Fuel Pump not running, electrical diagnosis...

a_bartle

New Member
Sep 5, 2018
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Peck, MI
I tripped on a barn (garage) find, a 1998 Mustang convertible with only 7,500 miles on the odometer. Owner died and his wife just kept the car in the garage. Had not been started or driven in at least 6 years. Car has a 3.8L V6 engine. I made a deal with her to buy the car, pulled the drive shaft and used a dolly to bring it home.

First thing I did was install a new battery, turned the key and I did NOT hear a fuel pump running (also note, the fuel gauge sits a ¾ and does not move). I checked the fuse under the hood, it was good, then I check the inertia cut-off switch in the trunk, also good (I actually tripped it and re-set it to make sure). I pulled apart the electrical connector in the rear behind the fuel tank, there are 4 pins, one had 12 volts, one had I think 7, the other two nothing. Is this correct?? (I saw a youtube video that implied I should have voltage on all 4?)

As far as a fuel pump relay, I learned that it is housed in Constant Control Relay Module (CCRM). I pulled the passenger side wheel & tire liner to expose it and pulled it out (looks like new, and my research says they are pretty reliable). I did check for voltage going to it (pin 5) and it was 12 V, but I’m not sure if there is a way to actually check the CCRM itself?

I did siphon the gas out through an upper vent tube opening in the tank and I’ve got the fuel filter off, ready for a replacement. Before I install the filter, I was planning on putting a hose on that fitting to drain the rest of the fuel out (if there is any left) once I get the fuel pump to run.

So what’s next to check to determine if the fuel pump is trash or it’s an electrical problem. Again, not sure if the electrical connector in the rear is suppose to have voltage on all 4 pins?

Thanks for any help you can offer!
Art
 
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wmburns

SN Certified Technician
Aug 14, 2009
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Test for +12 volts of key on power at the trunk mounted IFS switch using a KNOWN good ground. Best to use a test light that will "load" the circuit. The results of this one test will set the focus for the future tests. Be sure to not cut any corners.

IF there is power at the trunk mounted IFS switch then trouble shoot down stream towards the fuel pump.

IF no power at the trunk mounted IFS switch there's an electrical problem upstream. More tests are needed. Possible trouble examples:
  • Blown fuse
  • CCRM
  • bad ignition switch
  • bad CCRM ground
  • wiring fault

Note, if no power at the trunk mounted IFS switch it is possible to force feed +12 volts down to the fuel pump in order to test the fuel pump. Recommend doing this only if there is no power at the IFS switch.

The 1998 Mustang GT is an odd year in that there's a two speed fuel pump relay that will need to be trouble shot if there's no power at the IFS switch.
 
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