Spark Plug Gap Question

Discussion in 'Fox 5.0 Mustang Tech' started by Casey2552, Sep 16, 2013.


  1. Casey2552

    Casey2552 Member

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    Hi first post , I have a 1990 notch with ford racing motor with gt40 y303 heads , e303 cam , gt40 intake , 70 mm tb,prom mass air meter , 24lb injectors , egr was removed by previous owner , I installed a simulator on egr plug that did take care of alot of codes and turned engine light off my question is what should spark plug gap be , it idles pretty firm no surging but motor seem to jump all over with alot of shaking that runs through hole body , could this just be how the e303 cam idles all thaughts appreciated

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  2. Grabbin' Asphalt

    Grabbin' Asphalt Mustang Master

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    I have gt40p heads, i got mine at .035, but they're super milled heads, believe a safe area to tune would be .045 then go up or down and see how she takes it.
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  3. Casey2552

    Casey2552 Member

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    Thanks I tried .45 then tried .54 like ford racing tech said and now when I rev it it will go up come down and hang about 1100 rpm for a second then slowly come down to idle at 850rpm
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  4. Casey2552

    Casey2552 Member

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    So can anyone tell me if the hangin idle after rev is normal , seems like my old one done it but can't remember , when it was at .45 it came straight down to 850 fast with no hang thanks
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  5. Rick 91GT

    Rick 91GT SN Certified Technician Site Sponsor

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    Typically a hanging idle is not from a spark plug gap I would check the IAC valve.... And tps voltage

    Sent from my XT907 using Tapatalk 2
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  6. mikestang63

    mikestang63 Mustang Master

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    disconnect the IAC and see if the problem goes away.
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  7. Casey2552

    Casey2552 Member

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    I have set tps at .98 v I was told that would be best but iv read so much about tps most people say as long as it's below 1v it's good but I'm not sure on that issue
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  8. mikestang63

    mikestang63 Mustang Master

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    don't worry about the whole TPS has to be at 1.0 myth. As long as it's within the range of .90 to 1 you are fine. I would think it's a sticky or bad IAC.
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  9. Casey2552

    Casey2552 Member

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    Thanks I suspected that the hole time but I guess I told myself it should work I cleaned it lol , I'm just Gona replace it and go from there , in the process right now of undercoating with 3m rubberized undercoating any one have any good or bad things to say about undercoating
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  10. mikestang63

    mikestang63 Mustang Master

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    it's a **** to remove and will promote rust if you don't apply it properly with full coverage.
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  11. Casey2552

    Casey2552 Member

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    Well just did half the car and cleaned up bottom best I could , it was in great shape as it was not much rust at all , geuss I will just hope for the best lol to late now but sure looks cleaner now , like new
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  12. Grabbin' Asphalt

    Grabbin' Asphalt Mustang Master

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    My IAC sticks alittle too, I need to just buy a shiny one from Mike. Another way to to test in a manual car, is to put it in 1st gear and gain slow speed to 2500rpm and put in in nuetral and coast. Your sticky IAC should raise its ugly head and hover around 1200-1300-ish. My parking deck reminds me daily of my sticky one. Already got my gasket just lazy right now :rolleyes:
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  13. Mustang5L5

    Mustang5L5 Car used in adult film "Highway Gangbang-InDaButt" SN Certified Technician Founding Member

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    Spark plug gap is mostly dependant on ignition if you do not have a power adder or nitrous. On a stock N/A engine, there is no reason to reduce gap. The stock gap is 0.054".

    hanging idle could be dirth 10-pin connectors on back of intake.
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