2003 XC90 Drastic Reduction In MPG

mgjonesin · Post by **mgjonesin** » 28 Apr 2014, 05:26

Thanks in advance for any input.

Car use to get 18 MPG per the computer. Dropped to 14.5 recently so I changed the O2 sensors. This had no effect on the MPG. Next I cleaned the mass air sensor with CRC MAS cleaner. That screwed up the sensor, so I replaced it. Now the car is getting 10 MPG!

Where to next? Dealership for ECM reboot?

Thanks again,

Jon

Juankcrc · Post by **Juankcrc** » 29 Sep 2021, 12:26

Hello.

Did you resolve this issue with your car?

I have 2004 XC90 T6 with the same MPG.

I'll really appreciate if you share your experience.

Regards Juank

Post by **volvolugnut** » 29 Sep 2021, 17:23

What are your driving conditions? Mountains? All city stop and go? Drag race to next stop light? Carry lots of weight? Under inflated wide tires?
What is engine maintenance condition? Oil weight? Over filled with oil? What mileage do you get - 18, 14.5, or 10 MPG?

volvolugnut

Capndirk · Post by **Capndirk** » 03 Oct 2021, 09:24

My '09 3.2 XC90 has run at around the 15 mpg range during the go-nowhere city only Covid period, but that's kind of in the EPA spec.
Since then, I've reset the average mpg in the DIM at freeway driving for long distances and get in the 20's. Back in town, the average will decline at different rates, but slowly. Sitting at idle will knock the average down really fast. The odd thing about the average mpg function is that no amount of freeway driving will bring it up appreciably. I think that the only meaningful average mpg health indication is by resetting at freeway speeds.
Another mystery is how the algorithm for average speed works. No amount of high speed operation bumps that number up a significant amount.

Post by **xHeart** » 03 Oct 2021, 11:17

Capndirk wrote: ↑03 Oct 2021, 09:24 My '09 3.2 XC90 has run at around the 15 mpg range during the go-nowhere city only Covid period, but that's kind of in the EPA spec.
Since then, I've reset the average mpg in the DIM at freeway driving for long distances and get in the 20's. Back in town, the average will decline at different rates, but slowly. Sitting at idle will knock the average down really fast. The odd thing about the average mpg function is that no amount of freeway driving will bring it up appreciably. I think that the only meaningful average mpg health indication is by resetting at freeway speeds.
Another mystery is how the algorithm for average speed works. No amount of high speed operation bumps that number up a significant amount.

If your DIM dial allows _ _ Instantaneous MPG, then keep it there for a while. It varies, but a 70 mpg at 1600-1800 RPM going 30-35 mph is great, similarly <10 mpg when taking off.

Post by **volvolugnut** » 03 Oct 2021, 13:19

My 2001 V70 T5 appears to continue averaging all miles and fuel mileage until it is reset manually by the reset button. To reset on mine, you set to read average mileage and then press reset. The indication will show xxx for a couple seconds and then start averaging. On mine it appears to update about every 4 seconds. If the miles since reset are high (like several hundred city miles), it will take several hundred highway miles to see a change in the average.
Watching the instantaneous mileage is instructive when traveling at steady speeds. Slight slopes up or down can change miles per gallon by 5 to 10 MPG.
volvolugnut