Cold start

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

  1. Jcg_3v94

    Jcg_3v94 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

    Age:
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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 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 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 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 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
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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 Member

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    Plugs are good


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  13. Jcg_3v94

    Jcg_3v94 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
  15. JeremyH

    JeremyH 3V Fuel Guru S197 Team Member

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    The pprv is not a check valve as it's more of a back flow valve it's not designed to hold pressure just volume in the line while relieving pressure. You would not want a true checkvalve anywhere in a returnless pulse modulated setup, will cause pressure issues when loading/unloading the fuel system. You can completely delete the pprv on the hat and not have these symptoms. Slower to prime sure but wont cause stumbling after start ups. It is more likely injector leak by like you mentioned. Engine off pressure should read factory 39psi delta. Wont read less unless there is vacuum on the frps ie around 30psi at idle.

    OP you mentioned it started few months ago and its colder time of year. Before your next cold start attempt unplug the maf. If the car starts fine with maf unplugged, no stumbling or hard to start, Then your tune/sensors are adding too much fuel at startup.
     
    Last edited: Feb 19, 2020
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  16. GlassTop09

    GlassTop09 Member

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    Hi JeremyH,
    You had me kinda confused w\ the "pprv" abbreviation but a quick search fixed my confusion so I stand corrected as I have always heard this referred to as a check valve (even heard this called a check valve while watching a Go Tech video this morning)....after checking up on what PPRV means now I can relate.....positive pressure relief valve....so I fully know\understand now what you're talking bout & it's relation to a returnless fuel system so you're also correct...a true 1-way check valve would be bad for this fuel system design (or really any fuel system design for that matter), especially if the fuel system is\gets hot....good way to blow a line apart downstream of the check valve or blow an injector out the rails due to potential over pressure from liquid expansion w\o no way to relieve the built up line pressure.

    Also read where folks do remove these for performance reasons (this is what you were referring to)....mostly manual trans vehicles to cure potential slow engine RPM\power recovery after throttle cycling during high RPM shifting from fuel delivery cut caused by PPRV's trapping fuel line pressure spikes thus fooling PCM's thru the FRP reading to slow down fuel pump DC output from throttle cycling APP signal 100%-0%-100% thus causing engine output to momentarily drop off until the PCM tells the FPDM to ramp it back up..... Good to know this as I do have a manual equipped car & do plan to run it at the track...…..good reason to install a WOT box to set up no-lift shifting instead of removing the PPRV since these are available now...….

    But those that do remove this PPRV are aware of the need to allow the fuel pumps more time to restore adequate fuel pressure to the line\rails prior to starting the car....and the potential issues that derive from it's removal.

    1 thing I can think of to do on a car that has this PPRV intentionally removed is to thoroughly insulate the fuel line\rails from excessive heat sources to prevent fuel vaporization which can cause poor starting among other things...…..just saying.....

    This PPRV isn't technically supposed to leak off any fuel pressure below it's rated relief pressure set generally speaking (to protect from fuel line\fuel rail ruptures from overpressure....the purpose of a relief valve)….it should hold fuel volume in the line as you have stated, but also to prevent excessive fuel volume displacement from the line past the pump(s) from vaporization of hot fuel by maintaining some fuel pressure in the line\fuel rails so if the PPRV does leak off while the fuel system is hot, hard starting\stumbling after startup can occur due to vapor trapping (gas bubbles) in the fuel line\rails until the fuel pressure comes up enough to assist the fuel injectors to bleed this trapped gas out. Now if the fuel doesn't vaporize in the line\rails then all will be as you have said....so the hard starting from a bad PPRV\lack of a PPRV would most likely be noticed on a hot restart as opposed to a cold restart depending on how bad\quick the pressure leakoff occurs to determine how quick\much hot fuel will vaporize (flashpoint of std gasoline is 73*F at atmospheric pressure or 0 psi...ethanol is even lower than this) in the fuel line\rails during cooldown but it could also happen on a cold start if enough trapped gas accumulated in fuel line\rails from fuel vaporization occurring while the system was hot during shutdown due to fuel line pressure leakoff thru a bad PPRV\no PPRV....the stumbling reaction is somewhat similar to starting a vehicle just after a reconnect of an empty fuel rail & making a single quick key cycle of the fuel pump(s) to load up the fuel rails then immediately starting the car instead of cycling the key several times to fully load up the fuel rails before starting.....

    The whole purpose of maintaining fuel pressure in the fuel rails even when shut down is to reduce\eliminate hot fuel vaporization but also eliminate fuel line\rail overpressure....which the PPRV is supposed to accomplish but they do wear out.....I know this 1st hand as I have verified that my PPRV (that I thought was a check valve prior...thanks for the clarification) is leaking off & won't hold any fuel line pressure after sitting overnight so I do sometimes get some stumbling on some...not all...cold starts but the difference for me is that I know the issue isn't from other fueling issues (all injectors have been pressure tested & visually verified sound & tune OL cold start fueling has been checked & verified good as well...I had my car intentionally datalogged thru a cold start by my tuner w\ AAT's @ 26*F at the time--I live in the 4 Corners region of the US so it's cold here--due to me suspecting excessive fueling during cold starts thru the tune after checking injectors for leakage...the cause of the excessive fueling found was due to finding COT protection kicking in due to actual plug misfires that I caused unknowingly from using poor dielectric grease causing the cats to overheat from flashing off unburnt fuel\air inside them so the PCM upped fuel delivery to try to cool the cats off but also over fueled the engine during cold starts...yes this can happen) & when the fuel rails have trapped gas bubbles in them it makes cold starting worse when AAT's are colder vs warmer as well due to initially less fuel delivery (or lean, which isn't good during low AAT engine starts) until the injectors "catch up" (fuel rail pressure rises enough to allow the injectors to purge out the trapped gas bubbles & deliver the proper amount of fuel enrichment)….so to say that having no PPRV installed won't cause slow starting or engine stumbling just after a cold start...….

    Well let's just say we agree to disagree as my recorded data results says otherwise (also why I made the suggestions to the OP as I did)...………but thanks for helping clarify my confusion of understanding what "PPRV" meant.

    :beer:
     
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