Engine Help This Is Driving Me Nuts!!!!!!!!

Discussion in 'SN95 4.6L Mustang Tech' started by jdviper6, Oct 22, 2013.


  1. jdviper6

    jdviper6 Member

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    Hello fellas,

    I'm going nuts, this car is making me crazy. It does not want to run properly... to be more specific, when it's cold it doesnt GO when you press the gas, acts like it wants to die, hesitates horribly. ARRG!!! I need assistance! I'm to the point where I don't want to dump anymore money into it unless it fixes it! To give some background I have had this since it had 33,000 miles on it, it now has 140,000. I need a someone to point me in the right direction. I have replaced a bunch of stuff trying to narrow the search but so far unsuccessful.

    This is what I have done:
    Cleaned MAF
    Cleaned IAC
    Cleaned EGR
    The three above all work properly. I believe, let me know if you think otherwise.

    I have replaced:
    All 8 Spark Plugs with Autolite Double Platinum Plugs (with the correct torque I have had issues with this)
    Replaced all 8 coil Packs
    Seafoamed it
    Throttle Position sensor
    Replaced All 4 Oxygen Sensors with new NGK's

    All of the things I have replaced have improved performance but the issue is still there. I have had no LIGHT EVER it just runs like crap when its cold.

    Could it be a DPFE Sensor??

    Please Help!!!!!!!!!!!
  2. COramprat

    COramprat Drone Driver Mod Dude

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    I'd try fuel injectors (not replace...cleaned). Maybe a vacuum leak.
  3. jetmech807

    jetmech807 Mustang Master

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    I don't know if this helps, but my DPFE started setting codes a few months ago, but it always ran good. Changed it, and the only difference was no more codes. Sorry, I don't remember the code.
  4. Nightfire

    Nightfire Mustang Master

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    How about the fuel filter? A clogged filter will have similar symptoms.
  5. jdviper6

    jdviper6 Member

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    Fuel filter has been changed. I forgot about that.
  6. Noobz347

    Noobz347 Stangnet Facilities Maint Tech... Er... Janitor Admin Dude

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    I don't see any mention from the OP that codes were pulled.
  7. wmburns

    wmburns SN Certified Technician

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    +1 on pulling and posting all DTC codes. Confirm that the check engine light comes on during key on lamp test.

    Not a bad idea to post the model year of your Mustang.

    How does it run when at normal operating temperature? How's the gas mileage (now compared to the past)? Does the motor burn oil or coolant?

    How long has the problem been going on? What did the old spark plugs look like?

    If an injector problem is suspected, consider an injector cleaning and flow test service such as injectorrx.com.

    If you pull and plug the vacuum line to the EGR value does this improve performance?

    Do you have an ODB2 scanner that can read operational data?
    Last edited: Oct 28, 2013
  8. jdviper6

    jdviper6 Member

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    Has never thrown a code. I can confirm that my diablosport programmer. Also it is a 99 GT 5 speed
  9. jdviper6

    jdviper6 Member

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    Check engine light works
  10. jdviper6

    jdviper6 Member

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    Runs great at normal operating temps
  11. jdviper6

    jdviper6 Member

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    I have the torque app for android that provides live information. Will that work?
  12. jdviper6

    jdviper6 Member

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    The motor uses some oil (about 1 quart between changes)

    It has never given a code ( check engine light works at key on)

    I do not know what the old Spark plugs looked like (when one blew out the shop replaced all 8. They replaced them with Autolite Double Platinums they have 20,000 miles on them or so)

    "If you pull and plug the vacuum line to the EGR value does this improve performance?"

    I have not tried this. what would this be testing the EGR valve or the DPFE sensor or both??

    I do not believe it's the injectors, it runs good once it gets going. To be honest I'm not sure. I do not know what a car runs like with dirty injectors.

    It feels like the choke is stuck open on a carbed car. I don't know how else to describe it.
  13. wmburns

    wmburns SN Certified Technician

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    Double check that the fuel pressure vacuum intake reference line is connected and leak free. Double check there isn't any raw gas in the line.

    Would be handy to know the long term fuel trim (LTFT) values at idle and under load when cold and warm. Also would help to know the PCM reported fuel pressure, IAT, and ECT values.
  14. jdviper6

    jdviper6 Member

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    Could you break that down in layman's terms for me Lol. Or perhaps provide a diagram showing me where to look for those things.

    Thanks in advance.
  15. 1987stangman

    1987stangman Member

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    Burns has you on the right track! When there is an issue that doesn't throw a code it is always more frustrating to solve. It seems like if there was a egr flow issue or a vac leak it would throw a rich or lean code, nor would it run ok at operating temps. Sounds like the one thing you have not touched on fully is fuel pressure. FPDM may not be doing its job when cold, or the pump is going bad but, in my experience at least, they usually exhibit issues at any temp if not worse hot or just don't work. I like using a mechanical guage over PCM reporting. You can buy a guage cheap and there is a Schroeder valve on the fuel rail you can connect it to to check it at cold. If you have good pressure when the car is cold, running then the rail sensor like wmburns explained needs to be test next. As far as reading the cars fuel trims you will need a code scanner that is capable of reading live data, I know my SCT handheld does so your diablo sport may or may not as I have always used SCT programmers. If so you will need to hook up the programmer and select live data (it may be under, or named something different. Might have to consult the user guide as you will likely have to select the PIDs for them) once you start the data you can write down the average LTFT for the conditions wmburns asked for. There are also PIDs for the IAT and the ECT.
  16. jdviper6

    jdviper6 Member

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    I forgot to mention that I have replaced the fuel pressure sensor
  17. jdviper6

    jdviper6 Member

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    I will hook up my programmer later this afternoon and see if it can provide the data.

    Thanks again
  18. 1987stangman

    1987stangman Member

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    Great, let us know!

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