Junkyardjeff

My 88 bronco has a fuel issue,its hard to start after sitting a few days and starving for fuel at highway speeds. I still have to check the fuel pressure but how does one know what pump is bad.

Good old Bill

Assuming your full sized Bronco is similiar to my Bronco II. There is a high pressure pump located on the frame under drivers seat, and a low pressure pump mounted in the tank. The high pressure pump provides the pressure at the fuel rail necessary for the engine to run and is tested with a gauge, 30-40 psi is the normal readings. Check for power and ground during the 2-3 second run time upon initial key on activation. It provides all the pressure, as previously stated, but has very poor suction abilities, hence the tank mounted low pressure pump. It keeps the high pressure pump primed and is tested the same way as the high pressure pump.

This system was replaced in later years with the tank mounted high pressure pump system that is still presently used.

If you haven't replaced your fuel filter, you might consider that. I change my filter once a year on all my vehicles.

Junkyardjeff

I can hear the front pump so its getting power but how does one tell if the rear pump is not pumping enough fuel,I will have someone help me to see if I can hear the rear pump working.

Junkyardjeff

Checked the pressure and with key on and motor off it gets to about 50 and with motor running its about 38,disconnect the regulator and goes to 48 so I think the pressure is enough but when the key is turned off the pressure drops to zero quickly. I had the neighbor cycle the key and could not hear the rear pump and only the fuel coming back in the tank from the return line,I have no manuals for the bronco and does one fuel pump relay supply power for both pumps and if its the rear pump that is bad can I install a newer high pressure pump and cut off power to the front pump.