2001 Expd 5.4L - low vacuum after head replacement
 

Had mechanic pull and replace both heads after crossthreaded plug on cyl 3 fouled and causing misfires. 145,000 miles on engine. Heads were refurbished w/valve job, etc. almost good as new. Also had small leak in plastic intake - losing a little coolant - was also replaced with new

Truck now has loss of power at low RPM and is sluggish taking off from stand still. New all new coils installed. Mechanic replaced O2 and Mass Air Flow sensors - no improvement. No codes from computer now, and none from Snap On Diagnostic either. Mechanic is reading low vacuum level, but has double checked all hoses and connections. Any help on what other likely causes of sluggishness/low vacuum that could result after replacing heads? Mechanic is struggling now, and Ford dealer not helpful - they want to start from scratch and revisit some things our mechanic has already checked out.

Help! - 8 weeks in shop and counting!

...Welcome to Ford Truck Enthusiasts!

See you on the boards.:-X22 ….

Cam timing off a tooth can cause this if the cam timing is retarded.

Yes ,cam timing
did this mechanic chk compression after rebuild of top end?
Also do a propane test or carb cleaner spray on manifold are to see if he has a leak.
no codes doesn't mean anything ,how many drive cycles does the vehicle have after top end change?
Rich

Ditto on the cam timing.

It's probably the one thing that wouldn't throw a code unless the intake vacuum got so low as to cause a problem. See, a vacuum leak is un-metered air, and the computer would see a problem and log a code.

Retarded cam timing just plain produces low vacuum. There's almost no way the computer will see a problem, since there's a perfect mix, it's just that the engine isn't sucking in enough of it to do any good ;)