You are right, and I should have checked the picture of the timing belt path before I wrote. The HPFP pulley appears to be the same size as the crank pulley.
Looks like we are just running the same thoughts over again. LOL
eddif
CR engine HPFP analysis
- Thread starter oilhammer
- Start date
Looks like we are just running the same thoughts over again. LOL
eddif
The common fuel rail holds a volume of fuel that is pressure regulated. This acts as an accumulator that would have a shock absorber effect with regard to HPFP pulsations.
Jack Frost
Veteran Member
Since when?
Ski in NC
Top Post Dawg
Look up isothermal or adiabatic compressibility of liquids. Typically around 5-7% reduction in volume at 1000bar.
RNDDUDE
Veteran Member
^^^^That's a fact! I have visited well over 1000 bars, it it takes at least 7% more booze to get me drunk!
Liquid compressibility and or expansion of the rail and tubing likely represent a very small overall fluid volume. This is probably why the pump deliveries are timed to injection periods. To help maintain a stable rail pressure.
Even in the slow mo low pressure world of marine jerk pump systems, a leaking delivery check valve alters injection timing, peak pressures,and exhaust temperatures.
Combustion management in the world of CR automotive engines is way more complex. Piezo injectors manage injection timing independently of fuel rail pressure. Control automation needs to produce a stable adjustable CR pressure in order deliver power and meet environmental emission requirements.
I know you understand this. In my view this makes the case for why pump delivery needs to be timed to the engine cycle.
Adapters in the pump body can separate the flow of combustion fuel and create this kind of delivery path. Sketches were posted way back. The best this can really do is to limit damage to the LP side of the pump. This contains cost but does not address failure root cause.
Same is true for improved / supplemental filtration. Yes - It will marginally help. Filtering combustion fuel will limit damage to the HPFP and hopefully protect the balance of the fuel system.
In the end it makes sense to do everything possible. Even if these actions are primarily palliative care for a terminal design.
As Ski points out, this seems to be a facet of all CR systems. If its not a requirement, things would be a lot simpler in the fuel system.
In my mind the best way to grasp this requirement is to recognize that the control system (as is) really struggles to manage / control CR pressure. If pump delivery to the rail was not timed to coincide with fluid removal from the rail by injection events, CR rail pressure would be even harder to control. I've done some VCDS monitoring of operating engine parameters. CR pressure is managed and adjusted to help control engine power output. At the same time, during trailing throttle, the control systems really struggles to get control to limit how much the rail pressure spikes. Timing the pump to the engine cycle helps with control.
LOL - It's good to cover old ground, especially to help answer questions from new folks who are interested in this problem (Jack Frost, 2micron, and others new to this thread)
+1 Anyone who's done a Pub Crawl can relate. Anyone who's struggled thinking about these issues deserves to hoist a glass or two
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Ski in NC
Top Post Dawg
I agree the "re-plumbing" does not adress the root cause of the cam/roller failure. But that failure is rather rare and if that failure is contained to the pump ONLY, the failure is something I and most others would accept as one of those "sh!t happens" things and consider it ok.Adapters in the pump body can separate the flow of combustion fuel and create this kind of delivery path. Sketches were posted way back. The best this can really do is to limit damage to the LP side of the pump. This contains cost but does not address failure root cause.
Same is true for improved / supplemental filtration. Yes - It will marginally help. Filtering combustion fuel will limit damage to the HPFP and hopefully protect the balance of the fuel system.
In the end it makes sense to do everything possible. Even if these actions are primarily palliative care for a terminal design.
When the swarf gets into the rail and injectors, thats just not cool.
The re-plumbing would not involve any major design changes, just some re-routing of flows.
While you may have trouble compressing a fluid, what about air entrained in diesel fluid. While I am not smart enough to understand all of it I do think some folks think they do. http://www.parker.com/literature/Racor/Mobile_Air_Separation_In_Diesel_Fuel.pdf
There are several things going on in a CR: There is a fuel pressure regulator on the fuel rail, The fuel injectors are sometimes open while the pump is pumping, The quantity fuel valve does not put in much more fuel than is needed. Some of the fuel pressure regulation is redundant (?).
Now what kills the HPFP system is the fact that the wear materials from the low pressure chamber (the chamber with the cam and roller follower) passes wear material on to a screen that does not remove all wear materials but sends them to the HP (high pressure) piston. The fuel rail is filled with wear materials and thus the injectors are sent trash. The only way to save the whole stock system; is to filter the system, by adding one or more filters.
Now if there is any air in the low pressure chamber of the HPFP; will the air become entrained as the parts move? I know there are several places for removing entrained air in the system, I wonder if all entrained air is removed? If there is any entrained air it will compress.
The third paragraph is the one we have the most control of, and contains the information that tells us how to help prevent a whole TDI CR system failure.
The shadetree jerk from Mississippi
eddif
There are several things going on in a CR: There is a fuel pressure regulator on the fuel rail, The fuel injectors are sometimes open while the pump is pumping, The quantity fuel valve does not put in much more fuel than is needed. Some of the fuel pressure regulation is redundant (?).
Now what kills the HPFP system is the fact that the wear materials from the low pressure chamber (the chamber with the cam and roller follower) passes wear material on to a screen that does not remove all wear materials but sends them to the HP (high pressure) piston. The fuel rail is filled with wear materials and thus the injectors are sent trash. The only way to save the whole stock system; is to filter the system, by adding one or more filters.
Now if there is any air in the low pressure chamber of the HPFP; will the air become entrained as the parts move? I know there are several places for removing entrained air in the system, I wonder if all entrained air is removed? If there is any entrained air it will compress.
The third paragraph is the one we have the most control of, and contains the information that tells us how to help prevent a whole TDI CR system failure.
The shadetree jerk from Mississippi
eddif
Ski in NC
Top Post Dawg
Entrained air will most certainly be forced into solution at rail pressure. And if in large quantities, the air will prevent the plunger from pumping, causing engine to stop or otherwise act up.
Entrained air is not the same as cavitation, which can create damage. Air just causes engines to run sick til pushed through.
Entrained air is not the same as cavitation, which can create damage. Air just causes engines to run sick til pushed through.
eddif - Great Link. I'll bet the demo referenced in the article was something to see. Large (marine) fuel filters typically have vents to periodically purge any separated air.
Ski - I think Bosch has been very careful not to try to achieve zero delivery from the HPFP using the Fuel Metering Valve. Under the right conditions you could wind up with vaporization of fuel on the suction side of the HP piston / cylinder. Bosch chooses to selectively manage CR pressure by squeezing the HPFP suction side and bleeding from the CR rail.
For the rest of readers playing catch up, pages 32 to 41 of the narrative (link below) provides a good description of the components under discussion.
EDIT: Reposted link, initial posting was a broken link.
http://152.66.93.29/audi/download/vw...rail%20TDI.pdf
Ski - I think Bosch has been very careful not to try to achieve zero delivery from the HPFP using the Fuel Metering Valve. Under the right conditions you could wind up with vaporization of fuel on the suction side of the HP piston / cylinder. Bosch chooses to selectively manage CR pressure by squeezing the HPFP suction side and bleeding from the CR rail.
For the rest of readers playing catch up, pages 32 to 41 of the narrative (link below) provides a good description of the components under discussion.
EDIT: Reposted link, initial posting was a broken link.
http://152.66.93.29/audi/download/vw...rail%20TDI.pdf
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bluey
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- Australia
- TDI
- Skoda Yeti 2.0L 103kW CR TDI (CFHC) [MY09 Polo TDI 1.9 74kW (AXR) retired with hail damage]
(Specsalot - link malformed)
Design of HPFP (click for larger photo)
According to that schematic, any large metal particles from roller or roller tappet should quickly clog up the fine filters and cause the pump to stop without causing further damage. So is that schematic a newer design? That one looks pretty fail safe to me.
The diagram calls the "piston" the part that does the pumping - a long rod. The thing everyone on this thread is calling a "piston" is what we might alternatively call an inverted bucket tappet with integral roller.
Design of HPFP (click for larger photo)
According to that schematic, any large metal particles from roller or roller tappet should quickly clog up the fine filters and cause the pump to stop without causing further damage. So is that schematic a newer design? That one looks pretty fail safe to me.
The diagram calls the "piston" the part that does the pumping - a long rod. The thing everyone on this thread is calling a "piston" is what we might alternatively call an inverted bucket tappet with integral roller.
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Hey bluey - Welcome to the club. Sorry about the link - had problems inserting it. Try this one:
http://152.66.93.29/audi/download/vw/Engine/2.0L%20common%20rail%20TDI.pdf
The diagram you reference shows filters. In fact those components are mesh screens. These pumps run to the point of failure (typically loss of effective stroke) but the screens don't stop them as you think they might. This is why the entire fuel system winds up being showered with metal contaminants rather than just shutting down. Damage to the protective screen on the Overflow Valve is common in full blow failures. That screen is supposed to protect the valve and the balance of the fuel system.
I don't think it's common to lose injectors before the pump fails. This implies the pin filters in the injectors do a decent job protecting them. To really have a feel I would have to read each report in the NHTSA data. Perhaps others here have a better flavor for the totality of failure events. We know VW uses a shot gun approach - ie replace everything. So their inspections must show significant contamination on the HP side of the system. Hard to imagine metalic contamination successfully passing through the HP discharge valve, but I guess it does. Fouling that discharge check valve will shut the system down or code Low CR Pressure. Damage to the Fuel Pressure Regulator (ie CR bleed) would have the same effect. Failed systems do report intermittent low CR pressure faults. So I guess these events are part of the universe of failure modes.
Here are pictures of these protective screen elements:
End view of Overflow Valve
Side view of Overflow Valve
Fuel Metering Valve
Fuel Metering Valve Protective Screen
Developing a common nomenclature to discuss these issues is a challenge. People tend to use piston interchangeably because the tappet assembly does look like a piston of sorts. I think it's useful to refer to the inverted bucket tapped with integral roller as the "follower assembly" or "follower". In the end, context determines subject.
http://152.66.93.29/audi/download/vw/Engine/2.0L%20common%20rail%20TDI.pdf
The diagram you reference shows filters. In fact those components are mesh screens. These pumps run to the point of failure (typically loss of effective stroke) but the screens don't stop them as you think they might. This is why the entire fuel system winds up being showered with metal contaminants rather than just shutting down. Damage to the protective screen on the Overflow Valve is common in full blow failures. That screen is supposed to protect the valve and the balance of the fuel system.
I don't think it's common to lose injectors before the pump fails. This implies the pin filters in the injectors do a decent job protecting them. To really have a feel I would have to read each report in the NHTSA data. Perhaps others here have a better flavor for the totality of failure events. We know VW uses a shot gun approach - ie replace everything. So their inspections must show significant contamination on the HP side of the system. Hard to imagine metalic contamination successfully passing through the HP discharge valve, but I guess it does. Fouling that discharge check valve will shut the system down or code Low CR Pressure. Damage to the Fuel Pressure Regulator (ie CR bleed) would have the same effect. Failed systems do report intermittent low CR pressure faults. So I guess these events are part of the universe of failure modes.
Here are pictures of these protective screen elements:
End view of Overflow Valve
Side view of Overflow Valve
Fuel Metering Valve
Fuel Metering Valve Protective Screen
Developing a common nomenclature to discuss these issues is a challenge. People tend to use piston interchangeably because the tappet assembly does look like a piston of sorts. I think it's useful to refer to the inverted bucket tapped with integral roller as the "follower assembly" or "follower". In the end, context determines subject.
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nicklockard
Torque Dorque
Is the swarf 100% aluminum or does it have some iron to be magnetized, even slightly?
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Plus 3 Golfer
Veteran Member
The visible particles in my fuel system were not magnetic. Here's a couple of photos with the first being the top of my FF at 26k miles. I examined my FF (shortly after dweisel reported on his first HPFP failure) at about 22k miles and my top was pristine. Dealer cleaned canister and replaced FF at 26k and checked at 30k. I also checked at 30k and 35k and some particles were still visible on top of FF but the quantity was diminishing. The second photo is a section of a FF pleat showing two particles at 40k miles when I changed my FF. The top of the FF at 40k still had a few specks but nothing like the pic below. 4k miles later my HPFP failed.
To give persepective, the dimples in the second photo on the pleat are about 1 mm or 1000 microns in diameter. So, the larger speck is about 250 microns (clearly visible to the naked eye) and the smaller one is estimated at about 60-70 microns (visible once you know it's there). I could not find any other specks using a 6X magnifier on this pleat.
bluey
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- Australia
- TDI
- Skoda Yeti 2.0L 103kW CR TDI (CFHC) [MY09 Polo TDI 1.9 74kW (AXR) retired with hail damage]
OK got it, thanks. The diagram is misleading in its detail in terms of fineness, size, and location of the filters.
All the damaging metal particles have to pass through the fuel metering valve mesh screen. Would it be feasible to change the cylindrical mesh screen to a shaped sintered stainless steel filter??? (I read they use sintered stainless filters in refinery operations.)
see for example this manufacturer's photo
Also thinking about the roller/follower rotation problem. Couldn't the bore have keyways machined to accept a longer cam roller to constrain unusual cam follower rotation (not needing any load on the keyways in usual operatiion.
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Improving materials on the FMV screen might help protect the HP side. Looking at the filter mesh, I believe it's some kind of stainless steel already (at any rate it's non-magnetic). It's not very stout. The plastic cage which holds the screen forms a close seal on two different OD's of the FMV. I have to laugh, you're like me - multiple edits. Looking at your pictures above for the sintered filters, they might be a positive improvement for this unit.
Here are a couple pic's of the follower riding the cam. As you can see the follower protrudes from the bore too far to allow an extended roller to act as a key.
CAM at TDC (injection)
CAM on BASE CIRCLE
There might be room to key the follower within the bore. It would have to be aligned to the thrust axis so there would be no thrust loading of the keyway. As can be seen in the picture below the thickness of the bore doesn't offer a lot of material to work. Any loading on the key would likely generate more swarf.
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bluey
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- Australia
- TDI
- Skoda Yeti 2.0L 103kW CR TDI (CFHC) [MY09 Polo TDI 1.9 74kW (AXR) retired with hail damage]
OK. I figure cam follower rotation is an unlikely failure mode in any case. I think I'd rather have the round bore and cam follower than the square one in the Delphi HPFP.
More fancy shapes of sintered porous stainless filters are possible.
http://www.beot-filters.com/Cups-and-bushings.aspx
Apparently, parts can be made by "metal injection moulding". http://www.hoganas.com/en/Products--Applications/Sintered-Stainless-Steel-Filters/Manufacturing/
Typical pressure drops quoted on this page http://www.aegis-ceramics.co.uk/pormet.htm
Surely a simple replacement of the FMV mesh screen with a sintered stainless filter could be a cheap no-brainer damage mitigation upgrade for Bosch/Bosch OEM customers. They'd have to figure out filter cleaning or replacement intervals. Apart from that, preventing the rest of the multi-thousand dollar fuel system parts replacement in the case of HPFP failure has got to be cheap insurance, along with the HPFP internal surface engineering/coating changes.
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Nice links - Perhaps Bosch has folks reading this thread
Most people think failures are based on marginal tribiology in concert with low lubricity fuels. Many pumps have been found with flat spots on their rollers and grooves cut in the cam (ie 90 degree rotation of follower). This is why Delphi features / touts their constrained follower design.
The consensus on failures goes something like this:
1. Thrust loading on steel follower causes bore scarring releasing aluminum swarf. This is blamed on lubricity but is probably a result of poor material selection.
2. Aluminum swarf circulates impacting anti-friction coating on the steel carrier that holds the roller in the follower assembly.
3. Anti-friction coating damage sets the stage for steel on steel wear between the roller and carrier. This creates steel swarf. COF (coefficient of friction) between the roller and carrier changes. Roller begins sliding vs rolling across the cam surface. This creates steel on steel wear between the roller and cam. Metalic swarf in circulation really builds from this point forward. This change from rolling to sliding significantly increases thrust loading on follower accelerating bore damage.
4. Loss (however briefly due to trapped swarf) of parallelism between the roller and cam will cause the cam to rotate the roller 90 deg. Likely this happens as the cam / roller passes max lift point. From this point forward there are no significant forces present to restore the geometry of the system. It's basically game over for the HPFP.
The real problem developing a more detailed failure description is that typically failures total the pump before the fuel system exhibits identifying symptoms (low CR pressure). At that point it's a bit hard to tell what happened when.....
Still want a round follower?
No one is prescribing any maintenance practices for the HPFP. Bosch does not sell replacement component parts, only complete HPFP's. Anecdotal evidence in these forums suggest many dealers struggle with oil and fuel filter changes (right engine oil; proper fuel system priming). Can't really picture them doing brain surgery on HPFP's - Even though we all know this stuff isn't rocket science.
Most people think failures are based on marginal tribiology in concert with low lubricity fuels. Many pumps have been found with flat spots on their rollers and grooves cut in the cam (ie 90 degree rotation of follower). This is why Delphi features / touts their constrained follower design.
The consensus on failures goes something like this:
1. Thrust loading on steel follower causes bore scarring releasing aluminum swarf. This is blamed on lubricity but is probably a result of poor material selection.
2. Aluminum swarf circulates impacting anti-friction coating on the steel carrier that holds the roller in the follower assembly.
3. Anti-friction coating damage sets the stage for steel on steel wear between the roller and carrier. This creates steel swarf. COF (coefficient of friction) between the roller and carrier changes. Roller begins sliding vs rolling across the cam surface. This creates steel on steel wear between the roller and cam. Metalic swarf in circulation really builds from this point forward. This change from rolling to sliding significantly increases thrust loading on follower accelerating bore damage.
4. Loss (however briefly due to trapped swarf) of parallelism between the roller and cam will cause the cam to rotate the roller 90 deg. Likely this happens as the cam / roller passes max lift point. From this point forward there are no significant forces present to restore the geometry of the system. It's basically game over for the HPFP.
The real problem developing a more detailed failure description is that typically failures total the pump before the fuel system exhibits identifying symptoms (low CR pressure). At that point it's a bit hard to tell what happened when.....
Still want a round follower?
No one is prescribing any maintenance practices for the HPFP. Bosch does not sell replacement component parts, only complete HPFP's. Anecdotal evidence in these forums suggest many dealers struggle with oil and fuel filter changes (right engine oil; proper fuel system priming). Can't really picture them doing brain surgery on HPFP's - Even though we all know this stuff isn't rocket science.
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bluey
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- Oct 18, 2008
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- Australia
- TDI
- Skoda Yeti 2.0L 103kW CR TDI (CFHC) [MY09 Polo TDI 1.9 74kW (AXR) retired with hail damage]
Still trying to understand how the swarf circulates and how the cam follower rotates.
Aluminum is soft, so would presume in the first instance unable to cause wear, but could jam other parts. Do aluminum particles get in between the cam follower and bore and cause jamming or one-way rotation???
Particles in the fuel recirculation flow will be removed by the fuel filter. So we are talking about stuff in the HPFP just going round and round and round inside the HPFP body without really "circulating" per se. Just being stirred without any mechanism of filtration or removal?
Aluminum is soft, so would presume in the first instance unable to cause wear, but could jam other parts. Do aluminum particles get in between the cam follower and bore and cause jamming or one-way rotation???
Particles in the fuel recirculation flow will be removed by the fuel filter. So we are talking about stuff in the HPFP just going round and round and round inside the HPFP body without really "circulating" per se. Just being stirred without any mechanism of filtration or removal?
bluey
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- Joined
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- Australia
- TDI
- Skoda Yeti 2.0L 103kW CR TDI (CFHC) [MY09 Polo TDI 1.9 74kW (AXR) retired with hail damage]
Wondering if it's really there as anti-tamper or more as *protection*. All the high pressure in the CP4 is isolated to the small steel component containing the pump piston and valves. Apparently, that is what enabled the cost reduction as the whole pump need not be able to hold the high pressure. The high pressure bit could be vulnerable to fatigue fracture from any minor scratches - hence the plastic cover??
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nicklockard
Torque Dorque
Nice links - Perhaps Bosch has folks reading this thread
Most people think failures are based on marginal tribiology in concert with low lubricity fuels. Many pumps have been found with flat spots on their rollers and grooves cut in the cam (ie 90 degree rotation of follower). This is why Delphi features / touts their constrained follower design.
The consensus on failures goes something like this:
1. Thrust loading on steel follower causes bore scarring releasing aluminum swarf. This is blamed on lubricity but is probably a result of poor material selection.
2. Aluminum swarf circulates impacting anti-friction coating on the steel carrier that holds the roller in the follower assembly.
3. Anti-friction coating damage sets the stage for steel on steel wear between the roller and carrier. This creates steel swarf. COF (coefficient of friction) between the roller and carrier changes. Roller begins sliding vs rolling across the cam surface. This creates steel on steel wear between the roller and cam. Metalic swarf in circulation really builds from this point forward. This change from rolling to sliding significantly increases thrust loading on follower accelerating bore damage.
4. Loss (however briefly due to trapped swarf) of parallelism between the roller and cam will cause the cam to rotate the roller 90 deg. Likely this happens as the cam / roller passes max lift point. From this point forward there are no significant forces present to restore the geometry of the system. It's basically game over for the HPFP.
The real problem developing a more detailed failure description is that typically failures total the pump before the fuel system exhibits identifying symptoms (low CR pressure). At that point it's a bit hard to tell what happened when.....
Still want a round follower?
No one is prescribing any maintenance practices for the HPFP. Bosch does not sell replacement component parts, only complete HPFP's. Anecdotal evidence in these forums suggest many dealers struggle with oil and fuel filter changes (right engine oil; proper fuel system priming). Can't really picture them doing brain surgery on HPFP's - Even though we all know this stuff isn't rocket science.
So, has anyone magnetized the metallic components in your last picture post (#163) to try and attract/hold ferrous particles and arrest the failure cascade? If there's aluminum swarf present, the pumps will still probably fail, but could you buy enough time to allow an owner to detect the problem?
Also, has anyone listened to the pump with a stethoscope? It would be nice to capture digital files of sounds of normally operating pumps and then when they are about to fail. Also, +1 on the ceramic frit filter suggested by bluey. Would be nice to see if an off-the-shelf frit could be retrofitted.
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I've thought about this too.
I've never listened to a pump in failure mode, but I think the noise would be noticeable to a trained ear if a pump roller was failing.
I'm wondering about the piston to bore clearance in pumps that have failed. They have definitely changed the pump housing castings over time. Bad metallurgy could have caused the bore to distort with heat cycling causing a cam follower piston to stick in the bore and lose orientation. Pumps that are "well run in" with 100,000+ miles seem to survive well. A bore clearance that is too large would also be a problem, but I think pumps that have "well run in" piston to bore clearances are surviving.
The majority of wear materials (swarf) comes from the slide / roller / cam wear. The wear materials are thus mainly in the HPFP cam roller chamber.
1..This chamber feeds the high pressure (HP) piston (with only a screen protecting it. Any swarf going through the HP piston would go to the fuel rail and injectors. IMHO a small ceramic filter would not have the volume to filter and allow adequate volume over time, but (an adapter that added a 1 quart (?) filter assembly would work).
2..The pressure regulation valve (by-pass valve) is the only real flush method the HPFP chamber has. If trash (swarf) gets large enough to stop up the pea size screen, then the pressure builds up to the booster pump pressure and most wear materials (swarf) just stays in the HPFP chamber (a small amount goes to the HP piston). Before the complete clogging, all contaminated return fuel goes to the dirty side of the filter for warming or the filter thermal valve directs the fuel to the tank.
3..The stock fuel filter only filters the return fuel only while the filter thermal valve is directing the return fuel to the dirty side of the filter. After the thermal valve directs the HPFP return fuel to the tank no filtering is going on (all swarf goes to the tank).
One added filter can:
1..filter the HP piston fuel
2..filter the return fuel
Or
Two seperate added filters can do the job.
In either case you have to watch the pressure differential on the HPFP bushings.
+++++++++++++++++As long as the slide and roller assembly is slick in the bore the whole assembly will tend to stay in the correct position.
When the slide scuffs in the bore, the ability to return to correct alignment is almost gone.
If the slide winds up with the roller at 90 degrees the scuff marks can act as keyways to keep the slide in that position (scuff aluminum bonds to the slide forming something similar to keys as they cut into the alumimum bore).
Once the roller cuts a trench in the can lobe the slide assembly it is pretty much keyed by that trench.
I think the total 90 degree thing is rare, but the scoring causing some alignment problems is not.
+++++++++++
Just a total mess. Oh I am sorry. As a jerk from Mississippi I can not be expected to see any problems.
IMHO the adapters and extra filter are the only cost effective things that help a stock system.
OH WELL
eddif
bluey - The LP casing has a transfer port and the follower has holes to minimize pumping losses. These same features probably promote circulation which may be part of the thermal design of the pump. Interesting observation about the protection aspect. The CP 3.x on my jeep has no protection and operates at similar pressures. Anyone who's ever changed a torsion bar on a Porsche knows about corrosion induced fatigue failure. So your point is well taken.
Nick- The pump I have didn't experience a catastrophic failure and looked pristine inside. That said the swarf I photographed was ~ 25% ferrous.
Nick & SC - Audio signatures or other sophisticated monitoring could probably be used as a "health" indicator for the HPFP. Issue of course would be signal to noise with all the rest of what's happening in the engine compartment. Not simple stuff, but possible for sure.
Eddie - Great summation of the issues. You are on the money with the point about doing what can be done cost effectively. With failure rates as low as they seen to be, every expense becomes tough to justify. VW will of course be looking to deny warranty for "modified" systems. So that really kills wide spread adoption of useful things worth doing. Sooner or later all owners go out of warranty. People will then be at a number of decision points.
All - I've spun my "failed" pump with no load on the follower. It tends to oscillate (rotate) a bit. I believe this happens because the roller tends to lose parallelism with the cam. Once the roller starts sticking rather than rolling. It can easily wind up off axis due to debris in the pump. I estimate ~ 0.0015" diametrical clearance between the roller and carrier bore. Room for things to go wrong. Calculations show this roller spins (ball park) at 4 - 5 x engine RPM. Plenty of opportunity for problems. To me it remains amazing this pump runs at all. Of course the fact that it does run says the design is way more 'right' than 'wrong'.
Nick- The pump I have didn't experience a catastrophic failure and looked pristine inside. That said the swarf I photographed was ~ 25% ferrous.
Nick & SC - Audio signatures or other sophisticated monitoring could probably be used as a "health" indicator for the HPFP. Issue of course would be signal to noise with all the rest of what's happening in the engine compartment. Not simple stuff, but possible for sure.
Eddie - Great summation of the issues. You are on the money with the point about doing what can be done cost effectively. With failure rates as low as they seen to be, every expense becomes tough to justify. VW will of course be looking to deny warranty for "modified" systems. So that really kills wide spread adoption of useful things worth doing. Sooner or later all owners go out of warranty. People will then be at a number of decision points.
All - I've spun my "failed" pump with no load on the follower. It tends to oscillate (rotate) a bit. I believe this happens because the roller tends to lose parallelism with the cam. Once the roller starts sticking rather than rolling. It can easily wind up off axis due to debris in the pump. I estimate ~ 0.0015" diametrical clearance between the roller and carrier bore. Room for things to go wrong. Calculations show this roller spins (ball park) at 4 - 5 x engine RPM. Plenty of opportunity for problems. To me it remains amazing this pump runs at all. Of course the fact that it does run says the design is way more 'right' than 'wrong'.
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No need for sophisticated audio gear. If that roller was fouled with glitter or if it was riding the cam 90 degrees out of orientation, it would be making a racket to anyone with a trained ear.
Listening at the end of a screwdriver pressed against the aluminum housing would be enough.
bluey
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A small ceramic or perhaps preferentially sintered stainless steel filter to directly replace the cylindrical fuel metering valve protection screen is not normally doing any filtration duties. Under normal operation, only clean fuel passes through that. So I can't see why a small filter that prevents downstream injector damage needs to be any bigger than the screen. If it clogs, then the engine will shut down, which is not a bad option.
The bypass valve is the only potential flush mechanism, but can't be used for flushing without passing the swarf through the valve, which doesn't really work without risking valve malfunction.
To be able to effectively filter swarf through creating a "cleaning" circulation requires the bypass valve function to be taken off-board so the pea-sized screen can be replaced by a somewhat larger filter and still permit the bypass valve to operate. So to me, if one wishes to use an adapter to permit filtration of swarf from being stirred round the HPFP body, it should go where the overflow valve goes in preference to where the fuel metering valve goes which cannot provide any bypass circulation.
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sgoldste01
Veteran Member
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- Mar 14, 2010
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- None; Replaced 2010 Golf TDI with 2012 Subaru Impreza 5-door with manual tranny
Wait, let me make sure I understand what you're proposing here. After each fuel-up, you're going to open your hood and listen with a stethoscope to the sounds your engine is making? Really?
What would you do about it if you heard something that sounded wrong? Wouldn't it be safe to say that if you can hear a problem, the damage is already done?
Yep - I was thinking this very thing as I typed it above. I have a steth and it's going in the back with my additive box.
It would be much better to develop some form of monitoring that could detect issues earlier. An earlier stage issue should likely show an increase in internal friction. Issue is signal to noise - how to recognize this against a backdrop of varying ambient temperatures. A meaningful change in temperature rise of fuel through the pump would show something. Problem is DT changes due to convective heat transfer between idlying in traffic and driving on a highway. Not so simple. Looks like it would require data logging and statistical analysis. Once again answers are after the fact as you point out.
This also brings up a core question - How rapid on-set is this situation for most owners. Clearly under gross miss-fuel the pump doesn't last long. What about chronic use of marginal lubricity fuel. Bosch has published data warning about this second issue.
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Previous posts had that the older model Injector pump off the VE Bosch pump series ran at HALF the crank speed, had 4 rollers on a merry go round cam, was made of steel, had no DLC and ran at 300-400 bars, or 1/5 the pressure. And it doesn't fail on 520 wear scar fuel or contaminate the whole fuel system with swarf, or stall the motor from fuel starvation.