[hot]

Hi guys!

My car just passed MOT but my happiness did not last long - I noticed an increase in petrol consumption in my 9-5 Aero Estate Auto.

Steady 70 mph on a motorway with cruise control on used to be around 39 mpg (7.2 l/100km) but now it's around 32-33 MPG (8.6 l/100km).

Firstly I blamed my roof rails (aero shaped btw) and took them off - fuel consumption dropped a little but it's still more than it used to be. Then I checked tyre pressures - OK here.

What I noticed is that when I drive steady 30 through the town or steady 70 on a motorway my turbo gauge needle is higher than it was before - looks like I'm having more boost. It's still within the white range but higher.

What would you guys advice to do? I have a Saab specialist nearby- maybe pay him a visit? But it's a weird coincidents that right after my MOT (done by them) strange things are happening with my car - I'm not accusing - nice bunch of people, but on the other hand I don't trust garages at all. You know, I'm afraid someone could fiddle with something tiny I have no idea about for me to come back to fix it - my car did not need any work for MOT so you know where I come from...

Diagnostics? Boost adjust?

 

[AJ.Lintern]

How often do you reset the mpg display? I've been quite pleased to be getting 32mpg (reset when I bought my car about a month ago). It's been gradually improving in that time but I have started using Shell V-power, so thought it might be that. Would be very happy if I could get 39mpg!

 

[hot]

I reset it every time I fill up.

When I first got this car I was curious how thirsty it is si went on themotorway and sat at 70 and reset MPG display. After a moment it came up with a figure 39 mpg and held it for a many miles. I did the same couple of days ago, suspecting some issues and it came up with a figure of 33 mpg.

I'm little bit worried about that boost indication...

 

[SuperSwede66]

Not sure about the boost indication, but I'd suspect the pre-cat O2 sensor. Once they start going off-spec there can be a big impact on performance and fuel economy. What were the emission readings (especially the lambda reading) at the MOT?

I had a fuel economy (and a too-close-for-comfort MOT pass) problem that was traced to the O2 sensor. See here.

 

[sgould]

I agree with the O2 sensor. I had poor consumption and replacing it improved that markedly. Whether the cost of the sensor was less than the fuel saved is more dubious!!

 

[hot]

Should diagnostic point a faulty O2 sensor?

And one more thing - is there a relation between faulty O2 sensor and boost level? What I think is: Faulty O2 sensor gives bad reading to the ECU, ECU pumps more fuel, engine is running reach and more fuel causes another sensor to increase boost thinking we're going faster...

 

[Magnuspaisley]

I reset it every time I fill up.

When I first got this car I was curious how thirsty it is si went on themotorway and sat at 70 and reset MPG display. After a moment it came up with a figure 39 mpg and held it for a many miles. I did the same couple of days ago, suspecting some issues and it came up with a figure of 33 mpg.

I'm little bit worried about that boost indication...[/b]

33 mpg...I'd be pleased with that. I only get around 26-29 average. I better look at my 02 sensor then!!!!!

How is it checked guys? and what should the readings be?