Don't know but both the PDs I have owned have been noisier...
Re the OP, we use a firm at work who have a fleet of Superbs, all 130bhp PDs - the oldest are 52 reg and have clocked up over 250k trouble free miles... PDs good for high mileage? Yes!!
PS Use the proper oil, its about the same price as most synthetics now (it was overpriced originally), so its not worth skimping... and many oil manufacturers do them now so you don't have to use VW stuff!
Edited by b308 on 24/08/2008 at 17:45
|
|
|
Does anyone know why VAG commonrail is quieter than PD?
I am sure an expert will be along soon, but I believe that common rail systems are more flexible with timing and multiple injections either side of the main injection pulse.
|
|
Yea i always use the 505.01 oil and love the engine. Yes it is noisy but in my Fabia it absolutely flies and should last as i never really push it save for the weekly trash through the gears as recommended by HJ. It was the boss that made me ask about longevity though as in a Q & A in an old copy of Used Car Magazine he counsels caution against a person buying a Golf TDI PD as " the injectors tend to wear by 150K causing an uneven spray that tends to wear one side of the bore out" I am paraphrasing but that is what the man said.
|
" the injectors tend to wear by 150K causing an uneven spray that tends to wear one side of the bore out"
This was widely discussed in about 2000. I've never seen, or heard, of one single case; if it wasn't a faulty batch, or mis-reported TSB, then it would appear that it's been solved.
The only PD to avoid like the plague is the 150PS ARL.
|
|
|
All the characteristics of a traditional diesel (noise, smoke, vibration, brilliant economy, superb reliability) with real guts behind it. Mapped very cleverly to make it feel incredibly quick from low revs / gentle accelerator input, which is how most people drive.
Well regarded for a reason. Good engine. Some anecdotal evidence that the 2.0 is not as good as the 1.9 as a long term ownership prospect, but again, the same anecdotal evidence suggests they are more reliable in general terms than common rails.
Cheers
DP
|
|
I can vouch for the reliability - my 4.5 year old Golf 150bhp PD unit has just run to 140K and is still returning 55mpg. It is on longlife servicing, so needs the different spec longlife oil. Having said that, it tends to use about 4 litres every 10K, so does get a sort of oil change every 10K!!
|
|
I find it mildly amusing that vw pd engines need a "special "oil when land rover td5 engines dont have the same needs ,can anyone tell me why this should be ?
|
...Because the oil usually outlasts the engine on a TD5?
It's probably more to do with cam-follower wear that anything to do with the unit injectors.
|
|
Yes the cams are only around 10mm wide in order to accomadate the PD injectors and as a consequence of the pressure exerted on them per square inch being so high, the require a 505.01 or better oil (506.01 or 507.00)
|
>>pressure exerted on them per square inch
Please forgive the pedantry.
pressure is already force divided by area - it doesn't make sense to talk of pressure per square inch.
|
|
I was under the impression they both used bosch pd units so couldnt see the need for differant oils but a weaker camshaft set up on the vw would explain it
|
Yes, it's actually the cams which operate the engine's valves which are the problem on PD engines, the actuation of the unit injectors is quite robust.
|
I have got 2 VW 1.9 TDIs and a Defender TD5.
I have just been to fetch the Defender, from a field which I had combined, in a Golf 1.9TDI.
On leaving the Golf and getting into the Defender is like going back 30 years, talk about life on mars.
On the way to the field, 10 miles away, the Golf did 47mpg driving quite fast. Heaven knows what the Landy did on the way back.
Defenders are good at pulling trailers or going into fields, but as to comfort they are hopeless. Try driving on a hot day when the gearbox gets warm, it's like being in an oven.
As to oils, what are you supposed to use in a Landy gearbox? It is just as complicated as the VW oil stuff.
|
As to oils what are you supposed to use in a Landy gearbox? It is just as complicated as the VW oil stuff.
Texaco MTF74 according to Autodata; I think L/R do a special product.
|
As to oils, what are you supposed to use in a Landy gearbox? It is just as complicated as the VW oil stuff.
hytran works fine
|
>>Does anyone know why VAG commonrail is quieter than PD? Are there non-related mods that quieten the engine, such as a different block, more sound deadening euipment, etc?>>
PD is actually a very illogical design, running seperate unit injectors off a belt driven camshaft, putting additional load on that most fragile of components, the cam belt, and at the same time compromising the integrity of the valve train. Not to mention the fact that this approach means that the injection timing is intrisically linked to the cam timing and cannot operate indepentently to control knock etc as per a CR system - which answers the question.
|
Illogical in some respects, and logical in others.
The only currently produced diesel engine that doesn't rely entirely on the fuel to lubricate the injection equipment.
The only currently produced diesel engine without a single potential point of failure in a very expensive injection pump.
The overall result is a noisy, smoky, but remarkably fuel efficient engine with excellent performance, and which is almost universally praised by owners for its reliability and longevity. Whatever the rights and wrongs of the design, you rarely hear of expensive failures that don't involve skipped cambelt changes or some clot putting the wrong oil in.
I've never understood personally why they chose not to run the injectors off a separate chain driven cam with "full width" lobes, but then I'm not an engineer.
Edited by DP on 27/08/2008 at 10:04
|
>>PD is actually a very illogical design
I can't agree with that.
In VW's implementation, perhaps a chain drive would have been better than a belt drive - but, is there any evidence to suggest that the belt drive on these PD engines is actually a common failure point?
The idea of using some extra lobes on the cam to pressurise the fuel is a very good one (and has been used on some commercial vehicle engines for many many years. The advantages of doing this are that you can create higher fuel pressures than an externally mounted jerk pump, and, with electronic control of the injectors, the timing is not intrinsically linked to the cam timing, it's under ECU control, and the injectors can operate independantly.
Again, in VW's implementation, they haven't left enough room to make the cams which work the valves to be wide enough - hence the silliness with the engine oils.
Yes, common rail does give you more fuel pressure, and more flexibility, but, given a choice, at the moment, I would chose a PD every time. Well, actually, I would go for an inline injector pump. like the one fitted to our E300D!
|
|
I agree Unit Injectors are not illogical in themselves. Most heavy truck engines from the likes of Cummins, Scania run the system although Common Rail is increasing bcoming more popular. I agree though that VW should use Chain Cams. In factI am with HJ on this, all engines should have a chain and cost cutting by accountants on such a criical piece of componentry is criminal.
|
|
It keeps the "service centres" going when they have to be replaced, though, you've got to leave something interesting for them to do instead of oil changes all the time! ;)
|
Who says that chains are better than belts? A well-designed belt can easily match a chain for wear life; although I do accept that a chain may have an advantage if time becomes a factor. [Providing the oil is changed annually to prevent acidification from short runs.]
If VAG had taken the person who designed their PD belt tensioner out the back and shot him; then they would have had far less trouble with their belts. A wide belt with a gas-pressure roller does fine for the Japanese; the Germans forgot KISS.
Particularly in the era of stupidly-long service intervals; chains have no inherent advantage - another urban myth.
|
This thread coudn't have come at a better time - I've just ordered a Touran 2.0 tdi (140)...
Something else to obsess about!
|
Particularly in the era of stupidly-long service intervals; chains have no inherent advantage - another urban myth.
This is a genuine question - does a chain not usually give an audible warning in advance of a failure, or do they fail as "suddenly" as a belt?
By suddenly I mean with no symptoms visible or audible to the driver or casual observer.
Cheers
DP
|
DP
Your, valid, question contains an assumption that it's the belt that fails through fatigue. In most cases, it's an external cause that leads to catastrophic belt failure.
It is indeed quite easy to design a chain to rattle a warning once it exceeds the tensioner's abilities - except for Nissans Hi-Vo, of course...
[And no; I still haven't managed to get those Hi-Vo drive chains fitted...]
|
|
Well consensus seems very good compared with what I have read about common rails. If I get rid of my Fabia for womething bigger it will be an Octavia with the PD tech again. I won't bother with the new Commonrail engine due. I quite like the gravelly nature of the engine. It feels strong and unburstable like a commercial engine, which seeing that it is used in the Tranporter as well, is. Plus I have ever driven anything that has such response "out of the hole"(right at the bottom) this side of a V8. I doubt the VW CRs will punch so hard. This is what I hear from the mags.
Edited by Mattbod on 28/08/2008 at 12:25
|
I dispute the fact that the PD has better fuel economy that a CR (based on 50K on a common rail, and 70k in PD's)
Dynamically and efficiently the Renaul Dci has the PD whupped in economy, NVH, and power.
I like the PDs* power delivery tho, I kinda like its honest growl and its feel gutsty honest and responsive,
*105 - 140. The 170 is an awful thing with a nasty shoprt peaky power band
|
A quick note on cambelts etc, when I had my B5.5 Passat PD I looked into cambelt service intervals in different worldwide markets.
In the USA, the cambelt service interval on the PD engines used in Golfs & Passats is 100K miles, not the 60K recommended here (I was unable to establish the suggested time / years interval).
Why such a difference? I can't believe the US-market motors use a stronger cambelt, because the logistics of part numbers, spares stocks and assembly wouldn't make sense.
|
As a PD engine owner and (commercial) diesel engineer I would make the following comments concerning this engine:
Injected fuel pressures using this technique are higher than those produced by any other system including common rail. The AWX engine fitted to my car can inject at up to 2,000 bar (30,000 PSI) which is beyond the capabilities of standard pipe fittings - which of course these engines don't use. It is the high injection pressures which give the basic (1.9) PD engine its unmatched efficiency.
At high injection pressures which are necessary for a good performance/smoke ratio, roller follower wear in the pump element system is a problem particularly when the pressurising ststem is fuel lubricated (common rail). With the PD unit injector system, all of the highly stressed parts are engine oil lubricated. Bosch were responsible for the design and manufacture of the PD fuel system and no doubt stipulated the injector cam width. Unfortunately this left very little room on an existing basic engine (bore centres already defined) for the valve actuating cams which are narrow. The special oil was the "fix" - it's a pity and its implementation was cocked up royally by VAG but there it is.
Likewise, the cambelt drive was a carry over from the "old" diesel - tooling up for a chain drive would have required more radical engine changes and consequently a fairly durable belt drive was designed. Despite some almost desperate engineering measures such as wider teeth slots on the crank wheel at critical points to accomodate transient belt stretch when the injectors pressurise (camshaft slows down) and the engine fires (crankshaft speeds up) the system is fairly reliable. I do not believe that VAG UK's stipulation of a 4 year change interval represents world wide practice. Interpret this as you will.
The PD is noisier and rougher than a common rail engine because pilot injection is more difficult to arrange. The way it's done on the PD is a bit of a bodge but does not in any way detract from the engine's efficiency. It is not true as has been suggested that the injection timing cannot be varied by the ECU on a PD. The fuelling cam is arranged to pressurise the system over the whole range of engine operating conditions and the actual commencement of injection is under direct ECU control via the solenoid or peizo actuator fitted to the unit injector.
659.
Edited by 659FBE on 30/08/2008 at 20:46
|
659 ,thanks for educating me and perhaps others . Could you explain " pilot injection" and why that affects noise/roughness... in simple terms please!
|
Putting things as simply as possible, one reason why a diesel has the characteristic combustion "knock" is that the fuel tends to burn in a relatively uncontrolled manner following injection - unlike a petrol engine where the fuel/air mixture burns at a fairly well defined speed provided the ignition timing, engine compression ratio and the anti-knock properties of the fuel are favourable.
The way in which the fuel burns has direct implications as far as the rate of rise of cylinder pressure is concerned following fuel ignition. In a "simple" diesel, the rate of pressure rise is high and the engine feels and sounds rough.
As a means of limiting the rate of rise of cylinder pressure, one of two things can be done. The first method (old solution) is to inject the fuel into a pre-chamber annexed to the main combustion chamber and connected to it by way of a narrow passage. This has the effect of slowing the rate of rise of cylinder pressure in the main combustion chamber due to the constriction, and the engine runs more smoothly. This is the indirect diesel injection system (IDI) which works well enough but which gives sub-optimal efficiency due to pumping losses between chambers and because the dual chambers together have a poor surface area to volume ratio giving higher thermal losses.
A better way is to use direct injection (DI) but to introduce a small quantity of fuel (pilot injection) ahead of the main fuelling shot. This allows a flame front to be established without an unacceptably high rate of rise of pressure. Injection of the remaining fuel a few ms later allows a more controlled "burn" as a flame centre has been established by the pilot. Most modern DI engines (including the PD) use pilot injection as a means of controlling combustion rate, but it is fair to say that the vital control of both the quantity and timing of the pilot injection can be executed more precisely with a common rail system.
For me, I'd rather have an efficient engine which works well enough nearly all of the time (PD) than a system which tries to extract the almost impossible compromise of very high injection pressures derived from fuel lubricated roller followers (common rail HP pump) where the fuel lubricity is less well controlled than that of engine oil.
I must stop writing text books.
659.
Edited by 659FBE on 31/08/2008 at 00:24
|
|
Wasn't a PD type system used for years by Cummins???
|
The Cummins system was the PT (pressure time). It did use unit injectors but the implementation was not too clever - ECU mounted on the engine for instance. The incoming fuel from the tank was arranged to cool it but the soak back temperatures ensured that the ECU was thermally cycled beyond what was reasonable - in my judgement - for its method of construction.
659.
|
I must stop writing text books.
659,
Quite the reverse, both your posts on this topic are a model of clarity.
If you are not writing text books, you should be.
|
I must stop writing text books. 659.
Please dont stop!
|
|
|
>> Does anyone know why VAG commonrail is quieter than PD?
The trouble with PD is that although it achieves very high injection pressures only just matched now by the latest common rail systems, the noise is due to the lack of ability to do multiple and 'pilot' or pre injection cycles the way that you can with common rail.
But this noise is only evident at tickover and in fact my car (Audi A4 2.0 TDI) seemed less dieselly than a common rail 2.0 C Class Mercedes I recently went in.
It is this plus the limit to how much you can get the emmisions down to the new standards that has brought PD to the end of the road.
It was widely acknowledged a couple of years ago, that the VaG PD engine was the most efficient diesel out there, but all of the Euro iV emmisions gubbins now fitted to the 2.0 TDI engine have spoilt this.
|
|
Common rail is just a means of getting fuel to a high pressure, so its not intrinsically superior, SFAIK. In the PD the function of pump (the final part of 3 stage pressurisation) and injection control are combined. Multi-injection and pilot function is determined by the injector control system and the ECU. Perfectly possible to have PD with multi-injection cycles. The 170 hp 2.0 PD engine, and the V6 and V8 are fitted with these. IIRC, the cost of the piezo-electric devices, on top of the expensive PD system, and the development of higher pressure CR systems (still not as high as PD though!) have caused VAG to alter course to CR. Cost saving perhaps.
|
the development of higher pressure CR systems (still not as high as PD though!) have caused VAG to alter course to CR. Cost saving perhaps.
>>
Fair comment, but the new 2.0CR VaG engine is now whisper quiet, possibly the quietest 4 pot diesel on the market, especially as the PD engined cars had almost become the noisiest modern diesels. I still dont entirely agree that PD is as flexible in terms of multiple injections though.
Edited by Roly93 on 31/08/2008 at 20:52
|
The real limitation with the PD system as used by VAG is the control of pilot injection. It is effectively done hydraulically by means of a stepped upper plunger on the injector needle and a retraction piston above the injector needle spring which alters its preload. A lightly preloaded needle spring gives the low pressure pilot injection. The retraction piston then moves down its bore preloading the spring and main injection then occurs at full pressure.
Without posting diagrams it's difficult to explain this precisely, but suffice to say that with the PD as originally developed, the timing and quantity of the pilot shot are fixed by the injector geometry relative to the main fuelling quantity.
With a CR system, pilot injection is easy to control and both quantity and timing relative to the main fuel shot can be adjusted by the ECU to suit differing engine conditions of speed and load.
As pilot fuelling has little actual effect on engine efficiency and the vital highly stressed roller followers are engine oil lubricated on the PD it still gets my vote. There are many, many more specifications for the lubricating qualities of engine oil than there are for fuel.
659.
|
"With a CR system, pilot injection is easy to control and both quantity and timing relative to the main fuel shot can be adjusted by the ECU to suit differing engine conditions of speed and load." Any reason why the control is not possible on a later PD, given the piezo-electric being substituted for the original method? My take on this is that the PD is simply another pressurisation system plus control of varying subtlety. The later piezo-electric control achieves similar control over the dosing of fuel as CR, if CR is so equipped. I think.
|
I think the answer to your question is that there is no theoretical reason why timed and metered pilot injection could not be applied to the PD but there are strong practical reasons.
Remember that Bosch spent a lot of money on this fuel system and that in the end there was only one taker - VAG - albeit a high volume user. Further fundamental development by Bosch was therefore unlikely to happen given a climate of multi-user CR systems. The adoption of a piezo actuator to replace the solenoid fitted to the early PDs was about the only change made and the basic configuration of the unit injector assembly which has to fit the cylinder heads expensively tooled for by VAG could not materially change.
This leaves the control element positioned towards the top end of the nozzle and in the case of the electromagnetic type, having a high inertia armature (control plunger). I have not seen the drawings of the piezo version and would be reluctant to comment in detail for this unit, but I would suggest that the control element is too far removed from the actual nozzle in either type to make a precisely controlled pilot injection possible.
VAG's ultimate adoption of CR probably bears this out, but I have a suspicion that they are keeping PD engines on the books. If fuel density and viscosity can be adequately controlled, the PD system is admirably suited to multi-fuel applications, given its virtual non dependence upon fuel lubricity. If far-reaching changes to fuel quality should occur in the light of the recent price hike in mineral fuel, the PD might just have the last laugh.
659.
|
I think unit injectors are used in many commercial engines.
I may be wrong but I vaguely recall that patent issues with Fiat were behind the adoption of PD by VAG. Maybe those patents have expired now.
Edited by brum on 02/09/2008 at 00:52
|
|
Thanks 659. Could well explain the reported greater refinement of the CR TDI, along with changes to more central location of the injector in the combustion chamber due to the 4-valve layout of the 2 litre.
|
My last car was a 99 peugeot 406 HDI, which is a common rail diesel engine (Peugeot were always ahead of everyone else with diesel technology... I can't wait to see what they come up with next)
I currently have a Seat Toledo with a VW TDi engine and I also manage a fleet of VW's with PD engines. The old 406 was much smoother and quieter than the PD engines made 9 years later!
We recently got a new Audi A4 onto the fleet with the newer 2.0 CR engine and its smooth and quiet just like my old 406 HDi. I hope they roll out the CR engines over the whole range.
The PD has indeed been reliable (up to 100K per car max) We've covered around 2 million miles in VW PD engined cars and only had one catastrophic engine failure, which is pretty good going.
|
(Peugeot were always ahead of everyone else with diesel technology... I can't wait to see what they come up with next)
At my last company, the standard issue car for engineers was a 406 HDi 90 estate. Woefully underpowered, but very, very quiet and smooth. We had a fleet of 30 or so, all on V registrations. All suffered repeated issues with the CANBUS wiring system (horns going off at random, indicator stupidity, erratic instrument readings etc), but mechanically they were very impressive. Between 80,000 and 140,000 miles on all of them when they were returned to the lease company, and the only mechanical problems were caused by three of them being misfueled (and run).
I ran one for a few months, and apart from barely being able to pull itself up a hill when carrying any sort of load, thought it was a very pleasant car.
|
Without posting diagrams it's difficult to explain this precisely but suffice to say that with the PD as originally developed the timing and quantity of the pilot shot are fixed by the injector geometry relative to the main fuelling quantity.
Detailed diagrams and operational description here:
www.myarchive.us/richc/VW_TDI_with_PumpeDuse.pdf
|
|
Terrific link many thanks. All one ever needs to know about the TDI PD.
|
The final nail in the coffin of the PD was the requirement to provide burn-off fuel for a DPF. With a CR system it's easy - just open the injector whilst the appropriate exhaust valve is open and the fuel will go straight through to flame the soot filter.
The PD can't do this - the cam timing is such that it can only make pressurised fuel available at around the time the engine should be needing it - near compression TDC.
Ironical really - the PD is undoubtedly the best system for providing timed, highly atomised fuel precisely metered within a short time window, which is why the early PDs were amongst the most efficient diesels ever produced. They were also relatively insensitive to fuel lubricity. What has killed them is the (political) need to make diesel engines less efficient by introducing fuel which does no work.
659.
|
|
That explains reports I have heard of VW/SEAT/Skoda owners with DPF fitted PD engines having a lot of grief. There was even a warning in the Golf brochure not so long ago that said a DPF car may not be suitable for prolonged urban use.
|
|
There's no DPF in my Roomie - I'm glad, mind you its regularly given a sound thrashing.
|
|
Nor in my Golf, praise be.....but if I read you right, 659, there shouldn't be a DPF problem with common rail engines. Is that correct?
|
No - not necessarily. A soot filter is a bodge because it doesn't stop the engine producing soot. So, it has to go somewhere and the current solution is to burn it off. You can do this either by introducing useless extra fuel as outlined above, or by using an additive to induce regeneration (burn-off) at a lower exhaust temperature.
It seems to me on perusal of the test schedules, that the CO2 generated during the burn-off cycle is not included in the engine's CO2 rating (gm/km) - so the whole thing is rather mis represented.
My observations are that DPFs tend to cause trouble or considerable expense on any engine to which they are fitted and I wouldn't wish to own one.
659.
Edited by 659FBE on 08/11/2008 at 23:46
|
|
Many thanks. 659. Another reason (as I've said in the diesel 'hassle' thread) why next time if possible I'd like to find a truly efficient petrol engine which manages to combine strong low-down torque with good economy.
|
Without going back into text book mode, the Laws of Thermodynamics are against you.
Unless "political measures" as applied to diesel engines reach lunatic levels, you will never get a petrol engine to match the efficiency and low speed torque output of a diesel. They are fitted to ships, trains and HGVs for a good reason.
659.
|
|
How would I know whether a DPF is fitted to my wife's 57 reg Golf 1.9 TDI?
|
|
If its the same as the Roomie if you look at the data sticker in the Manual or in the Spare wheel well, you'll see a load of codes, one of these codes relates to the DPF. The manual will help you de-code it.
|
|
|
|
