Hard to Start
Definition: Engine cranks OK, but does not start for a longtime. Does eventually run, or may start but immediately dies.PRELIMINARY CHECKS
^ Refer to "Important Preliminary Checks," as described at start of "Symptoms." Testing and Inspection
^ Make sure the driver is using the correct starting procedure.
^ Check service bulletins for updates.
SENSORS
^ CHECK: Engine Coolant Temperature (ECT) and Intake Air Temperature (IAT) sensors
- using a Tech 1 scan tool, compare coolant and intake air temperatures with ambient temperature when engine is cold.
- If coolant or intake air temperature readings are 5 degrees greater than or less than ambient air temperature on a cold engine, check resistance in the ECT/IAT sensor circuit or sensor itself. Compare ECT/IAT resistance value to the "Diagnostic Aid" charts found within DTC 14/23 charts.
^ CHECK: Throttle Position (TP) Sensor
- If a sticking throttle shaft or binding linkage causes a high TP sensor voltage (open throttle indication), the control module will not control idle. Monitoring TP sensor voltage. Scan tool and/or voltmeter should display less than .85 volt with throttle closed.
^ CHECK: Manifold Absolute Pressure (MAP) sensor.
FUEL SYSTEM
^ CHECK: Fuel pump relay operation. Fuel pump should operate for 2 seconds when ignition is turned "ON." Refer to "CHART A-5". Chart A-5 Fuel Pump Relay Circuit Diagnosis
^ CHECK: Fuel pressure. Refer to "CHART A-6". Related Tests, Information and Procedures
^ CHECK: For water contaminated fuel.
^ CHECK: Injector driver circuit.
- Disconnect all injector harness connectors at the injectors. Connect J 34730-2B Injector Test Light or equivalent 12 volts test light between the harness terminals of each injector connector and note light while cranking. If test light fails to blink at any connector, it is a faulty injector drive circuit harness, connector or terminal. Injector resistance. Measure injector resistance of each injector(s). Nominal resistance of each injector should be 11.6 to 12.4 ohms at 20°C (68°F) for MFI, THI resistance is 1.16 to 1.36 ohms and for CMFI, the resistance is 1.37 to 1.77 ohms. Resistance will increase slightly at higher temperatures.
^ CHECK: Fuel injector(s).
- Perform injector balance test if applicable. Use CHART A-7 of appropriate VIN. Related Tests, Information and Procedures
Important
^ A faulty in-tank fuel pump check valve will allow the fuel in the lines to drain back to the tank after engine is stopped. To check for this condition, perform "Fuel System Diagnosis," CHART A-5. Chart A-5 Fuel Pump Relay Circuit Diagnosis
^ CHECK: Fuel pump relay.
- Connect test light between fuel pump "test" terminal and ground. Test light should be "ON" for 2 seconds following ignition "ON." If not, refer to "CHART A-5". Chart A-5 Fuel Pump Relay Circuit Diagnosis
^ CHECK: Vacuum control valve.
^ CHECK: Fuel injectors.
- perform injector balance test. Refer to "CHART A-7" of appropriate VIN. Related Tests, Information and Procedures
IGNITION SYSTEM
^ CHECK: Ignition system for:
- Proper ignition voltage output with spark tester J 26792 or equivalent (ST 125).
- Spark plugs; wet plugs, cracks, wear, improper gap, burned electrodes or heavy deposits.
- Bare and shorted wires.
- Moisture in distributor cap.
- Worn distributor shaft.
- Pickup coil resistance and connections.
- Loose ignition coil connections.
- Loose Ignition Control Module (ICM) connections.
- Faulty control module and ignition grounds.
- Misfiring or cutting out under load or at idle. Refer to "Misfire" chart in "Electronic Ignition (EI) System,". System Diagnosis - Electronic Ignition
Important
^ If engine starts, but then immediately stalls, remove the Crankshaft Position (CKP) sensor and check for improper resistance or faulty connections.
^ CHECK: CKT 423 (Ignition Control) for short to ground.
ENGINE MECHANICAL
^ CHECK: For proper valve timing, low compression, bent pushrods, worn rocker arms, broken or weak valve springs, worn camshaft lobes.
^ CHECK: Intake and exhaust manifold passages for casting flash.
ADDITIONAL CHECKS
^ CHECK: IAC operation - refer to "Diagnosis".