Miles Per Tank 400H

[Dewey]

Driving around town over the last 5 days commuting to work, (4 mile journey each way) I'm averaging around 24mpg, but there are some hills. Does that sound about right?

[stevet]

Yes about right. It will take a couple of miles to warm up. Not much chance to use the Battery power. Once warm in town you should average about 36mpg

[Boxbrownie]

The on-board fuel computer is always optimistic. Mine is around 2 to 3mpg out too.

But shouldn't it be more accurate? The ECU should know EXACTLY how much fuel is going into the engine as it controls the injectors and the odometer must be right, so the calculation should be spot-on. Or does the computer calculate it another way?

Surely us trying to fill the tank to exactly the same point every time is much more likely to be prone to error?

Why must the odometer be correct? Its driven by the same sensor and software that gives you the indicated speed........we know how accurate they are!

[ColinBarber]

The on-board fuel computer is always optimistic. Mine is around 2 to 3mpg out too.

But shouldn't it be more accurate? The ECU should know EXACTLY how much fuel is going into the engine as it controls the injectors and the odometer must be right, so the calculation should be spot-on. Or does the computer calculate it another way?

Surely us trying to fill the tank to exactly the same point every time is much more likely to be prone to error?

Why must the odometer be correct? Its driven by the same sensor and software that gives you the indicated speed........we know how accurate they are!

The speedo is designed to read over. The odometer is designed to be correct and is within certain tolerances.

[ColinBarber]

The on-board fuel computer is always optimistic. Mine is around 2 to 3mpg out too.

But shouldn't it be more accurate? The ECU should know EXACTLY how much fuel is going into the engine as it controls the injectors and the odometer must be right, so the calculation should be spot-on. Or does the computer calculate it another way?

Surely us trying to fill the tank to exactly the same point every time is much more likely to be prone to error?

No the ECU doesn't know, it uses a closed loop system to alter the fuel ratio until it reaches a desired ratio as detected by the O2 sensors. Each injector has manufacturing tolerances, that combined with wear, dirt and inconsistencies with fuel pressure means even if you accurately process the injector duty cycle you won't exactly know how much fuel went in.

[Dewey]

Drove to Derby at the weekend and back to the East Riding - avg mileage currently stands at 29mpg - which I don't think is too bad.

And boy that thing can shift if it needs too, surprised a few drivers lol - I've found my driving style has become more relaxed in the Lexus, on the motorway with cruise control on its a very easy and comfortable car to drive - I like it a lot!

[Boxbrownie]

Usually around 360 per tank but drove to Bristol at the weekend and got about 390 which is just over 28mpg, not bad for an old 3 litre 4x4 Automatic Mk1 RX.