I replaced my valve cover due to a slight leak and while I was in there did a timing chain replacement and new plugs. 105K - bought car new. S model.
NGK factory plugs, aftermarket parts from ECS tuning.
Car ran great before and after - no codes.
Mileage dropped from the 26's to the 23's - US gallons - three tanks measured at fillup confirmed.
Any similar experiences ?
No codes, no funny sounds, everything seems to be plugged back in correctly.

 

Okay, this will sound silly.

Winter blend gas.

Goes from like September to April ish. Cheaper, more ethanol, burns quicker.

I notice my MPG goes from around 28-30 to 25-26.

 

This may sound silly but by any chance did you warm up your car for 15-20mins on cold mornings? That would substantially reduce your MPG and most drivers are not aware of it by warming up their car to melt the frost on their windshield before driving it.

 

Silly, but entirely plausable. We do warm up - five minutes perhaps AND with winter gas we could have more than one cause.. BUT, the drop correlates directly with the work I did. My theory is that there is more drag in the new parts, new crank seal too, and I was hoping that someone else might have seen the same.

 

When mileage drop and you dont have a check engine light, it means the oxygen sensors are on their way out, i have seen this on my r52 and talked about it on the forums here. Then i got a CEL and the oxygen sensor went, first it was the front one then the rear one.