Poor mileage

[compadre]

Hi! Yes i know, it's been chewed more than 100 times, but.......
Have an issue with rubish mpg on a '97 300tdi auto and manual FIP.
On the clock 240630km (~150000miles). Running BFG AT 245/75x16 on 8 spoke modulars. MPG about 20.
What i've done:
-removed cat
-blanked EGR
-cleaned the sedimenter
-new fuel filter
-new lift pump
-changed the FIP, checked static pump lift for 1,4mm with a dial gauge
-new timing belt, timing ok
-new injector nozzles, opening at 200bar with "POP"
-cleaned the intercooler
-checked for damages on boost hoses, all ok
-boost pressure 0,9bar
-made a cylinder compression test; 26, 28,5, 28, 27,5bar
-checked valve clearnace, all at 0,20mm
-checked all fuel lines for leaks
-new air filter
-new engine oil and filter

No noticeable black smoke except at night in my rearview mirror in lights on a car behind me on accelerations.
No blue, grey or white smoke either.
No oil consumption or coolant consumption either.
The autobox shift's smooth, the torqueconverter locker lockes at 78km/h. Oil and filter in autobox is new, also.
Well, with no roofrack and bullbar, no towing, no hills, no citiy, on country roads 20mpg or 14l/100km is way toomuch, i think.

Any ideas? Did i miss something or did i something wrong?
Thanks in advance for your replyes. Sorry for my bad english

[miketomcat]

I'd only expect 30 ish mpg out of a manual on a run, 25 mpg normal driving. So for an auto your only a little down and you have got comparatively big at tyres.

Mike

[Nigelw]

Bonjour

What tyre pressures are you running?

Soft tyres make a world of difference!!!

Have you optimized the pump output? I ask this as although it should make sense to use moor fuel by injecting more fuel it almost works arze about face as you need to burn more to get the torque converter up to max efficiency as fast as possible, flooring it just gives poor fuel consumption.

Apart from that you have done just about everything possible, 300Tdi's have always been heavier on fuel in the auto variant, expect a manual to achieve around 11-12L/100Kms, I have heard of 9.5/10 but those are mostly long journeys with lots of flat motorway.

[ejparrott]

Auto's do use more fuel than manuals, I've also noticed they rev a hell of a lot higher before they change gear than I would in a manual

[ian_s]

you are running bigger tyres than standard, do you correct your mileage for the difference in sizes?

if you havent corrected it, bigger tyres mean you are covering more distance than your odometer actually reads, so your MPG might be better than you think

[Chicken Drumstick]

Some obvious things. How are you working out mpg? And how are you working out distance covered. Refining these might be worth considering, so that you know if your mpg figure is somewhat accurate or not. Not saying it isn't, but you'd be amazed how people try to guess/calculate mpg, which can lead to massive errors in the figures.

Next up driving style. How do you drive? It's not just the types of roads or use, but the bloke behind the steering wheel.

Are you able to offer a range of mpg you've recorded under different conditions? Cruising at 55-60mph on a motorway/dual carriage way should net you the best mpg.

If under this use it returns expected figures then it's probably fine and just down to driving style. If not it gives you more info to work with.

Checking for things binding (brakes) is probably worth doing. Does it have air con? Running aircon or a pump that never shuts off correctly will have a massive affect on mpg.

[compadre]

Hey

Tirepressure is 2.5bar. Today i fitted other tires, 234/70R16. Tomorrow i'll try to raise boost pressure to 1.1bar by shortening the rod on the wastegate acutator.

[Nigelw]

36psi for those that are still imperial

See how you go, that is a good stiff pressure for sure and there should be the minimum of rolling resistance at that pressure.

You could get the boost on sooner, are you planning to up the boost fueling on the pump too?

[Boydie]

On our recent desert tour, (Disco 300Tdi, Manual 5 speed R380 with Defender ratios) on the way home, on black-top with a vehicle well over 3 ton loaded and with Light Truck Bridgestone Dueller A/T 235/70R16 tyres cruising at 90kph (55mph) and with the tyre pressures at 55psi (the maximum allowable pressures quoted by Bridgestone is 60psi for these tyres) we achieved 1200 kilometres for a total consumption of 100 litres of fuel, in imperial that's 34mpg and very good fuel economy but a very harsh ride.

By comparison when we were crossing the Simpson Desert, in loose deep soft sand with the same pay load and with the tyres let down to 10psi front and 12psi rear and for 80% of the total distance we were in low range and with the diff-lock activated for about 40% of that total distance of 420 kilometres from Birdsville to Mt. Dare we burnt up (again) 100 litres and again converted to imperial that equates to 12mpg. On hard packed heavily corrugated tracks we achieved around 20mpg. Such are the varieties of fuel consumption that can be experienced. Incidentally before I converted my Disco to a manual in it's auto days the fuel consumption was fairly much in the same sort of ranges, that only reason for the change is that I can fix a manual out in the bush, repairing an auto is beyond my mechanical capability

.In short I don't think you have much to worry about, its all about, as the Chicken Drumstick said, changing your driving style. I'd also guarantee that this is your first diesel and you are possibly still driving it as you would a petrol engine, for example short-shifting in a manual diesel is a big no-no, it burns up fuel and puts additional strain on the gearbox.