BAD MPG

5ft24 · Post by **5ft24** » 02 Jul 2019, 15:37

My 04 T6 is only getting 14.7 MPG. I cleaned the MAF, fresh oil change to 5W30 Mobil 1 Synth, new plugs, new air filter, checked all hoses etc, new boost solenoid. It has 186000 miles on it. I do not know if anyone has ever changed the O2 sensors on it, but the cheapest I can find them is $370 each!
I have DICE and VIDA, and there are no DTC's. I did a reset on the ECM and put a couple hundred miles on it, then filled up, drove it and checked MPG when I filled it again and no change.
Any Suggestions? I have a 2006 Pontiac GTO with a 400HP 6.0L V8 that gets between 20 and 22 MPG on the same daily routine I have been driving the XC90 on...

Masscomguru · Post by **Masscomguru** » 02 Jul 2019, 17:34

I don't think you have the right part number. the Bosch O2 Sensors at rockauto are only 87 each.
https://www.rockauto.com/en/catalog/vol ... ensor,5132

tardcart · Post by **tardcart** » 02 Jul 2019, 19:00

thats a heavy vehicle with the unnecessary 6 cylinder and all wheel drive. Its expensive to carry around that much protection. you would get 17 if you got the t5

Masscomguru · Post by **Masscomguru** » 02 Jul 2019, 19:09

^^ this also. The mpg rating for that model was only 15 city/20 hwy. so if you do not much highway and your heavy on the pedal you are right on the money.

5ft24 · Post by **5ft24** » 02 Jul 2019, 19:25

My commute is 90% highway. I'm on cruise control for most of that unless I hit a little traffic.

Post by **oragex** » 02 Jul 2019, 19:34

What's the average speed on cruise ?

It is truly difficult to find the culprit when it comes to mpg on a car with significant miles. The front O2 sensor can go bad from rich mixture but usually it will mostly affect city driving because the O2 sensor acts mostly at accelerations.

On the engine side, I would pull the spark plugs and look closely, see how dark is the tip

The T6 transmission is also problematic, who knows if anything inside is dragging too much

May be worth lifting each wheel and spinning to check for any brake drag

Maybe also try a PCV test www.youtube.com/watch?v=gK8kUQxhT_8

But mostly I would think it has to do with engine combustion

wanderdüne · Post by **wanderdüne** » 02 Jul 2019, 21:14

Before my '03 T6 had it's transmission forward band break, mixed commuting was around 19mpg for me. Here's a link for Bosch O2 sensors w/ lifetime warranty: https://www.fcpeuro.com/Volvo-parts/XC9 ... 1&d=663&v=
How's your air filter?

5ft24 · Post by **5ft24** » 02 Jul 2019, 21:54

Air filter is new. Did all the basics when I brought it home so I would know everything was good

Post by **SuperHerman** » 03 Jul 2019, 00:09

Set the display to instant mpg setting and watch your mpg as you drive. Of course hit RESET before you start for your average.

This will help tell you what is going on.

Here is what I have found over the twelve or so years of 2004 XC90 2.9T ownership.

You should be getting about 20-24 mpg cruising at 60-65mph on flat terrain (normal highway). If you go much higher say 70-75 mph the mpg will drop to the 18mpg range.

Around town you will get 8-14mpg - depending on start/stop and terrain.

My wife averaged about 14-15 mpg, I average about 18 mpg. My driving is more interstate - hers more back roads (start/stop).

I don't think you have any issues - it is just a tire and suspension eating -gas drinking SUV.

5ft24 · Post by **5ft24** » 03 Jul 2019, 07:14

That sucks. At least it's comfortable. I'm 7ft tall, so it's rare I am comfortable in any car LOL