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PATH:DiagnosticsDiagnostic RoutinesPowertrainEngine Controls - 5.0L and 5.7LEngine Cranks But Does Not Run

Engine Cranks But Does Not Run
NOTE
Applicable vehicles:
§  Chevy Pickup, GMC Pickup, Suburban, Tahoe, Yukon (VIN C/K)

Engine Cranks But Does Not Run

Refer to Engine Controls Schematics .

Circuit Description

The diagnosis for an engine that cranks but does not run must have three elements present before proceeding with the diagnostic table. The following conditions must exist:

§  The battery must be adequately charged.

§  The engine cranking speed must be sufficient.

§  There must be an adequate amount of fuel in the fuel 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 Solenoid 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 VCM 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 open until the condition has been corrected.

Afterwards, reinstall the VCM and check the circuit. Replace the VCM only if the circuit is still inoperative.

An intermittent may be caused by any of the following conditions:

§  A poor connection

§  Rubbed through wire insulation

§  A broken wire inside the insulation

Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.

If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring Systems.

Test Description

The numbers below refer to the step numbers on the diagnostic tables.

  1. 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.
  1. This step will determine if the cause of the no start or start and stall is related to the VTD.
  1. If the signal is over 2.5 volts, the engine may be in the clear flood mode which will cause starting problems.
  1. If the engine coolant sensor is below -30°C (-22°F), the VCM provides fuel for this extremely cold temperature which will severely flood the engine.
  1. Voltage at the spark plug is checked using the J 26792 spark plug tester tool. No spark indicates a basic ignition problem.
  1. This test will determine if there is fuel pressure at the fuel injection unit and holding steady.
  1. Use the J 34730-375 injector test lamp in order to test the injector circuits. A blinking lamp indicates that the VCM is controlling the injector.

Step / Action / Value(s) / Yes / No /
1 / WARNING
Important: Before clearing the DTCs, use the scan tool Capture Info. to save the Freeze Frame and the Failure Records for reference. The control module's data is deleted once the Clear Info function is used.
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? / -- / Go to Step 2 / Go to Powertrain On Board Diagnostic (OBD) System Check
2 / Attempt to start the engine.
Does the engine start and continue to run? / -- / Go to Symptoms / Go to Step 3
3 /
  1. Install a scan tool.
  2. Monitor the VTD Fuel Disabled parameter.
  3. Crank the engine.
Does the VTD Fuel Disabled parameter display active while you crank the engine? / -- / Go to Diagnostic System Check - Theft Deterrent in Theft Deterrent / Go to Step 4
4 / 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 Throttle Position (TP) Sensor Performance / Go to Step 5
5 / Monitor the ECT sensor on the scan tool.
Is the ECT sensor below the specified value? / -30°C (-22°F) / Go to DTC P0118 Engine Coolant Temperature (ECT) Sensor Circuit High Voltage / Go to Step 6
6 / Check for spark at two spark plug wires using the J 26792 spark tester.
Is spark present at both spark plug wires? / -- / Go to Step 7 / Go to Enhanced Ignition System Diagnosis
7 /
  1. Reconnect the spark plug wires.
  2. Turn OFF the ignition.
  3. Connect the J 34730-1A fuel pressure gauge.
  4. Turn ON the ignition leaving the engine OFF
Is the fuel pressure within the specified range? / 379-413 kPa (55-60 psi / Go to Step 8 / Go to Fuel System Diagnosis
8 /
  1. Disconnect the injector connector at the intake manifold.
  2. Install the J 34730-375 injector test lamp into each injector circuit one at a time.
  3. Crank the engine with the injector test lamp in each circuit.
Does the injector test lamp flash for each injector circuit? / -- / Go to Diagnostic Aids / Go to Fuel Injector Circuit Diagnosis

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PATH:DiagnosticsDiagnostic RoutinesPowertrainEngine Controls - 5.0L and 5.7LFuel Injector Solenoid Coil Test

Fuel Injector Solenoid Coil Test
NOTE
Applicable vehicles:
§  Chevy Pickup, GMC Pickup, Suburban, Tahoe, Yukon (VIN C/K)
§  NPR/NQR

Fuel Injector Solenoid Coil Test

Click to Enlarge

Test Description

The numbers below refer to the step numbers on the diagnostic able.

  1. This step is the setup step for performing the injector coil test. Also read the instructions included with the tools used for this test.
  1. Engine coolant temperature affects the tool's ability to detect a faulty injector. If the engine coolant temperature is not between 50°F and 95°F, allow the vehicle to warm or cool as necessary.
  1. Due to a current surge, the first second of the voltage reading may be inaccurate; therefore, begin recording after the first second of the voltage reading. The voltage specification should be within range. The voltage reading may increase throughout the test as the injector windings warm up and the resistance changes. An erratic voltage reading (one that jumps up and down) would indicate an intermittent connection within the fuel injector.

Step / Action / Value(s) / Yes / No /
1 / Was the Powertrain On-Board Diagnostic (OBD) System Check performed? / -- / Go to Step 2 / Go to Powertrain On Board Diagnostic (OBD) System Check
2 /
  1. Turn OFF the engine.
  2. Relieve the fuel pressure. Refer to Fuel Pressure Relief Procedure .
  3. Connect the fuel injector tester J 39021 to B+.
  4. Connect the injector switch box J 39021-210 .
  5. Set the amperage supply selection to the 0.5 amp position.
  6. Connect the leads from J 39200 digital volt meter (DVM to the tenths scale (0.0).
  7. Connect the scan tool.
  8. Monitor the engine coolant temperature.
Is the engine coolant temperature within the specified value? / 10°-35°C / Go to Step 4 / Go to Step 3
3 / Allow the engine to warm or cool as necessary.
Is the engine coolant temperature within the specified value? / 10°-35°C / Go to Step 4 / --
4 / WARNING
Important: Perform the following test for each injector.
  1. Press the Push To Start Test button.
  2. Monitor the DVM.
WARNING
Important: Voltage may climb during the test. Watch for erratic readings (voltage that jumps up and down).
Do any of the injector voltage readings fall outside the specified value? / 5.44-7.53V / Go to Step 5 / Go to Fuel Injector Balance Test
5 / Replace the fuel injector and poppet nozzle assembly that was not within the specified value. Refer to Central Sequential Multiport Fuel Injector Replacement .
Is the action complete? / 5.44-7.53V / Go to Step 6 / --
6 /
  1. Using the scan tool, select the DTC and the Clear Info.
  2. Attempt to start the engine.
Does the engine start and continue to run? / -- / Go to Step 7 / Go to Step 2
7 /
  1. Allow the engine to idle until reaching the normal operating temperature.
  2. Select the DTC and the Failed This Ign.
Are any DTCs displayed? / -- / Go to the applicable DTC table / Go to Step 8
8 / Using the scan tool, select the Capture Info and the Review Info.
Are any DTCs displayed that have not been diagnosed? / -- / Go to the applicable DTC table / System OK

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PATH:DiagnosticsDiagnostic RoutinesPowertrainEngine Controls - 5.0L and 5.7LPowertrain On Board Diagnostic (OBD) System Check

Powertrain On Board Diagnostic (OBD) System Check
NOTE
Applicable vehicles:
§  Chevy Pickup, GMC Pickup, Suburban, Tahoe, Yukon (VIN C/K)

Powertrain On Board Diagnostic (OBD) System Check

Circuit Description

The On-Board Diagnostic (OBD) System Check is an organized approach to identifying a problem created by a control module system malfunction. The OBD System Check is the starting point for any driveability concern diagnosis. The OBD directs the service technician to the next logical step in diagnosing the concern.

Perform this check only if there is a driveability complaint or if you have been sent to this system check from another section in the service information.

Understanding the table properly reduces the diagnostic time. Proper use of the OBD helps prevent the unnecessary replacement of good parts.

Diagnostic Aids

WARNING
Important: Do not clear the DTCs unless directed by a diagnostic procedure. Clearing the DTCs will also clear valuable Freeze Frame and Failure Records data.

Inspect all related wiring and connections including the connections at the VCM. These may cause an intermittent condition.

Any base engine problem could alter scan tool data. Examples of these are: distributor timing, valve timing, and intake gasket leaks.

An intermittent may be caused by any of the following conditions:

§  A poor connection

§  Rubbed through wire insulation

§  A broken wire inside the insulation

Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.

If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring Systems.

Test Description

The numbers below refer to the step numbers in the diagnostic table.

  1. This step determines if the scan tool powers up when connected to the DLC.
  1. The MIL should be ON when the ignition is turned ON.
  1. Refer to Diagnostic Trouble Code (DTC) List for a list of valid DTCs.
  1. Refer to Data Link Connector Schematics in Wiring Systems to determine all of the modules communicating on the Class 2 Serial Data Circuit. If any of the modules are not present in the Diagnostic Circuit Check, then the module(s) never established communications. The scan tool will indicate a YES state for communicating modules and a NO state for modules that had established, yet no longer communicate.
  1. If the vehicle does not start or starts and stalls, the Passlock system could be the cause.
  1. This test determines if the MIL can be controlled by the VCM.
  1. Comparing the ACTUAL and TYPICAL scan tool data values will aid in determining if the engine parameter is within limits (i.e., Advanced timing can substantially alter sensor values.)

Step / Action / Value(s) / Yes / No /
1 / WARNING
Important: Check for applicable service bulletins before preceding with this test.
Perform this test only if there is a driveability complaint or if you have been sent to this table from another section in the service information.
WARNING
Important: Do not turn the ignition OFF when performing this diagnostic. Do NOT clear DTCs unless instructed by this diagnostic. Turn on the ignition leaving the engine OFF.
Does the scan tool power up? / -- / Go to Step 2 / Go to Data Link Connector Diagnosis
2 / Turn ON the ignition leaving the engine OFF.
Is the MIL ON? / -- / Go to Step 3 / Go to Malfunction Indicator Lamp Circuit Check
3 / Attempt to establish communications with the VCM.
Does the scan tool communicate with the VCM? / -- / Go to Step 4 / Go to Data Link Connector Diagnosis
4 / Save the DTC Freeze Frame and the Failure Records if any of the following DTC status are set in the scan tool DTC Information:
§  Last test failed.
§  Test Failed This Ignition
§  MIL Request
§  History DTC
Were any DTCs found? / -- / Go to the applicable DTC table / Go to step 5
5 / Monitor the Serial Data Class 2 message with the scan tool.
Are all other modules communicating with the scan tool? / -- / Go to Step 6 / Go to Data Link Connector Diagnosis
6 / Attempt to start the engine.
Does the engine start and continue to run? / -- / Go to Step 8 / Go to Step 7
7 / Check for any Passlock DTCs in Body or Chassis.
Were any DTCs found? / -- / Go to the applicable DTC table / Go to Engine Cranks but Does Not Run
8 / Command the MIL OFF with the scan tool.
Does the MIL turn OFF? / -- / Go to Step 9 / Go to Malfunction Indicator Lamp Circuit Check
9 / Compare the scan tool engine data with the TYPICAL scan tool values.
Are the values within typical ranges? / -- / Go to Symptoms / Go to Diagnostic Aids

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PATH:DiagnosticsDiagnostic RoutinesBodyTheft DeterrentDiagnostic System Check - Theft Deterrent