voltage terminal of ignition coil. Ensure ignition is off. Set ohmmeter for x1000 scale and zero pointer.
2. Contact ohmmeter to brass contact in high voltage terminal and to either primary winding terminal. The resistance should be 7700-9300 ohms at 75°F (24°C). A maximum of 112,000 ohms is acceptable if coil temperature is 200°F (93°C) or more.

IGNITION COIL OUTPUT TEST

1. Connect an oscilloscope to ignition coil. Refer to test equipment manufacturer's instructions. Start engine and observe secondary ignition voltage. CAUTION: DO NOT remove wires from spark plugs for cylinders No. 1 or 5 when performing next test because pick-up coil may be damaged. CAUTION: DO NOT operate engine with spark plug disconnected for more than 30 seconds because catalytic converter may be damaged.
2. Remove one spark plug wire from distributor cap. Observe voltage applied to disconnected spark plug wire on oscilloscope. This voltage, referred to as open circuit output voltage, should be 24,000 volts minimum with engine speed of 1000 RPM.

FUNCTIONAL TEST

1. Set parking brake. Shift automatic transmission to Park or manual transmission to Neutral. Start engine and attain normal operating temperature. Ensure A/C is off (if equipped).
2. Turn engine off. On 4.2L, disconnect 3-wire connector from 4 in. and 10 in. Hg vacuum switch assemblies.
3. On all engines, disconnect and plug vacuum hose connected to distributor vacuum advance mechanism. Connect timing light at No. 1 spark plug. Connect tachometer to coil negative terminal.
4. Start engine and slowly increase RPM while observing timing mark and index with timing light. The ignition timing should advance smoothly as RPM increases. (Scheme 106)
5. If timing advances unevenly, check and repair centrifugal advance mechanism.
6. Connect distributor vacuum advance hose and vacuum switch assembly 3-wire connector. Remove timing light and tachometer.

1. Set parking brake. Shift automatic transmission to Park or manual transmission to Neutral. Start engine and attain normal operating temperature. Ensure A/C is off, if equipped. Stop engine.
2. On 4.2L, disconnect 3-wire connector from 4 in. and 10 in. Hg vacuum switch assemblies.
3. On all engines, disconnect and plug vacuum hose connected to distributor vacuum advance mechanism. Connect hand vacuum pump to vacuum advance. Connect timing light at No. 1 spark plug. Connect tachometer to coil negative terminal.
4. Start engine. Increase RPM and apply 18 in. Hg vacuum. Observe ignition timing degree scale and index with timing light. The ignition timing should advance smoothly. NOTE: On 4.2L, a defective MCU or ignition system control unit can alter ignition timing.
5. Remove timing light and tachometer. Ensure all connections are correct.

Scheme 106

KNOCK SENSOR TEST

Note. Also see ELECTRONIC IGNITION RETARD TEST in (Scheme 95).

1. Connect Diagnostic Readout Box II (DRB-II) diagnostic tester to vehicle and proceed to state display mode. Start engine and observe knock unit value.
2. Using tip of screwdriver, gently tap cylinder block near knock sensor and observe knock value. Knock value should increase while tapping on cylinder block.
3. If knock value does not increase while tapping on the cylinder block near knock sensor, check knock sensor for proper connection. If connection is good, replace knock sensor.

PULSE INJECTION (4.2L)

To test pulse injection air switching system on 4.2L, see UPSTREAM and DOWNSTREAM SOLENOID TESTS. (Scheme 98)- (Scheme 101).

PUMP INJECTION (5.9L)

1. Inspect air pump drive belt and system hoses. Turn engine off and disconnect hoses at air injection upstream and downstream check valves. Start engine. Exhaust gases should not pass out of check valves. Replace valves as necessary.
2. Start engine and check for presence of manifold vacuum at air control valve. If vacuum is not present, check for disconnected or plugged vacuum hose. Disconnect vacuum hose from control valve. After 5 seconds, reconnect hose. Air should be discharged from by-pass port on control valve for 1-2 seconds.
3. When vehicle is cold, air injection should be delivered to upstream check valves. After vehicle has reached normal operating temperature, air injection should be delivered to downstream check valve.
4. If not, check Dual Coolant Temperature Override (DCTO) switch for plugged bleed filter, no vacuum supply, or failure to switch vacuum with change from cold to hot operation. No testing procedures or specifications for DCTO are supplied by manufacturer.

EVAPORATIVE FUEL SYSTEM

Inspect evaporative emission system hoses. Inspect canister for damage or fuel saturation. Replace components as necessary. There are no serviceable components in this system. If parts are defective, they must be replaced. See VACUUM DIAGRAMS article.

EXHAUST GAS RECIRCULATION (EGR) SYSTEM

Note. Condition of exhaust system can affect EGR system operation. Excessive backpressure caused by exhaust system restrictions may create driveability problems. Exhaust system leaks may decrease backpressure enough to prevent proper EGR operation. Visually inspect exhaust system if leaks are suspected.

SYSTEM TEST

1. Bring engine to normal operating temperature and curb idle. Apply manifold vacuum (or an outside source of at least 12 in. Hg) directly to nipple on EGR valve and note engine idle.
2. Engine should idle roughly or stall. If this occurs, valve and EGR passages are okay. Proceed to testing of individual components. If idle did not change, remove EGR valve and inspect valve and exhaust passage in manifold for blockage. If no blockage is present, replace EGR valve.

EGR VALVE OPENING TEST (4.2L)

With engine at normal operating temperature and curb idle speed, rapidly open and close throttle. Throttle should open sufficiently to allow engine speed to reach 1500 RPM. A distinct movement should be noticed in EGR control diaphragm.

If the diaphragm does not move the probable causes are

1. Faulty vacuum hose to EGR valve
2. Defective EGR valve diaphragm
3. Defective backpressure sensor diaphragm
4. Leaking vacuum hoses

EGR VALVE CLOSING TEST (4.2L)

1. With engine at normal operating temperature and curb idle speed, manually depress EGR valve diaphragm. There should be an immediate drop in engine RPM (indicating that EGR valve has been properly preventing flow of exhaust gas to the intake manifold at idle speed). If there is no change in RPM and engine is idling properly, exhaust gases are not reaching combustion chamber.
2. The probable malfunction is a restricted passage between EGR valve and intake manifold. If engine idles improperly and RPM is not greatly affected by depressing EGR valve diaphragm, the EGR valve is not preventing flow of exhaust gases to intake manifold. There is either a fault in vacuum hoses, improper hose connection or valve is defective.

COOLANT TEMPERATURE OVERRIDE VALVE (4.2L)

1. Ensure engine coolant temperature is less than 115°F (46°C). This is calibrated opening temperature of Coolant Temperature Override (CTO) valve.
2. Inspect vacuum hoses for leaks and correct routing/connections. Disconnect hose at Thermal Vacuum Switch (TVS) and connect it to a vacuum gauge.
3. Operate engine at approximately 1500 RPM. No vacuum should be indicated. If vacuum is indicated, replace EGR CTO valve.
4. Operate engine until coolant temperature exceeds 115°F (46°C). Accelerate engine to 1500 RPM. Carburetor ported vacuum should be indicated on vacuum gauge. If not, replace EGR CTO valve.

COOLANT TEMPERATURE OVERRIDE VALVE (5.9L)

1. Ensure engine coolant temperature is less than 155°F (68°C). This is calibrated opening temperature of Coolant Temperature Override (CTO) valve.
2. Inspect vacuum hoses for leaks and correct routings/connections. Disconnect hose at Thermal Vacuum Switch (TVS) and connect it to a vacuum gauge.
3. Operate engine at approximately 1500 RPM. No vacuum should be indicated. If vacuum is indicated, replace EGR CTO valve.
4. Operate engine until coolant temperature exceeds 155°F (68°C). Accelerate engine to 1500 RPM. Carburetor ported vacuum should be indicated on vacuum gauge. If not, replace EGR CTO valve.

EGR THERMAL VACUUM SWITCH

1. Ensure air cleaner intake air less than TVS calibrated temperature, 40°F (4°C). Disconnect vacuum hoses from Thermal Vacuum Switch (TVS) and connect vacuum pump to inner port.
2. Apply vacuum to TVS. Vacuum should be maintained by TVS check valve. If vacuum is not maintained, replace TVS. Start engine and warm the air cleaner intake air to above 55°F (13°C). Vacuum should not be maintained. If vacuum is maintained, replace TVS.

EGR VACUUM TRANSDUCER (5.9L)

1. Disconnect transducer vacuum lines and backpressure line, Remove transducer. Plug transducer output port.
2. Using a vacuum source, apply 1-2 pounds air pressure to transducer backpressure port.
3. Apply 12 in. Hg to input port. Replace transducer if it will not hold vacuum.

POSITIVE CRANKCASE VENTILATION (PCV) SYSTEM

1. Start engine and allow it to reach normal operating temperature. Ensure engine is at normal curb idle. Remove PCV valve from grommet. If valve is okay, hissing will be heard as air passes through it. Strong vacuum should be felt over inlet valve.
2. With finger over valve inlet, check for vacuum leaks at all connections. Reinstall PCV valve and remove crankcase air inlet hose at air cleaner.
3. Loosely hold piece of stiff paper over opening at end of inlet hose. After about a minute, paper should be sucked against hose opening with noticeable force. Remove and shake PCV valve. Ensure metallic clicking can be heard, indicating valve is free.
4. If system passes both engine running and stopped tests, it is functioning properly. If it fails either test, replace defective components and retest. If it does not pass on second try, clean system.

Scheme 107

Scheme 108

AIR VALVE VACUUM MOTOR TEST

1. With engine off, detach ambient air duct at air cleaner and observe position air valve. It should be fully open to incoming ambient air (heat OFF position). Start engine and observe position of air valve. Air valve should be fully closed to incoming ambient air (heat ON position).
2. Depress throttle rapidly (1/2-3/4 position) and release. Air valve should briefly remain stationary and then move toward heat OFF position and back to heat ON position. Loosely attach the ambient air duct to air cleaner and warm engine to normal operating temperature.
3. Remove ambient air duct and observe air valve. It should be either fully open to ambient air or at a mixture position that provides the correct inlet air temperature to the carburetor.
4. Stop the engine and connect ambient air duct to air cleaner. If air valve does not function as described, inspect for: Mechanical bind in snorkel. Vacuum hoses disconnected. Air leaks either at vacuum motor, thermal switch, reverse delay valve, intake manifold or vacuum hoses.
5. If valve manually operates freely and no hose disconnections or air leaks are detected, connect a hose from intake manifold vacuum source directly to vacuum motor and start engine. If air valve closes, either thermal switch, reverse delay or check valve is defective and must be replaced. If air valve does not close, replace vacuum motor.

THERMAL SWITCH TEST

1. Disconnect vacuum hoses from thermal switch. Connect vacuum pump to vacuum source side of sensor and a vacuum gauge to vacuum motor side of switch.
2. Apply 14 in. Hg vacuum to switch. With thermal switch temperature less than 95°F (35°C), vacuum should be maintained.
3. Heat switch to 95°F (35°C). The air vent valve should open and decrease vacuum to zero. Replace switch if defective. The temperatures listed are nominal switching values.

AIR CLEANER TRAP DOOR TEST

1. With engine off, remove air cleaner cover and observe position of trap door. It should be closed.
2. Remove vacuum hose from intake manifold vacuum source and apply external vacuum of approximately 2-4 in. Hg. Trap door should open.
3. If door does not open, apply vacuum directly to vacuum motor on air cleaner intake duct. If door still does not open , inspect for binding/distortion and adjust as necessary. Replace motor if door swings freely.
4. If door opens in step No. 3), inspect vacuum hose for obstruction, cracks and kinks. Correct as necessary and retest.
5. If vacuum hose is not defective, remove reverse delay valve, join vacuum hose with an adapter and retest. If door opens, replace reverse delay valve.

REVERSE DELAY VALVE

Reverse delay valve provides approximately 100 seconds delay before allowing trap door to completely close.

1. Remove vacuum hose from end of valve that is not black in color and apply an external vacuum of approximately 2-4 in. Hg.
2. Using a stop watch, note time required for atmospheric pressure to pass through valve and eliminate vacuum.
3. Replace valve if time required is less than 4.5 seconds or more than 13.2 seconds. Install replacement reverse delay valve with Black end toward trap door vacuum delay motor.