As our few diesel boys will know, I've been putting some work into reducing the urban fuel consumption of mine, currently achieving on last check 36mpg. This is a bit of an uplift on the "book" figure of 26mpg.
I found the cold-running program was responsible for much of the fuel losses, and I did it without a reprogram of the micro. The retarding of fuel injection was too much and for too long.
I could do a little article on this, but it's a lot of work, and it can't translate to petrol engines as the cold-running enrichment and acceleration enrichment methodology doesn't exist with diesels. That would need a completely different approach, although I guess SOME fuel savings could be made.
But if anyone wants, I WILL outline my diesel modifications which are simple and could be done by anyone in half an hour or so. De-modification would take only minutes.
Leedsman.

 

Leedsman - 36mpg??......thats terrible for a diesel!

My A6 around town routinely gets around 38mpg and once on a longer run here n there can achievemid 40's.
If I'm on a really long run consistently I get much hugher and have seen 52.1mpg

I and other oi burners wuld be really interested to read your process on this though, so if you can post I'd really appreciate it

 

Here are the Gov. mpgUK figures for diesel cars similar to the S-type 2.7D., URBAN ONLY. All are automatic.

Jaguar S-type 2.7D.........26mpgUK.
VW Passat 2ltr...............28mpgUK.
Citroen C6 2.7D..............23.5mpgUK (Similar engine to S-type).
Audi A6 2.7D..................28.5mpgUK.
Audi A6 2ltr....................32.1mpgUK.
BMW 530D.....................26.6mpgUK.
Merc. E-class 220...........32.1mpgUK.
Merc. E-class 280...........28mpgUK.

These figures indicate that, as usual, the bigger the engine one has in a car, the worse the fuel consumption. This is especially true if using hypermiler driving techniques. The figures indicate all the cars are very similar, the Jaguar being neither especially good, nor especially bad. The Citroen C6, having a very similar engine to the Jaguar has actually a WORSE fuel consumption. Indicating that Jaguar's modifications to the 27D Peugeot engine has had beneficial effects. This is prob. due to the piezoelectric fuel injectors. I can't imagine that the Jaguar weighs less than the C6.

When evaluating my own Jag. 2.7D., mpgUK., I used the brim-brim method, not the fuel consumption computer, as it is too erratic, can easily have an error of + or - 10%.
Fuel used as test is BP "Ultimate" diesel, all short journeys less than 15mile.

The fuel economies have worked out as follows in order of effectiveness:--
1) The cold-running injection timing mod.
2) Sump heating the engine oil electrically, before morning start: about 1.5 to 2 Kw/h.
3) Driving techniques similar to hypermiling, and using the autobox change-strategy.
4) Ensuring the tyres are properly inflated; overinflating does not save fuel, but underinflating certainly wastes it. Currently using 35lbs front, 30lbs rear.

So I don't think going from Gov fig. of 26mpgUK urban to my own fig. of 36mpgUK urban is 'terrible for a diesel'. I think I can give myself a little pat on the back; certainly need it after all the work!

Talking of work, I will outline the latest methodology if anyone else is seriously interested, but it IS work.

Leedsman.

 

WOW, leedsman, sounds like your on the right track, keep posts and we can follow yor work.

maybe some details of what you did!
ron

 

darn ,if only we could get someone to modify the ECU programs&maps for the diesels, here in USA not many people interested in diesel cars.

we cant even buy a Jag s type diesel car.

 

It depends a bit on driving style. If I conciously drive econically my XF 2.7 gets 33mpg in urban mix involving lots of very short trips (1 - 2 miles) and some 30 mile trips. If I adopt a press on style it drops to abot 29mpg. (Measured over one week at a time with a very similar pattern of trips.)

 

I would comment that the Gov. fuel consumption figures are actually qualified by the Gov. dept. doing the test as "comparative" figures. They are carried out indoors using a rolling road and under closely controlled conditions following an identical test pattern for all vehicles tested. There is a cold-running test. They themselves point out that in actual driving conditions and with different drivers the fuel consumption figures will vary considerably from the totally controlled conditions of the test.
Leedsman.

 

i didnt see the VW Jetta 2 L TDI listed!

one of the few diesel cars we can get in USA.

some people,who practice Hyper mileing, have reached around 48-50 miles, US gallon , per mile, using the latest version of VW TDI.

it works, but takes practice, and you better not be in a hurry.

 

Leedsman - sorry, my bad!
My comment about being "terrible for a diesel" was aimed at those figures as against motorway driving and not Urban, please accept my apologies.

I for one as a diesel driver of many years am very interested to see what you've done in more detail.

Please post it up when you can

 

My old XJ6 (2006) Executive TDVi used to get a regular 48-50 average on motorway runs. I reset the com while driving at 68mph on the M1 Bedford to Luton one night and the com suggested average was 66mpg. This might explain the general average of high 40's and low 50's.

I now have the XJ6 Sovereign LWB 2007. Tried it in this one and again, high 40's is a regular at 68mph in cruise. I tried resetting while cruising and got 64 mpg displayed until either peddle pressed. Then it drops like a brick to mid 50's.

If only other people were able to drive at a steady speed and save me from having to come out of cruise. These cars are absolutely incredible on fuel.

Ray

 

Leedsman??
Are you going to share??

I'd be interested to see whats what for sure..........

 

I also have noted that the cold running performance on my 2.7D seems a bit excessive. Would be very interested to see what you did Leedsman.

 

Davidbr, please read my previous postings re. 2.7D fuel consumption. The program-shift for cold-running injection timing was achieved by wiring a 10K0 (10,0000 ohm) half watt carbon film resistor across the coolant temperature sensor. With this value, the main cooling fan was not actuated improperly, but as the start-program is separate, there was no change to start-up. For half a mile or so, the engine is very slightly noisier, just like old diesels. This mod. has been in use for over a year -- no problems.

Do not waste your time doing anything with engine oil or employing engine oil additives. They make no measurable difference. Except in your pocket. The only real way to improve cold-running economy, is to take "cold" out of the equation by pre-heating the engine before you start. BTW, the front-panel engine temp. guage is so non-linear, it is unreliable to judge if the block is at normal-hot temperature. I have a separate block temp. check of my own, it indicates that it can take 10 miles urban running, even in ambient of 18*C. to get to 70*C. When the front panel reads normal-hot, the engine is only at 47*C. This has nothing to do with the mod. Curiously, the engine takes a very long time to cool down when parked. After 3 to 4 hours it is still at 40*C.

Around 70% of engine friction is between piston, rings, and cylinder wall. When engine is cold, this friction coefficient rises between three and FIVE times depending on which boffin you read. Hence poor economy performance when engine is cold, made worse due to the long diesel warm-up time coming from the superior efficiency of diesel system -- i.e., much less combustion heat wasted in the coolant.

Hope this helps in your endeavors.

Leedsman.

 

Anyone considered Terra Clean?

http://www.google.co.uk/url?sa=t&rct...iRXu3p6HGqJ81w

As seen on Wheeler Dealers





This process is available for both petrol and diesel engines.

Something I'm considering doing to my Audi A6. She's now sitting at 95k miles and is running fairly sweetly to be honest.

I have recently replaced the fuel filter and also removed the EGR valve and decarbonised that, I stopped short of removing the intake manifold though so I'm sure I could still see some benefit from this.

Anyone?

 

one of the products we use around here is SEAFOAM fed into the fuel rail, seems alot of people do like the results!

myself have used a water mist spray for many years,on different vehicles. FYI.

nowa days they have dedicated water/alcohol injection systems that vary the output according to requierments.

i have taken some of the engines down for inspection and found them amazingly clean in ports and chambers!

 

Does the carbon film resistor method still works to have better mpg ?