I have the 99 F-150 4.2 engine stick shift with only 5,000 miles and still feel a power surge when accelerating, usually in 3rd gear between 3rd and 4th gear.When i step on the gas, at times it doesn't accelerate but holds back power. The engine check light doesn't come on so the engine must be o.k. Could it be that the engine isn't broken in yet or possibly restrictive air flow from the stock air system? I know the 4.2 doesn't have much guts but should have more than what i've experienced.

 

I wanted to clarify what i said in my question. I meant to say "when accelerating in 3rd gear", not shifting into 4th. Thanks.

 

I think what you feel is the secondary intake tract opening up like the secondarys on a four barrel carb mine does the same thing.I think they are supposed to open some where between 2500 and 3000 rpms.

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------------------------- 99 SILVER XLT/REG.CAB/4.2/5SPD/3.55/K&N Airbox Mod/Rhino muffler/Westin Black nerfs and now SuperChiped

 

Secondary intake tract?
4 barrel carb?