Originally Posted by Top-Ace
^^ If you would please inform us of where exactly you read that proposal in my post, I would appreciate that.
What would of happened is that timing belt was not done corretly, just off enough to cause problems.
You said the timing might be off. The posts are about a sudden change of fuel economy. The Zetec timing is not VCT and is secured on the cam shaft by a very large heavy duty bolt that gets torqued down to 50 foot/lbs. The gear basically gets "pressed" onto the end of the cam shaft Their is no keying so if it was loose enough to slip then it would continue to slip. The stock cam shafts are keyed on the other end so they can only be locked one way when the gears are put on. the gears can only be locked when the motor is in Top Dead Center.
To change the belt (in a nut shell), you "lock" the cams. loosen the tension pulley, pull the belt, install the new belt and then re set the tension pulley.
So on a normal motor the only way the timing could change "overnight" was if the belt jumped which would cause a lot more problems then just bad fuel economy.
Edit: another thing to remember is that the Zetec motors are "old" as they get old the HP does drop ( a 1960's Mustang if with the stock motor will have less HP and fuel economy now then it did in the 60's ). I would check the IAC valve (that was not mentioned on your replace list on your previous post) in your case. and for the previous posters I would say dragging caliper, or stuck drum, or perhaps the system never goes into a closed loop state, or an array of other still possible reasons before thinking the timing is a problem