Why is the lift pump not working on my GMC 6.5L diesel?
Why is the lift pump not working on my GMC 6.5L diesel? Another problem associated with the OPS is that the lift pump is supposed to send fuel through the IP and back to the tank, helping to cool the IP and the FSD= fuel solenoid driver, the little black box mounted on the driver's side of the IP. This is basically the brain of the electronic IP. What causes a GMC 6.5L diesel to stop? The OPS (oil pressure switch) sends power to the fuel lift pump that is mounted on the driver's side fram rail underneath the cab....