New Engine Running Poorly. Need Help

Discussion in 'SN95 4.6L Mustang Tech' started by 99Blownstang, Oct 24, 2013.


  1. 99Blownstang

    99Blownstang Member

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    Well I blew the factory motor in my 1999 mustang gt quite awhile back. It has the 2.1 KB, 90mm mass air, 36lb injectors, 75mm throttle body, KB BAP and switch chip. I built a 4.75 stroker and put all of the goodies back on including a new clutch, 255lph fuel pump(also running BAP) cat deletes, and MIL eliminators. I started it up for the first time and my wideband was showing it was running super lean. So I killed it and fired it up again and it said it was running super rich. It does this every time I start it, either really lean or really rich. Also it won't idle down lower than 1600rpms. Any ideas?
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  2. 99Blownstang

    99Blownstang Member

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    Vacuum leak?
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  3. superstang01

    superstang01 Member

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    It could be something as simple as the tune. Could the MIL eliminators affect this? I seem to think it could, but i dont know for sure!
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  4. usaf_branham

    usaf_branham Member

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    I would suspect a vacuum leak.
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  5. 99Blownstang

    99Blownstang Member

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    I'm pulling as much vacuum as before but at idle it will be pulling a lot of vacuum either way. The rpms hang if i give it gas. I'm guessing its a vacuum leak but I can't find one anywhere
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  6. 99Blownstang

    99Blownstang Member

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    Can't find it sucking anywhere
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  7. wmburns

    wmburns SN Certified Technician

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    Suggest starting first by CONFIRMING that the fuel pressure sensor intake vacuum reference line is connected and leak free. Confirm there isn't any raw gas in the line.

    Use an ODB2 scanner to see what the PCM "thinks" the fuel pressure is. Post. Even better, measure the fuel pressure with an external gauge. Post.

    Remember, the PCM is not adjusting fuel based upon the wide band O2's. It's using the narrow band units installed in the exhaust. Use the ODB2 scanner to monitor the long term fuel trim values (LTFT). Post the LTFT values (bank 1 and 2) at idle and at 1500 RPM, and 2500 RPM.

    It would also be handy for us to know HOW the wide band O2's have been installed. Please confirm that they haven't been installed in place of the narrow band units.

    Confirm that the vacuum line is connected to the super charger bypass value. Confirm there isn't any linkage binding.
    #7

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