A useful article on PD injection in today's Sunday Times Motoring:

'Among car makers the VW group is alone in choosing the PD (Pump Duse) unit injection system for its diesel engines. While most use common-rail injection, VW continues with the costlier PD system because of certain advantages.

The fundamental difference between it and other diesel injection systems is that with PD each engine cylinder has its own pump to generate the high pressure needed for fuel injection. PD integrates the fuel injector and this pump in one neat unit mounted in the cylinder head and operated by the camshaft. Unlike common rail, there is no reserve of fuel held at a high pressure: injection pressure is newly generated by the PD unit for each engine cycle.

Higher pressure can be achieved with PD injection (more than 2,000 bar against a typical 1,600 bar), which produces greater engine torque and cleaner emissions due to more finely atomised fuel droplets. Fuel economy also benefits for the same reason.

Take a look at the torque from VW's 1.9 TDI PD 130 engine, for example: its 229 lb ft is more than you get from rival engines of similar capacity without PD injection. Vauxhall's 2.0 DTi engine, using distributor-pump injection, puts out only 170 lb ft, while Fiat's common-rail 1.9 JTD motor manages just 188 lb ft.

So why haven't other makers used PD? Because it cannot be applied to existing engines without heavily re-engineering the cylinder head. Also, due to the very small window of opportunity for injection as the engine cams turn to operate the PD pump-injector, less time is available for applying the multiple injections that are ideally needed for super-fine control of combustion, to keep it subdued.

So while PD diesels are the better choice for muscular performance, they tend not to be as refined as common-rail engines.'

Interesting article Denis.

So while PD diesels are the better choice for muscular performance, they tend not to be as refined as common-rail engines.'

I do find my vRS has lots of feedback and can be subtle in response due to the ubersensitive throttle pedal. In which case, I wonder what other common-rail TDis are like to drive :confused:

Xavier, maybe it's a noise thing rather than throttle response. I can't say I recall any significant criticisms of the PD engine from Briskoda owners. What the article doesn't mention is that the PD engine needs sophisticated oil to provide adequate lubrication for the top end of the engine - hence VW 505 01 and 506 01 being specified as appropriate.

Interesting, Denis, thanks for the post. Presumably, locating all the pump and injector bits together gives better control over injection cycle, and reduced chance of pressure variation in the rail.

Clever, those Germans.......

Phil

Interestingly after years of "no common rail for us ", the VW group have a nice new common rail diesel going in the new A8, which I belive is a 3l unit.

Just found out from a friend of mine who works for a car reseach company that the ECU in the fabia vRS is adaptive in the way that as the miles roll on the ecu changes to a different mapping to increase power, that is why the car is alot faster and has better MPG once there is a few miles on the clock.

Interestingly after years of "no common rail for us ", the VW group have a nice new common rail diesel going in the new A8, which I belive is a 3l unit.

I think that the same lump thats fitted to the VW Toureg (sp?)

450+ lbft torque!

I think that the same lump thats fitted to the VW Toureg (sp?)

450+ lbft torque!

I thought the Toureg had a 5litre V10 diesel and the A8 had only "V8" diesels?

V10 is a bit of a monster.

Just found out from a friend of mine who works for a car reseach company that the ECU in the fabia vRS is adaptive in the way that as the miles roll on the ecu changes to a different mapping to increase power, that is why the car is alot faster and has better MPG once there is a few miles on the clock.

I used to frequent Saabscene, a bulletin board just like this one, but for Saabs (we'd never had guessed :P), there was a few people on there who said similar things and told you how to teach your engine to give more power. IIRC you had to stick your car in 4th gear and boot it from below 2000 to above 4500 which would take you above 100mph and then do it again.

Also, it was widely rumoured that the ECU didn't allow full power until the engine was run in at 60,000 miles :eek:

Vince

I used to frequent Saabscene' date=' a bulletin board just like this one, but for Saabs (we'd never had guessed :P), there was a few people on there who said similar things and told you how to [b']teach[/b] your engine to give more power. IIRC you had to stick your car in 4th gear and boot it from below 2000 to above 4500 which would take you above 100mph and then do it again.

Also, it was widely rumoured that the ECU didn't allow full power until the engine was run in at 60,000 miles :eek:

Vince

Its the same with most modern ECU cars.. especially scoobs.. leave ecu unplugged over night when filled with optimax.. and then labour the engine for as long as possible... the engine will adapt the timing to suit the fuel. its not the only way to do it.. but it is the fastest.

IIRC the Octavia 20vt is the same.. which is why it takes 3-4 tanks of optimax to get a big improvement

I used to frequent Saabscene' date=' a bulletin board just like this one, but for Saabs (we'd never had guessed :P), there was a few people on there who said similar things and told you how to [b']teach[/b] your engine to give more power. IIRC you had to stick your car in 4th gear and boot it from below 2000 to above 4500 which would take you above 100mph and then do it again.

Also, it was widely rumoured that the ECU didn't allow full power until the engine was run in at 60,000 miles :eek:

Vince

That would be for cars based on trionic systems. Later Saab 9000 and above.

Known as an adaption run.

There is a fuse to pull that removes stored settings, but retains the normal standard ecu codes.

Basically, if you make any changes (even something as simple as a cone filter, or uprated FPR, ECU reprogram, or changing from Premium unleaded to Optimax) pull that fuse, then do the run as described.

The ECU then learns what the car can do with the changes, and allows for the extra go.

Not owning a Trionic car, I can't say what it does, but it is supposed to give impressive improvements if you have made a lot of small changes, and not done it.

BTW, you can simulate the 100+ MPH by giving the engine something to pull against, such as up a long incline with a full load of passengers, rather than risk your license.