Help?!?!?!?
I put a free flow muffler on my 99lariat today.it ran fine and sounded good till I came home and parked it for a couple of hours
when I cranked it and drove away,engine began to skip BAD,rough idl stumble when accelerate,barely running at all.What have I done?this only mod to stock 5.4 auto 4x4.Can anyone give me a clue?

 

Try disconnecting you battery for one half an hour and see if that helps. That would be my guess

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1999 F150 4x4 XLT BLACK ORP 4.6 5 SPEED 3.55
LUND HOOD SHEILD
K&N
FLOWMASTER SERIES 40
PREMIUM SOUND W/CHANGER
PIONEER 6815's(for now)
SUPERCHIP
AIRBOX MOD
WAAG BRUSH GUARD