4.0 no power under 2500rpm

[gigi2012]

I have a 2005 Sportrac, 4.0, SOHC that has an acceleration problem. It has no power under 2500 rpm. After that it runs fine. I've replaced the intake manifold gaskets, wires plugs coil pack. Fuel filter and pump. MAS checks out good. No knocking, it just won't accelerate. Any ideas???

 

[gigi2012]

Also dropped the exhaust to verify there was not an issue with cats. no change noticed.

 

[crazymind]

Do you have check engine light? Does it act like its misfiring?

 

[gigi2012]

Found it. Crank case pulley was cracked. previous owner replace the pulley but used the old bolt. the pulley loosened up and moved. the key in the keyway broke which cracked the pulley. The pulley then moved back on the crack shaft thereby retarding the timing, causing misfires, rough idle, no power on acceleration.

Only took 4 different shops to find the problem. Ford wanted to replace the motor -not!

The other shops replaced the MAF, fuel filter, fuel pump, intake manifold gaskets. of course non of these fixed the problem

$2k later it runs great.