GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1999 🢒 GMC C-Series Medium Duty Truck B7 🢒 Engine 🢒 Engine Controls - 7.4L 🢒 Engine Cranks But Does Not Run

Description

The Engine Cranks but Does Not Run diagnostic table assumes that battery condition and engine cranking speed are OK. If the battery condition and the cranking speed are not OK, refer to Wiring Repairs for diagnosis. Make sure that there is adequate fuel in the tank(s).

Diagnostic Aids
    • Check the duct work between the Mass Air Flow (MAF) sensor and the throttle body for air leaks.
    • A malfunctioning MAF sensor may cause a no start or a stall after start. If you suspect this, disconnect the MAF sensor. The PCM will default to the speed density (MAP, IAT, RPM) in order to calculate the load and the air flow. If this corrects the condition and the connections are OK, replace the MAF sensor.

If the steps above check OK, refer to Symptoms .

Test Description

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

  1. If the PCM does not detect a Crankshaft Position (CKP) signal soon after energizing the starter relay the PCM will de-energize the starter relay.

    2.

  2. This step will determine if sufficient fuel pressure is being supplied to the fuel injectors.

    3.

  3. This test will determine if the PCM is controlling all of the injectors.

    4.

  4. This step will determine if the PCM has turned the injectors OFF because of an engine kill request from the aftermarket PTO control system.

Step

Action

Value(s)

Yes

No

1

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 stop cranking after the specified value?

2 seconds

Go to DTC P0335 Crankshaft Position (CKP) Sensor Circuit

Go to Step  3

3
  1. Turn the ignition switch to the OFF position for the specified value.
  2. Turn the ignition switch to the ON position.
  3. Listen for the fuel pump operation.

Does the fuel pump run for the specified value?

10 seconds

2 seconds

Go to Step 4

Go to Fuel Pump Electrical Circuit Diagnosis

4

Turn the ignition switch to the ON position.

Does the scan tool indicate a Throttle Position (TP) sensor voltage greater than the specified value?

2.5 volts

Go to DTC P1120 Throttle Position (TP) Sensor 1 Circuit

Go to Step 5

5

Does the scan tool indicate an Engine Coolant Temperature (ECT) 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

Notice: Twist the spark plug boot one-half turn in order to release the boot. Pull on the spark plug boot only. Do not pull on the spark plug wire or the wire could be damaged.

  1. Disconnect an ignition wire from a spark plug.
  2. Install a spark testerJ 26792
  3. Crank the engine while observing the spark tester.

Does the tester indicate spark is present?

--

Go to Step 7

Go to Electronic Ignition (EI) System Diagnosis

7

  1. Turn the ignition switch to the OFF position.
  2. Relieve the fuel pressure. Refer to Fuel Pressure Relief

    3. Caution: Wrap a shop towel around the fuel pressure connection in order to reduce the risk of fire and personal injury. The towel will absorb any fuel leakage that occurs during the connection of the fuel pressure gage. Place the towel in an approved container when the connection of the fuel pressure gage is complete.

  3. Install the fuel pressure gauge or equivalent.
  4. Turn the ignition switch to the ON position for the specified value, position leaving the engine OFF.
  5. Bleed the air out of the fuel pressure gauge into an approved gasoline container.
  6. Turn the ignition switch to the OFF position for the specified value.
  7. Monitor the fuel pressure gauge and turn the ignition switch to the ON position.

Important: The ignition switch may have to be cycled more than once in order to obtain the maximum fuel pressure.

Is the fuel pressure within the specified value while the fuel pump is running?

2 seconds

10 seconds

379-427 kPa (55-62 psi)

Go to Step 8

Go to Fuel System Diagnosis

8

  1. Disconnect the fuel injector harness connector at the rear of the engine.
  2. Install the injector test lamp J 34730-380 to the injector harness (PCM side).
  3. Observe the test lamp while cranking the engine.

Does the test lamp flash for each of the injectors?

--

Go to Step 13

Go to Step 9

9

Is the vehicle equipped with an aftermarket PTO device?

--

Go to Step 10

Go to Fuel Injector Circuit Diagnosis

10

  1. Disconnect body builders electrical harness connector at the right side engine/chassis harness connector.
  2. Attempt to start the engine.

Does the engine start and run?

--

Go to the PTO manufacturer/upfitter for PTO control system diagnosis

Go to Step 11

11
  1. Connect a test lamp J 35616-200 to battery ground and probe the engine kill request circuit at the engine/chassis harness body builders connector.
  2. Turn the ignition switch to the ON position.

Is the test lamp ON?

--

Go to Fuel Injector Circuit Diagnosis

Go to Step 12

12
  1. Turn the ignition switch to the OFF position.
  2. Disconnect the PCM connector containing the engine kill request circuit.
  3. Connect a test lampJ 35616-200 battery positive voltage and probe the engine kill request circuit at the harness connector.

Is the test lamp ON?

--

Go to Step 14

Go to Step 15

13

Perform the following checks:

    • Check the air intake ducts between the Mass Air Flow (MAF) sensor and the throttle body for air leaks.
    • A malfunctioning MAF sensor may cause a no start or a stall after a start. If you suspect this, disconnect the MAF sensor electrical connector. The PCM will default to the speed density (MAP, IAT, RPM) in order to determine the engine load and intake air flow. If disconnecting the MAF sensor corrects the condition, and the connections are OK, replace the MAF sensor.
    • Inspect the spark plugs for being fouled. If the plugs are fouled, determine the cause of the rich condition.
    • Inspect for an engine mechanical failure that causes no start condition (i.e. timing chain, low compression).
    • Compare the MAP/BARO parameters to that of another vehicle. The values should be close to each other.

Did you find and repair a problem?

--

Go to Step 16

Go to Symptoms

14

Repair the short to ground at the engine kill request circuit between the PCM and the body builder connector.

Is the action complete?

--

Go to Step 16

--

15

Important:: Reprogram the replacement PCM.

Replace the PCM. Refer to Powertrain Control Module Replacement .

Is the action complete?

--

Go to Step 16

--

16

Attempt to start the engine.

Does the engine start and continue to run?

--

System OK

Go to Symptoms