Engine Controls - System/component Tests Geo Storm I

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 a minimum 10-megohm input impedance, unless stated otherwise in test procedure. Use ohmmeter to isolate wiring harness shorts or opens.

SECONDARY AIR CONTROL (GSi)

1. Disconnect vacuum supply hose from secondary air control (intake air) Vacuum Switching Valve (VSV), located at rear of engine compartment. The VSV contains a White/Blue and Black/Yellow wire connector. Using vacuum gauge, check vacuum reading at supply hose with engine idling.
2. Vacuum reading should be 10 in. Hg. If reading is not correct, repair vacuum leak. If reading is okay, connect vacuum pump to vacuum supply side of VSV.
3. With ignition on and engine off, apply vacuum and note linkage operation at vacuum actuator for auxiliary valves.
4. If linkage moves, proceed to step 7). If linkage does not move, disconnect electrical connector at VSV and repeat step 3). If linkage moves with electrical connector removed, check for short to ground in White/Blue wire from ECM to VSV or faulty ECM. The ECM is located under left side of instrument panel, left of steering column. CAUTION: Automatic transaxle Electronic Control Unit (ECU) on 4-speed transaxle may be mounted on left side of steering column. DO NOT confuse this with the ECM. The ECM contains 24-pin and 32-pin connectors, and the ECU contains 16-pin and 20-pin connectors.
5. If linkage does not move, disconnect vacuum hose at vacuum actuator. Install vacuum gauge and note vacuum reading with engine running. Vacuum reading should be at least 10 in. Hg.
6. If vacuum reading is not correct, VSV is defective. If vacuum reading is correct, check for binding linkage or defective actuator.
7. Install jumper wire between terminals No. 1 and 3 of ALDL connector, located behind right side of instrument panel, near kick panel. (Scheme 39) Apply vacuum and note linkage movement. If linkage does not move, secondary air control system is okay. If linkage moves, proceed to step 8).
8. Disconnect electrical connector from VSV. Turn ignition on with engine off. Ensure jumper wire is still installed in ALDL connector. Using test light, check for voltage between VSV electrical connector terminals.
9. If voltage exists, VSV is defective. If no voltage exists between connector terminals, check for power between Black/Yellow wire of VSV electrical connector and ground.
10. If no power exists, repair open circuit in Black/Yellow wire between VSV and 15-amp engine fuse in fuse block, located behind left kick panel. If power exists, check for open circuit in White/Blue wire between VSV and ECM, defective connections or defective ECM.

Scheme 39

Ground Circuit Checks

Check ground circuits to ECM for continuity to ground. Using a DVOM, touch negative voltmeter lead to a good ground. Touch positive voltmeter lead to each ground terminal. With vehicle running, voltmeter should indicate less than one volt. If voltmeter reading is greater than one volt, check for open, corrosion or loose connection on ground lead. See appropriate wiring diagram in WIRING DIAGRAMS article in the ENGINE PERFORMANCE Section.

Power Circuit Checks

Using DVOM, check power circuits to ECM for opens or shorts. See appropriate wiring diagram in WIRING DIAGRAMS article in the ENGINE PERFORMANCE Section.

Coolant Temperature Sensor

1. Remove coolant temperature sensor. Coolant temperature sensor is located on thermostat housing.
2. Measure resistance of coolant temperature sensor at designated temperatures. Replace if not within specification. See «COOLANT TEMPERATURE SENSOR RESISTANCE»(/geo/storm/i-1990-1993/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table.

COOLANT TEMPERATURE SENSOR RESISTANCE

EGR TEMPERATURE SENSOR

See EMISSIONS SYSTEMS & SUB-SYSTEMS.

INTAKE AIR TEMPERATURE (IAT) SENSOR

IAT Sensor is located on intake manifold. The IAT contains a Blue/Black and Black wire connector. Using ohmmeter, check resistance across IAT sensor terminals. Replace IAT sensor if resistance is not within specification. See IAT SENSOR RESISTANCE SPECIFICATIONS table.

IAT SENSOR RESISTANCE SPECIFICATIONS

MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR

1. The MAP sensor is located on firewall. With ignition on, check supply voltage from ECM to MAP sensor on designated wire terminal. See «MAP SENSOR WIRE TERMINAL IDENTIFICATION»(/geo/storm/i-1990-1993/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. Reading should be approximately 5 volts.
2. Disconnect vacuum hose at MAP sensor, and install hand-held vacuum pump. Turn ignition on. Check signal voltage at designated wire terminal of MAP sensor. See «MAP SENSOR WIRE TERMINAL IDENTIFICATION»(/geo/storm/i-1990-1993/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table.
3. Apply vacuum and note change in signal voltage. As vacuum reading changes, signal voltage should change. Reading should vary from approximately 1 to 1 1/2 volts at high vacuum (idle position) to 4 to 4 1/2 volts at low vacuum (full throttle position).

MAP SENSOR WIRE TERMINAL IDENTIFICATION

OXYGEN SENSOR

Information is not available from manufacturer.

OXYGEN SENSOR HEATER (STORM GSi)

1. With ignition off, disconnect 3-pin connector at oxygen sensor. Turn ignition on with engine off. Using voltmeter, check for battery voltage on Black/Yellow or White/Blue wire at connector. If battery voltage exists, proceed to step 3).
2. If battery voltage does not exist, check for open circuit in Black/Yellow or White/Blue wire between oxygen sensor and 10-amp oxygen sensor fuse. Fuse is located in fuse/relay box, in left side of engine compartment, near the battery.
3. Start engine. Connect test light to battery voltage and backprobe Black wire of oxygen sensor connector. If battery voltage exists, proceed to step 4). If battery voltage does not exist, check for open circuit in Black ground wire.
4. Using ohmmeter, measure resistance between Black wire and Pink or Light Blue wire. The Pink or Light Blue wire becomes the White/Blue or Black/Yellow wire after the connector. Resistance should be 3.5-14 ohms.
5. If resistance is within specification, heater portion of oxygen sensor is okay. Replace oxygen sensor if resistance is not within specification.

PARK/NEUTRAL SWITCH

1. Park/neutral switch contacts are closed in Park or Neutral and open in all other gears. Park/neutral switch provides current to neutral relay when in Park or Neutral. Neutral relay contacts close, causing signal voltage on Pink/Blue wire from ECM to decrease.
2. ECM monitors signal voltage and determines vehicle is in Park or Neutral when signal voltage decreases to less than one volt.
3. To check switch and circuit operation, turn ignition on with engine off. Install Scan tester. Scan tester should display "P/N" with transaxle in Park or Neutral and "R-D-L" in all other gears.
4. If Scan tester displayed correctly, park/neutral switch and wiring circuit are okay. If Scan tester does not display correctly, disconnect electrical connector from neutral relay. Neutral relay is located in relay box in right corner of engine compartment, near strut tower.
5. With transaxle in Park or Neutral, Scan tester should display "P/N". If "P/N" is displayed, proceed to step 6). If "P/N" is not displayed, Pink/Blue wire between neutral relay and ECM is grounded or ECM is defective. The ECM is located under left side of instrument panel, left of steering column. CAUTION: Automatic transaxle Electronic Control Unit (ECU) on 4-speed transaxle may be mounted on left side of steering column. DO NOT confuse this with the ECM. The ECM contains 24-pin and 32-pin connectors, and the ECU contains 16-pin and 20-pin connectors.
6. Using fused jumper wire, ground Pink/Blue wire terminal at neutral relay electrical connector. Scan tester should now display "R-D-L". If "R-D-L" is displayed, proceed to step 7). If "R-D-L" is not displayed, check for open circuit in Pink/Blue wire between neutral relay and ECM or for defective ECM connector. If wiring and ECM connector is okay, ECM is defective.
7. Connect test light between White/Blue wire terminal on neutral relay electrical connector and ground. Test light should come on when transaxle is in Drive or Reverse.
8. If test light comes on in Drive or Reverse, proceed to step 12). If test light does not come on, proceed to step 9).
9. Using test light, probe Red/Black wire at park/neutral switch, located on top of transaxle, near the battery. Test light should come on. If test light comes on, proceed to step 11).
10. If test light does not come on, check for open circuit in Red/Black wire between park/neutral switch and fuse C-11 (15-amp fuse for Storm) or C-12 (10-amp fuse for Storm GSi), located in junction block behind left kickpanel.
11. If test light comes on, check park/neutral switch adjustment or for open circuit in White/Blue wire between neutral relay and park/neutral switch. If wiring and switch adjustment are okay, park/neutral switch is defective.
12. It test light comes on with park/neutral switch in Drive or Reverse, check for defective electrical connection at neutral relay. If electrical connection is okay, check for open circuit in Black ground wire to neutral relay. If wiring is okay, neutral relay is defective.

POWER STEERING PRESSURE SWITCH

1. Power steering pressure switch is located on power steering pump. Disconnect Green/Yellow wire at power steering pressure switch with wheels in straight-ahead position.
2. With ignition on, ensure battery voltage exists on Green/Yellow or Blue/Orange wire. If battery voltage does not exist, check for open circuit in Green/Yellow or Blue/Orange wire between ECM and power steering pressure switch. The ECM is located in center of instrument panel, behind console.
3. Connect ohmmeter across switch terminals. Start engine. Check for continuity to ground while turning wheels from straight-ahead position to full turn. Switch should close and continuity should exist when wheels are in a full turn position. Replace switch if defective.

Note. If power steering pressure switch fails to close, or open circuit in wiring between ECM and pressure switch exists, engine may stall when wheels are turned. If power steering pressure switch fails to open, or short to ground exists in wiring between ECM and pressure switch exists, idle quality will be affected, and, on Storm and Storm GSi, A/C clutch will be de-energized.

THROTTLE POSITION SENSOR

Disconnect TPS electrical connection. Install proper thickness feeler gauge between stop screw and lever. Using ohmmeter, check continuity or resistance between designated terminals. Apply 5-volts to Blue/Orange wire terminal. With Black/White wire grounded, at idle, voltage should be less than 1.25 volts at Blue/Red wire and approximately 5 volts at wide open throttle. Sensor is nonadjustable, replace TPS if not within specification.

VEHICLE SPEED SENSOR

1. Vehicle speed sensor is mounted in rear of instrument panel. Sensor uses a reed switch to indicate vehicle speed. When speedometer cable rotates, magnet on end of speedometer shaft rotates, which opens and closes ECM signal to ground 4 times per cable revolution.
2. Frequency to ground depends on speedometer shaft rotation and vehicle speed. If a vehicle speed sensor failure exists, a Code 24 will be set in ECM memory. For vehicle speed sensor diagnosis, see TESTS W/CODES article in the ENGINE PERFORMANCE Section. No other information is available from manufacturer.

MOTORS

IAC Motor

See IDLE CONTROL SYSTEM.

EFI MAIN RELAY

Note. The EFI main relay may be referred to as the main relay.

1. The EFI main relay is located in fuse/relay block on left side of engine compartment, near the battery. Remove EFI main relay from fuse/relay block.
2. Using ohmmeter, ensure continuity exists between Black and Black/Yellow wire terminals of EFI main relay. Apply battery voltage to Black/Yellow wire terminal and ground Black wire terminal. Continuity should exist between Red/White and Red/Green wire terminals of relay. Replace EFI main relay if continuity is not as specified.

FUEL PUMP RELAY

1. Fuel pump relay is located in fuse/relay box on left side of engine compartment, near the battery. Remove fuel pump relay.
2. Using an ohmmeter, ensure continuity exists between Black and Pink/White wire terminals of fuel pump relay. Apply battery voltage to Pink/White wire terminal and ground Black wire terminal. Continuity should exist between Red/White and Black/Red wire terminals of fuel pump relay. Replace fuel pump relay if continuity is not as specified.

FUEL DELIVERY SYSTEM

Note. For fuel system pressure testing, see BASIC TESTING article in the ENGINE PERFORMANCE Section.

FUEL INJECTOR

Check resistance across fuel injector terminals. Replace fuel injector if resistance is not within specification. See FUEL INJECTOR RESISTANCE SPECIFICATIONS table.

FUEL INJECTOR RESISTANCE SPECIFICATIONS

IDLE AIR CONTROL (IAC) VALVE

1. Set parking brake. With ignition off, connect IAC Driver from Kit (J-37027) to IAC valve. The IAC driver is used to extend and retract IAC valve. Movement of IAC valve is verified by change in engine speed.
2. Start engine. Note idle speed with transaxle in Park (A/T) or Neutral (M/T). Using IAC driver, extend and retract IAC valve while noting engine speed. If engine speed changes, proceed to step 3). If engine speed does not change, check for plugged IAC passages. Replace IAC valve if passages are not plugged.
3. Engine speed should change smoothly within a range of 700-1500 RPM each time IAC driver light flashes and IAC valve is extended or retracted.
4. If engine speed changes with IAC driver light operation, proceed to step 5). If engine speed does not change with IAC driver light operation, check for plugged IAC passages. Replace IAC valve if passages are not plugged. NOTE: If IAC valve is extended too far (less than 700 RPM), engine will stall. If IAC valve is retracted too far (more than 1500 RPM), IAC light may flash several times before engine speed starts to decrease.
5. Install Node Light from Kit (J-37027) in IAC valve wiring harness to check IAC valve wiring circuits.
6. Cycle IAC driver. Node lights should cycle Red and Green, but never go off, when IAC valve is cycled and engine speed changes.
7. If node lights operate correctly, proceed to step 8). If node lights do not operate correctly, check for defective connections, open wiring circuits or faulty ECM. The ECM is located under left side of instrument panel, left of steering column. CAUTION: Automatic transaxle Electronic Control Unit (ECU) on 4-speed transaxle may be mounted on left side of steering column. DO NOT confuse this with the ECM. The ECM contains 24-pin and 32-pin connectors, and the ECU contains 16-pin and 20-pin connectors.
8. Using ohmmeter, check resistance between wire terminals "A" and "B" (Brown/Yellow and Brown/Red wires) and wire terminals "C" and "D" (Brown/White & Brown/Black wires). Resistance should be 40-80 ohms. If resistance is correct, proceed to step 9). If resistance is incorrect, replace IAC valve.
9. Using ohmmeter, check continuity between wire terminals "A" and "D" (Brown/Yellow and Brown/Black wires) and wire terminals "B" and "C" (Brown/Red and Brown/White wires). If continuity does not exist, proceed to step 10). If continuity exists, replace IAC valve and retest.
10. A slow or unstable idle may be caused by a system problem that cannot be overcome by IAC valve. If problem still exists, idle problem may be caused by the following: Vacuum Leak - If high idle exists, stop engine. Using IAC driver, fully extend IAC valve. Start engine. If idle speed is greater than 800 RPM, check for vacuum leaks. System Too Lean - If air/fuel ratio is too lean, idle speed may be too high or too low and disconnecting IAC valve may not help. Scan tester or digital voltmeter (10-megohm) will read an oxygen sensor output less than 300 mv (.3 volt). Also, check for low fuel pressure or water in the fuel. System Too Rich - If air/fuel ratio is too rich, idle speed will be low and Scan tester will usually indicate more than 80 counts. System may exhibit Black exhaust smoke. Scan tester or digital voltmeter (10-megohm) will read an oxygen sensor output greater than 800 mv (.8 volt). Also, check for high fuel pressure or fuel injectors leaking or sticking. A silicone-contaminated oxygen sensor may cause slow oxygen sensor voltage changes, resulting in a rich condition. Throttle Body - Remove IAC and inspect bore for evidence of IAC valve binding in the bore. IAC Valve Connections - Inspect for corroded or loose connections. PCV Valve - Incorrect PCV valve may cause an incorrect idle speed.

IGNITION SYSTEM

Note. For basic ignition checks, see BASIC TESTING article in the ENGINE PERFORMANCE Section. For ignition system testing on Storm and Storm GSi, see Chart C-4C in DIAGNOSTIC CHARTS at end of article.

Electronic Ignition Timing Advance

1. Electronic Spark Timing (EST) is controlled by ECM. Ignition module sends a reference signal on Yellow/Red wire to ECM when engine is cranking. With engine speed less than 400 RPM, ignition module controls ignition timing.
2. With engine speed greater than 400 RPM, ECM applies 5 volts on by-pass line (Yellow/Green wire) to switch timing control to EST mode. In EST mode, ECM controls the ignition timing. If problem exists with EST, a Code 42 will be set. See TESTS W/CODES article in the ENGINE PERFORMANCE Section.

The EGR temperature sensor is located near EGR valve. Using ohmmeter, check EGR temperature sensor resistance in relation to exhaust gas temperature. Replace sensor if resistance is not within specification. See EGR TEMPERATURE SENSOR RESISTANCE table.

EGR TEMPERATURE SENSOR RESISTANCE

EGR System Check

1. With engine cool, grasp top of EGR valve and check for looseness. If looseness is felt, replace EGR valve. Warm engine to normal operating temperature. Place finger on bottom of EGR valve diaphragm. Start engine and increase engine speed. Note if EGR valve diaphragm moves. CAUTION: Wear gloves if EGR valve is hot.
2. If diaphragm does not move, allow engine to idle. Disconnect vacuum hose from EGR valve and apply 10 in. Hg of vacuum to valve. Vacuum should hold and engine should run rough or stall. If vacuum does not hold, go to step 4).
3. If engine did run rough or stall and EGR valve held vacuum, check components controlling vacuum supply to EGR valve (i.e. EGR modulator, EGR vacuum switching valve, vacuum supply and hoses). Also, check ECM control of ground circuit to EGR vacuum switching valve and verify EGR vacuum switching valve has power when ignition is on. For wire colors and ECM terminal identification, see appropriate wiring diagram in WIRING DIAGRAMS article in the ENGINE PERFORMANCE Section.
4. If EGR valve did not hold vacuum, replace EGR valve. If engine did not run rough or stall, remove EGR valve and check for plugged EGR valve or EGR passages in intake/exhaust system. Clean or replace as necessary.

EGR Vacuum Supply

Locate EGR vacuum supply port on throttle body or intake manifold. Disconnect vacuum supply hose and connect vacuum gauge to port. Start engine. Increase engine speed to 2000 RPM and note vacuum reading. At least 10 in. Hg of vacuum should be obtained. If vacuum is low, check vacuum supply port for restriction (carbon, dirt, etc.).

EGR Modulator

1. Remove EGR modulator. Plug one upper vacuum hose fitting while blowing air into remaining upper vacuum hose fitting. Air should pass through the filter.
2. Connect vacuum pump to one of the upper vacuum hose fittings. Plug remaining upper vacuum hose fitting (exhaust gas pressure port). Blow air into the bottom vacuum hose fitting, while applying vacuum with vacuum pump. Vacuum should be obtained. Replace EGR modulator if defective.

EGR Vacuum Switch Valve (VSV)

1. With ignition off, disconnect vacuum hoses and wiring from solenoid. For location of VSV, see «EGR VACUUM SWITCHING VALVE LOCATION»(/geo/storm/i-1990-1993/remont/testing-diagnostics/#engine-controls-systemcomponent-tests) table. Using ohmmeter, ensure resistance between terminals of VSV is 33-39 ohms.
2. Blow into tube No. 1 and ensure air flows through filter only. (Scheme 40) Apply battery voltage and ground to VSV terminals. With VSV energized, blow into port No. 1 to ensure air flows out port No. 2. Replace VSV if defective.
3. Check ECM control of ground circuit to EGR VSV and ensure VSV has voltage with ignition on. For wire colors and ECM terminal identification, see appropriate wiring diagram in WIRING DIAGRAMS article in the ENGINE PERFORMANCE Section.

EGR VACUUM SWITCHING VALVE LOCATION

Scheme 40

Fuel Evaporation Canister

1. Connect a section of hose to PCV purge port and attempt to blow through it. (Scheme 41) Little or no air should pass into canister. A small amount of air may pass if canister has a constant purge orifice.
2. Apply 15 in. Hg of vacuum to control vacuum signal port. Blow through hose connected to PCV purge port. An increase flow of air into canister should be observed. Replace fuel evaporation canister if valve is defective.

Scheme 41

PCV Valve

Remove PCV valve from valve cover. Run engine at idle and place thumb over end of hose to check for vacuum. If vacuum does not exist, check for plugged hoses or plugged manifold port. Turn engine off and remove PCV valve. Shake valve to ensure needle inside valve is free. Replace valve if needle is not free.

MISCELLANEOUS CONTROLS

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

A/C CLUTCH SYSTEM CONTROLS

Note. When A/C is operated, ECM will supply a ground to compressor relay. The compressor relay then supplies voltage to A/C clutch.

A/C Clutch System Functional Check

1. With engine running, turn A/C on and off while noting A/C clutch operation. If A/C clutch does not engage, proceed to step 2) If A/C clutch engages, no problem exists in A/C clutch control system.
2. Install Scan tester and request A/C. Scan tester should display YES for A/C request and ON for A/C clutch. If Scan tester does not display correctly, proceed to step 3). If Scan tester displays correctly, problem exists in A/C clutch power or ground circuit.
3. With engine off and ignition on, connect test light to ground and probe Green/Orange wire at ECM connector with A/C requested. The ECM is located on left side of instrument panel and contains 24-pin and 32-pin connectors.
4. If test light comes on, proceed to step 7). If test light does not come on, turn ignition off. Remove A/C thermorelay, located in relay box at right corner of engine compartment, near strut tower.
5. Turn ignition on with A/C requested. Connect test light to ground and probe Green/White wire of A/C thermorelay. If test light comes on, proceed to step 6). If test light does not come on, check for open pressure switch or open circuit in Green/White wire from A/C thermorelay to pressure switch. Pressure switch is located near receiver-drier.
6. If test light comes on, check for open circuit in Pink/Green wire between A/C thermorelay and thermoswitch. Thermoswitch is located behind right side of instrument panel, near blower motor and contains Light Green, Green/Yellow and Pink/Green wires. Check for open circuit in Green/Orange wire from A/C thermorelay to ECM. Check for defective thermoswitch or A/C thermorelay. NOTE: On Storm GSi with A/T, also check for defective A/C control unit by disconnecting electrical connector at A/C control and installing jumper wire between Green/Orange and Orange/Purple wires. The A/C control unit is located behind right side of instrument panel, near blower motor.
7. Connect test light to battery voltage and backprobe Gray/Red wire at ECM. The ECM is located on left side of instrument panel and contains 24-pin and 32-pin connectors. If test light comes on, proceed to step 8). If test light does not come on, check for defective ECM connector or ECM.
8. Check for open circuit in Green wire between compressor relay and cut-out switch on A/C compressor. Compressor relay is located in relay box at right corner of engine compartment, near strut tower.
9. Check for defective compressor relay or cut-out switch or defective connections. Check for open circuit in Gray/Red wire between ECM and diode assembly, located in relay box at right corner of engine compartment, near strut tower.

Shift Indicator Light (Storm M/T Models)

1. Turn ignition on and note shift indicator light. If shift indicator light is off, proceed to step 4). If shift light is on, proceed to step 2).
2. Turn ignition off. Disconnect ECM connectors. The ECM is located on left side of instrument panel and contains 24-pin and 32-pin connectors. Turn ignition on and note shift indicator light. If shift indicator light is off, system is operating properly.
3. If shift indicator light is on, check for short to ground in Orange/Blue wire between ECM and shift indicator light relay or defective shift indicator light relay (internal short to ground). Shift indicator light relay is located behind right kick panel and contains a Brown wire connector.
4. Turn ignition off. Disconnect ECM connectors. The ECM is located on left side of instrument panel and contains 24-pin and 32-pin connectors. Turn ignition on. Place transaxle in gear with clutch engaged. Install jumper wire between Orange/Blue wire of ECM connector and ground. Note shift indicator light operation.
5. If shift indicator light is on, check for defective connection at ECM or for faulty ECM. If shift indicator light is off, install jumper wire between Blue/Orange wire from shift indicator light relay to shift indicator light and ground. Shift indicator light relay is located behind right kick panel and contains a Brown wire connector.
6. If shift indicator light remains off, check for defective bulb, open in power supply circuit to shift indicator light or open in Blue/Orange wire to shift indicator light.
7. If shift indicator light is on, check for open circuit in Orange/Blue wire between ECM and shift indicator light relay or defective shift indicator light relay.

CHART C-4C, IGNITION SYSTEM CHECK

Note. Test numbers refer to test numbers on diagnostic chart.

1. Two spark plug wires are checked to ensure open circuit does not exist in a spark plug wire. 1A) If spark exists with 4-terminal distributor disconnected, pick-up coil output is too low for Electronic Spark Timing (EST) operation.
2. Spark indicates problem is distributor cap or rotor.
3. Battery voltage should exist at "C" and "+" terminals. Low voltage would indicate an open circuit or a high resistance circuit from distributor to ignition coil or ignition switch. If "C" terminal voltage is low, but "+" terminal voltage was 10 volts or more, wiring circuit from terminal "C" to ignition coil or ignition coil primary circuit is open.
4. This checks for a shorted distributor module or grounded circuit from ignition coil to distributor module. Distributor module should be turned off. Normal voltage should be approximately 12 volts. If distributor module is on, voltage would be low, but greater than one volt. This could cause ignition coil to fail from excessive heat. With open circuit in ignition coil primary winding, a small amount of voltage will pass through distributor module from BATT terminals to the TACH terminal.
5. Applying 1.5-8 volts to terminal "P" on distributor module, should turn distributor module on and voltage on TACH terminal to decrease to approximately 7-9 volts. This determines if distributor module or ignition coil is defective or if pick-up coil is not generating proper signal to turn distributor module on. Test can be performed using a 1.5-8 volt DC battery. Test light is used to probe the "P" terminal. Some digital meters can be used to trigger distributor module by selecting ohms, usually the diode position. In this position, digital meter may have voltage across the terminals which, will trigger distributor module.
6. This should turn distributor module off and cause a spark. If no spark occurs, ignition coil is probably defective, as defective distributor module would have been determined by this time.

Scheme 42

Scheme 43

See also:
• COOLANT TEMPERATURE SENSOR RESISTANCE