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[MeegaRob]

Hi All,

I've had a niggling feeling for a while that my fuel economy isn't quite what it should be. Not bad, but then again not good.
E.G. I'm getting low to mid 30s on a motorway run ( 2.2 Petrol auto ).

I think I see the reason here



As you can see the o2 sensor voltage is consistently too low. It should vary around the 0.45V rather then 0.1.
The data was taken using the logging facility on torque pro ( android ) for a short journey on a duel carriageway.
There are no ECU faults stored or pending.

Great I think. I'm running lean, just need to find that pesky vacuum leak, and it will all be sorted.
My problem is, I just can't find any leaks.
I've tried butane and carb cleaner, and even water to isolate the leak.

I swapped over the o2 sensor with a known working one from another car - Just in case. There was no change.

Here is my long term fuel trim.





So where do I look now? Is there a common place the vacuum system leaks? Or perhaps something else.

Thanks

Rob

[steve6367]

Hello and welcome 

If it helps my 2.2 does around 33mpg on a motorway run so sounds like your doing ok. Or are you saying your MPG has dropped?

Steve

[MeegaRob]

Hi Steve,

The MPG has been bad for a while.
I have two 2.2 omegi, which makes for a good reference, and means it's a doddle to swap over parts.

I've only just learnt how to use the obd logging on torque pro.  So was interested to see that the good/blue 2002 omega has on o2 voltage oscillating around the 0.45V where as the bad/gold 2001 one oscillates around 0.1V.

I consistently get 42MPG on a motorway run from the blue one, but only 32-35MPG from the gold one.
Around town is difficult to quantify, but the gold one is less economical.

I know the stated MPG from the computer isn't a great guide, and I haven't done a brim to brim comparison, as it will cost a fortune to fill both tanks. Perhaps the logging info shows a problem though?

Thanks

Rob

[zirk]

I could get low to high 30 mpg on a 3.0 Auto on a run. If you swap Lambdas over to the other side, just to confirm its ok and the heater is working. No leaks, my next step would be Maf.

[MeegaRob]

Hi Zirk,

Good suggestion, thanks.
I swapped over the MAF this morning, along with the ducting between the air filter and throttle body.
No change. The car still runs nicely with plenty of power, but the o2 voltage remains low.

Rob

[Marks DTM Calib]

Whats the coolant temperature sensor saying?

[MeegaRob]

Hi Mark,

The ECU reports 85C, which is the same as the dashboard gauge.

Rob