1. Water Intrusion:
* Underhood: Thoroughly inspect the entire engine bay for any signs of water leaks or pooling. Pay close attention to:
* Wiring harnesses: Look for chafing, damaged insulation, or corrosion on any wiring connectors, especially those near the firewall and along the bottom of the engine bay. Water can cause shorts or intermittent open circuits.
* Distributor (if applicable): Although unlikely on a 7.3L Powerstroke which is electronically controlled, check for any signs of moisture intrusion.
* Sensors: Inspect all sensors (like the crankshaft position sensor, camshaft position sensor, and others) for corrosion or water damage. These are vital for engine operation.
* Fuse box: Check for corrosion and ensure all fuses are properly seated and intact.
* Inside the cab (less likely but possible): Check for water leaks inside the cab that could be affecting electrical components related to the engine's control system.
2. Electrical System:
* Battery terminals and connections: Clean and tighten all battery terminals and connections. Corrosion can cause high resistance and intermittent power loss.
* Alternator: Test the alternator's output voltage. A failing alternator can cause the engine to shut down.
* Wiring harness: This is a crucial area. You might need a wiring diagram to trace the main power and ground wires from the battery to the engine control module (ECM). Look for breaks, corrosion, or chafed wires. A professional auto electrician might be needed for a thorough harness inspection.
* ECM (Engine Control Module): While less likely, a faulty ECM can cause unpredictable shutdowns. This is a more advanced diagnosis and usually requires professional diagnostic tools.
* Ignition Switch: A failing ignition switch could lose connection, causing a shutdown.
3. Fuel System (less likely but possible):
* Water in fuel: Though less likely to be related to rain directly, water in the fuel can cause intermittent engine stalling. Check the fuel filter and the fuel water separator (if equipped).
* Fuel pump: A failing fuel pump might struggle to supply sufficient fuel, leading to shutdowns, though this is usually accompanied by other symptoms like hard starting or hesitation.
4. Other Possibilities:
* Glow plugs (cold-weather related): While less likely in warmer weather, faulty glow plugs can contribute to starting issues and potentially intermittent shutdowns.
* High-pressure oil system: Although less common, issues with the high-pressure oil system (like a faulty oil pressure sensor or relief valve) could lead to a shutdown for safety reasons, though usually there are accompanying warning lights.
How to proceed:
1. Start with the simplest checks: Battery terminals, underhood visual inspection for water, and fuse box inspection are the quickest and easiest things to do.
2. Use a multimeter: A multimeter is essential for testing voltage, resistance, and continuity in the electrical system.
3. Obtain a wiring diagram: A wiring diagram for your specific year and model F250 is highly recommended to trace wiring effectively.
4. Professional diagnosis: If you're not comfortable working on your vehicle's electrical system, or if the problem persists after your initial checks, take it to a qualified mechanic specializing in diesel engines. They'll have the proper diagnostic equipment to pinpoint the issue.
Remember safety first when working on your vehicle. Disconnect the negative battery terminal before performing any electrical checks. The rain correlation strongly suggests a water-related electrical problem, so focus your efforts there first.
