Poor Diesel Economy

[prospector27]

My 4x4 non turbo Diesel Nav just seems to have **** fuel economy since i had the gearbox rebuilt, and just before it went in for the rebuild i changed the fuel filter. Im wondering if i did something with the filter, or if it was the box rebuild that has affected my economy ? I used to get around 560-70km, then id fill up (could prob push til 590km, but now im lucky to get just over 500km and the gauge is on empty. I used to get 160km out of the first quater of tank, then 120 from 3/4 to half, but look at this pic from today, i filled it up and have done 213km, and see where the gauge is? Any ideas fellow diesel heads?

 

[Dion]

Don't trust the gauge that much. Measure your economy properly and we can offer some input on whether it is unreasonable.

Fill the tank till you can see the fuel in the filler neck.
Reset your trip meter.
Run down the tank towards empty, the more you use before refill the longer the averaged period.
Refill the tank to the same mark as before and note the number of litres filled.
Note the kilometres on the trip meter, and reset.

Divide the fuel volume by how many hundreds of kilometres you've driven,
ie. 56L for 560km is 56L/5.6=10LphK

And let us know what that figure is.

 

[Old.Tony]

As above.

The gauge is a needle. It's accuracy wavers - and there's nothing you can do except the above. However, you've been using it for some time and must have a feel for it and have seen a variation, so looking at what causes poor economy might help you spot what's happened.

Dirty air filters, larger tyres, heavier loads, lower tyre pressures, more traffic, lengthy idling, dirty intake manifold (get a catch can and block your EGR), collapsing air intake hoses (not so common) ... there's a few things.

 

[Dion]

dirty intake manifold (get a catch can and block your EGR)

Catch can is worthwhile but there's no EGR on TD27 non turbo in the D21

 

[prospector27]

Yeah what originally raised my suspisions was the gauge, but then i did as suggested ie refilling and measure litres etc, and that is where i noticed the 50-70km difference per tank..... Ive did the air filter when i did the fuel filter, have had balance and alignment done also, still no imporvement. I took the manual hub locks off and noticed the front drive train wobbles aroudn when i pushed it, is it supposed to ? Not that it woudl affect economy in 2 wheel mode........

 

[Dion]

So how many litres per hundred kilometres? A TD27 should do 10-11L/100km in an unloaded D21.

You mean the splined spigot could be pushed in and out when you had the front locking hubs taken off? That's fine, that's just your CV joint float to allow the front halfshafts to change in length as required as the wheel moves through its full travel. There's a circlip that restrains the splined spigot when the hubs are installed.

 

[prospector27]

Well according to that calculation 10.2-11 I am gettin is normal then ? Only other thing when i bought it the guy told me he was putting this diesel power **** in the fuel, he gave me his leftover bottle, and i was using it for a couple months, maybe that gave me a little bit extra in KM...

 

[d22dave]

Where does the speedo drive from? Older holders had a adaptor between cable and box tp alter ratio for different diff ratio/gearbox, any chance that its just the speedo reading different after the rebuild then,

 

[Dion]

Where does the speedo drive from? Older holders had a adaptor between cable and box tp alter ratio for different diff ratio/gearbox, any chance that its just the speedo reading different after the rebuild then,

Nah the drive gear is what varies it, if the box is a changeover box then that could indeed be different. If it's direct rebuild then it should be the same.