CR engine HPFP analysis

[nicklockard]

The latter + smaller nozzle holes.

 

[specsalot]

GENTS - More updates on the effects of fuel tank level on fuel temps. I ran the same test circuit. I ran the car almost out of fuel, finishing the circuit at the filling station I used. I squeezed 14.7 gallons of fuel into the tank to give an idea of how low I took things.

The numbers from this same test run were not really any different from the run I did that was posted earlier (done at ~ 3/8 tank).

I'm going to do some more loggings and probably post a summary of results in a separate thread. I saw the pretty much the same numbers as before. That was a bit of a surprise. I guess this is why VW doesn't fit a fuel cooler. I suspect it may also be why the HPFP is made of aluminum. The cars with fuel coolers probably have steel HPFP's.

 

[nicklockard]

Interesting. And great work. Sounds like temps can be ruled out as a key contributing factor to HPFP death pretty much. Kudos for running it down.

 

[dweisel]

Interesting. And great work. Sounds like temps can be ruled out as a key contributing factor to HPFP death pretty much. Kudos for running it down.

I don't think several runs and logged temps on one vehicle is enough data to come to a conclussion. Other cars running different fuel may have totally different results. Lots of varibles to consider.
Member tdiatlast is also going to check fuel temps on both his 09 Jetta and his 2012 Passat. It will be interesting to see the results.

 

[scdevon]

Meh. Depends a lot on where you live. I live in a cool climate (Rockies). Even with a quart of fuel total in the fuel system circulating between the tank and and the fuel rail, it experiences significant cooling in the fuel lines between the tank and the engine and back again.

Not such a big deal in my climate. It could be a huge deal in Phoenix or Miami.

 

[eddif]

GENTS - More updates on the effects of fuel tank level on fuel temps. I ran the same test circuit. I ran the car almost out of fuel, finishing the circuit at the filling station I used. I squeezed 14.7 gallons of fuel into the tank to give an idea of how low I took things.

The numbers from this same test run were not really any different from the run I did that was posted earlier (done at ~ 3/8 tank).

I'm going to do some more loggings and probably post a summary of results in a separate thread. I saw the pretty much the same numbers as before. That was a bit of a surprise. I guess this is why VW doesn't fit a fuel cooler. I suspect it may also be why the HPFP is made of aluminum. The cars with fuel coolers probably have steel HPFP's.

Thanks for all the testing. What I am curious about I would not want you to test.

I wonder what is going on when driving with little fuel when:
You are on an extreme driveway slope
Playing Johnny road racer on curves
Sloshing fuel on purpose (so we would know what accidental sloshes do)
Testing on a roaring hot day
Drain the tank and put one gallon of fuel in (so you would know the amount of fuel)
Drive the car 35 miles on the one gallon doing all the tests listed above
Put one ounce of gasoline in the gallon and retest
Put three ounces of gasoline in the gallon and retest

Just a mess when all this could have been tested at the get go. Or either take the low fuel light off the cars and suggest never running the cars low on fuel. It bothers me when folks feel comfort in running cars low on fuel, especially when things can be happening in accidental extremes

The shadetree jerk from Mississippi
eddif

 

[eddif]

Meh. Depends a lot on where you live. I live in a cool climate (Rockies). Even with a quart of fuel total in the fuel system circulating between the tank and and the fuel rail, it experiences significant cooling in the fuel lines between the tank and the engine and back again.

Not such a big deal in my climate. It could be a huge deal in Phoenix or Miami.

My post was a lot of the same thoughts. I took forever to post so I guess I missed your post. Folks have a lot of different conditions to deal with.

The flatlanders usually do not have all the hill grades. The hill folks do not usually have all the temps. Of course a strange driveway in the flatlands could do both.

eddif

 

[dweisel]

Thanks for all the testing. What I am curious about I would not want you to test.

I wonder what is going on when driving with little fuel when:
You are on an extreme driveway slope
Playing Johnny road racer on curves
Sloshing fuel on purpose (so we would know what accidental sloshes do)
Testing on a roaring hot day
Drain the tank and put one gallon of fuel in (so you would know the amount of fuel)
Drive the car 35 miles on the one gallon doing all the tests listed above
Put one ounce of gasoline in the gallon and retest
Put three ounces of gasoline in the gallon and retest

Just a mess when all this could have been tested at the get go. Or either take the low fuel light off the cars and suggest never running the cars low on fuel. It bothers me when folks feel comfort in running cars low on fuel, especially when things can be happening in accidental extremes

The shadetree jerk from Mississippi
eddif

eddif, even with only a half inch of fuel in the fuel tank the fuel sending unit bucket stays full at all times.

The return fuel dumps directly into this bucket which keeps it full at all times. All the above you mentioned would have minimal affect on how the fuel system is supplied with fuel. Doesn't matter what the fuel is doing in the tank the bucket stays full as the return fuel is always greater volume than what is being consumed.

Below pic: fuel sending unit. White bucket always stays full of fuel unless you run your tank COMPLETELY DRY. In actuality your fuel sending unit float could be sitting on bottom of its stroke and your gauge showing E and you could still have the volume of the fuel sending unit full.

Hope that helps.

 

[specsalot]

I don't think several runs and logged temps on one vehicle is enough data to come to a conclussion. Other cars running different fuel may have totally different results. Lots of varibles to consider.
Member tdiatlast is also going to check fuel temps on both his 09 Jetta and his 2012 Passat. It will be interesting to see the results.

I agree completely. I'm hoping more folks log and report results. Comparisnos with the MY12 Passat will probably be eye opening. I believe VW redesigned the system to in part impact fuel temps. I believe over time the data will tell it's own story. For now the data I have isn't enough to cause me to change my normal fueling pattern (fill up at 1/2 tank). At least I don't have to worry as much about running down to 1/4 tank from a temperature perspective.

 

[FloridaJohn]

I'm going to do some more loggings and probably post a summary of results in a separate thread. I saw the pretty much the same numbers as before. That was a bit of a surprise. I guess this is why VW doesn't fit a fuel cooler. I suspect it may also be why the HPFP is made of aluminum. The cars with fuel coolers probably have steel HPFP's.

I would be interested in seeing what the temperature would be with a full tank. That would theoretically be the coolest the fuel temperature would ever be (since there is more fuel in the tank to disapate the heat. Just an idea for the next time you are running tests.

 

[specsalot]

Full tank runs, it takes ~ 20 minutes for fuel to reach steady state temps. The interesting question (I think) has to do with the relationship between fuel temps and outdoor ambient temps. I've done a few full tank runs under varying ambients, but haven't pulled the data together yet. There are a lot of factors that influence fuel temps including:

1. Fuel tank temperature
2. Position of the pre-heating valve in inside the fuel filter.
3. Engine operating point (this would determine how heavily high pressure bleed was being used to control CR pressure. Under dynamic conditions, this is probably too highly variable to be trackable with the tools we have.
4. Outside ambient air temperature
5. Vehicle speed
6. Friction inside the HPFP

I believe that one indication of overall HPFP health would be pump temperature. Another might be vibration or sonic profiling. Problem is with all the dynamics involved the only time you would really identify a problem would be a statistically significant deviation (2+ standard deviations beyond norm). When the "norm" is wide ranging the issue would likely be missed until thing were bad. Spread data might be a better alternative than single data point monitoring. In the real world, critical equipment is typically subject to real time condition monitoring. In our case as many have pointed out, the signal to noise problem make it hard to identify issues. Monitoring is a reactive practice. To really get ahead on potential issues we have to find pro-active things to do.

Filtration and additives make sense, but there is no "proof" behind these ideas.

 

[Jack Frost]

...There are a lot of factors that influence fuel temps including:

1. Fuel tank temperature
2. Position of the pre-heating valve in inside the fuel filter.
3. Engine operating point (this would determine how heavily high pressure bleed was being used to control CR pressure. Under dynamic conditions, this is probably too highly variable to be trackable with the tools we have.
4. Outside ambient air temperature
5. Vehicle speed
6. Friction inside the HPFP

...

Although theoretically, there is some friction inside the fuel pump, it is pretty much neglible as long as it is being lubricated. Most friction occurs inside the liquid fuel itself as it has viscosity and anytime a viscous fluid is forced to move, the viscosity (which is a type of friction) turns into heat. For example, the temperature of the water that flows over the Niagra falls increases by a degree to two from the churning that takes place.

The fuel system has a valve (called a Fuel Pressure Regulater) that bleeds high pressure fuel not consumed by the engine back to fuel tank. This "regulater" acts like a safety valve on a steam engine. If it did not operate, the fuel lines would burst or the the fuel pump would experience something like a hydrolock and self destruct. Whenever, the fuel travels through the Fuel Pessure Regulater, the fuel would heat up as it is forced to travel extremely fast through a microscopic crack produced by the regulater from a high pressure area to a where there is no pressure at all. All the mechanical energy that the car's engine used in pumping the fuel up to high pressure has to turned into heat and this is where it would occur.

I believe the Fuel Pressure Regulater is adjusted by the engine's computer. If that is so, I would also expect that the pressure of the fuel would be increased as the RPMs increased. Higher fuel pressure would allow the injectors to produce finer fuel atomization inside the cylinder and a faster burn rate. Conversely, at low rpms, the fuel pressure would be lowered to reduce the burn rate of the fuel. That is something a CR diesel can do that gasoline engines cannot do.

At high rpm's the fuel pump pumps faster and the engine's computer increases the fuel pressure accordingly. If there is little load on the engine, most of the fuel would be bled back to the low pressure of the fuel tank heating it.

Sustained high engine speeds with little load on the motor would heat up the fuel more than anything else as the fuel pump would be pumping fuel like crazy up to high pressure only to have most of it returned to the fuel tank as heated fuel.

 

[Elfnmagik]

Sustained high engine speeds with little load on the motor would heat up the fuel more than anything else as the fuel pump would be pumping fuel like crazy up to high pressure only to have most of it returned to the fuel tank as heated fuel.

Like running a DSG in 'Sport' around town with RPM's at 3k all the time.

 

[kjclow]

I believe the Fuel Pressure Regulater is adjusted by the engine's computer. If that is so, I would also expect that the pressure of the fuel would be increased as the RPMs increased. Higher fuel pressure would allow the injectors to produce finer fuel atomization inside the cylinder and a faster burn rate. Conversely, at low rpms, the fuel pressure would be lowered to reduce the burn rate of the fuel. That is something a CR diesel can do that gasoline engines cannot do.

I may be mistaken but I thought the pressure across the rail was fairly constant, regardless of engine load.

 

[bluey]

There are a lot of factors that influence fuel temps including:

1. Fuel tank temperature
2. Position of the pre-heating valve in inside the fuel filter.
3. Engine operating point (this would determine how heavily high pressure bleed was being used to control CR pressure. Under dynamic conditions, this is probably too highly variable to be trackable with the tools we have.
4. Outside ambient air temperature
5. Vehicle speed
6. Friction inside the HPFP

Being bolted to the head, isn't the HPFP temperature dependent on engine temperature? I see the fuel temp sensor is not at the HPFP. The engine cover would also keep the common rail warm.

 

[oilhammer]

Not really bolted to the head. Bolted to a bracket, then the bracket is bolted to the block. There is no heat exchange between the fuel and the coolant until after the HPFP.

 

[Jack Frost]

I may be mistaken but I thought the pressure across the rail was fairly constant, regardless of engine load.

If you have a copy of the Bentley Service Manaul, under the section "Product Familization" (page 02-18) in my edition it states clearly that the pressure is adjusted by the engine's control module:

"The high-pressure pump produces a maximum pressure of 2175.5 psi (150 mbar). The fuel pressure requested by the engine module is adjusted by the fuel pressure regualotr valve (N276). The pressure is regulated between 725.1 psi (50 bar) and 2175.5 psi (15 bar) depending on engine requirments".
​

What are those reqirements is not stated. However it is well known that higher pressure will produce a finer mist. Unlike a gasoline vapour charge that is ignited a gasoline engine, diesel fuel must burn at the liquid/air interface as it does not exist inside the cylinder as a vapour. Diesel droplets will burn four as fast as droplets that are twice the size and nine times as fast as droplets that are three times the size and 16 times as fast as droplets that are four times as size.

So it makes sense that the CR motors can control how fast the burn takes place. By lowering the fuel pressure at low rpms, the motor is able to run at lower rpms without lugging. By increasing the fuel pressure, the CR motor is be able to perform at the higher rpms by increasing the burn rate of the fuel allowing it to be fully combusted before the exhaust stroke takes place. However it makes sense, but I havent' seen any documentation that specfically say that. But why would it work the opposite way?

But it is my feeling that those on this forum who advocate racing their motor without a signficant load applied to the engine are giving their followers bad advice. When you do this, it is my suspicion that the fuel pump on the CR motors work very hard to pump lots of fuel to very high pressure only to have the fuel not get used and return to the tank heated. This is called "stress".

When mechanical components are taken close to the operating limits, it takes only one thing to go wrong before everything collapses. Fuel that is less than perfect, fuel that is already warm can has lost some of its lubricity as a result, and a little bit of float off the cam inside the fuel pump, or perhaps a bad mapping value from the engine's control module..... any one of those under a stress condition .... and ka-blammy !

 

[specsalot]

Although theoretically, there is some friction inside the fuel pump, it is pretty much neglible as long as it is being lubricated. Most friction occurs inside the liquid fuel itself as it has viscosity and anytime a viscous fluid is forced to move, the viscosity (which is a type of friction) turns into heat. For example, the temperature of the water that flows over the Niagra falls increases by a degree to two from the churning that takes place.
The fuel system has a valve (called a Fuel Pressure Regulater) that bleeds high pressure fuel not consumed by the engine back to fuel tank. This "regulater" acts like a safety valve on a steam engine. If it did not operate, the fuel lines would burst or the the fuel pump would experience something like a hydrolock and self destruct. Whenever, the fuel travels through the Fuel Pessure Regulater, the fuel would heat up as it is forced to travel extremely fast through a microscopic crack produced by the regulater from a high pressure area to a where there is no pressure at all. All the mechanical energy that the car's engine used in pumping the fuel up to high pressure has to turned into heat and this is where it would occur.
I believe the Fuel Pressure Regulater is adjusted by the engine's computer. If that is so, I would also expect that the pressure of the fuel would be increased as the RPMs increased. Higher fuel pressure would allow the injectors to produce finer fuel atomization inside the cylinder and a faster burn rate. Conversely, at low rpms, the fuel pressure would be lowered to reduce the burn rate of the fuel. That is something a CR diesel can do that gasoline engines cannot do.
At high rpm's the fuel pump pumps faster and the engine's computer increases the fuel pressure accordingly. If there is little load on the engine, most of the fuel would be bled back to the low pressure of the fuel tank heating it.
Sustained high engine speeds with little load on the motor would heat up the fuel more than anything else as the fuel pump would be pumping fuel like crazy up to high pressure only to have most of it returned to the fuel tank as heated fuel.

Like running a DSG in 'Sport' around town with RPM's at 3k all the time.

I may be mistaken but I thought the pressure across the rail was fairly constant, regardless of engine load.

Great comments

Jack - Great description of what happens with fluids, specifically the conservation of energy (internal energy converted to thermal energy) during a throttling process. If anyone's ever seen this first hand it's hard to forget. According to the VW SSP the Bosch EDC-17 manages CR rail pressure by controlling both the FMV (fuel metering valve) and the FPR (fuel pressure regulator). They provide a graphic to illustrate the multi-mode control being used (inserted below). This graphic tells / suggests several things:

1. It helps explain the tendency of fuel temperature to rise during stopped idling conditions.

2. It suggests that at idling conditions the FMV (N290) isn't an effect way to control CR pressure. The exact reasons remain a guessing game at this point.

COMMENT: Every time I look at this graph my initial reaction is to think the blue and teal colors are reversed on the legend. But after a while I realize that injection cut off following higher engine loading (trailing throttle - 0 injection quantity) would create significant CR pressure spikes if it weren't for the fact that the FPR was already open and working. It takes time for all controls to operate. Opening FPR lightly wider is probably the fastest type of control response that can take place under operating conditions.

Elfnmagik - Sounds like something that will need to be logged with VCDS to validate. What I do know is that the EDC-17 does a better job of managing CR pressure spikes during trailing throttle in sport mode. On the basis that lower CR pressures equate to lower HPFP component stresses, I use sport during stop and go traffic.

kjclow - My loggings (VCDS) suggest that CR pressure is targeted based on RPM and torque demand. It seems to be a moving target. It's clear that off take from the rail (i.e. changes in load / fuel injected quantity) is balanced by changes in both the FMV and PCV signals. Here are a couple graphs of VCDS (sorry they're busy) showing a drive over the same piece of road at ~ same speed. For both graphics the following color scheme applies:

GREEN=Injection Quantity; RED=Engine RPM; LIGHT BLUE (near bottom)=Vehicle Speed; YELLOW=CR Pressure; WHITE (IIRC)=FMV%; BLUE (IIRC)=FPC%

This first graph shows parameters while the DSG is in DRIVE mode.

Here's the same stretch of road with the DSG in SPORT mode.

Both graphs show a period of 0 fuel delivery. This is where the car was decelerating approaching a rotary feature in the roadway. I like how the CR pressure seems to be better controlled under sport mode. This may be because the EDC does a better job managing CR pressure at higher RPM's. Or it may be that desired CR pressure is mapped lower at higher RPM for the torque input I was operating at. Not really sure.

The interplay of component stresses (unit surface loading), metalurgies, and fuel lubricity are the primary determinants of HPFP longevity. The random nature of failures is whats really hard to understand about this issue. If Bosch & VW are correct that this is about bad fuel, it is really incumbent on them to design a better pump to be fit for service given the range of fuels in the market for which they intend to sell their vehicles.

It looks like in Europe regulators have mandated FAME (bio-diesel) content. Perhaps that needs to occur in the US as well to improve the lubricity of US ULSD. Some states are beginning to mandate biodiesel content.

 

[oilhammer]

One popular software mod for CR engines is to raise the rail pressure, and this is of course done by controlling the duty cycle of the pressure regulator.

 

[kjclow]

Thanks to all for the corrections on my assumptions and all of the other details.

 

[specsalot]

Looking at the graphs above - You can infer that SPORT mode tends to carry higher CR pressure and operates with more of an overlap between HPFP delivery and CR bleed off. I like the idea that CR pressure seems to experience smoother transitions. Obvesiously more parameter logging is needed. Perhaps others with VCDS will post up some log graphics.

 

[kjclow]

Looking at the graphs above - You can infer that SPORT mode tends to carry higher CR pressure and operates with more of an overlap between HPFP delivery and CR bleed off. I like the idea that CR pressure seems to experience smoother transitions. Obvesiously more parameter logging is needed. Perhaps others with VCDS will post up some log graphics.

I just got my vcds. How do I log this info? I can compare the golf and jsw side by side to see if there is any real world difference.

 

[specsalot]

I just got my vcds. How do I log this info? I can compare the golf and jsw side by side to see if there is any real world difference.

You need to connect up VCDS and start the car. Then you need to log into the engine controller. Click the 01-Engine button.

This will open up available controller options. (Note this is not the screen for the engine controller, but they all look similar)

Under Basic Functions you can choose either Meas. Blocks-08 or Adv. Meas. Values. Advanced Measuring Values is easier to work with. You can only log 12 values for either option. In using the advanced option, you will get a large list. This is what they look like, but I could only capture part of the list in one screen shot. Some values are in the pick list more than once. The closer they are together, the more concurrent the data time stamps will be.

When you have a list made up, you can right click the VCDS logo in the upper left corner of the value selection window and save the list. The location column shows which measuring block value you are recording. Basic Measuring Blocks are values grouped together primarily for diagnostic purposes. You can load up a saved list using the same mechanism. I'm still fine tuning the lists I use for logging. Some of the measuring blocks shown in the lists do not produce data. For example "Oil Temperature" doesn't show data on the MKVI engines.

Ross-Tech has a decent description of the process in their on line manual at the following link:
http://www.ross-tech.com/vag-com/tour/adv-meas-blocks.html

Working with VCScope is a separate subject. Not a lot of documentation available. Kind of trial and error. But you can't beat the price (free). You can always open a log file using MS Excel. But for visual display, VCScope is pretty decent once you figure it out.

Did you get the HEX+CAN or microCAN?

 

[specsalot]

Actually there's a decent amount of info about VCScope on the Ross-Tech site. Here is a link:

http://www.ross-tech.com/vag-scope/index.html

Much easier than learning via "trial and error". Just found this section and realized that VC Scope can display real time data. Be sure you are the co-pilot not the driver if you are trying to do that. When I'm logging solo, my rule is not to look at the data screen during the run. Eyes on the road....

 

[specsalot]

Hello All,
Here are some obvious differences in a Czech Made 2012 Passat Pump VS our "Regular" German 2.0 tdi Pumps:
.
1.) The Cam has a 0.058" (1.5mm) LONGER stroke.
...
6.) The FCV is a different part Number.
.
Here are the similarities:
...
3.) Same Diamond coated roller shoe and roller diameter.
4.) Same High pressure Plunger Diameter and Head with Valve.
5.) Same internal COV valve.
.
The good news:
The new Czech Pumps for our cars will most likely have the above improvements, but not the longer stroke for the Passat. (the Passat has different injectors.)
All the best,

2micron - Great summation of the newer Czech pump. Great pictures. Here are some obvesious questions that we are mostly going to have to wait on documentation to answer. Food for thought anyway.

1. Is the higher stroke of this pump is due to a difference in injector design (i.e. increased injector return line flow)? Or does it provide for better delivery control from a revised Fuel Metering Valve?

2. Were the dimensions of the pump chamber increased to partially offset the longer pump stroke? [Benefits of this type of change?]

3. Does the Passat FIE operate at higher CR pressures? Someone with VCDS might be able to answer this. After all Euro 6 emission standards are already in place (link below) for 2014 debut.

http://en.wikipedia.org/wiki/European_emission_standards

 

[Niner]

2micron - Great summation of the newer Czech pump. Great pictures. Here are some obvesious questions that we are mostly going to have to wait on documentation to answer. Food for thought anyway.

1. Is the higher stroke of this pump is due to a difference in injector design (i.e. increased injector return line flow)? Or does it provide for better delivery control from a revised Fuel Metering Valve?

2. Were the dimensions of the pump chamber increased to partially offset the longer pump stroke? [Benefits of this type of change?]

3. Does the Passat FIE operate at higher CR pressures? Someone with VCDS might be able to answer this. After all Euro 6 emission standards are already in place (link below) for 2014 debut.

http://en.wikipedia.org/wiki/European_emission_standards

The internal volume of the Common Rail would affect plunger stroke also, remember, it acts as a pressure dampener also. This is is reference to 2012 Passats vs earlier V1 2009 on jetta, jsw and golf CR common rails.

 

[specsalot]

So the rail is different as well? What benefits accrue to these changes?

 

[2micron]

Rail facts: Passat vs MK6

Hello all!!
Here are some facts about the rails, injectors and controls in comparing the MK6 and 2012 Passat.
.
MK6:
- 9mm (0.354")hole through the body.
- 11.25 long (end to end)
- Part# 03L 130 089
.
Passat:
- 9mm (0.354")hole through the body.
- 10.25 long. (end to end)
- Part# 03L 130 089 J
.
The Injectors are quite different as well.
The Pressure sensor is identical and the Pressure Control Valve is the same size and shape, but with a slightly different Part Number.
The feed line from the HPFP is the same diameter, but slightly shorter and enters in a different location on the Passat.
The Injector Bleed off (Return Lines) are also quite different.
The Passat Rail is slightly smaller in outside casting diameter, in certain areas.
The rails themselves are very robust. Much discussion has been generated about the rail expanding with the pressure. If expansion does occur, it would be so minute, it would not most likely affect the volume.
.
Enjoy the pictures, let me know if any one wants part numbers for the other bits.
.
Passat Injector Top, MK6 Bottom.

.

.
Pressure Control Valve Left, Pressure Sensor Right.

.
Passat Rail Top, MK6 Bottom.

.

.
Passat part Number Below.

.
MK6 part Number Below. (My 2010 is the same Part #.)

.
9mm Through Hole.

.
Passat with Injectors.

.
MK6 with Injectors.

.
All the best,

 

[specsalot]

2micron - Great pictures - Thanks for posting them.

Interesting changes:

1. Sequence of off take is different (assume Passat has same firing order).
2. Spacing of Passat off take points is less uniform.
3. Passat injectors are very different. Wonder if they are still piezo electric operated?

It appears Bosch knows a lot more about rail vibrations / transient pressure distributions. They appear to be tailoring the rail to dampen line vibrations and perhaps improve delivery pressure uniformity. The older beefier rail looks more robust. Part of the redesign is probably to lower costs. It's hard to conclude that CR pressure has gone up on the Passat except that pump physical stroke (not to be confused with effective stroke) is longer. The use of AddBlue probably simplifies combustion management. I believe AddBlue is associated with an SCR (selective catalytic reduction) reaction to reduce NOx.

 

[FloridaJohn]

They appear to be tailoring the rail to dampen line vibrations and perhaps improve delivery pressure uniformity.

Interesting. I had a different take on the changes than you did.

My first thought was they changed the take-off points to account for the bends in the tubing. You can't always use the closest take off point because you won't have enough room to make the bends in the tubing, so you connect the injector to one further away. It also looks like the spacing between the rail and the injectors is closer in the Passat than the MK6, making the bends more difficult, so more distance between the rail and injector (along the tube) is useful for that reason. Also, I would imagine the wall thickness of the tubing is pretty large, making tight bends more difficult.

Also, I thought the idea behind a "common rail" is that the fuel pressure leading to all the injectors would be more or less equal all the time (in the rail).