Fuel economy deteriorating??

[newbrz]

Hi guys I really need your help in this one. I love this forum from all that I have learned about my car and I'm counting on you to help me with this. My BRZ has 16k miles on the odometer. At around 12k, I dropped a perrin CAI and catback and a few miles later got it tuned with ECUTEK. I noticed that the fuel economy was being great; but about 3 weeks ago I've seen it getting worse. A LOT. My comparison is based through this process: I normally use the cruise control (I make a lot of long trips) at X speed. The mileage dropped about 4-5mpg at the same speed. This has happened before but if it is windy, or I have a lot of stuff in the trunk, or having a bike rack on. Nevertheless, this is becoming constant. I used to have almost 27mpg on average and dropped around 26mpg. My driving style hasn't change or anything; even if it did, just by comparing consumption with cruise control is alarming for me. Also note, as soon as I had the accessories installed, there was no change in consumption, it even got better! I've been experiencing this for around 3 weeks while the accessories where mounted around 3 months ago. I don't know if it may be normal for the those upgrades or probably a deeper problem. Thank you beforehand for any help!!

[fatherfork]

Check your tire pressure. Under-inflated tires can cause lowered mileage, and the timing sounds about right.

[subwaynm]

Just a hunch but have you serviced your Trans as yet ? I've read I think two threads on servicing your Trans due to issues with them; and that might hurt your MPG also

[Pete156]

Wait, your average mPG went from 27 to 26 and that is A LOT worse? WOW

[humfrz]

Originally Posted by newbrz

Hi guys I really need your help in this one.

Hi ya newbrz .....

Let's see if I'm understanding you correctly. Your fuel mileage has dropped from 27 to 26 MPG .... ??

Or, dropped 4-5 MPG .. ??

If it's the former, that just could be within experimental error. Or, that winter blends of gasoline sometimes yield less fuel economy. Or, like mentioned, tire air pressure might be a bit lower.

How are you checking your mileage (calculation vs. the onboard monitor)?

humfrz

[Wo6M]

Lmao a less than 1 mpg drop?
Come on man

[thehapaone]

mine dropped 3 MPG when the winter blend gas came out whats wrong with 1 mpg?

[Pizzman]

Cruise control is not efficient, especially on hills, that with tire pressure, and driving style are the other options. You would hear and or feel (if you are one with your car. IE bearings or trans)any mechanical issues that would result in heavy fuel consumption. Also are you running the recommended oil. That would f up your mpgs as well. Take it in for service if none of these sound like a problem.

[mav1178]

Winter blend gasoline.

... and 1MPG is not conclusive. How are you measuring this 1MPG drop?

-alex

[Poodles]

Tire pressure is out because of the TPMS system. It's more likely the winter blend gasoline.

[strat61caster]

Originally Posted by Poodles

Tire pressure is out because of the TPMS system. It's more likely the winter blend gasoline.

Even a couple PSI is noticeable in relation to fuel economy, the light isn't a gauge, just a 'check your tires dummy' light.

They could easily be down around 32 psi and for fuel economy I wouldn't be surprised if people were running the oem tires up to ~40 psi. For the record I believe recommended pressure is 35-36.

[zohare]

Mine's gone to shit after a long block replacement, from about 31 cruise, 33 self modulated to I CANNOT break 27. No matter what. But I hadn't considered winter blend? Thinks to be noted... tire pressure is slightly low at times.... worth maybe 1 or 2 tops mpg wise. I'm suspecting a manifold leak though.... The motor replacement has been an absolute nightmare. As far as servicing the trans, you're talking MT right?

[ntron1]

Do you have actual data or are you guessing based on the car computer?

[Bad Habits]

Originally Posted by newbrz

Hi guys I really need your help in this one. I love this forum from all that I have learned about my car and I'm counting on you to help me with this. My BRZ has 16k miles on the odometer. At around 12k, I dropped a perrin CAI and catback and a few miles later got it tuned with ECUTEK. I noticed that the fuel economy was being great; but about 3 weeks ago I've seen it getting worse. A LOT. My comparison is based through this process: I normally use the cruise control (I make a lot of long trips) at X speed. The mileage dropped about 4-5mpg at the same speed. This has happened before but if it is windy, or I have a lot of stuff in the trunk, or having a bike rack on. Nevertheless, this is becoming constant. I used to have almost 27mpg on average and dropped around 26mpg. My driving style hasn't change or anything; even if it did, just by comparing consumption with cruise control is alarming for me. Also note, as soon as I had the accessories installed, there was no change in consumption, it even got better! I've been experiencing this for around 3 weeks while the accessories where mounted around 3 months ago. I don't know if it may be normal for the those upgrades or probably a deeper problem. Thank you beforehand for any help!!

Mine drops 2mpg if I drink too much lager and eat too much pizza.