Hard Start. GMC Truck GMC C-Series Medium Duty Truck B7 2002

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC C-Series Medium Duty Truck B7 🢒 Engine 🢒 Engine Controls - 8.1L 🢒 Hard Start

Checks

Action

DEFINITION: Engine cranks OK, but does not start for a long time. Does eventually run, or may start but immediately dies.

Preliminary

•	Refer to Important Preliminary Checks Before Starting in Symptoms - Engine Controls .

•	Check the PCM grounds for being clean, tight, and in the proper locations. Refer to Engine Controls Schematics .

•	Search for bulletins.

Sensor/System

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Check the engine coolant temperature (ECT) sensor for being shifted in value. Connect a scan tool. Compare the ECT against the intake air temperature (IAT) on a cold engine. The ECT and IAT sensor values should be within ± 3°C (5°F) of each other. If the ECT sensor is out of range with the IAT sensor, check the resistance of the ECT sensor. Refer to Temperature Versus Resistance for resistance specifications. Replace the ECT sensor if the resistance is not within the specification. If the sensor is within the specification, repair the ECT signal circuit for high resistance.

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Check the mass air flow (MAF) sensor installation. A MAF sensor that is incorrectly installed may cause a hard start. Important: The embossed arrows on the MAF sensor indicate the direction of the intake air flow. The arrows must point toward the engine. Install the MAF in the proper direction. Refer to Mass Airflow Sensor/Intake Air Temperature Sensor Replacement .

•	Check the camshaft position (CMP) sensor for proper mounting and/or a bad connection. A long crank time occurs if the PCM does not receive a CMP signal.

Fuel System

•	Check the fuel pump relay operation. The fuel pump should turn ON for 2 seconds when you turn ON the ignition. Refer to Fuel Pump Electrical Circuit Diagnosis .

•	A faulty in-tank fuel pump check valve allows the fuel in the lines to drain back to the tank after the engine stops. Refer to Fuel System Diagnosis .

•	Check both injector fuses for being open. An open injector fuse causes four injectors and four ignition coils not to operate. Replace the fuse. Inspect the injector circuits and the ignition coil circuits for an intermittent short to ground.

•	Check for incorrect fuel pressure. Refer to Fuel System Diagnosis .

•	Check for a restricted fuel filter. Refer to Fuel System Diagnosis .

•	Check for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

Ignition System

•	Check both injector fuses for being open. An open injector fuse causes four ignition coils and four injectors not to operate. Replace the fuse. Inspect the ignition coil circuits and the injector circuits for an intermittent short to ground.

•	Check for proper ignition voltage output with J 26792 Spark Tester. Refer to Electronic Ignition (EI) System Diagnosis .

•	Remove the spark plugs and check for the following:

-	Correct heat range

Wet plugs

Cracks

Wear

-	Improper gap

-	Burned electrodes

-	Heavy deposits

Refer to Spark Plug Inspection .

•	Determine the cause of the fouling before replacing the spark plugs if the spark plugs are gas, coolant, or oil fouled. Refer to Spark Plug Inspection for diagnosis of fouled spark plugs.

•	Check for bare or shorted ignition wires. Refer to Spark Plug Wire Inspection .

•	Check for loose ignition coil grounds. Refer to Electronic Ignition (EI) System Diagnosis .

Engine Mechanical

•	Excessive oil in combustion chamber--Leaking valve seals. Refer to Oil Consumption Diagnosis in Engine Mechanical.

•	Low cylinder compression--Refer to Engine Compression Test in Engine Mechanical-8.1L.

•	Combustion chambers for excessive carbon buildup. Clean the chambers using top engine cleaner. Follow the instructions on the can.

•	Inspect the following components for incorrect basic engine parts:

-	Cylinder heads

Camshaft

-	Pistons, etc.

Refer to Symptoms - Engine Mechanical in Engine Mechanical-8.1L.