Cold start

Discussion in '2005+ Mustang GT 4.6L Tech' started by Jcg_3v94, Feb 10, 2020.

  1. Jcg_3v94

    Jcg_3v94 Junior Member

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    I have an 07 mustang gt with 112k. About 2 months ago I noticed on every first cold start my car starts very sluggish, eventually it would just crank but no start at all. I have to pump the gas peddle while cranking and eventually it starts. Other times it does start on its own, barely but it does. Noticed white/blue smoke. After the first cold start the car starts super strong, no cel, no power loss, no bog. I did an engine block test and it passed. Any ideas? Thank you.


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  2. Dino Dino Bambino

    Dino Dino Bambino I have a red car

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    Your throttle body could be dirty. If there are enough dirt deposits to partially obstruct the small opening between the blades and the bores, insufficient air will enter the intake manifold effectively choking the engine. The exhaust smoke is caused by unburnt fuel.
    Also make sure that the CAI tube has a good airtight seal to the TB so that unmetered air doesn't get into the engine.
     
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  3. Jcg_3v94

    Jcg_3v94 Junior Member

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    Ill definitely remove my throttle body and clean it up.


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  4. Laga

    Laga Member

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    Possible dirty fuel filter. How old is existing?
     
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  5. Jcg_3v94

    Jcg_3v94 Junior Member

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    About 2 years old


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  6. Laga

    Laga Member

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    That’s not that old.
     
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  7. Jcg_3v94

    Jcg_3v94 Junior Member

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    Yea its been about 8k mikes with it on


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  8. GlassTop09

    GlassTop09 Member

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    Sounds like the check valve in your fuel pump is leaking off overnight. Next time cycle key on w/o starting engine a couple times before starting to reload fuel rail pressure then start it....if it starts normally then you’ll verify this. If you have a scan tool you can monitor the FRP after shut down to see if check valve is leaking off fuel rail pressure. Or you may have a fuel injector leaking fuel rail pressure off as well. Check for this after you check your TB.
     
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  9. Jcg_3v94

    Jcg_3v94 Junior Member

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    Forgot to mention i have the duel gt500 fuel pump set up. But yea ill check that right now. How many times should i prime it?


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  10. GlassTop09

    GlassTop09 Member

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    Just cycle KOEO 2-3 times listening for the pumps to start up then stop when the fuel rails are pressured up then start car to see if it starts right up....if it does then you know. Another way to confirm check valve leakoff is to hook up scan tool, pull fuse #41 in BEC (kills power to fuel pump relay to kill power to fuel pumps FPCM's & injectors) then go KOEO then check the live FRP PID for a reading before starting the car....if the reading is 0 then you know either the check valve(s) is\are bad or at least 1 injector (or more) is\are leaking. Then you'd have to distinguish between the 2 to find the actual culprit.

    Note: Don't forget to put the fuse back in after you're done...…...won't start unless you do...……..

    PS--My car does this as well but I know my fuel pump's check valve leaks off slowly, it's fine until it is down overnight as I have already done what I have suggested for you to do to find out.
    If you're familiar w\ working on these engines you can remove the fuel rails w\ the injectors still installed in the rails w\ fuel line still attached to the rails then turn KOEO w\ fuse #41 still in then visually inspect the injectors to see if 1 or more are leaking or not to make final determination.
    Then you can decide what to do about it. With my situation I just remember to KOEO for a few seconds to allow the fuel rails to reload before hitting the starter on initial cold start as my fuel pump is the OEM unit that came w\ car off the line so has over 153,000+ mi on it, but even doing this it will still on occasion stumble a little while starting up due to vapor buildup in fuel rails displacing fuel due to the pressure dropping (this will happen sometimes while all is cooling down, depending on how fast the leak bleeds down).
     
    Last edited: Feb 13, 2020 at 6:22 PM
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  11. RED09GT

    RED09GT Senior Member S197 Team Member

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    How are the plugs?
     
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  12. Jcg_3v94

    Jcg_3v94 Junior Member

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    Plugs are good


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  13. Jcg_3v94

    Jcg_3v94 Junior Member

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    So i tried the koeo about 4 times, it actually started way better than other times, a bit sluggish but way better.


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  14. GlassTop09

    GlassTop09 Member

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    Ok, then if you have a scan tool available I would follow up w\ a FRP check after an overnight sitting before startup to verify that the FRP is low\0. Remember to pull fuse #41 to kill the pumps\injectors before going KOEO to check FRP thru scan tool.....should find FRP low (below 10 psi) or at 0 psi (you're running a GT500 dual fuel pump hat w\ 2 FPCM's so still return less fuel system so normal FRP should be around 30 psi w\ engine not running (no vacuum reference on FPS) to verify what you've reported. If FRP is tested good then your issue lies elsewhere...……...most likely getting cavitation from a fuel pump(s) or vapor lock from excessive heat on gas feed line causing gas bubbles in fuel line which will cause the same stuff when bubbles gather\settle in fuel rails as the gas bubbles will have to be bled out thru the injectors causing poor fuel delivery thus bad starting until bled out.

    If you get verification of excessive FRP leak off then you have 3 choices:
    1. Live w\ it
    2. Check injectors for leak off to determine actual cause...if injectors are sound then it is leaking check valve(s) since you have 2 pumps so 1 or both are leaking back. If injectors then will need to replace the leaking ones then retest.
    3. If bad check valve(s) but both pumps are good then install a single aftermarket inline fuel check valve in fuel line after fuel pump hat to resolve the issue. This should have been done in the 1st place by Ford IMHO & placed at same area w\ the fuel filter for easy access.

    Hope this helps.
     
    Last edited: Feb 14, 2020 at 12:13 AM