2008 GT M/T not starting

Discussion in '2005+ Mustang GT 4.6L Tech' started by Jello_08GT, Sep 20, 2020.

  1. Jello_08GT

    Jello_08GT Junior Member

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    I measured for flow when i turn key in start position and i get nothing in the clutch safety switch.
    If i short the wires manually PIN 30 and 87 the starter spins, so I know that's good.
    PIN 85 is the one that is never coming alive, that power comes from the clutch switch and i think the clutch safety never gets power because the PCM never sends a start enable signal
     
  2. Jello_08GT

    Jello_08GT Junior Member

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    Thank you for that , i didn't know about such manual , I will do all the testing and hopefully i don't have a bad PCM , I will clean all grounds even if they look okay. Thanks again
     
  3. Jello_08GT

    Jello_08GT Junior Member

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    [​IMG]
    So i went home and cleaned the grounds for the PCM, and boom it started right away....i crank about 6-7 times....put everything together since my interior was half apart, my gf comes home and show her that is fixed and it doesn't start anymore. I remove the ground and put them back and it starts again wtf! I know they are touching bare metal and shouldn't have any issues, I still don't know if when I'm driving and i start somewhere i need to pull out my 10mm and remove the cable and put it back to make my car start, maybe when I do that it resets the pcm ? I hope is not a pcm going bad at this point :(

    https://ibb.co/jTbS07X[​IMG]
     
  4. Laga

    Laga Member

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    Since moving the wires made the car start, there could be corrosion between the wire and eye terminal. Cut them off and replace with new before diving into PCM. Check for breaks or shorts in wire also.
     
  5. Jello_08GT

    Jello_08GT Junior Member

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    that was my next thing, how can I check for shorts ?
     
  6. DieHarder

    DieHarder Member

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    Suggest following Laga's advice and check/replace eye terminals that look oxidized. Unlikely that your PCM is at fault. IMHO you're seeing wiring/loss of ground failures. Like all electrical systems electricity has to have a path to flow. Ford puts grounds all over the car; with good reason.

    Since symptoms changed when you cleaned a few grounds/moved wiring it's likely corrosion within the wiring/at the ends of the wiring where it's exposed or bad (corroded) grounds are the issue. There may also be breaks in wiring but unlikely if nothing was touched. If you haven't already I would remove and clean the starter positive and ground wiring in addition to the others you've cleaned with a wire brush. Then I would do continuity checks from ground wires to the negative terminal and on the wires themselves from end to end to ensure they're good. You should have less than an ohm (like a tenth of an ohm) on most wires.

    A quick fix you can do to improve grounding for the engine is to add an 04 gauge copper stranded cable (with eyelets on the end) and run it from the passenger strut tower to a bolt on the engine. I ran mine from the passenger strut tower to a bolt on the alternator. (That solved a low voltage output reading I was experiencing with my expensive DOB alternator. Never a problem since). If you don't have a crimper that size a hammer & punch will do the job for crimping the eye terminals. That should help improve starting if the problem is poor grounding. You can find the cable and eye terminals at any hardware store. I would also check the fusible link (bend it to see if your symptoms change when trying to start the engine). If it does you'll likely need to replace it. I have heard of them corroding internally.

    Additionally, I would look at disconnecting/cleaning/reconnecting every single ground wire in the engine bay and a few in the passenger compartment for the SJB.
     
  7. DieHarder

    DieHarder Member

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    Just as a test you can quickly determine if you have an engine ground issue using a jumper cable. Connect one end to the passenger strut tower ground lug and the other to a bolt on the engine. If the engine starts reliably you have found your problem. Now it's simply a matter of determining which ground/s are at fault. A quick work around is adding the extra ground cable. Not ideal but if nothing else works it'll do the job in the interim until you can nail down what/where the problem is.
     
  8. Jello_08GT

    Jello_08GT Junior Member

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    Thank you, I bought some eyed terminals and plan on replacing once I get home and check for ohm resistance as well :) , sorry the stupid question but what's a fusible link ? is that the premade wire i just cleaned ?
     
  9. Jello_08GT

    Jello_08GT Junior Member

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    what's specs on that fusible link ? so i can replace it
     
  10. DieHarder

    DieHarder Member

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    Fusible link is in the secondary power cable that runs from B+ to the alternator (under blue plastic if your cables are stok). Not needed for cranking (primary purpose is recharging the battery). My bad to mention it. More important right now to check main battery cable to starter & main grounds for the electrical system to ensure you have all conditions needed to crank the starter. I would also continue to chase that clutch position switch issue until you can determine it's operating properly. If cleaning/redoing the grounds doesn't fix the cranking/starting issue go through the trouble shooting procedure in the manual to nail it down to a particular electrical subsystem and we'll go from there.
     
  11. gbstang

    gbstang Junior Member

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    I would suspect a relay...
     
  12. Jello_08GT

    Jello_08GT Junior Member

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    Cleaned all grounds , did a big 3 upgrade with extra ground from battery to chassis and ground to engine block, I went to work , lunch, came back home and parked my car, later had to move my car and it doesn't start, unscrew pcm ground and reseat, starts again :(
     
  13. DieHarder

    DieHarder Member

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    After eliminating everything else it should be obvious what the problem is....

    Apparently you're chasing the worst kind of electrical issue... An intermittent. Could be anything. Relay, open wire that when flexed makes contact and works for awhile or an intermittent short. If moving/reseating the PCM ground always allows the car to start I would trace that wiring (test continuity end to end) and try jumping around it to see if that takes care of your symptoms. If it does determine if the wiring is at fault, connectors, eye terminals, etc. (I still have a hard time believing the PCM could be intermittently working. To be sure you'd likely have to take it to a dealer to run tests/check for any codes).

    If symptoms do not improve I would follow the trouble-shooting procedure again in the manual and look at all components that are supposed to change state during the starting cycle (switches, relays, etc). Is everything (voltages, grounds) available where they're supposed to be for the car to start? Does the Clutch Position Switch work yet? Also look at the SJB circuit.

    This might be repeating the obvious but in case it helps it could be worth another look.

    Pin Point Test A: The Engine Does Not Crank And the Relay Does Not Click:

    Normal Operation: In normal operation, voltage from the BEC is supplied to the ignition switch through circuit 1050 (LG/PK). When the key is turned to start that voltage is supplied through circuit 1522 (DG) to the SJB.

    For a manual (when the key is turned) voltage from the SJB runs to the CPP (Clutch Pedal Position) switch via circuit 32 (RD/LB). Then when the clutch pedal is depressed, that CPP voltage is routed to the starter relay coil in the BEC. At the same time ground is supplied from the PCM through circuit 1419 (LG/YE). (That should energize the starter relay).

    When the starter relay is energized, voltage supplied to the relay switch is sent to the starter motor solenoid through circuit 113 (YE/LB). B+ is present at the starter through circuit 2037 (RD) at all times.
    End

    If relays are not closing and/or voltages and grounds are not present where/when they're supposed to be you have to determine why (open, no ground, relay not completing the circuit, short, etc). Easy to test the relay using another of the same type. For SA, even components you've already replaced can be compromised. Should be fairly straight forward to test for grounds and voltages at the BEC, SJB & CPP.

    Additionally, might help to search no start conditions online for similar problems, what failed and fixes/pointers to nail down what went wrong.

    If nothing pans out could be worth an hour of troubleshooting at the dealer. I know not ideal and even in my own case all the dealer did was help me eliminate a couple of items; not fix what my problem was.
     
  14. Juice

    Juice forum member

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    I would still monitor the pcm live data just to see why the pcm does not allow start. There are the clutch position switches, start request, etc.
    Note all those inputs and outputs when it does not start.
    Do the pcm reset to get it.to start, and monitor again to see what is (if anything) is different.
    I find the pinpoint tests can go down thw wrong path at times.
     
  15. Jello_08GT

    Jello_08GT Junior Member

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    Exactly what I'm planning on doing , got the ELM with usb and yesterday got it to work on my mac with a Virtual machine , i see that when my car "works" the clutch Pedal Position gets a pressed/depressed reading, waiting for car to not start again and check codes, it is tricky since it's intermittent and have to check it on the spot !
     
  16. Jello_08GT

    Jello_08GT Junior Member

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    I might have to do all of that, take SJB , PCM, BEC all out and check for corrosion and continuity at all spots, going to be a crazy chase , and I appreciate all the help you are giving me :)
     
  17. DieHarder

    DieHarder Member

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  18. DieHarder

    DieHarder Member

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    Agree w/Juice. Need to monitor PCM output to determine if outputs are present when the car doesn't start. One of the checks recommended in the videos below is swapping the PCM power diode with the one for the aircond. See if pulling/swapping/reseating has any affect. The other video goes through the troubleshooting process in some detail for the starting circuit and nails that problem down to grounds and a CPP switch adjustment.

    Here's both videos for reference:

    (PCM Diode bad)

    (Bad grounds & CPP Switch issue)
     
    09brian0 likes this.
  19. DieHarder

    DieHarder Member

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    Oops, sorry about the first one, you've already seen it. My bad...
    If you don't already have one a relay tester (4 post) may come in handy to help verify relay operation/voltages.
     
  20. DieHarder

    DieHarder Member

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    A couple more videos that may help.

    (Mustang starter circuit explained)
    (PCM power relay corrosion failure)
     
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