Great thread, thanks to all

Very informative Ross, i think everything i wanted to add was said by rotodiesel.

Wasn't CR invented by FIAT of all people :eek:

One question i have. I thought that CR diesels with a DPF went into a regeneration cycle every so often when needed. If the PD uses an extra 'blip' on the cam does that mean it is always regenerating or have i missed something?

I would imagine the next big step for car diesels will be SCR, many trucks have been using it for years now. I wonder how long before we start having to fill up with urea and been taxed on that as well as diesel.

SCR is only one technology for particulates reduction; EGR also applies, and is already used in light diesel applications.

SCR is only one technology for particulates reduction; EGR also applies, and is already used in light diesel applications.

The problem with EGR is it can only go so far, its surely just putting off the inevitable! All truck engine manufacturers had to choose a path.. EGR or SCR. I remember a few years ago the manufacturers who chose EGR were banting around 'Ad Nothing' in response to the urea being called 'Ad Blue'. Its all carp really as they will have go SCR eventually. To my knowlege you just cannot achieve the kind of reductions needed for Euro 6 with EGR alone.

Thats an interesting article, I've often wondered why VAG moved from PD. I guess now I know.

Thanks everyone

As I understood it another factor was that PD units were significantly dearer to produce 'per car' because there are effectively 4 pumps whereas a CR engine only uses one fuel injection pump.

It's very difficult to make a cost comparison as there are so many differences and the costly bits are all supplied by (in this case) Bosch who will have their own pricing policy. I suspect they let VAG have the PD kits very cheaply as an incentive to other vehicle makers - it didn't work.

A set of 4 unit injector nozzles would certainly cost less to buy OE than a pump + 4 nozzles. Added to this, there is no plumbing, so lower assembly time and no separate high pressure pump drive.

The downside is that the camshaft drive, camshaft, followers and rocker gear are all special and made to be about twice as strong as conventional drives - look at the width of a PD engine cambelt.

I suspect that overall, the PD installation would have been priced by Bosch to represent an overall saving in engine cost (including assembly time) in relation to its performance. Other events (DPF) overtook it though.

The PD is still about the most efficient oil burning prime mover ever produced - I'm glad to have owned one.

rotodiesel.

Superb thread, very informative. Much better than the "What tyres are best" kind of thread.

Very informative Ross, i think everything i wanted to add was said by rotodiesel.

Wasn't CR invented by FIAT of all people :eek:

One question i have. I thought that CR diesels with a DPF went into a regeneration cycle every so often when needed. If the PD uses an extra 'blip' on the cam does that mean it is always regenerating or have i missed something?

I would imagine the next big step for car diesels will be SCR, many trucks have been using it for years now. I wonder how long before we start having to fill up with urea and been taxed on that as well as diesel.

The Touareg is already running a urea based system on the V10 diesel.

Both the CR and PD engine regen when they need to on top of the regular passive regeneration. The solenoid on the PD injector controls fuel quanity so even if the plunger is down driven off the camshaft it can open up the return line so no fuel is injected.

In terms of advantages then....

CR systems allow lower static compression lowering rattle/noise and further reduce it by early pre-squirts of fuel.

CR systems allow fuel timing to be altered as engine revs increase, increasing the effective rev range, and in theory, the maximum power.

PD systems allow greater efficiency but over a smaller effective rev range.

PD systems control of fuel timing is limited by the camshaft timing operating the PD units.

.........................

In terms of what is required to meet emissions regulations. I had a feeling that EGR is primarily used to reduce NOx emissions whilst DPFs trap and later burn particulates - i.e. partially carcinogenic soot.

..........................

Abstract thought... Does this mean you can regenerate your DPF by p*ssing down the exhaust manifold?

J.

Yes EGR does reduce NOx but it does it by recirculating the exhaust gas back into the cylinder. SCR works differently, its a chemical reaction between the exhaust gases and the urea that happens inside of a catalyst. Both reduce NOx, just SCR is better at it. Here is some science for you Selective catalytic reduction - Wikipedia, the free encyclopedia

DPF's are different, they capture exhaust particulates and produce smaller particulates. From what i recall, thats all they do. Make the particulates so small they cannot be measured by standard testing equipment, lovely

A few points. The PD system does allow for ECU controlled timing of the injection, it's just that the cam profile places limitations as to how long pressurised fuel is available for late injection for DPF afterburn. (Hence the modified camshafts for the DPF vehicles).

The CR system allows for fuel to be injected at any point in the cycle but, significantly, it allows far greater freedom of pilot injection control. This enables a small pilot quantity of fuel to be injected ahead of the main fuelling shot in order to establish a flame front and also limit the rate of rise of cylinder pressure on main injection. This is why the CR engines are smoother and quieter than the PDs.

The pilot injection system on the PD nozzle (stepped plunger) is a bodge and allows no independent pilot control - that's why it doesn't work very well.

However, the PD system has one huge advantage over CR. The fuel pressurising cam and roller run in engine oil and not fuel. The lubrication of CR pumps is very marginal at the operating pressures used - which is why a dose of petrol kills them. Not so with the PD, but don't try it.

The PD is unrivalled for efficiency (pilot injection does not influence engine efficiency) and for durability - which is why so many commercial diesels use unit injectors (common speak for PD). Given the continuing problems with DPFs under conditions of heavy traffic and the dubious long term prospects of CR pumps (see how Ford are getting on), I'll take good care of my non DPF (AWX) PD - its output and efficiency are outstanding.

rotodiesel.

Seems like a good excuse to use Miller DieselSport 4 or even a shot of 2stroke oil to add lubrication the diesel fuel (as the sulphur content has been got rid of).

Edited 6 May, 200917 yr by bahnstormer vrs

Intresting read, thanks mate for highlighting the diffrence.

so if the PD engines unit injectors are lubricated by engine oil, in theory you can run even the newer PD140/170 on pretty much any oil thin enough to get through the injectors? i.e. warm, filtered veg oil?

Just as you could spend a lot of money on a racehorse and feed it on Weetabix.

If you are going to invest in sophisticated machinery, it's best to stick to the maker's recommendations. The PD fuel system is durable but not immune to misuse.

rotodiesel.

Well your completely fukced if you put petrol in a CR...lol

.

I have a question around your quote above,

I am ashamed to admit after 20 years of owning a diesel, I put 90p worth of unleaded in my car at the start of filling up, then immediately topped up with £23 of diesel, whilst at the time i was not overly concerned, having had a PD Fabia vRS, & read lots of info on this not being a major problem,

I am now slightly concerned that I may have done some damage based on your quote above & given that Fiat also use CR on their current diesels.

My question is . Dear Dr am I right to bt concerned ?

I have a question around your quote above,

I am ashamed to admit after 20 years of owning a diesel, I put 90p worth of unleaded in my car at the start of filling up, then immediately topped up with £23 of diesel, whilst at the time i was not overly concerned, having had a PD Fabia vRS, & read lots of info on this not being a major problem,

I am now slightly concerned that I may have done some damage based on your quote above & given that Fiat also use CR on their current diesels.

My question is . Dear Dr am I right to bt concerned ?

P.S. I have since had 4 full tanks of diesel on top of this, & the only reaction I got were 2 slight pops, around 3/4 empty tank ( when petrol was put in).

I'm pretty sure you've got away with it then. It used to be quite common to run 5% petrol in truck engines in really cold weather, but that was with fully mechanicial low pressure (all things are relative) indirect injection engines.

I don't think it would be wise to run a PD on veggie oil to be quite honest.The system is durable but the top end ,particularly the followers that drive the pump, are under tremendous pressure. This is why you have to use a special oil in these engines which is specially blended to protect the top end.

Steve I think you have been v lucky. CR systems from what I have read are normally wrecked by petrol as they need the lubricity of Diesel. I would get my tank drained even if I had only put a litre in however your car seemed to run fine on Friday!

The unit injector roller followers don't usually give trouble on the PD engines - they're over engineered with an input from Bosch. To make room for the giant injector cams, the valve cams are very narrow and operate at high pressures - hence the special oil. Valve cam and follower failure is becoming fairly common on PD engines now as they all age, especially when the oil is not to spec.

Worryingly, camshaft shell bearing failures are showing up - the PD rocker pressurises the camshaft onto its lower bearing shell - which is where the oil feed is. As oil should always be introduced into a plain bearing on the unloaded side, I'm not surprised they fail. The bearing surface is also cut back to clear the valve followers - just where it's needed most.

It's almost as though VAG forgot when they designed the PD camshaft that the forces all apply in the opposite direction - due to the rockers.

Pity, but it's still a very efficient engine and probably worth one top-end rebuild in its lifetime - especially when pattern spares become available.

rotodiesel.

At what sort of miles do they start to give trouble Rotodiesel? I thought that they are a very robust engine. I'm not too worried as my engine has only done 37K and I have it serviced on the dot every 10K. Is 505.01 o.k to offer sufficient protection or would you recommend my asking for the fully synthetic variable servicing oil for extra protection at my next service?

It's almost impossible to predict - some engines will go for miles and others develop light scoring of the cams which quickly degenerates into a mess.

If your vehicle duty cycle is normal, I would stay with 505.01 but consider more frequent changes. I have a gut feeling that the higher viscosity of the 505.01 over the 507.00 gives the top end a measure of protection. It's interesting to note that the old 506.01 has a lower viscosity that 507.00, suggesting VAG had second thoughts based on operating experience.

I use 507.00 but my operating conditions are unusual - I tow a lot. As the engine spends a lot of time under boost, the turbine and hence bearing temperatures are high and varnish formation on the shaft is a real risk. The use of a synthetic oil minimises this.

Life's a lottery but you can improve matters by being careful about regular and frequent maintenance - there are plenty of neglected cars out there with the wong oil in them. I've seen 130 PS PD engines with starship mileages (although the cams always look to be in poor shape at the end of the engine's life) but the later PDs seem to suffer more - especially the 150 PS and the twin cams.

rotodiesel.

I see where you're coming from. My own thoughts would be that a higher viscosity oil might cling to the cam lobes better, but equally it might pump up the followers more easily (hydraulic tappet engines only).

This is the first time I have heard that these have a weak top end. Have you actually had one of these in bits Roto. As far as the oil is concerned, I would stress that anyone thinking of buying a PD car secondhand asks for documentary proof the correct oil has been used and not just settle for stamps. VW have a lot to answer for with its confusing codes. Should have just a colour code or something simple.

Anyway is the PD better in terms of reliability and life than a CR? Would a PD Octy 2 VRS be a good bet over a CR for a lot less?:confused::

I have seen a few failed engines in bits and one with camshaft bearing shells down to the copper - in places.

The higher powered >130PS engines seem to be the ones at risk and the PD fuel system is definitely less accident prone than the common rail systems of other makers. I have no feedback yet on the VAG common rail. I suspect that as the HP pump is fuel lubricated rather than oil lubricated as on the PD, it will be as damage prone as all the others.

A low powered PD is a fairly safe bet if it has been correctly maintaned - provided you can stand the noise and harshness.

rotodiesel.