hi all...

my punto has gone from 50+mpg down to 41 over the past 2 weeks.
I put in focus induction kit & have reset ECU to adjust fuelling, started to use a heavier oil due to suspect bad piston rings.

Just wondering if its due to the heavier oil thats caused lower MPG...?

Suspect piston rings will cause a drop in MPG. Run the car with the breather pipe open to the air, rev the engine and look for any smoke coming from there. Worn piston rings will release smoke from there

All that, but the engine may be running rich simly 'cos it's re-learning.

The ECU will always go rich to protect the engine. Will take approx 350 miles to relearn. The Focus induction kit will be adding more cold air and therefore the ECU will need to add more fuel.

Heavier oil will screw with consumption.

If you are bothered by consumption why did you buy an induction kit rather than a set of rings?

Cheers

D