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[mkaminski100]

HI. I have Omega estate 2.0 16v (automatic gearbox). The petrol consumption is quite high. It’s about 15-16l/100km (ca18 m/gal, average 16,5 on the computer) in city and 9-10/100km on the highway (up to ca 30 m/gall, 26 average on the comp). I’ve changed the manifold (had a crack) and spark plugs (GM), fixed end exhaust box (few holes), changed lambda sensor (from Vectra 2.0 16V), and air flow sensor (form same engine), air filter and it’s still the same. I did the paper clip test and there were no errors (light didn’t flash).  
What I found odd is that when I press the throttle gently it goes down to 7.5 m/gal, and when I press it hard (to the floor) it goes to 7.1m/gal.
I don’t know if this is normal consumption or if I have to check my car again.  I had a Vectra with the same engine and the petrol consumption was 26 m/gal (city) and up to 41m/gal on the highway.  It’s about 30% less than Omega.
If there is any leakage from exhaust (before the lambda sensor), will it be shown on higher lambda sensor reading?
I've checked 2 sparkplugs (first and last) and both are almost white without any black spots or oily marks.  I will check remaining two today. I wanted to change all fuel injectors (with the rail with petrol pressure regulator), but if sparkplugs are that clean, I think it might not be the problem.
I dont have more ideas. I will check the compression soon (waiting for tool).
Is there anybody around Reading (30-40 miles radius) who can check it using Tech-2, or any other cable to find out if everything is ok with this car.

[Craig_R]

james had a problem with his old 4 pot 2.0l it was drinking fuel it got a lot better after he changed something to do with the coolent system i think it was the water temp sensor.

Just to give you a guild my 2.0l does about 40-45 mpg on petrol on a long drive at about 65 to 70 Mph

[Abiton]

What year is the car?  The coolant temperature sensors tend to read low with age, causing overfuelling. Tech1/2 should be able to tell you if that's the case.

[mkaminski100]

It's the 1999 (NOV) so one of the first post lift ones.
I was also thinking about this sensor, but read that when it;s faulty (not broken, but reading lowered temp) I should have problems with starting up the engine when it;s cold. Isn't it?
Where can I find it?

[Abiton]

No I think it'll start from cold OK, but possibly have trouble hot starting 'cos of the excess fuelling.

But...when you say you paperclipped it and got no flashes, that makes me wonder whether you got this right, 'cos on my '96 at least, you see code 12 (test initiation) repeated continuously, even with no faults.

The sensor is at the back of the engine, below the DIS-pack, access not nice...

EDIT: Your clean spark plugs goes against my CTS theory anyway.

[Craig_R]

you dont get code 12 three times with later 2.0l 4 pot omegas, its a 4 digit code not a 2 or 3 digit one it threw me for ages as mine is a w reg facelift with a 4 digit read out when paper clipped

[mkaminski100]

It's the same with old lambda sensor. Theoretically it works fine so there will be no error, but it idle on “high” and will make you ECU supply more fuel all the time. Then you have to connect TECH2 to find you a current reading.
I was told that the same think might happen with the coolant temp sensor. It works but somehow, instead of giving the right temp (ex 80) it will supply a false, lowered reading (ex 40). It won’t be shown as an error.  
It might be that when the sensor is broken, the engine goes into a “faulty” mode omitting faulty sensor and assuming that the temp is low. Then I would have a start up problem. I think that because the sensor is just lowering the temp, the ECU is giving just bit more petrol and that’s why everything is ok (no errors, clean sparkplugs). I hope that this might be a problem as I don’t have any other ideas…

What do you think about actual consumption at 7.1-7.5 when accelerating? Isn’t it too much? When I had a Vectra it was going down to 13-14 when accelerating with “heavy foot” and 20 with normal. The lowest I could get was 9m/gal with 4 people and pedal on the floor.
Regarding paperclip test “CraigR” has explained the thing. As far as I know, if there is no error, the light will not flash.

[theowletman]

I have had both manual and auto X20XEV Omegas. The auto was significantly heavier on petrol around town and on short journeys, 18 - 20 MPG. On the motorway it was reasonable at 35mpg. However my current car 1995 2.0 CD manual returns 25mpg around town and 40 - 41mpg on a run at steady 65 to 70 mph.Take it to a friendly MOT station and ask if they will do an emission test on the car, they have the gear.

[mkaminski100]

How can I check this sensor?
Do you know anybody around Reading (London, in radius of 40 miles) who can check my car using Tech-2 and does the emission test?  
I begin to think that this is normal consumption and I can’t really do anything with it. Or maybe there is somebody else with the same engine (and automatic gearbox) who’s Omega needs less petrol than mine…
I know that I will have to put an LPG installation this year. Fortunately it’s only £600 for third generation (LPG injection).

[ians]

I think those consumptions are too high.   My 3L auto does c 25 mixed town driving and I reckon 30+ on a cruise, you should be doing better.

It might be worth cleaning out throttle body/ICV/breathers, replacing the (cheap) gaskets to ensure no leaks.
Are air, fuel filters recent?

[mikkethealarmguy]

a 2.0l 16v i once owned and used as a taxi
was great on fuel for an auto.
the 3.0l i have at the moment is pretty good too
far better than the 3.0l 24v senator i just scrapped
which was juicy !
probably due to me doing 120 in it everytime i got on a decent  stretch lol

[mkaminski100]

There is no problem with throttle.It's clean as well as pipes and idle control. Do you think that there might be any conjunction between dirt throttle/ breathers etc and high petrol consumption?
Air filter was changed recently but I don't know when the fuel filter was replaced (again - if it would be clogged then the engine would have less power).
I need to chcnge the camshaft cover gasket as it's old and leaking (oil around spark plugs, and on the side of the engine).
I am waiting for the GM gasket and GM oil filter.

[tunnie]

make sure the exhaust is good and tight, no leaks. I noticed a 3-4 mpg improvement with the exhaust sealed correctly.

basics too like tyre pressurs can increase it by 1-2 mpg.

My facelift 2.2 manual does 34mpg with the cruise set at 85...

Over a mixed run it will average 31mpg

[mkaminski100]

I have already changed the manifold, and checked exhaust. I can’t find any black spots (soot). I will have to check the manifold once again, but doesn’t have any crack and its ok on the top of the gasket (will have to check the bottom once again).
What bothers me is the air recycle system. When starting, I can smell unburned petrol and I think that it might be from the valve (or its ok).  It stops after few seconds. I will check it within few days.
I begin to wonder if it's not normal, as so many people confirm that manual needs much less petrol than automatic.  
Do you think that the petrol filter might have anything to do with a high consumption?

[JamesV6CDX]

Check the obvious first - are there any fault codes? Is the engine getting up to temperature?