23mpg from a 320d

[golfdsg]

I have a e46 320d and have owned it for about 10 weeks now.
According to the obc I am getting 35-50mpg but for the last 4/5 fill ups I have been calculating mpgmanually and I am only getting 23mpg, out of a 4 pot diese in london traffic!

If i knew theyre this bad I would have got the audi s3 i wanted.

I have taken it to a mechanic and they have fixed the faults it had (not mpg related) but cant seem to find anything that is causing the low mpg.
The Thermostat is a weak point on these cars but evem that is fine because temp is normal (99 degrees).

Can anybody shed some light as to why im getting such low mpg

Thanks

[Cemesis]

Have you taken it for a decent run on a motorway and see what it does? If its also poor it points to a general issue

[Driver101]

London traffic I think is the issue. If you aren't moving anywhere, the consumption is always going to be poor.

[ferrariF50lover]

Either you can't add or something is happening to the fuel after the point at which usage is calculated. The computer can't be that far out.

Simon.

[ging84]

mpg is usually calculated by the amount of fuel injected, this is based on the time the injectors are open for, or the time they are meant to be open for.
There are a few likely possibilities to cause this to not match the fuel your putting in
1 a fuel leak
2 a failed injector which is not closing, or not closing properly
3 the previous owner installed some sort of after market 'tuning' box which has upped the fuel pressure

[Blue Oval84]

Take it for a longer run and see if it works properly there. London traffic will most likely be killing the economy.

[ging84]

Blue Oval84 said:

Take it for a longer run and see if it works properly there. London traffic will most likely be killing the economy.

How is london traffic fooling the obc?

[golfdsg]

Ive tried gettting better and worse mpg, for one tank of fuel I was constantly ragging the car everywhere (not dangerously) and then for another tankfull I drove conservatively without going over 2000rpm at any point, despite those two different driving styles my mpg was still in the 22-24 range.

Should I get the injectors looked at?

[Dracoro]

Can you tell us exactly how you are calculating the mpg please?

[golfdsg]

Dracoro said:

Can you tell us exactly how you are calculating the mpg please?

I am calculating it manually. Miles divided by gallons. By doing this I get 23mpg however the on board computer states 35-50 mpg.

[Dracoro]

So fill up, reset counter, use a tank or so, fill up again and calculate how much actual fuel used to fill up(e.g 50litres) then divide that by 4.54 so 11gallons. Then divide mileage covered since fillip/reset (say 300) by 11 giving 27mpg.

I only ask as I know a lot of people don't calculate correctly (not saying you aren't but wanted to check).

[xRIEx]

golfdsg said:

Dracoro said:

Can you tell us exactly how you are calculating the mpg please?

I am calculating it manually. Miles divided by gallons. By doing this I get 23mpg however the on board computer states 35-50 mpg.

Not enough info on its own. Do you full the tank to the same level each time (i.e. brim it)? Are you measuring mileage over each tank full or averaging over the entire course of ownership?

[PositronicRay]

Just a thought, on this model is it possible to set your odometer (accidentally) to KM?

[jkh112]

If the actual and the indicated mpg are that different, i would suspect a tuning box .

[motco]

Driver101 said:

London traffic I think is the issue. If you aren't moving anywhere, the consumption is always going to be poor.

It still should be 35 at least.

[Willy Nilly]

motco said:

Driver101 said:

London traffic I think is the issue. If you aren't moving anywhere, the consumption is always going to be poor.

It still should be 35 at least.

bks, while the car is stationary and running it is using an infinite amount of fuel per unit of distance.

[golfdsg]

jkh112 said:

If the actual and the indicated mpg are that different, i would suspect a tuning box .

Would a proper remap from a reputable tuner be able to cancel out the tuning box and restore mpg?

[xRIEx]

motco said:

Driver101 said:

London traffic I think is the issue. If you aren't moving anywhere, the consumption is always going to be poor.

It still should be 35 at least.

Based on what information? Which London roads are being driven on? What time of day?

[jkh112]

A tuning box can just be physically removed. Assuming you have one fitted then it will be pugged into the loom, often near the fuel rail. You may need to remove some covers tonget to it. I have seen them with quite long cables and tucked away in a variety of discrete locations. I have not seen one on a 320d so cannot help with where it may be on your car.

[HarryW]

If the traffic is heavy and your averaging 5mph then 23mpg is probably right.