ENGINE MISSES TILL WARM?

If your 1998 Chevrolet truck is experiencing a misfire when cold but runs fine after driving for 20 minutes or longer, despite replacing the rotor button, fuel pump, and spark plugs, there are a few additional possibilities to consider:

Ignition Wires: Faulty or worn ignition wires can cause misfires, especially when the engine is cold. Check the condition of the ignition wires and replace them if they are damaged or worn.

Ignition Coil: The ignition coil is responsible for producing high voltage to ignite the spark plugs. If the coil is weak or failing, it can cause misfires, particularly when the engine is cold. Consider having the ignition coil tested or replaced if necessary.

Fuel Injectors: Clogged or malfunctioning fuel injectors can lead to misfires, especially during cold starts. Over time, fuel injectors can become dirty or develop deposits, affecting fuel spray patterns. Consider having the fuel injectors cleaned or professionally inspected.

Coolant Temperature Sensor: The coolant temperature sensor provides information to the engine control unit (ECU) about the engine's temperature. If the sensor is malfunctioning, it can cause incorrect fuel delivery and result in misfires. Consider having the coolant temperature sensor checked and replaced if necessary.

Intake Manifold Gasket: A worn or damaged intake manifold gasket can cause vacuum leaks, affecting the air-fuel mixture and leading to misfires. Inspect the intake manifold gasket for signs of leakage and replace it if needed.

Mass Airflow (MAF) Sensor: The MAF sensor measures the amount of incoming air and provides data to the ECU for proper fuel delivery. If the MAF sensor is dirty or malfunctioning, it can disrupt the air-fuel mixture and result in misfires. Consider cleaning or replacing the MAF sensor as needed.

If the issue persists, it's recommended to have a qualified mechanic perform a thorough diagnosis. They can use specialized tools to analyze data from the engine control system and pinpoint the exact cause of the misfires. This will help ensure an accurate and effective repair.