On deceleration instantanous mpg goes down

volvomadness · Post by **volvomadness** » 04 Jun 2016, 17:42

On the s60's I have owned in the past when I decelerate the instantaneous would go up sometimes like 80 mpg. It would make sense since my foot is not on the gas.

I am trying to diagnose a slight vibration in my steering wheel on idle. Its not the motor mounts (new). Its not the Maf (new). Don't have a vacuum leak no idle fluctuation. The LTF is a zero and the STF only fluctuates =-3% under load and idle,

What I do notice is when I decelerate the mpg goes lower rater than higher. I'm talking about 9 mpg. BTW my gas mileage is only 18mpg which is low. I am leaning towards a bad MAP but don't want to change part unless its bad. Is there a way with my scan tool to determine if the MAP is bad?

Madness

Post by **abscate** » 05 Jun 2016, 03:09

A bad MAP will usually pop a code. No code, hold off. My autel tool reports actual manifold pressure via the MAP (ME7 car) so I think a good code reader would sort that out.

Post by **oragex** » 05 Jun 2016, 05:16

Miles on it? When my front O2 went, I was getting horrible mpg in stop and go traffic and while waiting at a light I would see 99l/100km on the instant display - similar to 0mpg basically. Like a hole in the gas tank.

What brand are the new engine mounts/bushings?

volvomadness · Post by **volvomadness** » 05 Jun 2016, 11:34

mounts are oem. 145k. scan tool indicates 02 functioning no cel.

Post by **oragex** » 06 Jun 2016, 05:07

Old worn out front O2 doesn't necessarily throw a code. Mine had no code as well, but was completely busted, with new sensor the mpg displayed normal values and fuel consumption got reasonable again. Not saying it's surely the O2, but it can be checked with a special voltage reader. On the other side, if the front O2 is original at 145K miles, it has fully lived it's life. I used NTK off Ebay and it's doing well (mine is the non turbo engine).

Is the engine shaking at idle? Might have to do with some misfire.

Post by **vtl** » 06 Jun 2016, 06:12

Front O2S is current-based, not voltage, can't really read it with multimeter without splitting the wire.

Front sensor in my wife's 02 V70 died this spring, it threw actual code. Car was a lazy dog for last couple of years, but no codes. 145k miles.

My 05 XC70 with 150k miles has 18MPG as well. I was thinking it is because of my driving habits, but then we've got a new XC60 with 5 cyl engine, which has both lot more weight and engine power, and yet better MPG. So I might change the O2S. On the other hand, XC70 pulls harder from the stop, while for XC60 it takes time to convince itself it's time to kick in. Then it pulls like train.