Bigger than normal MPG drop?

[ksa8907]

Has anyone else noticed a bigger than normal hit to mpg? I typically get around 24 in winter and now I'm getting about 22. I normally wouldn't be concerned but i have 6, soon to be 7 consecutive tanks below average. My route doesn't change, 56 miles straight highway with no traffic except the last 5 miles.

I got a new battery and set of tires right before the decrease, 3k miles ago. One half of the engine injects about 10% more fuel than the other, but it has been that way since i got the car.

Anybody else seeing lower than normal fe?


Edit: looking back at '14/15 i see that my mileage is in line... perhaps last year was more mild than i thought. But this year has been rather mild also... idk.

[ThermionicScott]

It's been pretty mild in my area as well. I wonder if your ECM "relearned" something incorrectly after the battery was reconnected. Those 6 or 7 tanks have all been since then, right?

Being a software nerd, I can't help but wonder if disconnecting the power and trying again might clear it up.

[oil pan 4]

My guess is that it is the tires.

[JRMichler]

Another vote for the tires.

A tire data point: The local rural mail delivery guy has a Prius. His mileage drops 3-4 MPG when he puts his winter tires on.

Temperature could be part of it. My truck mileage changes almost exactly 1 MPG for every 10 degrees F temperature change.

[ksa8907]

Update:

Since temps have come up a bit, but now gone back down, the last 3 tanks since 1-18-17 have been 24 to 25 mpg. Wich is pretty normal. I think the low mpg was probably to do with the weather. Though i also noticed the mpgs drop very quickly above 70, 2 to 4 mpg hit between 70 and 75. Cam phasing must be doing something around 2100 rpm.

[Stubby79]

3 tanks in less than 2 weeks?

[ThermionicScott]

Originally Posted by ksa8907

Though i also noticed the mpgs drop very quickly above 70, 2 to 4 mpg hit between 70 and 75. Cam phasing must be doing something around 2100 rpm.

Doubt it's anything to do with your cam. Speed kills for all of us. Do you need to be driving over 70 MPH?

[ksa8907]

Yes 3 tanks, i drive 57 miles each way to/from work.

Don't need to be, but sometimes i do. My thought is that as the drag increases, the throttle position gets to the point where the cam phasing starts to engage.

[slowmover]

10% drop is reason for investigation. This rule was old when I first heard it in 1970s. Fuel and air filters first back then. Next was spark plugs and points. These were after tire related.

[ksa8907]

Originally Posted by slowmover

10% drop is reason for investigation. This rule was old when I first heard it in 1970s. Fuel and air filters first back then. Next was spark plugs and points. These were after tire related.

Its really odd, ever since i got the car it would ping with regular gas and then feel like a monster (for what it is) on premium. Now lately, the last couple months, it hasn't been pinging on regular and holds gear with much more throttle input.

I know there is something wrong since one side of the engine injects about 10% more fuel, the o2 sensors and cat temperature confirms this. But i dont know if it is the o2 sensors or the timing chain stretched.

I found out i have wideband o2 sensors stock, how do i view the afr?