Mike,
Is this really a poor design by VW or is this supplier issue Bosch. If I remember correctly this is a Bosch design fuel pump and fuel system; VW may design the fuel lines to the injector.
I know that when I was designing hydraulic system on larger mining machines for Cat; we use REXROTH Hydraulic piston pumps. The Germans kept telling us nothing was wrong with their pump design, it was our lines routing that was causing the failures on the machines at first. The German machines that used this design pump did not have the issues we did at CAT. Will after we tore down several of their pumps and showed them their errors. The pumps were redesigned to improve the life of the piston pumps past 10,000 hours.
I have always found that the German designs are very complicated for what they do and are very touchy; things have to be just right to prevent failures. The suppliers always have the attitude that the user is using the product wrong or the fuel/hydraulic oil quality is poor. It is not their product that could have the design flaw. Bosch just needs to be shown their errors.
Just my $0.02
Jim W.
Jim,
Thanks, good input.. I have looked into the internals, over at the TDICLUB they have people who have tried to find a way to solve the problem.
I believe it is compounded errors, in this order: Bosch goes to the CP4.x pump, because it is way cheaper and easier to produce, but it requires fuel lubricant, and the cam/roller is very sensitive to any bad fuel, or in the US, damn near all ULSD fuel, hence the issues. Next VW who brought these cars to market, saying they don't need additives, and US ULSD fuel would be OK made a big miscalculation on failure rate and risk.. One person posted the US ULSD spec for lubricity is 520um, which is only had by additives, since refined product is about 675.. The consensus is that Bosch said the pump needed 460um lubricity to be able to attain reasonable service life. This pump is an issue on the newer Ford and GM diesels as well (CP4.2), it is the same basic design with 2 pistons vice a single piston for the VW.
From there it gets even more interesting.. so VW is at fault for saying it will be OK, when it is not in many cases.. But I doubt that even at 460um the Bosch design is a good one.. Here is why:
The Cam/Roller concentrates massive forces over a very small contact area of the cam and roller.
There is no anti-rotation feature to keep the roller inline with the cam, failures show the roller eventually goes 90 degrees out, then rapid wear of both cam and roller, and massive heavy/hard/abrasive metal contamination in both the HP and LP sides of the system.. which gets to the next flaw, this may be VW...
The flow in the system allows some fuel to go from the cam/roller region of the pump to the HP inlet, the rest comes post filter to the inlet.. there is no reason any fuel needs to move from the cam/roller area where it serves as a lubricant/coolant. The flow needs to recirculate to the supply, and be filtered as a safety precaution, but it is not designed that way.
When the pump fails, metal goes both to the injectors, and flows back to the tank via the return line, the ENTIRE system is compromised. 2Micron over at TDIclub did some back yard engineering and completely isolated the contamination on the system to the pump itself, by adding a return side filter, and separating the inlet flow to the HP side so only fuel from the pump, post filter, goes to the injectors.. this is not that complicated of a fix, and VW needs to retrofit these to do this NOW, because they are putting the customers on the hook post warranty for a massive repair bill with a pump that can fail suddenly without warning, and cause this massive damage.. really that is now a poor customer service and product support issue.
Below are links to data and pictures, as a fellow engineer I'm sure you will appreciate this as a failure analysis project. In contrast the CP3 on the Cummins does not have any cam/roller whatsoever, I really think this cam/roller is the real root cause, it is just TOO sensitive to fuel lubricity, and at best is not going to be a long life durable design, but clearly far less complex to manufacture, and thus about half the cost of a typical CP3 pump, this no doubt was the driving factor in its use, not any improvement in design...
http://forums.tdiclub.com/showthread.php?t=375803
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Pictures of failed pump internals:
http://pics.tdiclub.com/showphoto.php?photo=86414&title=ebay-pump&cat=500
http://pics.tdiclub.com/showphoto.php?photo=86412&title=ebay-pump&cat=500
This last link may be my path forward, a swap out from the CP4.1 to the CP3 pump used on other applications, like the Jeep 3.0 CRD. The guy has more than a dozen complete, and his own working for over a year, with only symptom being faster engine start (3 pistons vs. 1 (cycling at 2x speed) that would do it!).
http://forums.tdiclub.com/showthread.php?t=367804&highlight=cp3&page=8
Having said all the above, Jim, you nailed it on German engineering! This is my first German car, and I can see exactly what you mean, even what could be fairly simple systems are overly complicated.. but it does drive great, and is generally a good car.. when I did the 40K service I had to add a builders level to my standard auto tool kit, as the car must be precisely level to do the DSG fluid change, as it has no fill hole, but a snorkel in the drain hole, and fill is from the bottom, requires a special tool! And I had to get the VCDS connector and software, because post fill the fluid has to be warmed to precisely 35 deg C, then the excess drained.. the reading from the connected PC!! add to that, just to change the filter, one needs the computer to cycle the pumps on, you can't do it like the Cummins where you just cycle the key to on a few times and it primes itself.. Needlessly complicated for sure.
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