High-Probability Issues:
* Fuel System:
* Fuel pump failure: The lift pump (electrical) or the injection pump (mechanical) could have failed. A failing lift pump often makes a whining noise before it quits entirely. Listen carefully for this.
* Fuel filter blockage: A completely clogged fuel filter would starve the engine of fuel. This is a quick and cheap check.
* Fuel shutoff solenoid: This is an electrical component that can fail, preventing fuel from reaching the injectors. This is less common but possible. (These trucks often have a manual shutoff on the IP as well - be sure it's in the RUN position).
* Water in the fuel: Water can separate from the fuel and cause the engine to stop.
* Ignition System (though less likely on a diesel):
* Glow plug relay or controller failure: Though diesel engines don't need glow plugs to run *once* warmed up, failure to properly pre-heat the plugs could make starting difficult after the engine is already hot, and subsequently fail to start after already being fully warm.
* PMD (Power Module Driver) failure (for 1994-1997, check your year - this is a more likely suspect for this year, but possibly still relevant): This is an external module that controls the injection pump. A common point of failure in these engines, it often fails when hot. This is less probable if it ran fine before shutdown, but still worth checking.
Medium-Probability Issues:
* Electrical System:
* Battery or connection problems: A bad battery connection can prevent the engine from cranking. Check all battery terminals and cables for corrosion or looseness.
* Alternator failure: Though unlikely to cause immediate failure, a completely dead alternator could have drained the battery.
* Engine Mechanical Issues:
* Timing issues (very unlikely if it ran fine moments before): A very serious problem that would require extensive diagnosis and repair.
Low-Probability Issues:
* Injection Pump Issues (beyond fuel delivery): Internal issues within the injection pump itself could cause failure. This is a much more extensive and costly repair.
* Engine Sensor Failure: While a sensor failure *could* cause a shutdown, it's less likely to do so suddenly.
Troubleshooting Steps:
1. Check the fuel filter: This is the easiest and quickest check. If it's clogged, replace it.
2. Check the fuel: Is there fuel in the tank?
3. Check battery terminals and cables: Make sure they are clean and tight.
4. Try to crank the engine: Does it crank at all? If not, check the battery voltage, starter motor, and all related connections.
5. Listen for the fuel pump: Can you hear the lift pump priming when the key is turned on?
6. Check the glow plug indicator light (if equipped): Does it come on as it should?
7. Check fuel pressure (if possible): This requires a fuel pressure gauge and some knowledge of the system.
8. Check fuses and relays: Make sure all fuses and relays are intact and working.
9. (If applicable): Check the PMD for overheating and condition.
If you're not comfortable working on your own diesel engine, it's best to take it to a qualified mechanic specializing in diesel vehicles. A proper diagnosis is important to prevent further damage and costly repairs. Diagnosing this type of problem often requires specialized tools and knowledge.
