Base Engine Misfire without Internal Engine Noises. GMC Truck Envoy

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 2003 🢒 Envoy - 2WD 🢒 Engine 🢒 Engine Controls - 4.8L, 5.3L, and 6.0L 🢒 Base Engine Misfire without Internal Engine Noises

Cause

Correction

Fuel injector harness connectors are connected to the incorrect fuel injectors/cylinders

Relocate the fuel injector harness connectors, as necessary.

Abnormalities, such as severe cracking, bumps, or missing areas in the accessory drive belt

Abnormalities in the accessory drive system and/or components may cause engine RPM variations and lead to a misfire DTC. A misfire code may be present without an actual misfire condition.

Replace the drive belt. Refer to Drive Belt Replacement - Accessory .

Worn, damaged, or mis-aligned accessory drive components or excessive pulley runout

May lead to a misfire DTC.

A misfire code may be present without an actual misfire condition.

Inspect the components and repair or replace, as required.

Loose or improperly installed engine flywheel or crankshaft balancer

A misfire code may be present without an actual misfire condition.

Repair or replace the flywheel and/or balancer, as required. Refer to Engine Flywheel Replacement or Crankshaft Balancer Replacement .

Restricted exhaust system

A severe restriction in the exhaust flow can cause significant loss of engine performance and may set a DTC. Possible causes of restrictions include collapsed or dented pipes or plugged mufflers and/or catalytic converters.

Repair or replace, as required.

Improperly installed or damaged vacuum hoses

Repair or replace, as required.

Improper sealing between the intake manifold and cylinder heads or throttle body

Replace the intake manifold, gaskets, cylinder heads, and/or throttle body, as required.

Improperly installed or damaged MAP sensor

The sealing grommet of the MAP sensor should not be torn or damaged.

Repair or replace the MAP sensor, as required.

Worn or loose rocker arms

The rocker arm bearing end caps and/or needle bearings should be intact and in the proper position.

Replace the valve rocker arms, as required.

Worn or bent pushrods

•	Replace the pushrods.

•	Inspect the top of the pistons for valve contact. If the top of the piston shows valve contact, replace the piston and pin assembly.

Stuck valves

Carbon buildup on the valve stem can cause the valve not to close properly.

Repair or replace, as required.

Excessively worn or mis-aligned timing chain

Replace the timing chain and sprockets, as required.

Worn camshaft lobes

Replace the camshaft and valve lifters.

Excessive oil pressure

A lubrication system with excessive oil pressure may lead to excessive valve lifter pump-up and loss of compression.

•	Perform an oil pressure test. Refer to Oil Pressure Diagnosis and Testing .

•	Repair or replace the oil pump, as required.

Faulty cylinder head gaskets and/or cracking or other damage to the cylinder heads and engine block cooling system passages

Refer to Diagnostic Starting Point - Engine Cooling in Engine Cooling.

Coolant consumption may or may not cause the engine to overheat.

•	Inspect for spark plugs saturated by coolant. Refer to Spark Plug Inspection in Engine Controls - 5.3L.

•	Inspect the cylinder heads, engine block, and/or head gaskets. Refer to Coolant in Combustion Chamber .

•	Repair or replace, as required.

Worn piston rings

Oil consumption may or may not cause the engine to misfire.

•	Inspect the spark plugs for oil deposits. Refer to Spark Plug Inspection in Engine Controls - 5.3L.

•	Inspect the cylinders for a loss of compression. Refer to Engine Compression Test .

•	Perform cylinder leak down and compression testing to identify the cause. Refer to Cylinder Leakage Test .

•	Repair or replace, as required.

A damaged crankshaft reluctor wheel

A damaged crankshaft reluctor wheel can result in different symptoms depending on the severity and location of the damage.

•	Systems with electronic communications, DIS or coil per cylinder, and severe reluctor ring damage may exhibit periodic loss of crankshaft position, stop delivering a signal, and then sync the crankshaft position.

•	Systems with electronic communication, DIS or coil per cylinder, and slight reluctor ring damage may exhibit no loss of crankshaft position and no misfire may occur. However, a P0300 DTC may be set.

•	Systems with mechanical communications, high voltage switch, and severe reluctor ring damage may cause additional pulses and effect fuel and spark delivery to the point of generating a P0300 DTC or P0336.

Replace the sensor and/or crankshaft, as required.