Hi, I have a 1999 Mustang GT that suddenly wont start. It's lower mileage with only 62,000 mi on it. Ran great the last time I drove it 3 months ago.
I cannot hear the fuel pump turn on like usual when I turn the key to RUN before Cranking. so assume its the pump or wiring or both. I say the wiring because mice have got into it and chewed into the wiring under the back seat and maybe other areas I haven't found yet. Sucks cause otherwise the caris was pristine until the mice destroyed it.
I have done some digging around on the web and found some schematics to help with testing but cannot find a description of how the pump is controlled. Looking at the schematics, it looks like once the ignition key is in the Run or Crank position, the fuel pump relay is energized in the CCRM and sends B+ on the Dark Green/Yellow wire to the inertia fuel cutoff switch and then to the FPDM on the Pink/Black wire. It looks like the FPDM then sends power to the fuel pump on the Brown/Pink wire.
I cannot however discern from the schematics how the PCM controls the pump which leads me to a few questions I was hoping someone would know.
1. Does the PCM shut power off to the fuel pump at the CCRM or the FPDM after the initial pump prime at startup? Think just turning the key to RUN but not Crank when pump runs for about 3 seconds then shuts off.
2. Since the fuel pump voltage is variable, what should I see for voltage on the Brown/Pink power wire to the pump?
3. The Brown/Pink pump power wire should only have voltage on it for a few seconds when turning the key to RUN without cranking the engine over. Correct?
4. Is the pump prime, RUN and duty cycle of the pump controlled on the power or ground circuit?
I ask these questions because I may have two issues here. I only did some limited testing so far but I found when back probing the Brown/Pink wire at the FPDM, it does not power up when I command the fuel pump on with my scan tool and the Pink/Black wire has power at all times when the key is in the RUN position. Commanding the pump on or off with the scan tool has no effect on the Pink/Black wire.
Lastly the car does have a code P1237 Fuel pump secondary circuit and I did try jumping the Pink/Black wire to the Brown/Pink Wire. I then checked and found I did have power on the Brown/Pink wire at the fuel pump harness connector under the rear bumper but the pump still didn't run.
I'm thinking one of the modules may be bad or the Pink/Black wire is shorted to voltage somewhere because of the mice and the pump is also bad. I think I can diagnose the module or wiring issue if I could understand how the circuit works to control the startup prime and variable voltage to the pump.
I cannot hear the fuel pump turn on like usual when I turn the key to RUN before Cranking. so assume its the pump or wiring or both. I say the wiring because mice have got into it and chewed into the wiring under the back seat and maybe other areas I haven't found yet. Sucks cause otherwise the car
I have done some digging around on the web and found some schematics to help with testing but cannot find a description of how the pump is controlled. Looking at the schematics, it looks like once the ignition key is in the Run or Crank position, the fuel pump relay is energized in the CCRM and sends B+ on the Dark Green/Yellow wire to the inertia fuel cutoff switch and then to the FPDM on the Pink/Black wire. It looks like the FPDM then sends power to the fuel pump on the Brown/Pink wire.
I cannot however discern from the schematics how the PCM controls the pump which leads me to a few questions I was hoping someone would know.
1. Does the PCM shut power off to the fuel pump at the CCRM or the FPDM after the initial pump prime at startup? Think just turning the key to RUN but not Crank when pump runs for about 3 seconds then shuts off.
2. Since the fuel pump voltage is variable, what should I see for voltage on the Brown/Pink power wire to the pump?
3. The Brown/Pink pump power wire should only have voltage on it for a few seconds when turning the key to RUN without cranking the engine over. Correct?
4. Is the pump prime, RUN and duty cycle of the pump controlled on the power or ground circuit?
I ask these questions because I may have two issues here. I only did some limited testing so far but I found when back probing the Brown/Pink wire at the FPDM, it does not power up when I command the fuel pump on with my scan tool and the Pink/Black wire has power at all times when the key is in the RUN position. Commanding the pump on or off with the scan tool has no effect on the Pink/Black wire.
Lastly the car does have a code P1237 Fuel pump secondary circuit and I did try jumping the Pink/Black wire to the Brown/Pink Wire. I then checked and found I did have power on the Brown/Pink wire at the fuel pump harness connector under the rear bumper but the pump still didn't run.
I'm thinking one of the modules may be bad or the Pink/Black wire is shorted to voltage somewhere because of the mice and the pump is also bad. I think I can diagnose the module or wiring issue if I could understand how the circuit works to control the startup prime and variable voltage to the pump.
