Quote:
Originally Posted by partsbob67
here we go. 89 mustang 5.0 stocker. changed from the stock tank and lines to a fuel cell and an external pump. starts breaking up at 4500 ever since. the only thing I haven't replaced is the mass air flow meter and the cell. it's an 4 gallon aluminum cell. no foam. --10 line from tank to the pump. -8 line up and back. I change over to a 4bbl intake and carb and it runs great. any ideas. i'm to the point where i'm ready to put the stock tank back in.
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As others have suggested, have you verified fuel pressure? Is the regulator the correct one for EFI? An -8 return seems big but should not be an issue if the regulator is working correctly (possibly returning too much fuel). What does the O2 sensor read during the event?