car not starting on new tune

Discussion in 'Fox 5.0 Mustang Tech' started by tobalx, Feb 11, 2013.


  1. tobalx

    tobalx Member

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    this gonna be long winded,sorry for that. origanally i had a dyno tune with a jaybird j3 (moats) chip.i had 19 lb injectors with a 70mm maf. i was shooting a 125 shot with it and i do have h/c/i so the injectors were way maxed out. i then switched to a pmas 95 mm maf and 30 lb injectors and my innovative afr guage was reading i was leaning out at wot. i then had a buddy change a few parameters on my tune and reburnt my chip. now
    erratic idle at start,adjusted blade wont be erratic , but 1100 idle.
    switch to two position on chip for nos tune ,get check engine light
    now i went to start it after putting the blade back and it will start and idle perferect but only once. if i try to start right after just turns over.
    if i feather the gas at start up it will chug up to idle then stay there and run fine.
    i have no clue about tuning but i did watch him do it and he just changed the base settings of the cars fuel system. if you want to read my tune let me know as i can bring it up and maybe do a copy paste thing if that works. or do i just have a mechanical thing that i have to go through,the only thing is it ran perfect before but it has sat a few months inbetween playing with it.
    i did check the tps voltage ,fuel pressure etc.
    while it chugs up it runs rich about 12 to 13 then flatens out at idle to 14 -15.5 afr.
    #1
  2. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    See the "Surging Idle Checklist” for help with all your idle/stall problems. You can guess at the problem and throw parts at it, or you can use the checklist to help you find the problem quickly and inexpensively. The checklist is right here in the Stangnet 5.0 Tech forum and you don’t have navigate to some other unknown web site. It‘s free and doesn’t cost anything: at last count there were more than 103,000 visits and still climbing

    The quick and easy way to dump the codes is in there too, and all you need to do it is a paper clip! The first two posts contain all the fixes & updates. At last count there were 24 possible causes and fixes for surging idle/stall problems. I continue to update it as more people post fixes or ask questions.
    #2
  3. tobalx

    tobalx Member

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    so i bought an equus 3145 and got a 15,21,24
    the cannot read rom
    coolant sence temp
    and iat out of range
    i can buy new sensors but i would assume the cant read rom is my j3 chip? is safe to say the chip was a bad burn?
    #3
  4. f8tlfiveo

    f8tlfiveo My wife likes my spool and blow-off valve.

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    Go to eectuning.org. You won't get too much tuning advice on this site
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  5. tobalx

    tobalx Member

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    will do, thank you
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  6. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    He may not have a tuning problem, just some sensors or wiring that needs attention. If he dumped the codes on a cold day with a cold engine, the code 21 and 24 may be incorrect. Always dump codes on a warn engine to prevent getting false errors.

    Code 15 - No Keep Alive Memory power to PCM pin 1 or bad PCM (Memory Test
    Failure). The voltage to the Keep Alive Memory (KAM) is missing (wiring problem)
    or the KAM is bad. The KAM holds all of the settings that the computer "learns" as
    it operates and all the stored error codes that are generated as a result of
    something malfunctioning while the engine is running. Use a voltmeter to check
    the voltage to the pin 1 on the computer - you should always have 12 volts. No
    constant 12 volts = bad wiring. If you do always have the 12 volts, then the KAM is
    bad and the computer is faulty.

    If the computer has to "relearn" all the optimum settings every time it powers up,
    the initial 5-30 minutes of operation may exhibit surges, poor low speed performance,
    and rough idle.

    Note that some aftermarket chips will cause code 15 to set. Remove the chip,
    clear the codes and retest.


    Before replacing the computer, remove the battery ground cable for about 20
    minutes. This will clear all the codes. Retest after several days of running. If the 15
    code is gone, then don't worry about it. If it is still there, then you get to do some
    troubleshooting.

    See the following website for some help from Tmoss (diagram designer) & Stang&2
    Birds (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/

    Diagram courtesy of Tmoss & Stang&2birds
    [​IMG]

    http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

    http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

    http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif


    Code 21 – ECT sensor out of range. Broken or damaged wiring, bad ECT sensor.
    Note that that if the outside air temp is below 50 degrees F that the test for the ECT can be in error. Warm the engine up until you get good hot air from the heater and then dump the codes again.

    The ECT sensor has absolutely nothing to do with the temperature gauge. They are different animals. The ECT sensor is normally located it the passenger side front of the engine in the water feed tubes for the heater.

    The ACT & ECT have the same thermistor, so the table values are the same

    ACT & ECT test data:

    Use Pin 46 on the computer for ground for both ECT & ACT to get most accurate readings.

    Pin 7 on the computer - ECT signal in. at 176 degrees F it should be .80 volts

    Pin 25 on the computer - ACT signal in. at 50 degrees F it should be 3.5 volts. It is a good number if the ACT is mounted in the inlet airbox. If it is mounted in the lower intake manifold, the voltage readings will be lower because of the heat transfer.

    [​IMG]

    Voltages may be measured across the ECT/ACT by probing the connector from the rear. A pair of safety pins may be helpful in doing this. Use care in doing it so that you don't damage the wiring or connector.

    Here's the table :

    50 degrees F = 3.52 v
    68 degrees F = 3.02 v
    86 degrees F = 2.62 v
    104 degrees F = 2.16 v
    122 degrees F = 1.72 v
    140 degrees F = 1.35 v
    158 degrees F = 1.04 v
    176 degrees F = .80 v
    194 degrees F = .61
    212 degrees F = .47 v
    230 degrees F = .36 v
    248 degrees F = .28 v

    Ohms measures at the computer with the computer disconnected, or at the sensor with the sensor disconnected.

    50 degrees F = 58.75 K ohms
    68 degrees F = 37.30 K ohms
    86 degrees F = 27.27 K ohms
    104 degrees F = 16.15 K ohms
    122 degrees F = 10.97 K ohms
    140 degrees F = 7.60 K ohms
    158 degrees F = 5.37 K ohms
    176 degrees F = 3.84 K ohms
    194 degrees F = 2.80 K ohms
    212 degrees F = 2.07 K ohms
    230 degrees F = 1.55 K ohms
    248 degrees F = 1.18 k ohms

    Diagram courtesy of Tmoss & Stang&2birds

    [​IMG]

    See the following website for some help from Tmoss (diagram designer) & Stang&2Birds
    (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/

    Ignition switch wiring
    http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

    Fuel, alternator, A/C and ignition wiring
    http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

    Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
    http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

    Vacuum diagram 89-93 Mustangs
    http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

    b]Code 24[/b] - Intake Air Temperature (ACT) sensor out of range.
    Bad sensor, bad wiring. The ACT for Mustangs built before 95 is in the
    #5 intake runner. It measures the air temperature in the intake to help
    computer the proper air/fuel ratio.

    Note that that if the outside air temp is below 50 degrees F that the test for the ACT can be in error. Warm the engine up to operating temperature and retest.

    ACT & ECT test data:

    The ACT & ECT have the same thermistor, so the table values are the same

    Pin 7 on the computer - ECT signal in. at 176 degrees F it should be .80 volts

    Pin 25 on the computer - ACT signal in. at 50 degrees F it should be 3.5 volts.
    It is a good number if the ACT is mounted in the inlet airbox. If it is mounted in
    the lower intake manifold, the voltage readings will be lower because of the heat transfer.
    Here's the table :

    50 degrees F = 3.52 v
    68 degrees F = 3.02 v
    86 degrees F = 2.62 v
    104 degrees F = 2.16 v
    122 degrees F = 1.72 v
    140 degrees F = 1.35 v
    158 degrees F = 1.04 v
    176 degrees F = .80 v
    194 degrees F = .61
    212 degrees F = .47 v
    230 degrees F = .36 v
    248 degrees F = .28 v

    Ohms measures at the computer with the computer disconnected,
    or at the sensor with the sensor disconnected.

    50 degrees F = 58.75 K ohms
    68 degrees F = 37.30 K ohms
    86 degrees F = 27.27 K ohms
    104 degrees F = 16.15 K ohms
    122 degrees F = 10.97 K ohms
    140 degrees F = 7.60 K ohms
    158 degrees F = 5.37 K ohms
    176 degrees F = 3.84 K ohms
    194 degrees F = 2.80 K ohms
    212 degrees F = 2.07 K ohms
    230 degrees F = 1.55 K ohms
    248 degrees F = 1.18 k ohms
    #6
  7. f8tlfiveo

    f8tlfiveo My wife likes my spool and blow-off valve.

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    Does your Maf match the injectors or are you running a different Maf transfer in the tune?
    #7

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