* Faulty Crankshaft Position Sensor (CKP): This sensor tells the engine's computer the position of the crankshaft. A failing CKP can cause misfires, especially in a specific cylinder. It's relatively inexpensive and easy to replace.
* Faulty Cam Position Sensor (CMP): Similar to the CKP, but it monitors the camshaft's position. A malfunctioning CMP can lead to timing issues and misfires.
* Damaged or Leaking Intake Manifold Gasket: A crack or leak in the intake manifold gasket can cause a vacuum leak, leading to a lean air/fuel mixture in one or more cylinders, resulting in a misfire. Inspect this carefully.
* Worn Valves or Burnt Valves: While less likely if the engine was running acceptably before the recent repairs, worn or burnt valves in cylinder 4 can prevent proper combustion. This requires a more involved diagnosis (compression test).
* Compression Issues in Cylinder 4: Low compression in that cylinder could indicate a problem with the piston rings, valves, or cylinder head. A compression test is necessary to check.
* Wiring Issues: Even with new parts, there could be a short, break, or poor connection in the wiring harness related to cylinder 4. Carefully inspect the wiring leading to the injector, coil pack, and sensor.
* Incorrectly Installed Parts: While less likely, double-check that all the new components are properly installed and seated correctly.
* Exhaust System Restriction: A severely clogged catalytic converter or exhaust restriction can affect back pressure, causing a misfire.
Troubleshooting Steps:
1. Check for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to retrieve any stored trouble codes. These codes can pinpoint the problem area.
2. Perform a Compression Test: This test measures the compression in each cylinder. Low compression in cylinder 4 points to internal engine issues.
3. Inspect the Intake Manifold and Gasket: Look for cracks, leaks, or signs of damage.
4. Visually Inspect the Wiring: Check the wiring harness for any damage, breaks, or loose connections.
5. Check the CKP and CMP Sensors: These are relatively easy to test and replace.
Recommendation: A compression test and a scan for trouble codes are the next crucial steps. If you're not comfortable performing these yourself, take your truck to a qualified mechanic for diagnosis. Trying to troubleshoot further without these basic checks can lead to wasted time and money.
