* Fuel Filter: A clogged fuel filter, even a new one (they can be faulty), will severely restrict fuel flow. This is the most common and easiest to check first. Replace the filter regardless of its apparent age or condition.
* Fuel Lines: The fuel lines from the tank to the engine can be corroded, kinked, or partially blocked with debris. Inspect them visually for damage and check for restrictions by blowing compressed air through them (carefully, and with appropriate safety measures). Old, rubber fuel lines are prone to collapsing or clogging internally.
* Tank Sender Unit: The fuel tank's sending unit (the part that measures fuel level and also houses the fuel pump) could be partially clogged or have a faulty pickup tube. Sediment build-up in the tank can settle around the pickup, preventing the pump from drawing fuel effectively.
* Fuel Pump Installation: While unlikely with a new pump, ensure the pump was installed correctly. A faulty installation (incorrectly seated, wiring issues, etc.) can significantly impair performance. Check all connections and the pump's mounting.
* Wiring/Electrical Issues: A problem with the wiring leading to the rear pump, such as a poor connection, short, or damaged wiring harness, can prevent the pump from receiving the correct voltage or ground. Check all wiring for damage and corrosion. Verify power is getting to the pump using a voltmeter.
* Pressure Regulator: A faulty fuel pressure regulator can cause low fuel pressure, resulting in sluggish performance.
* Bad Fuel: Believe it or not, bad fuel can clog filters and injectors very rapidly, especially if the tank has been sitting for a long time with contaminated fuel.
* Evaporative Emission System (EVAP) Issues: In some cases, a problem with the EVAP system could affect fuel delivery, although this is less likely to cause the symptoms you describe.
Troubleshooting Steps:
1. Check the fuel filter: This is the easiest and cheapest step. Replace it immediately.
2. Inspect fuel lines: Look for kinks, rust, or damage. Try blowing air through them.
3. Check fuel pressure: Use a fuel pressure gauge to measure the pressure at the fuel rail. Compare it to the specifications for your engine. This will help determine if the issue lies with the pump or further downstream.
4. Investigate the fuel tank: If possible, drop the tank and inspect for sediment or debris at the pickup tube.
If you've replaced the filter and checked the lines and still have problems, taking it to a mechanic familiar with classic trucks might be necessary to diagnose the more complex issues. Remember safety first when working with fuel systems – always disconnect the battery before working on electrical components and avoid sparks near gasoline.
