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2002 GMC Sierra 4.8L Engine Misfire and P0101/P0300 Codes After Head Gasket Replacement

Model: 2002 GMC Sierra Fault Code: P0101 Posted: 2015-02-19 10:46

I own a 2002 GMC Sierra with a 4.8L V8 engine. Recently, I performed a head gasket and cylinder head replacement myself as a precaution—my truck had never overheated before. The repair was extremely challenging for an intermediate mechanic, but I’ve not observed any coolant loss or white smoke from the exhaust. Since the work, my truck has become unrideable under load. It runs smoothly at idle and during gentle acceleration (I left it idling for 40 minutes with no error codes), but experiences severe misfires and stumbles when accelerating. The vehicle now shows persistent fault codes P0101 (Mass Airflow Sensor Range/Performance Problem) and P0300 (Random/Multiple Cylinder Misfire). My truck has just under 200,000 miles on it and is equipped with a K&N cold air intake. It sat for five months before the repair, and only had a small amount of fuel in the tank at that time—after which I added 5 gallons of 91 octane gasoline. Despite this, the issue persists. I’m looking for advice as I can’t afford to take it to a shop. Could a minor head gasket leak be contributing to these symptoms? Any guidance on troubleshooting would be greatly appreciated.

Related fault codes
P0101P0300
Comments (6)
Anonymous 2015-02-19 11:37

Start by removing the K&N cold air intake. Then clean the Mass Airflow (MAF) sensor and check fuel pressure. These are common causes of P0101 and misfires in older V8 engines.

Anonymous 2015-02-19 13:17

I cannot remove the K&N intake as it was installed when I originally purchased the truck, and I do not have the original stock air filter available.

Anonymous 2015-02-19 14:03

Try switching to a conventional air filter instead of an oiled one. Still perform MAF cleaning and fuel pressure check. Have you made any other modifications—such as using performance chips, miracle magnets, spark plug upgrades, or throttle body spacers? Any changes like these could affect engine performance.

Anonymous 2015-02-20 11:09

I replaced the air filter and cleaned the MAF sensor. I also verified fuel pressure at 53 psi—still within range—but the codes persist and the truck continues to misfire under load. If there was a small leak in the head gasket, could that be causing these symptoms?

Anonymous 2015-02-20 11:52

Fuel pressure appears low—verify against manufacturer specifications to confirm. Do you have an OBD2 scanner? If so, check readings for ECT (Engine Coolant Temperature), MAF, MAP, and fuel trim values to get a clearer picture of the system’s performance.

Anonymous 2015-02-20 16:46

I do own an Actron CP9145 OBD2 scanner, but I’m not very experienced with interpreting its data or using it effectively for diagnosing these specific codes.