Circuit Description
The diagnosis for an engine that cranks but will not run must have three elements present before proceeding with the test table. The battery must be adequately charged. Engine cranking speed must be sufficient and there must be adequate fuel in the tank.
Diagnostic Aids
If no trouble is found in the fuel pump circuit or the ignition system and the cause of an Engine Cranks But Will Not Run has not been found, check the following conditions:
| • | Perform the Fuel Injector Coil Test . |
| • | An after-market vehicle theft deterrent system could cause a start then stall or a no start condition. |
| • | Fouled spark plugs |
| • | An EGR valve stuck open |
| • | Water or foreign material in the fuel system |
| • | A grounded or intermittently grounded ignition control (IC) signal circuit |
| • | Restricted exhaust system |
| • | Check the following ignition components: |
| - | A grounded tach circuit |
| - | Worn distributor cap |
| - | Worn distributor rotor |
| - | Check ignition wires by lightly spraying them with water in order to identify intermittent no starts |
Check the following mechanical components:
| • | Cylinder valve timing |
| • | Loose or broken timing chain |
| • | Low compression |
| • | Worn camshaft lobes |
| • | Bent or burned intake or exhaust valves |
The PCM has integrated circuits that are fault protected; therefore, if a circuit has failed, the integrated circuit may not be damaged. If that is the case, then the system will keep the circuit open until the condition has been corrected.
Afterwards, reinstall the PCM and check the circuit. Replace the PCM only if the circuit is still inoperative.
An intermittent may be caused by any of the following conditions:
| • | A poor connection |
| • | Rubbed throuhg wire insulation |
| • | A broken wire inside the insulation |
Thoroughly inspect any circuitry that is suspected of causing the intermittnet complaint. Refer to Testing for Intermittent and Poor Connections or Wiring Repairs in Wiring Systems.
Test Description
The numbers below refer to the step numbers on the diagnostic tables.
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If the engine starts, the problem could be intermittent. Basic engine mechanical problems, the vehicle theft deterrent (VTD) system (if equipped), and poor connections could cause a no start condition.
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This step will determine if the cause of the no start or start and stall is related to the VTD.
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If the signal is over 2.5 volts, the engine may be in the clear flood mode which will cause starting problems.
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If the engine coolant sensor is below -30°C (-22°F), the PCM provides fuel for this extremely cold temperature which will severely flood the engine.
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Voltage at the spark plug is checked using the spark plug tester tool . No spark indicates a basic ignition problem.
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This test will determine if there is fuel pressure at the fuel injection unit and holding steady.
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Use the injector test lamp in order to test the injector circuits. A blinking lamp indicates that the PCM is controlling the injector.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 |
Important: Before clearing the DTCs, use the scan tool Capture info. to save the Freeze Frame and the Failure Records for reference. The control modules data is deleted once the Clear info function is used. Did you perform the Diagnostic System Check-Engine Controls? | -- | ||
Attempt to start the engine. Does the engine start and continue to run? | -- | |||
Does the VTD fuel disables parameter display active while you crank the engine? | -- | Go to A Diagnostic System Check - Theft Deterrent in Theft Deterrent | ||
Monitor the TP sensor on the scan tool. With the throttle closed, is the TP sensor more than the specified value? | 2.5 V | Go to DTC P0121 | ||
Monitor the ECT sensor on the scan tool. Is the ECT sensor below the specified value? | -30°C (-22°F) | Go to DTC P0118 | ||
Check for spark at two spark plug wires using the J 26792 spark tester. Is spark present at both spark plug wires? | -- | |||
Is the fuel pressure within the specified range? | 379-413 kPa (55-60 psi | Go to Fuel System Diagnosis | ||
Does the injector test lamp flash for each injector circuit? | -- | Go to Diagnostic Aids | Go to Fuel Injector Circuit Diagnosis | |
