Degrading fuel economy

[kivnul]

My fuel economy has been steadily decreasing each tank by about 1 mpg.

http://www.fuelly.com/car/ford/fiesta/2016/kivnul/419958

My tire pressure is stable and at the recommended psi, stock tires. My commute is the same, and I have been trying to drive in a consistent manner while I try to figure this out. I am also using the same gas station and grade. (Costco). Oil was changed about 3500 miles ago, the air filter (stock) looks in prime shape. Total miles on the car is about 4k.

Using OBD Fusion and a dongle, I see that long term fuel trim is hovering between -6% to -7% while at highway cruse speed. I am not that knowledgeable about other codes, but nothing looks out of the ordinary. The car does get up to temperature and stays there. Most always showing closed loop mode.

Does anyone have any Ideas why this is happening? My thoughts are:
- Leaking/loose boost hoses. Some older forum posts show that sometimes the clamps come loose. Dunno if this is a current problem.
- Ambient air temperature has been steadily rising on the average. So from 30's to 70's (F) over the course of the fuelly log.

Thanks for reading.

 

[CanadianGuy]

To be fair your car @ 4k will start to be broken in and normalize to what it will be. Now in the last few weeks, in Canada at least, the gas is being converted from Winter to Summer. The difference is with some additives. This could also impact economy.

 

[kivnul]

I tightened up the clamps on the air hoses. They were looser than I would like but not loose enough to normally be a worry. I am 1 1/2 tanks of gas since and my fuel economy has risen back from 32.57 to 34.75. This is just one data point but could be useful if somebody else notices a similar drop in economy.

As to the switch from winter to summer grade fuel, the Costco I frequent gets nearly daily shipments.. I would not think that my fuel economy degrading over a months worth of fuel ups would be due to the fuel. Thanks for the reply.