Here's a breakdown of how to diagnose the problem:
1. Check the fuses and relays:
* Locate the fuse box(es): Your E350 likely has multiple fuse boxes, one under the hood and possibly one inside the cabin (often under the dash). Consult your owner's manual to pinpoint their locations and identify the fuses and relays related to the fuel pump. Common names include "Fuel Pump," "EFI," or similar.
* Inspect the fuses visually: Check for blown fuses (broken filaments). Replace any blown fuses with the correct amperage rating. *Important:* If a fuse blows immediately after replacement, there's a short circuit somewhere in the system – don't keep replacing it.
* Test the relays: Relays are electromechanical switches. You can usually test them visually by checking for corrosion or damage. You can also test their operation with a multimeter (checking for continuity when energized). A bad relay will need replacing.
2. Check the fuel pump relay circuit:
* Identify the fuel pump relay: Once you've located the relay, you can trace the wiring back from it to verify continuity. Use a multimeter to check the power going in and coming out of the relay.
3. Check for power at the fuel pump itself:
* Locate the fuel pump: This is usually located inside the fuel tank. Accessing it may require dropping the tank (a significant job).
* Check power at the fuel pump connector: With the ignition ON (but engine OFF), use a multimeter to test for power at the fuel pump's wiring connector. You should have power at one wire. If you do not have power here, the problem is before the pump itself (likely wiring, fuses, relay or a control module)
4. Check the inertia switch:
* Locate the inertia switch: This safety device cuts power to the fuel pump in the event of a collision. It's typically located under the dash or in the engine compartment.
* Reset the inertia switch: If it's tripped, you'll usually hear a click when you reset it.
5. Check the wiring:
* Inspect the wiring harness: Look for any signs of damage, corrosion, or loose connections along the fuel pump wiring. This requires carefully tracing the wires from the fuel pump connector back to the fuse box and relay.
6. Check the fuel pump control module (PCM):
* The PCM controls the fuel pump: A faulty PCM can prevent power from reaching the fuel pump. This is less likely but possible. Diagnosing a PCM failure generally requires specialized tools and expertise.
7. Consider professional help: If you're not comfortable working with automotive electrical systems or if you've checked all the above and still can't find the problem, take it to a qualified mechanic. Incorrect diagnosis and repair could lead to further damage or even fire.
Remember to consult your vehicle's repair manual for detailed diagrams and specifications. This will be invaluable in identifying the correct fuses, relays, and wiring for your specific E350 model.
