Manual:HUMMER Hummer H3 Base 2010Page:10120 / 37523

Base Engine Misfire without Internal Engine Noises — 2010 Hummer H3 Base, Automatic Service Manual

Base Engine Misfire without Internal Engine Noises

Cause	Correction
Abnormalities (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.
Worn, damaged, or mis-aligned accessory drive components or excessive pulley runout and 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.
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 head or throttle body.	Replace the intake manifold, gaskets, cylinder head, 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.
Damage to the MAP sensor housing and/or O-ring seal	Replace the intake manifold.
Worn or loose valve 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 valve lash adjusters	Replace the valve lash adjusters.
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 rocker arms.
Excessive oil pressure	Perform an oil pressure test. Refer to Oil Pressure Diagnosis and Testing . Repair or replace the oil pump as required.
Faulty cylinder head gasket and/or cracking or other damage to the cylinder head and engine block cooling system passages. Coolant consumption may or may not cause the engine to overheat.	Inspect for spark plugs saturated by coolant. Inspect the cylinder head, engine block, and/or head gasket. 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. Inspect the cylinders for a loss of compression. Refer to Engine Compression Test . Perform cylinder leak down and compression testing to identify the cause. 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 re-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.