Engine Codes And Electrical Problems Help!

Discussion in 'SN95 V6 Mustang Tech' started by NewEdgeSC, Sep 12, 2013.

  1. OK I have a 2000 Mustang v6 that I just completed an SC swap on. After I tuned the computer with my SCT I started noticing weird problems a couple days later. I have returned the computer to stock and still same issue. The speedometer jumps around and the car starts bucking and misfiring. I checked the codes and I got p0340 and p0721 which are codes for the cam sensor and speed sensor. Well I read that code p0340 is usually a bad alternator so I installed a new motorcraft one and still have the same problems. I am now thinking my pcm is bad because it is an intermittent problem.

    Any help with diagnosing these issues would be greatly appreciated.
  2. Well I see it's a total waste of time to ask for help on this site. I haven't found a decent mustang forum yet, this one is probably the worst.
  3. P0340 codes on a 96-04 Mustang should have the alternator checked for correct output and excessive AC ripple. A bad alternator diode will mess up the cam signal and confuse the PCM. This causes a false P0340 DTC. Being that you have changed the alternator and still have the code, have you investigated that the cam sensor might in fact be faulty?

    Rockauto.com sells the Output speed sensor (P0721) for $15 and the Cam sensor (P0340) for $15.

    For $30 in sensors, that's where I would start before buying a new PCM.