Vehicle: 2016 Chevy Silverado 1500, 4WD, V8-5.3L, Automatic Transmission/Transaxle

Mileage: 198,947 miles

Problem: The owner of this Silverado dropped it off at the shop because the engine sometimes continued to run briefly after shutting the ignition off. The problem seemed to start after the in-tank fuel pump was replaced.

NOTE: To help eliminate an engine run-on issue, the ECM cuts off fuel to the fuel injectors when the following conditions are met. This helps protect the powertrain from damage and improve drivability:

• The ignition is off, preventing engine run-on.
• The ignition is on, but there is no ignition reference signal. This prevents flooding or backfiring.
• The engine speed is too high, above the red line.
• The vehicle speed is too high, above rated tire speed.
• This occurred during an extended, high-speed, closed throttle coast down, a condition to reduce emissions, increase engine braking, and improve fuel economy.
• During extended deceleration to prevent damage to the catalytic converter.

Case Details: After connecting a scan tool, the technician noted that both short- and long-term fuel trims were running -25 to -35 at idle on both banks. The fuel pressure from the in-tank low-pressure fuel pump was in the desired range (75 psi at idle), and the fuel alcohol level was 10%. The injector fuel cut was operating normally.

Fuel Pressure Specifications.

• Low-pressure pump - between 46–84 psi (320–580 kPa) with the fuel pump running 
• High-pressure pump - between 290 to 2,176 psi (2 to 15 MPa)

A call went out to ALLDATA Tech-Assist for some diagnostic advice. The consultant said that, based on the diagnostics done so far, it’s possible that the high-pressure fuel pump (HPFP) is leaking into the crankcase. He recommended removing the oil filler cap and smelling for fuel vapors coming from the crankcase. If so, confirm the problem by following these steps:

• Disconnect the dirty air side of the PCV system.
• Plug the vacuum supply.
• Start the engine and monitor the fuel trims in closed loop. 
  • If the fuel trims return to normal, this is a good indicator that the high-pressure fuel pump is leaking. 
  • If you end up replacing the HPFP, be sure to replace the engine oil and filter then reset the fuel trims. The technician noted a strong fuel smell from the crankcase, so he plugged off the PCV and checked the fuel trims. They both returned to normal.

Confirmed Repair: The technician replaced the HPFP, did a complete oil and filter change, then reset the fuel trims. Afte the repairs, the engine performed and shut down as designed. Fixed!