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Niece Equipment

How to Troubleshoot your Fuel and Lube Trucks

by: Niece Equipment / April 9, 2019

Air Compressor Assembly Figure 1When operating a fuel and lube truck in a sometimes-rough condition, it’s important to be able to troubleshoot an issue quickly. Here are a few common troubleshooting Q&A’s:

Air Compressor

Why won’t the air compressor run? 

  1. Verify that the air compressor switch on the rear control panel is on.
  2. Verify that the bed power switch is on inside the cab of the truck.
  3. Check if air gauge on compressor has shut off at 120 psi.
  4. Check the compressor coil with a voltmeter for 12V.
  5. Check the compressor’s oil level - verify compressor has not locked up.
  6. Verify the hydraulic reservoir is not low on hydraulic oil.

Why won’t the air compressor shut off?

  1. Check if the pressure gauge is exceeding 120 psi. If so, adjust the regulator to 120 psi.
  2. Check if the electrical wiring to the compressor coil is still intact. Repair any damaged wiring.
  3. If 1 and 2 do not work, replace the air regulator.

Rear Control Panel Figure 3Why is the air compressor blowing the top off the air dryer, or making the lubricator leak?

  1. Check if the regulator is set over 120 psi. If it is, adjust the compressor regulator to below 120 psi.
  2. Verify all water has been drained out of the air compressor.
  3. If air regulator will not adjust, replace the regulator. 

Fuel Pump

Driver Side Emergency Shut Off Switch Figure 4Why is the fuel pump not pumping or surging off and on?

  1. Check if either of the two Emergency Shut Off Switches (Fig. 3-1, Fig. 4-1) are in the closed position.
  2. Check both of the Emergency Shut Off Switches for leaks, and if they exhaust when disengaged.
  3. Verify that the air supply line (Fig. 5 - 3) is attached to the air cylinder (Fig. 5 - 2) on the Emergency Valve (Fig. 5 -1) under the fuel tank.
  4. Disconnect the Bypass Fuel Pressure Switch (Fig. 6 - 1) to see if it is faulty. If so, replace the switch and fuel filter.
  5. Confirm the fuel tank has fuel.

Fuel Tank Underside Emergency Valve Assemby Figure 5WARNING! Do not operate the truck with the Fuel Pressure Switch disconnected!

The fuel pump’s hydraulic motor comes on but will not turn the fuel pump?

  1. Engage the fuel pump and confirm that the rubber gear coupling (Fig. 6 - 2) between the fuel pump and the hydraulic motor is rotating. If the coupler is broken, check if the fuel pump has locked up. If the pump rotates freely replace the coupler. If not, replace the pump.
  2. Verify that the set screws on the metal couplers that house the rubber gear coupler are not loose.Fuel Pump Hatch Compartment Figure 6

Why is the fuel pump surging when the air compressor comes on?

  1. Check the hydraulic reservoir to see if it is low. If not, contact our Service Manager at Niece Equipment.
  2. Verify that the operator has not adjusted the hydraulic flow on the fuel pump or air compressor. 

Keeping your fuel and lube trucks operating efficiently means keeping your fleet of constructions vehicles operating even better.  Remember to always refer back to the Niece Equipment Operations, Maintenance, Technical Data, Parts List Manual for additional troubleshooting tips and part details. If you need further information and/or assistance please contact us Toll Free at (800) 252-6618 or email at Or submit our contact form by clicking the button below. 

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Topics: fuel & lube trucks