Vacuum and bad mpg or something else?

[Ross-N-Chicago]

Guys,

My mileage has come down a couple mpg's lately with no changes to X. It seems to bog at start up and the first few accelerations which = rich. Can you point me in a few directions to start.

Newer fuel filter
Newer FPR
Newer plugs and wires- 1 yr
Newer exhaust but old, orig cat (have new one and haven't installed yet from Summit)
Newer O2 sensor- 1 yr

I read that even though PCV will rattle sometimes they are bad and should use Ford PCV only. I also haven't run the scanner (I will) but am looking for ideas.

 

[MattPersman]

how is your fan clutch? if its bad it can run on high speed all the time making the MPG go down alot. Mine does it, but I am going to replace it with an electric fan.

just a thought.

maybe MAF is dirty? engine is just worn out if its down on compression fuel mileage will suffer as well.

there is not always an easy answer unfortunately

 

[94expo]

Look for a vacuum leak or Intake leak. O-rings a known to go utt on the intakes.

 

[Ross-N-Chicago]

What about this?

I switched to Amsoil's 0W-40 oil for the cold CHicago winter and wonder, since I KNOW I have bad valve seals, if its pooling up overnight and really causing it to bog down at startup. It doesn't do it later in the day after it has been running for awhile or driven around.