99 Mustang GT fuel pump issue


New Member
Jul 2, 2022
This Mustang was my father's and I gave it to my brother when he passed. My brother parked it and left it to rot for about 3 years. He is not mechanically inclined and doesn't have the tools or money to work on it. Needless to say I took it back. When I went to work on it the ignition switch was jammed, I fixed that. It had a no crank no start, fixed the no crank, but still no start. So I towed it home. The issue I have is I'm not getting gas to the fuel rails. When I turn the key to the run position I can hear the pump click but it does not run. The steps I've taken so far.

  • Checked 20amp fuse for pump under the hood which is fine.
  • Checked the Schrader valve on the rail no gas
  • Installed New Battery and new terminals. Double checked that no ground wires were missed.
  • Checked inertia switch in the trunk, reset, and bypassed with a jumper. 12.8v in and out
  • Checked my voltage on pump harness at the rear of the car 12.3 volts while in the run position
  • Dropped the tank drained old gas and replaced the fuel pump.
  • Checked voltage on the pig tail that plugs directly into the pump getting 12.3 volts hitting the pump while in the run position
  • Replaced the FPDM
  • Replaced the fuel pressure sensor
  • Sprayed starter fluid into the intake to confirm I have fire and the motor runs.
After I reassembled the pump, put the tank back up, and put 5 gallons of fresh gas in the tank I still have the same issue. If I lay under the tank and have someone turn the key I can hear the pump click but it does not run. The odd thing is if I disconnect the FPDM and jump out the harness the pump will run and I get fuel to the rails. I replaced the FPDM and still have the same issue, pump clicks but will not run. Checking the harness I am getting 12.8v on the constant from the inertia switch, the main ground is fine with a good connection. The only issue I cannot figure out is the pulsing ground to the pump. Everything I have seen says that I should see my 12v while in the run position which should drop to 0v while cranking and return to 12v when not cranking. I have 12.8 in the run position 10.2 while cranking and returns to 12.8 after cranking. Im wondering if I am having a grounding issue on the harness from the FPDM to the pump housing or in the housing itself.

Also other oddities and info if it helps. The odometer does not show the milage just ----------- and while troubleshooting the odometer is now blank. The theft light does not come on now. The radio when powered on I can hear noise in the speakers but it does not light up. Same with the CD changer if I hit eject it attempts to eject a disk but does not light up. The car does run, I shot some starter fluid in her and she fires right up. Any ideas would help.
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