Electrical Key On, Key Off My Son....

Discussion in 'SN95 4.6L Mustang Tech' started by Nateg313, May 14, 2014.

  1. Right now as the car sits I have a crank no start issue. I have checked grounds, fuses , ccrm connector and wiring and the module ( opened it up for a visual)

    With communication I have power to the IFS and also the fuel pump driver module seems to be in working order as well...

    With the key initially turned to the on position I can hear the ccrm relays click. Next one of two things happen 1) it clicks again and the fan turns on, and I have no communication with the PCM (cluster is all dashes)
    2) it only clicks once and the fan stays off and I have communication with the processor.

    Today a buddy of mine came by to see if he saw anything I was missing. We decided to supply 12volts and ground to the pump to verify operation and nothing. So I believe I have two issues. 1) intermittent no communication with the processor 2) fuel pump has died.
    My next step is to replace the pump and see if the car runs when I do have communication. However I need to figure out exactly why I don't have communication with the processor to completely remedy the issue.

    Does anyone have any suggestions on what to look for in the system ?
    I have electrical schematics and a multi meter, but no manual for pinpoint tests which I rely on for these type of issues or situations.

    If anyone could help me out that would be awesome, and I will make sure to post results so if anyone has the same issue they can read an entire thread without getting to the end with no solution to the issue.

  2. The clicking at the CCRM could be caused by a bad CCRM ground. Normally I would say to check all of the grounds around the radiator core support. Since you have stated that the grounds are OK, we will move forward from there.

    Might be handy to mention the model year of your Mustang. Why is this important? Because if this is a return-less fuel system, then attempting to force the fuel pump to run by injecting power at the IFS switch won't force the fuel pump to run.

    I'm going to assume 1999-2004.

    In that same vein, need to know the model year to tell you which fuses to monitor. Monitor power in fuse F2.34 and F2.2 with the key on. An "add a fuse" is one easy way to do this.

    If power drops on F2.34 the thought should be bad ignition switch.

    Where as if the power is stable on F2.34 but drops at F2.2 the thought should be a bad CCRM or bad CCRM ground.

    Also monitor power at the trunk mounted IFS switch with the key on.

    IF there is no power the problem is upstream (CCRM, fuse, ignition switch, ground, PCM)

    IF there is power and the fuel pump does not run, then the problem is down stream (FPDM, Fuel pump, PCM, wiring).

    If ask to handicap this thread, my guess is that the ignition switch is bad. That explains why it works sometimes and not others.

    Other possible causes are weak PCM/CCRM grounds back to battery negative.
    #2 wmburns, May 15, 2014
    Last edited: May 20, 2014
  3. It's a 2000 sorry, I got ahead of myself. I have not had any time to monitor the fuses as you suggested but I will let you know the outcome when I do. Thanks for the reply, I will be upgrading my fuel pump this weekend and I hope to have her running.