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[jandroa]

We found a disconnected small tube near the intake manifold with a smoke machine. We have put it back in and now we have to drive the car to see if the consumption returns to normal.

[Doctor Gollum]

That's the vacuum line between the throttle body and the fuel pressure regulator.

Really easy to miss if you remove the TB or plenum as it will fall out on a whim if disturbed.

[jandroa]

Hello everyone, despite the repair, the car continues to use a lot of fuel. The mechanic told me that it may take time to stabilize consumption after repairing the vacuum leak, is this normal?

I have reset the LTFT values as well as the average consumption calculated in the on-board computer.

Thanks!

[TheBoy]

If you reset trims, it should learn the new values, which should be 0%, within a couple of miles, then refine constinuously.

[Doctor Gollum]

Would running the fuel pressure regulator without a vacuum potentially damage the diaphragm

[cam.in.head]

it shouldnt do as the spring will be holding it closed and if the diapragm split you would know about it with pressurised fuel squirting out of it ( the vac port)

[Doctor Gollum]

it shouldnt do as the spring will be holding it closed and if the diapragm split you would know about it with pressurised fuel squirting out of it ( the vac port)

Would that count as over fuelling if it was being hoovered in by the throttle body

[cam.in.head]

definately but it would be sending in a heck of a lot unless its a slight pinhole
with the engine running (or pump) nothing  should be coming out of there ! 

[jandroa]

If you reset trims, it should learn the new values, which should be 0%, within a couple of miles, then refine constinuously.

I will check if it learn the new values and keep them consistently near 0%.

definately but it would be sending in a heck of a lot unless its a slight pinhole
with the engine running (or pump) nothing  should be coming out of there ! 

That sort of things should be easy to notice, isn't it?

[Doctor Gollum]

Is the high fuel consumption a new thing having driven the car 1,000s of kilometres? Or is it high compared to previous/other cars you have?

9.4l/100km would be a reasonable good average, significantly higher if you only drive short distances or around town.

[jandroa]

Fuel consumption of this car used to be about 10,5l/100km (with 1000s of kilometers driven in the past), now it has increased to 15-16l (it fluctuates a lot because since the car was repaired I have not driven enough kilometers to let the car calculate a consistent average).

Is it true that since the repair I have only driven short distances in town. Maybe all I need is to wait and drive more (especially out of town).

[polilara]

I sometimes check the (minimum) fuel consumption of my 2.6 Elegance so that I go to highway and accelerate to 85 km/hour, put cruise on and reset the average fuel consumption value from the car display. After a couple of kilometers I can see average consumption below 9 litres/100km. Can you do this in your Omega and have you tested this?

[jandroa]

That's a great idea, I'll check it out as soon as possible.

Driving in town now it has a very strange behaviour (at least for me), if I reset the average fuel comsumption and drive at a stable speed, the average consumption goes down, but when I stop the car at a traffic light, the average comsumption starts to increase again.

I will get back with the result of this test.

[Doctor Gollum]

That's a great idea, I'll check it out as soon as possible.

Driving in town now it has a very strange behaviour (at least for me), if I reset the average fuel comsumption and drive at a stable speed, the average consumption goes down, but when I stop the car at a traffic light, the average comsumption starts to increase again.

I will get back with the result of this test.

That's down to how the computer works. It sees the fuel flow/speed. When speed is Zero  it can't accurately process the fuel consumption, so the consumption becomes a poor guesstimate.

Also, cold start enrichment cripples the consumption until the engine is up to temperature, so a car that is only driven 12-16km from cold will never warm up properly and will severely impact the fuel economy of one that is driven for some time.

The difference in fuel used between a cold start  journey of 12km vs one of 24 is negligible.

Point being that if the fuel consumption is within the range of other Omegas, then it's something that you can either live with or not, but if it's significantly worse then consider the various temperature sensors and the thermostat.

[jandroa]

Thank you so much for the explanation, it all makes sense to me now.

I'll try to do the test that @polilara told me and also wait until I have driven a significant number of kilometers excluding short distances in town which are not representative of the car's real average fuel consumption.