car won't stay running for longer than about 30 minutes

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  1. #1
    Senior Member Array P49Y-CY's Avatar
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    Default car won't stay running for longer than about 30 minutes

    was wondering if anyone has any suggestions on what i should do next.

    2004 cobra, 126k miles, daily driven, mostly stock, 2.80 upper pulley car, ~450whp

    the car starts and runs for about 30 minutes, but then will stall out. it's almost like clockwork. the exhaust does smell rich (bassani catted-x) but it could just be my imagination because all the plugs look fine.

    i have two cobras so i have been able to swap out parts without spending too much money so far. i have changed every single part i can think of that might cause it to do this - all intake, spark, and fuel related parts such as the maf, air filter, iac, tb, tps, iav, cop's, plugs, frps, pcv valve, egr valve, injectors, fuel pumps, fuel filter, fprm, ccrm...

    to me the only thing that can possibly be left is a break in a wiring harness somewhere or the actual vehicle pcm/ecu.

    actually as i write this i realize i still haven't changed the oxygen sensors, but would that make any sense? because the car is up to regular operating temperature and idles there long before it stalls (cooling fan cycles on/off several times).

    i do not have the proper diagnostic tools to make a determination, but maybe i should start investing in some now that my car is getting older.

    thanks for any ideas

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  3. #2
    Senior Member Array dsg2003mach1's Avatar
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    Any chance your O2 sensor harness got swapped (at the front)? if so when it makes the open/closed loop switch it'll stall and die. It drove me nuts when my car did it post motor swap. If this might be possible get something that will log it and you'll see both front O2s go full rich, full lean and back and forth.

    are your fan speeds set to normal turn on temps? If they're set low maybe the car isnt actually making the closed/open switch for a bit triggering the whole backwards O2 situation or something else closed/open loop related

  4. #3
    Senior Member Array P49Y-CY's Avatar
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    Quote Originally Posted by dsg2003mach1 View Post
    Any chance your O2 sensor harness got swapped (at the front)? if so when it makes the open/closed loop switch it'll stall and die. It drove me nuts when my car did it post motor swap. If this might be possible get something that will log it and you'll see both front O2s go full rich, full lean and back and forth.

    are your fan speeds set to normal turn on temps? If they're set low maybe the car isnt actually making the closed/open switch for a bit triggering the whole backwards O2 situation or something else closed/open loop related
    the fans are set low for the 170 thernostat. i will bump them back up to closer to stock and give that a try, thanks for the suggestion. i will also check out the connections to the o2 sensors on the midpipe

    what is weird about it is that i hadn't made any changes to this car at all for at least a year and it was running fine. last thing i did was change the oil about two weeks before this problem started, lol

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  6. #4
    Senior Member Array dsg2003mach1's Avatar
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    Quote Originally Posted by P49Y-CY View Post
    the fans are set low for the 170 thernostat. i will bump them back up to closer to stock and give that a try, thanks for the suggestion. i will also check out the connections to the o2 sensors on the midpipe

    what is weird about it is that i hadn't made any changes to this car at all for at least a year and it was running fine. last thing i did was change the oil about two weeks before this problem started, lol
    if it was running fine before and nothing was done differently then the harness isnt backwards. Theres no need to change your fan temps I was just saying you can't use that as an indicator of closed vs open loop.

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    Senior Member Array P49Y-CY's Avatar
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    question about this even though the title of the thread is no longer accurate.

    for about the past month or so the car won't start at all (no fuel pressure). it appears that the pcm is not sending the duty-cycle signal to the fpdm to run the pumps. the pumps prime normally with key on, but engine won't start. the engine starts right up if i bypass the pcm by jumpering the terminals at the fpdm connector, sending power and full ground directly to the pumps.

    i bought the ford wiring manual for this car and i've tested every wire in the vehicle related to fuel delivery, and they all have continuity. i again tried a known-good fpdm, just to make sure. and i have returned the tune back to stock.

    so my conclusion is that the fpdm must not be getting the signal from the pcm to drive the pumps.

    my question is what are the drawbacks of, if any, and for how long am i able to bypass this pcm to keep the pumps running? thx

  8. #6

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    Chris,

    If the system is a return style system the answer is you can run the pumps continuously w/o problem. If the system is a returnless system you can not, even for brief periods of time. The reason is that a returnless system will continuously vary pump speed to accomodate the engine's appetite for fuel. When the appetite for fuel is low and pump speed is high a severe over pressure / over rich condition will occur.

    If you are using a custom tune, I suspect something in the tune may have changed that is precipitating the problem. The fix could be as straightforward as just refreshing the ECU with the last tune. If you are using an OEM tune then I would be suspicious of an electrical component failure within the ECU which would require ECU replacement.


    Ed

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    Senior Member Array P49Y-CY's Avatar
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    okay thanks for the heads up, ed. i wouldn't want to do any damage unnecessarily.

    looks like i might be bringing this ford back to the same dealership for the first time since i purchased it from them over 15 years ago (which isn't really too bad a deal when you think about it). ecu replacement programming looks like it might be well outside my diy capabiltiies.
    Last edited by P49Y-CY; 01-17-2020 at 07:29 PM.

  10. #8

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    Quote Originally Posted by P49Y-CY View Post
    okay thanks for the heads up, ed. i wouldn't want to do any damage unnecessarily.

    looks like i might be bringing this ford back to the same dealership for the first time since i purchased it from them over 15 years ago (which isn't really too bad a deal when you think about it). but ecu replacement programming looks like it might be well outside my diy capabiltiies.

    The only reason to re-flash the ECU, Chris, would be if you modified the OEM tune. If you didn't then the problem sounds like a component failure in the ECU and that is definitely a dealership visit. Someone told me a year or so ago that Ford no longer offers ECU's for the 03/04 Terminators.

    If that is true and you can not find one, I have a brand new unused ECU from Steve when he was at Tousley. He sold it to me at the then low discount prices they used to be able to offer. If you need one I'll give it you for the same price I paid for it — which should be decidedly less than you can buy it for from any dealer today.

    Hopefully it will be something simple and inexpensive.


    Ed

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    Quote Originally Posted by eschaider View Post
    The only reason to re-flash the ECU, Chris, would be if you modified the OEM tune. If you didn't then the problem sounds like a component failure in the ECU and that is definitely a dealership visit. Someone told me a year or so ago that Ford no longer offers ECU's for the 03/04 Terminators.

    If that is true and you can not find one, I have a brand new unused ECU from Steve when he was at Tousley. He sold it to me at the then low discount prices they used to be able to offer. If you need one I'll give it you for the same price I paid for it — which should be decidedly less than you can buy it for from any dealer today.

    Hopefully it will be something simple and inexpensive.


    Ed
    hey thanks very much, ed. that is very nice of you to offer and i appreciate it. i will send you a pm. cheers

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