ENGINE MECHANICAL
Before performing any on-vehicle adjustments to fuel or ignition systems, ensure engine mechanical condition is okay.
VALVE CLEARANCE
Note. All engines are equipped with hydraulic lifters, except for 6.6L diesel engine. Adjustments are not required. The 6.6L diesel engine is equipped with mechanical roller lifters. Adjustment is not required as routine service. Adjustment is only performed after disassembly of engine components. See 6.6L V8 DIESEL in ENGINES.
IGNITION TIMING (GASOLINE)
Note. On all models, ignition timing is controlled by control module and is not adjustable.
INJECTION PUMP TIMING (DIESEL)
Note. Injection pump timing is not adjustable on 6.6L diesel engine.
GASOLINE ENGINES
Note. DO NOT attempt to adjust idle mixture and idle speed. Both are controlled by Powertrain Control Module (PCM). Incorrect idle speeds are normally caused by dirty throttle plate or vacuum leaks. Ensure all vacuum components are functioning properly.
DIESEL ENGINES
Note. Diesel engines are equipped with electronic fuel injection in which PCM controls all fuel delivery modes based on inputs from APP, ECT and BARO sensors. Idle speed is not adjustable.
GASOLINE ENGINES (EXCEPT 8.1L)
Note. Throttle position sensors are not adjustable.
DIESEL ENGINES & 8.1L GASOLINE ENGINE
Throttle control is electronic with no mechanical link from engine to accelerator pedal. PCM monitors position of accelerator pedal based on signals from a non-adjustable Accelerator Pedal Position (APP) module. APP module is mounted near accelerator pedal.