PD - modifying to beat VE engine efficiency

greg123

Veteran Member
Joined
May 24, 2005
Location
UK
TDI
Passat, now Pug 405 TD, later Passat again!
Hi,

This isn't a mpg thread. It's a thread regarding the efficiency of the PD which seems to be less than the VE. For the same car, with a PD the CO2 emissions are higher than VE (indicating more fuel burnt) and mpg real world is between 5-15mpg less.

BUT - it's more or less the same engine and runs very well/clean. Just higher injection pressures and atomisation which shouldn't, by it's self, be a bad thing.

So - what's causing the issue?

I have heard it said that the PD injectors take a lot more moving, more spring pressure and more resistance on the cam. This would add friction loads to the engine. HOW much different it is to a VE pump I have no idea. Same tyres/car/transmission maybe someone has a dyno figures for the engine drag on coastdown from a full power run?

Ignoring the above it's my thoughts that the catylist and exhaust may be more restrictive. So (if legal where you are) a large bore race exhaust would fix that.

Also I think the tune was set up for NOX etc, deleting the EGR & looking with a chip tuner at how far the timing advance can go before it gets too advanced would be interesting. I hear the PD runs way off optimum timing, too retarded, for EGR and NOX purposes. The PD doesn't even sound 'crisp' like a well set up VE, it sounds muted which smacks of too retarded.

Then how about reducing the injection pulses to single pulse or two stage? A bit more noise, but fuel in earlier with longer time to burn and mix.

Can anyone think of anything else and has anyone gone down any of these routes? Has anyone got any g/kwh figures for the best TDI, the late euro 110tdi VE, compared to a typical PD say a 130PD?

Greg.
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
As usual, many times when the efficiency is increased, it is spent on making the engine more powerful. Which is the case with the PD over the VE, and now the CR over the PD.

So I am not really sure what your question is? In the US, we got only a 90hp VE, and then a 100hp PD. The PD typically uses a bit more fuel, but it makes more power, so that efficiency level is pretty much a wash. Now if they took the same PD technology, and kept the hp level at 90, then you could theoretically see say a 1.7L 90hp PD that gets BETTER fuel economy that the 90hp 1.9L PD. But instead they used the newer technology to gain power not fuel economy.

Same has happened with the CR. The new CR engine, now a 2.0L for the A5 platform, makes 140hp. They could have just as easily made a 1.6L 90hp CR engine, and give it WAY better fuel economy.

Just consider yourself lucky you actually have a choice in the matter in Europe. Because we don't. :mad:
 

greg123

Veteran Member
Joined
May 24, 2005
Location
UK
TDI
Passat, now Pug 405 TD, later Passat again!
I think I didn't explain quite right. I'm lucky in that I go collect and drive some distance 1 or 2 customer cars each week. Many times the same shell and cc (eg b5 passat, Octavia, Golf) but some with PD and some with VE. Taking it easy, sitting behind the trucks, I can get a VE up to 73-80mpg by the time I'm back home. A pd, 53ish is the best I managed. When driving normally, I can managed about 39-45 on a PD, but regularly hit the upper 50's on a VE. We are talking the SAME HP put down. Nothing to do with using any extra PD power.

In fact, I have had a back to back comparison of a PD100 passat and an earlier VE 110. The 110 VE was 10hp more powerful, yet used FAR less fuel. The PD100 ran great and was in great condition, but really struggled to get anything over the 40's. No I wasn't driving hard. This pattern is the same, time and time again, many many cars.

So my post above is really a query on the technical side of what makes the PD use so much more fuel for a given amount of HP.

Which is why I'd be interested in coastdown engine losses on a dyno, to see if the PD is significantly harder to turn. Though that wouldn't really test the resistance when pumping in fuel via those high pressure injectors.

Hope that makes sense.

Greg.
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
OK, then to answer the simple question of "why does a similar output PD use more fuel than a PD?"

Answer: emissions. The PD runs a tighter air-fuel ratio, simply for emissions reasons. We have been dealing with this crap in the US for years. Newer "cleaner" cars that use more fuel. :rolleyes:

The PD's higher injection pressures are part of the equation as well.
 

greg123

Veteran Member
Joined
May 24, 2005
Location
UK
TDI
Passat, now Pug 405 TD, later Passat again!
I agree that I think it's emissions as well. But air fuel ratio? No such thing on a diesel, there is such a thing as too little air and smoke resulting. I do suspect that the timing is way off optimum (I'm hoping a chip tuner will post with some information if they have played with timing) and I also suspect that the catalyst in the exhaust and amount of EGR used may hamper efficiency.

Agreed again about the injection pressures, if it puts a serious load on the camshaft. I just don't have any data, comparing spinning the cam and PD injectors compared to spinning a VE pump. Hoping someone may know....

If it's just the state of tune and EGR, a chip tuner here in the UK (where 'smog' isn't as tight so you'll pass the MOT no matter what you do really, unless it's running bad and smoking) would be able to set the timing and the EGR and have it match the VE efficiency. But I have NEVER seen a PD, even chipped ones, approach a VE's mpg.

Having said that, I have never met anyone who set up the map for economy and also removed the cat/OE exhaust and otherwise ran it stock. So it's hard to compare.

Greg.
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
You need to study how the PD EDC16 system works. There IS a fuel ratio of sorts. They are throttled. And they have a Planar Lambda sensor. This is all there to insure EGR operation and catalyst function.

The PD absolutely does run "richer" than a VE.

Keep in mind, when I say air/fuel ratio, I am not talking about a pre-combustion mix, but I have no other way of describing it.

Essentially, the PD has more fuel AND less air going through the engine at any given RPM/load than a VE does. That make more sense?
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
A quick test you can do to see what I am talking about.

Drive a VE TDI with the scan tool at a set speed/load on level ground. Record the MAF readings.

Now drive a same displacement PD, on the same road, and hopefully in the same platform. You may have to make sure the gear ratios are the same. Look at the MAF readings. It will show lower grams. In fact, the MAF sensor readings on a normally operating PD at light load/RPM would indicate a bad MAF on a VE under the same circumstances. :eek:

My BHW 2.0L PD at 70 MPH is actually moving substantially less air through the engine than a 1.9L ALH at the same speed. Its MAF reading is somewhere between a VE TDI's and a (turbo) gasser engine. Closer to the VE, though, and that reading reflects almost a linear comparison to fuel economy.
 
Last edited:

greg123

Veteran Member
Joined
May 24, 2005
Location
UK
TDI
Passat, now Pug 405 TD, later Passat again!
Okay that makes sense, I see what you mean now ;-)

Question is, WHY. Extra air is a good thing in general. Is there an emissions reason that the PD wants to run it close to poor combustion/smoke limit?

I'm guessing it's something to do with the operation of the cat?

In which case, it would be interesting to see a remap with pleanty of spare air (but not so muc that you are wasting energy creating un-necessary back pressure) and the cat/sensor/EGR taken out of the equation.

Greg.
 

PDJetta

Top Post Dawg
Joined
Nov 6, 2003
Location
Northern Virginia
TDI
'04 Jetta GLS TDI Pumpe Duce Platinum Grey w/ Leather
This is my take on the PD effeciency:

The biggest reason the PD uses more fuel over the VE TDI is the higher injection pressures. It takes a lot of energy to pump those injectors. Think of it like the air conditioning system and the energy it takes. This causes a higher "parasitic loss" for the PD. 30,000 psi injection pressure versus about 20,000 PSI? for the VE. The higher injection pressures cause the fuel injection event to happen faster, thus allowing a retarded (from optimal timing) and lowering the NoX (this is the adverse emissions component) of the injection timing and keeping drivability at the same time. This lowers economy a little as well, I think. Finally there is the throttle plate that closes off under light load operation to draw more exhaust through the EGR valve, than would other wise flow through naturally. I am not sure if the throttle lowers effeciency, since the exhaust gasses bleeding into the intake will prevent a manifold vacuum.

The O2 sensor's sole function is to fine tune the EGR flow that is determined by ECU mapping by allowing the ECU to modulate the EGR valve and throttle plate (both are electrical), based on O2 sensor input voltage fluctuation. More O2 in the exhaust roughly equates to higher NOx production. The O2 sensor does not control the fueling amount whatsoever (this info came from Pierburg, who makes the EGR system, or Bosch, who makes the engine management/injectin system for the PD).

My experience is that blocking off the EGR and removing the throttle plate has little effect (if any) on fuel economy on the PD. I have done both and do not notice much difference. I generally get 47 MPGs, combined driving, in mine and have gotten as good as 51 if I REALLY try.

I am not sure how much chiptuning advances the injection timing curve under light load operation. I would like to know this. I have RC 2 and the fuel usage stayed pretty much the same, IF I DRIVE THE SAME! I think under heavy load, even the stock programming has an optimal power advance curve for drivability. Emissions testing I think occurs under steady state, and all the manufacturer cares about is getting certified under test conditions. Recently, I think the EPA requires a driving cycle, so this may have changed.

--Nate
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
Yep, the oxygen sensor's function is for EGR, not fuel control. But, simple laws of physics show that more EGR = less airflow through the intake pre-EGR, and when the IQ stays the same, the end result is more fuel less [oxygen-containing] air.

So technically speaking, the air/fuel ratio is not controlled, but if you divide that term 'air' into fresh high oxygen content air and oxygen depleated air, you can see where I am coming from.

I guess it would be better decscribed as an "oxygen/fuel ratio", agreed? ;)

On a typical diesel, textbook speaking, the exhaust gas while it can get hot has very little combustible fuel leftover to make any type of catalyst work. This is why early TDIs got the ill-fated 5th injector system, simply to keep the catalyst working. There is always potentially ample oxygen leftover in a diesel's exhaust to burn the fuel, there is just no fuel.

Gassers do the same thing, they run slightly rich from time to time (the duration and frequency depends on the particular car/system) merely to keep the cat(s) going.

If it were not for NOx, both gas and diesel engines could be made WAY more fuel efficient, PM would go way down, soot would go way down, and we really would not even need catalysts, because the engines would run so lean there would not be anything left in the exhaust CO/CO2/HC-wise to clean/burn up anyways.
 
Last edited:

PDJetta

Top Post Dawg
Joined
Nov 6, 2003
Location
Northern Virginia
TDI
'04 Jetta GLS TDI Pumpe Duce Platinum Grey w/ Leather
"My BHW 2.0L PD at 70 MPH is actually moving substantially less air through the engine than a 1.9L ALH at the same speed. Its MAF reading is somewhere between a VE TDI's and a (turbo) gasser engine. Closer to the VE, though, and that reading reflects almost a linear comparison to fuel economy."

That's because the throttle plate is closing off to draw in more exhaust, thus lowering the amount of air the engine can take in, to reduce combustion temps and oxygen amounts even further, to lower NOx amounts. (I think I just worded it differently than you did). I see how this equates to a richer mixture. I also read that the PDs have an extremely aggressive EGR flow rate under light load, up to 45% of the intake charge volume can be exhaust gasses--Nasty! That can not be good for engine longevity.

I do know that chip tuners can change the ECU programming to request much more air under all conditions, thus keeping the throttle plate open and the EGR valve closed under most conditions and not throwing a CEL. Then, the engine will draw in as much air as physically possible, limited by the design constraints. Air requested (by the ECU) will almost always be higher than air actual. What throws the CEL for "insuffecient EGR flow" is air actual is MORE than air requested. This indicates that the EGR has been blocked off, since the exhause gasses dilute the intake charge, thus meaning there is more air flow through the Mass Air Flow sensor, since the EGR is blocked off.

--Nate
 
Last edited:

meby

Veteran Member
Joined
Sep 28, 2007
Location
Southwest Michigan
TDI
2000 Ford Winstar ALH TDI 5 spd
PDJetta said:
This is my take on the PD effeciency:

This causes a higher "parasitic loss" for the PD. 30,000 psi injection pressure versus about 20,000 PSI? for the VE. --Nate
I think the ve would pop closer to 2500-3000 psi. On the Cummins engine with a VE 44 Bosch this is the case. I can't imagine the tdi VE being much different as the pumps are very similar, number of cylinders aside. I'm not sure exactly how the PD works, but 30,000 psi sounds like a cr engine. (Stock Cummins CR is around 25,000 psi iirc.)
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
york77777 said:
Just trying to do a little out of the box thinking here, but wouldn't it be possible to throw a heater of some kind onto the cat in order to keep it hot and not use fuel burn to do so? Say throwing a "glow plug" into the side of it, in essence using an electrical component to keep it hot and working which would allow the combustion process to not have to take into account the need to keep the catalyst hot with "fuel" burn? This also might allow much more efficient functioning of the catalyst upon initial start up and driving (say the first 2-3mins or 5 mins in winter).
Already been done. Not sure what engine, models, etc. but the technology exists. Problem is cost and complexity, as well as emissions compliance over time.

 

pjj

Member
Joined
Jul 24, 2008
Location
scotland
TDI
passat tdi 115, passat tdi 110
I have two Passats, one is a 110 VE and the other a 115 PD.
On the PD in the summer I usualy average 63mpg according to the computer and about 60mpg if I do the sums on how much fuel it takes between fillups. The VE does not have a computer but does not seem to clock up so many miles for the same fuel.
To be fair the VE does do more shorter runs but I think the main reason is the fact the PD has so much more torque and gear changes can be made at 1800rpm compared with 2200rpm for the VE.
Could it be the 115 is the most efficient of the PDs ?
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
york77777 said:
I would assume that such a system would have to be replaced a lot more often than standard ones?
I honestly don't know. But it likely is pretty 'spensive. Heated lambda sensors are costly enough! :eek:
 

GoFaster

Moderator at Large
Joined
Jun 16, 1999
Location
Brampton, Ontario, Canada
TDI
2006 Jetta TDI
couple other things here.

The PD100 is burdened with the BorgWarner turbo which as I understand it, is more restrictive on the exhaust side. Also the engine programming commands more boost pressure at part load (even if the EGR is working). That adds up to more exhaust back-pressure, and that costs a bit of efficiency.

It's quite likely that the part-load settings have the injection timing later than optimum for economy, in the interest of emissions and noise control.

I don't think many of the chip-tuners muck around with the part-load settings. It would be interesting to see what happens if the injection timing at part load were advanced a couple degrees.

For what it's worth, my chipped Mk5 Jetta P-D gets fuel consumption comparable to my old '96 VE-pump Passat TDI and the car is almost the same size, weight, and drag coefficient. But, I skipped the Mk4 generation with their VNT15's that were apparently a bit more efficient and in cars that weighed a bit less.
 

GoFaster

Moderator at Large
Joined
Jun 16, 1999
Location
Brampton, Ontario, Canada
TDI
2006 Jetta TDI
for what it's worth, last fillup involved a lot of driving at 110 km/h give or take and only a little stop/go and minimal A/C usage, and it recorded 5.0 L/100 km. Keep in mind I've got a taller 5th gear, and ECU programming that caused something to happen to the EGR, and I've done the speedo recalibration (actual recorded distance is now about 3% high), AND I'm running 18" wheels, AND that was on B50 fuel.
 

greg123

Veteran Member
Joined
May 24, 2005
Location
UK
TDI
Passat, now Pug 405 TD, later Passat again!
Yes, I'm thinking the same about part (and maybe even full) load advance. Tuners only ever do graphs of full power runs.

I'd be very interested to see, say, a PD130 with a VNT20 and a straight through exhaust mapped out with good boost levels (enough to have excess air all the time) and timing optimised through the very low load range upwards.

I do a lot of work with diesels and nearly always I find that the timing is retarded and actually even a few degrees on the pump over stock makes the vehicle start and run a lot better. I have never 'pushed' the advance much past optimum, but if you do it sounds like a tractor. Had a guy in with a 1.9TD that wouldn't start well, his timing was WAY retarded. Ran okay, but quiet.

I set it stock, it was still too quiet for my liking, muted one would say. I pushed advance a bit beyond stock and my word, it now starts on one swing of the starter (he brought it in with 5 seconds of cranking and a shuddering idle) and though still quiet and smooth it does sometimes have a touch toward a nice healthy diesel crackle. Still quiet compared to the peugeot IDI diesel or any DI though!

He mailed me back last night, can't believe how easily the vanogon goes up hills and cruises on less throttle.

I have a pretty keen ear but maybe a knock sensor would pick up timing too advanced better and could be adapted for a diesel? Then custom mapping software and some sort of knock warning light, so you can go driving and essentially see at what loads/speeds the engine may be nearing the point of too much advance. I'd also be interested to see if there is any efficiency to reducing the injection pulses. As I recall from studies, 2 stage gave some performance advantages but some disadvantages and there may be something in putting the fuel in all at once, so it's got longer to mix and burn.

I don't think anyone has been down this road, which is why I'm interested.

I run all my VE's with static timing set a bit advanced (excellent starts) and dynamic timing 3 degrees advanced across the board, they sound better and do run better. But I think the VE wasn't far off optimum as it is, the PD I think is another story. I can just feel it. That engine is smooth, but it just doesn't feel crisp. Something is muting out those explosions!

Like I say I drive a lot, back to back, so I'm not comparing what one person gets over another person with different driving and car, same platform the PD is ALWAYS 5-15mpg less on me.

Greg.
 

PDJetta

Top Post Dawg
Joined
Nov 6, 2003
Location
Northern Virginia
TDI
'04 Jetta GLS TDI Pumpe Duce Platinum Grey w/ Leather
meby said:
I think the ve would pop closer to 2500-3000 psi. On the Cummins engine with a VE 44 Bosch this is the case. I can't imagine the tdi VE being much different as the pumps are very similar, number of cylinders aside. I'm not sure exactly how the PD works, but 30,000 psi sounds like a cr engine. (Stock Cummins CR is around 25,000 psi iirc.)
The PDs do in fact have an injection pressure of near to 30,000 PSI. True, that is about the pressure of commom rail diesels.

"Built to incredibly precise tolerances (at or under one micro-meter or .00004 in.) the pump can deliver fuel pressures of 2,000 bars (or 29,000 psi and about 20% higher than common rail systems) to the V10's five 0.15 mm injector holes."

http://www.europeancarweb.com/features/0411ec_volkswagen_tdi/index.html

Even though this article is for the V-10 VW TDI, the injection pressures are similar for the 1.9 liter pumpe duse TDIs, according to the Robert Bosch Corporation.

Also, due to the close tolerances (cited above), the CAT 2 micron fuel filter is a wise investment. The stock VW diesel filter filters at about 10 microns!

I may be incorrect as to the VE TDI injection pressure. It may be a good bit under 20,000 PSI. It is way lower than the PD, and that is what I was trying to illustrate as being the reason for the higher fuel use of the PD compared to the VE TDI.

--Nate
 
Last edited:

meby

Veteran Member
Joined
Sep 28, 2007
Location
Southwest Michigan
TDI
2000 Ford Winstar ALH TDI 5 spd
PDJetta said:
The PDs do in fact have an injection pressure of near to 30,000 PSI. True, that is about the pressure of commom rail diesels.


I may be incorrect as to the VE TDI injection pressure. It may be a good bit under 20,000 PSI. It is way lower than the PD, and that is what I was trying to illustrate as being the reason for the higher fuel use of the PD compared to the VE TDI.

--Nate

Ok, I found it, the stock pop pressure on VE 44 (Cummins) is 245 bar(approx 3600 psi). Like I said, I don't really know much about the PD's, but I taken several VE 44's apart and have seen quite detailed pics of a rebuild of the VE on our tdi's and they are very similar. The design won't let the pump put up with much higher pressure and still live a long life.:) At least this is the way it works on the Cummins and I can't imagine the tdi version being much different.
 
Top