Caterpillar C4.4 Low Fuel Pressure At High Idle

Confirmed cause: A piece of foreign plastic debris was partially blocking the fuel tank pickup tube screen. Repair performed: Removed the fuel pickup tube assembly from the tank. Removed the plastic debris from the screen and cleaned the pickup tube. Reinstalled the assembly with a new gasket. Verification: The engine was started and run at low and high idle for an extended period. Fuel pressure, monitored with the mechanical gauge, remained stable and within the manufacturer's specification at all speeds. No fuel pressure warnings were observed. Technician notes: - This type of restriction is difficult to diagnose because it may not be apparent at low fuel flow (low idle). - The debris acts like a check valve, limiting flow only when the transfer pump tries to draw more fuel at higher engine speeds. - Always check the simplest things first, but be prepared to test the entire system. Running from a separate fuel can is a very effective way to isolate supply-side vs. engine-side fuel system problems.