1. Fuel System:
* Fuel in the tank: Sounds obvious, but make sure you have enough fuel.
* Fuel filter: A clogged fuel filter is a very common cause. Replace it.
* Fuel pump: The lift pump (located in the tank) might be failing to supply enough fuel pressure to the high-pressure injection system. Listen for the hum of the pump when the key is turned to the "on" position (but not cranking). Lack of hum suggests a failed pump. Low fuel pressure even with a hum suggests a weak pump.
* Fuel pressure regulator: This regulates fuel pressure to the injectors. A faulty regulator can lead to insufficient fuel pressure. Requires testing with a fuel pressure gauge.
* Injector issues: Clogged or faulty injectors prevent proper fuel delivery. Requires testing with an injector diagnostic tool. This is less likely if you're getting good cranking.
* Fuel lines: Check for leaks or kinks in the fuel lines.
2. Ignition System:
* Glow plugs: Diesels rely on glow plugs to preheat the combustion chamber. If they're failing, the engine might crank but not fire. Check the glow plug system for proper function (some have indicators).
* High-pressure oil (HPOP): The high-pressure oil pump supplies oil to the injectors. A faulty HPOP will result in low or no fuel injection. This requires testing with a gauge. A common failure point on the 7.3L.
* Injector control module (ICM): The ICM controls the timing and injection of fuel. A faulty ICM prevents proper fuel delivery. This requires testing and often needs replacement.
3. Air System:
* Air filter: A severely restricted air filter can starve the engine of air, preventing combustion. Replace it. However, this is less likely to prevent starting entirely, usually leading to rough running.
4. Other Possibilities:
* Timing: While less common if it was running before, a serious timing issue could prevent starting. This is a major repair requiring specialized tools and knowledge.
* Security System: Check for any issues with your vehicle's security system that might be preventing starting.
* Batteries: Weak batteries can crank slowly, and insufficient power might prevent the engine from starting.
Troubleshooting Steps:
1. Check the obvious: Fuel level, fuel filter, air filter.
2. Listen for the fuel pump: Does it hum when the key is turned on?
3. Visual inspection: Look for any obvious leaks or damage to fuel lines or other components.
4. Code reader: Use an OBD-II code reader (possibly an adapter might be needed for older 7.3Ls) to scan for any diagnostic trouble codes (DTCs). This will often give a clue.
5. Professional Diagnosis: If you're not comfortable working on your truck, take it to a qualified mechanic specializing in diesel engines. They have the tools and experience to properly diagnose the problem.
The 7.3L Power Stroke is a robust engine, but troubleshooting requires systematic checking. Starting with the fuel system is the most efficient approach. Remember safety first – always disconnect the battery negative terminal before working on the fuel system.
