How to Troubleshoot a Chevrolet Z71 Fuel System


Chevrolet's Z71 engine is used in its heavy-duty line of trucks like the Silverado, Avalanche and Tahoe. Any problems with this engine's fuel system can result in wasted fuel and increased pollution, or it could make the truck not run at all. If you are looking to check your Z71's fuel system for problems, you should mainly check the fuel pressure. Problems in the fuel pump, filter or pressure regulator can lead to problems here.

Things You'll Need

  • Fuel pressure gauge
  • Wrench
  • Turn the ignition key on with the windows up. Listen for a soft, brief whirring sound--it might lasts for just a second or two. If you hear this sound, it means the fuel pump is working. If you don't hear it on the inside, listen for it on the outside; remove the fuel filler cap, depress the spring-loaded door in the filler neck and have someone else turn on the ignition while you listen.

  • If you don't hear the fuel pump, check the fuel pump fuse and relay within which are located in the engine fuse box. Check the wiring to the fuel pump if the fuse and relay are good. If the wiring is good also, you likely have a bad fuel pump.

  • Have the Powertrain Control Module (PCM) checked if the fuel pump runs continuously while the ignition key is on. The PCM should only be looked over by a qualified service or repair shop.

  • Relieve the pressure from the fuel system before proceeding further. Unscrew the fuel cap and remove the fuel pump relay from the fuse box. Crank the engine for a few seconds and wait for it to start and quickly stall (or it might not start at all).

  • Connect a fuel pressure gauge to the fuel pressure test port on the fuel supply rail (remove the port's cap). The gauge needs an adapter that will connect to the test port's Schrader valve.

  • Turn the ignition key to the "On" position. Check the pressure on the gauge. The pressure should be 60 to 66 pounds per square inch for a V6 engine. On V8 engines, the pressure should be 48 to 54 psi for engines that take E-85 ethanol gas and 55 to 62 for the others.

  • Check for restrictions in the fuel system, including the fuel filter and inlet strainer, if the pressure is lower than it should be. If there are no restrictions, you likely have a bad fuel pressure regulator or fuel pump. Replace the pressure regulator if the pressure is higher than specified.

  • Disconnect and inspect all lines in the fuel system, including the fuel supply and return lines and the Evaporative Emission Control vapor lines. Replace any lines that are dry, cracked or leaking. Look for any dirt in the lines and blow it out with compressed air.

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