I Need Your Help With A Pcm Problem, Wmburns?

Discussion in 'SN95 V6 Mustang Tech' started by Rick.B, Jun 13, 2014.


  1. Rick.B

    Rick.B New Member

    Joined:
    Jun 13, 2014
    Messages:
    8
    Likes Received:
    0
    Trophy Points:
    1
    2003 V6 mustang. Here is the back story, I bought it from a guy who was having PATS issues a month or so ago. He finally gave up and I bought it now here I am. It is not a pats issue because I sent the PCM to have it turned off in a tune. What happens is that it wont start but it is random. it started 10 times in a row last night and the would not start. It will probably start at some point today. when it wont start, you know its not going to because the fan comes on with the key. That means no communication from pcm right? As far as I can tell, I have the power to the pins at the pcm connector (55, 71,97). Also with the key on I checked a couple sensors and I have 5 volts. The guy that had the car had a new pcm installed so I don't think it is that. For some reason the pcm just decides not to power up at times. the cluster goes to dashes when this happens. WMBURNS or anyone else have any ideas on where I can start?
     
    #1
  2. wmburns

    wmburns SN Certified Technician

    Joined:
    Aug 14, 2009
    Messages:
    3,172
    Likes Received:
    58
    Trophy Points:
    69
    Location:
    Houston Texas
    Let's start with an "add a fuse" in BJB fuse F2.2. Use a VOM with a good set of clips to monitor power at F2.2 and a known good ground. What we are looking for is to see if power drops when the problem occurs.
     
    #2
  3. Rick.B

    Rick.B New Member

    Joined:
    Jun 13, 2014
    Messages:
    8
    Likes Received:
    0
    Trophy Points:
    1
    ok , wouldn't you know it, the car fired right up today. it has not fired in 2 days and now that I have a test to run, it starts. no worries tho, at some point over the weekend, it will crap out. it does it pretty regularly
     
    #3
  4. Rick.B

    Rick.B New Member

    Joined:
    Jun 13, 2014
    Messages:
    8
    Likes Received:
    0
    Trophy Points:
    1
    ok, got a chance to check it today when it did this, turn key on, fan comes on, cluster goes ------------ and I still have 12 volts at f2.2
    looked the same as when it was starting.
     
    #4
  5. wmburns

    wmburns SN Certified Technician

    Joined:
    Aug 14, 2009
    Messages:
    3,172
    Likes Received:
    58
    Trophy Points:
    69
    Location:
    Houston Texas
    The fact that power never drops to F2.2 proves the ignition switch and CCRM. So we can look else where for the problem.

    What about the condition of the battery terminals and grounds around the radiator core support? Are they clean and tight? Do all of the ground wires to the battery making a solid connection?

    Has the area around the PCM been inspected for signs of water or rodent activity?

    Disconnect the battery positive. Remove the PCM. Make note of the condition of the Pins. Any bent/pushed pins? Any corrosion present? Inspect the PCM print circuit board itself. Look for signs of burning. Look for any after market add on Chips installed in the external socket.

    Measure the resistance from PCM pin # 25, 51 ,76, 77, 103 back to battery negative. The wire colors should be black or black with white strip. Be sure to use a fresh battery in the VOM and zero the meter before using. Be careful probing the PCM body connector to not bend any pins. The resistance values should be very low.

    Do you have access to an ODB2 scanner? It may prove to save you a ton of time.
     
    #5
  6. Rick.B

    Rick.B New Member

    Joined:
    Jun 13, 2014
    Messages:
    8
    Likes Received:
    0
    Trophy Points:
    1
    1. battery terminals are all new, clean and tight. grounds on cores support are clean and tight. I ground away any paint that was on the core support just to be sure.

    2. no signs of water or rodents around pcm kick panel area.

    3. pcm pins are good, no bends, no corrosion. new pcm that the previous owner installed trying to fix this problem. pcm works fine on bench. no chips installed.

    Will do the resistance test tomorrow evening. had to work late last night and again tonight.
    Also, yes I have a scanner. I will get codes next time it starts. Scanner wont connect during the times it wont start.
     
    #6
  7. Rick.B

    Rick.B New Member

    Joined:
    Jun 13, 2014
    Messages:
    8
    Likes Received:
    0
    Trophy Points:
    1
    I think you may be on to something and I am ready to bust open that pcm. I think it may be bad even tho the po just changed it. I talk to this kids dad this morning and he said that it didn't start this random no start until after the pcm was swapped back in march. the kid told me that is why it was swapped but dad says he is wrong.
     
    #7
  8. Rick.B

    Rick.B New Member

    Joined:
    Jun 13, 2014
    Messages:
    8
    Likes Received:
    0
    Trophy Points:
    1
    mr burns, I think I have somewhat confirmed that even tho this pcm is new, it is bad. I made a bench harness and got another pcm from the junkyard. when I plug in the pcm that is in play when this happens, I get no link to my code reader but when I plug in the junkyard pcm, I get codes.
     
    #8
  9. Rick.B

    Rick.B New Member

    Joined:
    Jun 13, 2014
    Messages:
    8
    Likes Received:
    0
    Trophy Points:
    1
    also, I plugged in the junkyard ecm and turned the key on, my cluster responds as it should and the fan stayed off as it should. this pcm is bad.
     
    #9
  10. Rick.B

    Rick.B New Member

    Joined:
    Jun 13, 2014
    Messages:
    8
    Likes Received:
    0
    Trophy Points:
    1
    i finally got the suspect pcm to boot up and it had 1 code.
    code P0193 - fuel rail pressure sensor circuit high.
     
    #10

Share This Page