MPG

[sweeney1987]

There's no common rail in a pd though. It's also no more complicated than a HDi, literally the only difference with fuelling is the HDi uses a mechanical pump to pressurise the fuel and the pd uses what's effectively a mechanical pump for each injector. Both solenoids operate in exactly the same way at the nozzle end. Which Chris seems to have failed to understand, yes its a different delivery system, but it does exactly the sane thing, even using the same sensors and actuators! It even uses an edc15 ECU the same as the HDi iirc....

And hdis aren't more complicated than xuds either.....give some computer geek a mechanical pump he'll have no idea what to do....give him an ECU he can write a map. Just because new tech is different doesn't make it MUCH more complicated, its how you personally percieve it, different people find different things easier.

What's interesting though, is I'm looking at a car atm with with a 6 speed box and gt1749 vnt turbo (same as the golf)....BUT with common rail instead of pd.....if I go for it, will be interesting to see what the mpg difference is... Obviously there's a few more variables, but still...

[quote='sweeney1987' pid='193358' dateline='1357939779']
Yes I read it, but its gotta be well atomised to run well with a DI engine in the first place, I just can't see how slightly better atomisation would make such a major difference, I'll take your word for it though. I agree the higher ratios are better (sit in 6th at ~40 just above idle and watch the mpgs mount up), but the low ones (1,2,3) are still awful as with any diesel....there's really no point in 1st as it doesn't get you anywhere, I know its meant for tugging a caravan or whatever though lol.

Anyway....I'll stop now.

VAG opted for the PD engines so as not to pay fiat/GM(forget off top of head but fiat started research) royalties for using common-rail.
the unit injector system has higher pressures than hdis see, thus improving atomisation of fuel, as said the better the atomisation the cleaner the burn and less waste(heat/unburnt fuel) in cylinder thus improving mpg.
There are much technological improvements just you may not be bright enough to notice them
Older design injectors that didnt use piezo crystals for instance dont meter fuel as accurately, causing more fuel than desired entering cylinder, as piezo ones open and close far quicker.
tolerences etc have also got finer in development of the engines.
yes the PD and hdi are of a similar year but comparing two different systems and wondering why one gets better mpg is very dim...

I would love to know how I only managed 45.8mpg on the last tank when driving like a saint when the previous tank got 51 driving spiritedly and idling for ages to defrost. Same route everyday. Low rpm is worse?

very possible, if youre labouring engine instead of using it in torque band you will more than likely use more fuel.