Engine/Transmission (1998.5 - 2002) If the Vp44 is calibrated at 13.5 psi, what's the calibration rpm?

[rweis]

Read and re read and re read again



Target = 13. 5psi with slight variations acceptable, of course if you could do NO variations then you have nailed the psi really well. Now how do we do that?



ALL this assumes you are delivering clean, good volume, lubricated fuel.



I wonder if the Bosch test bench is designed to deliver 13. 5 under ANY rpm. I bet it is or the calibration process would be very difficult. I would think the test stand has as few variables as possible.



We are trying to simulate a mobile test stand (our truck) so as to be as close to calibration as possible and therefore as less stress as possible on the VP44 trying to make it as long in longevity as possible.



Be careful of the law of dimenshing returns that when you get closer and closer to the objective the value of additional "adjustments" gets less and less.



I have a RASP system. The RASP system depends on the VP return bypass valve to set the input fuel psi. I have mine as close to 11 1/2 - 15 1/2 as I can get (ie 13. 5 + - 2). Just for experimentation sake I will get another VP bypass, set it also to 11 1/2 - 15 1/2. The comment from someone about the RASP at 1500 rpm could throw fuel across his driveway has lead me to a thought that a single bypass may not pass enough fuel at cruise rpms. I'll see if I can test out the concept that 2 VP bypass valves set to the same bypass psi are better able to control the VP input fuel psi with the objective of 13. 5 +-0.



You guys with a FASS type system, can you set a particular bypass psi? Does it change with load? What is your range of psi?



Tweak, tweak, tweak but getting pretty close to optimal.



Bob Weis



I can't help but throw in the concept of cooling the fuel, see other threads on that though.

 

[paulb]

I have a RASP system. The RASP system depends on the VP return bypass valve to set the input fuel psi.

Bob, that's not true with the RASP system that I have. Mine has an external bypass valve, which opens when the pressure gets above a preset amount. The spring inside can be changed as well as adding shims. Doesn't yours have this as well?



Paul

 

[NoSeeUm]

...



Bob Weis



I can't help but throw in the concept of cooling the fuel, see other threads on that though.

This something that just came to your mind very recently in a flash of exceptional thought?



Jim

 

[Edward]

Ok Here is how I see it. The bypass valve is on the low pressure side located at the top of the VP44. The bypass valve has a bleed hole that allows fuel or air to escape below the preset bypass pressure. As stated earlier attempts to blow air through the VP44 by mouth have not been successful so the term "isolation" was used to describe the bypass valve as "isolated" in reference to the inlet port.

I believe that the term "isolation" is incorrect because both the inlet and bypass valve are on the low pressure side of the VP. Again the term "isolation" was used after someone performed an oral airflow test. I tried to simulate this test on a dial air pressure gage and could not even produce one pound of pressure. Since the Carter transfer pump produces between 8 to 13 PSI a less than one PSI test could hardly be conclusive in a system that has an optimal rating of 13. 5 on the low pressure side. This would indicate to me that the oral test was insufficient to conclude that the bypass was indeed "isolated". Obviously the Carter pump can produce enough pressure to force the air through the rotary low pressure pump where it moves to the top of the fuel channel located near the top of the VP44 where the bypass valve is located. I bet if someone put 8 PSI of air pressure on the inlet side that they would indeed feel air escaping out the bleed valve indicating that there is no isolation at operating pressures.



Edward

 

[rweis]

paulb



I was not exactely clear in the way I wrote that.



Mine is like yours, the RASP VP bypass valve I ment to convey is the brass bypass valve that comes in the RASP kit that goes on the VP input fuel return line to the tank.



Sorry, about not describing it better. I went back and I really did not do a very good job of writing that.



However, thanks for bring it up so others will not read it and get an incorrect impression as to how it works.



Bob Weis

 

[rweis]

I worked on my RASP brass Vp44 bypass valve today to adjust the pressures the VP44 inlet sees and to try to get as close to 13. 5 psi at the Vp44 inlet under all circumstances as possible.



First I took the brass bypass valve apart and measured the spring. It was 1 11/32" from end flat to end flat so I would know what I started with. This length gave me 12 to 16+ (slightly over 16). Then I reassembled the bypass valve and drove it again just to be absolutely certain where I started from for adjustments.



WELLLLLLLLLLLLLLLLLLLLLLLLLLLLLL I put the internal part of the valve in backwards (the internal moving seat was at the wrong end and had no seat to close onto hence the really low pressures, and the spring was way way too tight, hence the really high pressures), The first indication I had screwed up was the min psi was 8 and the max psi was 20. Obviously something was not right. But my point here is IF you put your valve back together backwards your expected pressures and what you read will be WAYYYYYYYYYYYYYYYYYYYYY different.



So back to the house and put the bypass valve back together correctly and compress the spring to 1 9/32" to try to lower the psi range (from 12 - 16) just a touch. With 1 9/32" I get (rpm/psi) 850 (idle)/11psi (-2 1/2 psi from optimum), 1000 (any throttle at all)/12psi (-1 1/2 psi from optimum), 1500/13psi (- 1/2 psi from optimum), 1750 and above(went to 2500 rpm)/14psi (+1/2 psi from optimum). I figure that most of my driving is between 1500 rpm and 2500 rpm and the psi is within +- 1/2 psi from optimum in the majority of travel time.



What I wanted was to be a tad low at idle when the VP44 is at its lowest rpm and least demand (and lowest stress and lowest internal dynamic forces). Then as the rpms build (and the internal stress builds and the internal dynamic forces build) the input psi gets closer and closer to the precise calibration psi. Hence when you are at the highest rpms (and highest stress and highest dynamic forces) you are as close to optimum calibration input psi as possible.



Remember I have a RASP so I build psi as the rpms go up, a lot of you have FASS or equivalent so if you take the same approach, I think you are going to start at a higher psi at idle (15 psi ???) and pull it down to 13. 5 as you get the VP44 up to higher rpms and stress / dymanic forces.



I would like Brett or Brady or someone at II to comment to just reassure if I have thought of this correctly and applied the correct inputs to the VP44 input fuel psi.



Bob Weis

 

[Gary - K7GLD]

Ok then how does the air get out of the VP44 with just electric fuel pump pressure if the bypass/bleeder valve is isolated? The fact remains that the air has to go someplace or it would be impossible to prime the fuel filter and

VP44 after a filter change. If the air can't get to the bypass due to Isolation where does the air go when priming the fuel filter?



Edward

I believe trapped air eventually works it's way into the bypass valve, but by a diverse path that allows relatively low flow - it (air) gets mixed with the fuel circulating inside the VP-44 cavity, and EVENTUALLY is vented along with the fuel thru the bypass valve - but NOT a directly connected route between the input and bypass ports.

Ok Here is how I see it. The bypass valve is on the low pressure side located at the top of the VP44. The bypass valve has a bleed hole that allows fuel or air to escape below the preset bypass pressure.

NO, actually, the primary air bleed hole you speak of IS NOT at the bypass valve, though that is where it eventually escapes along with the bypassed fuel - it is deeper inside the VP-44 near the point where the high pressure fuel is distributed to the injector lines. After all, it's the air that potentially is headed to the injectors we want to eliminate. (as I understand it!)



The popular misconception regarding the function of the VP-44 bypass valve, is that it is to regulate fuel PSI ENTERING the VP-44 - but it's not - it is to regulate the VP-44 INTERNAL fuel pressure as generated by the VP-44's own internal vane pump - and it is that internal vane pump with spring loaded vanes that effectively (within reason!) isolates the fuel inlet port from the bypass port.

 

[paulb]

Bob,



Thanks for the earlier clarification. I wasn't completely sure which one you were talking about.



Is your RASP bypass valve between the fuel filter and the VP44?



Remember too that spring preload in the bypass valve is not the same thing as spring rate. If you increase the spring preload, you will increase the pressure when the bypass valve is mostly closed. The change when the RASP is at a higher rpm, the pressure bypass will be different depending on how far the bypass valve is open. For example if you are at 2000 rpm, with light load the RASP bypass valve will be way open, bypassing a lot of fuel. At the same RPM with a heavy load (especially for us way under fueled guys ), the bypass valve will not be open as far. Changing the spring tension rather then the spring preload, seems to even out the pressures more. In other words replacing the spring instead of shimming the spring seems to work better, but you can't get the pressure as close, because you are limited to what springs are available. Kinsler fuel injection has a spring select kit, but there is still a pretty good gap.



Just my . 02 worth...

 

[mhenon]

Bob, You've had the answer all along..... 13. 5 psi plus or minus a few. If it were a stationary generator with a fixed load you could maintain an exact 13. 5psi. But the engine's in a pickup with varying loads and RPM's.

The sweet spot is obviously between 10 and 16 psi or so. If the fuel pressure stays within those parameters I would think it's good to go. Just don't see where nailing it down to plus or minus 1/2 psi would gain anything.

Mike

 

[rweis]

paulb -



Yes my RASP brass bypass is between the fuel filter and the VP44. The actual fitting is about 3" before the Vp44. I got as close as I could to minimize any varience.



Well, I know nothing about springs, but you have a source at least. Any idea on the specs of the spring in the RASP brass VP bypass?



I can see where what happens changes with load as you suggest. I hope that by getting really close unloaded it will be close enough loaded like mhenon suggest. I was just trying to get as close as I possibly could and adjust it only 2 or 3 times.



I guess that proof will be on the next RV outing at the end of next month. Depending on what happens with the RV I may need to adjust the empty psi up or down some so as to even it all out doing either.



Who knows, I might have to take higher psi empty to get acceptable psi loaded. I am sure it will be several iterations to get a workable solution, but at least we have a target (13. 5 psi)



Bob Weis



RV psi: If unloaded more fuel goes to RASP brass bypass because less is going to the injectors and therefore creates more psi effect in opening it (14 psi). If loaded and less fuel goes to RASP brass bypass and therefore will have less psi because more fuel is going to the injectors will the bypass psi be less? (12 psi). Towing you are requesting more APPS (pedal) to maintain the same speed. Any one have thoughts on this?

 

[paulb]

RV psi: If unloaded more fuel goes to RASP brass bypass because less is going to the injectors and therefore creates more psi effect in opening it (14 psi). If loaded and less fuel goes to RASP brass bypass and therefore will have less psi because more fuel is going to the injectors will the bypass psi be less? (12 psi). Towing you are requesting more APPS (pedal) to maintain the same speed. Any one have thoughts on this?

That's about the difference I see in mine between cruise and WOT at the track (16 to 14 at WOT). I would guess that I am flowing a little more fuel through the VP44 at WOT, then you are towing, but I am also turning the RASP quiet a bit quicker (2500 - 3200 going down the track). In your case if you are turning the same RPM while towing that you are when at cruise (I doubt you are, but just as an example), then 2 psi drop is probably correct. If you are towing at a higher rpm, then the difference will decrease. That's one of the cool parts about the RASP.



Paul

 

[rweis]

paulb -



I went to the Kinsler fuel injection web site. Very interesting.



On the constant flow section on page 35-M the 6AN High Flow Jet Can High Speed looks exactely like the RASP bypass valves. I think I am going to call them tommorrow and get both of the spring sets to see if they will fit and what difference they make. I will also mic the RASP bypass spring to see what it is. Your comment about the spring changing rather than messing with the orgional one makes sense.



I think the 2 psi lower at the same rpm empty vs towing is about right as well, but I will test that.



Thanks for the comment about Kinsler.



Bob Weis

 

[NoSeeUm]

Some components inside the VP44 are not 100% pressure tight. Leakage is a good thing for keeping pump parts cool and air a avenue to escape. The air venting system has been well thought out by Bosch. The overflow valve is the ultimate venting devise as Bob has pointed out. When changing filters, cycling the supply pump several times makes for easier starting. You can crank the engine for long periods and then get the fuel to inject to the engine, but not advisable. As in all diesel injection pumps, test plans are used to calibrate the injection pump. Test plans are very specific as to the fuel supply pressure. This pressure will always relate to the needed pressure on the vehicle. Changing this pressure more than slighly will change the calibration of the pump as the pump was calibrated with that pressure. The higher you change the fuel inlet pressure the more heat will develope. 13. 5psi is and has always been the target pressure. Being out of spec a slight amount is not that bad. Excessive high pressure will alter the calibration of the injection pump. We have already covered what happens with pressure being too low. Thanks, Brady

Thanks Brett, I guess this is what I was mostly thinking about.

Once you get air in the high pressure side, you must bleed the air from the high pressure fuel lines.

Jim

 

[Edward]

I believe trapped air eventually works it's way into the bypass valve, but by a diverse path that allows relatively low flow - it (air) gets mixed with the fuel circulating inside the VP-44 cavity, and EVENTUALLY is vented along with the fuel thru the bypass valve - but NOT a directly connected route between the input and bypass ports.







NO, actually, the primary air bleed hole you speak of IS NOT at the bypass valve, though that is where it eventually escapes along with the bypassed fuel - it is deeper inside the VP-44 near the point where the high pressure fuel is distributed to the injector lines. After all, it's the air that potentially is headed to the injectors we want to eliminate. (as I understand it!)



The popular misconception regarding the function of the VP-44 bypass valve, is that it is to regulate fuel PSI ENTERING the VP-44 - but it's not - it is to regulate the VP-44 INTERNAL fuel pressure as generated by the VP-44's own internal vane pump - and it is that internal vane pump with spring loaded vanes that effectively (within reason!) isolates the fuel inlet port from the bypass port.

Gary

The bypass valve is to regulate the pressure on the low pressure side of the VP44, any excess pressure going into the high pressure side is released by the pressure relief valve. Whether that pressure is generated by the internal low pressure rotary vane pump or the supply pump feeding the VP44. The bypass valve with it's bleeder or weep hole is locate at the top of the VP44 where it needs to be after all air goes up. Those who have a pusher pump setup know that if the original pump on the engine fails the pusher pump they located back on the frame can push fuel through the factory rotary vane pump. That is all that is happening inside the VP44 when the air is bled off during the priming procedure after a filter change. The bypass valve is not isolated from the inlet any more than the fuel filter is isolated from the pusher pump. The fuel just has to go through the factory Carter pump to get to the fuel filter. The internal rotary vane pump inside the VP44 is capable of having fuel pushed through it just like the Carter rotary vane pump on the side of the engine. Try this test. Take the bypass hose off of the VP44 and add a long length of hose to the VP44 draining into a bucket. Then initiate the filter priming procedure that you normally would do after a filter change (do not allow the engine to start). If the bypass is isolated no fuel should drain into the bucket. However if fuel does indeed run into the bucket there isn't an isolation and the bypass valve is relieving the pressure from the supply pump as well as forcing the air out of the system through the bypass/bleeder valve.





Edward

 

[rweis]

paulb -



I ordered the 6AN High Flow Jet Can High Speed (3081) from Kinsler today. I also ordered the 3034 set of shims (1@ . 183 6@. 030) and the 3303 (. 016, . 018, . 019, . 021, . 024) & 3304 (. 028, . 032, . 036, . 039, . 042) springs. The 3081 looks exactely like the RASP bypass valve. If it works the same, has the full flow and can be spring swap adjusted as you suggested vs cutting or modifying the spring, then we may have a ready made option of how to fine tune the VP input psi.



This should work with a RASP, FASS, AirDog etc, the carter's, holley's, anything that puts out more than enough volume and psi, then put a Jet Can in the return line to manage the actual psi at the input of the VP44.



IF this works, then anyone can have the pressure of their choice regardless of how it is generated. Just change the spring to set the presure you want, and you're done. There are 10 springs to choose from. I however have ZERO idea even if these springs will give us the pressure we want.



When I made the order the sales person asked me what pressure to set the Jet Can to, I told him 14 psi, he came back and asked if 15 psi was ok and I said yes. We may be on to something or we may not, but we shure will know in a week or so.



Since you know more about springs, what are some other places to look for springs in case these do not fit within the psi range we want?



Might have something off the shelf we ALL can use.



Bob Weis

 

[paulb]

Bob,



I really don't know that much about springs. It's just that I have been working with mechanical fuel injection for longer then I want to admit. Kinsler is one of the leaders in the mechanical fuel injection area.



The salesman was probably wondering what in the world you were working on. A high speed bypass valve is normally set in the 55 to 75 psi range. A main bypass is normally in the 14-15 psi range. A high speed set to 15 should work pretty good though. The RASP's bypass has a pretty heavy valve inside of it. The one you should be getting will be a lot lighter. It will respond to pressure changes quicker, but I'm not sure that is a good thing.



The heavy spring kit you ordered, will have to heavy of springs in it. I am currently running a . 019 spring in mine. A . 018 with two . 030 shims comes out about the same, but the pressure change with load changes is greater with the . 018.



I've wondered why more people have used these as pressure regulators. Very simple, and they work well.



Paul

 

[rweis]

paulb -



Can you give me specs for these springs.



I actually know nothing about springs, so this is a learning curve.



Wire size probably, turns per inch probably, something about the rate of travel probably, preload probably, physical length probably.



What range of psi"s does your . 019 give you? empty?, loaded? When you tried the . 018 and 2@ . 030 shims what was the range of psi's? Did you try a . 020 shim?



Your experimentation will help give me a better understanding of how these things work. A softer spring shimmed? a stiffer spring not shimmed? How would length come into play? Longer softer, what would that do? Shorter softer, what would that do?



If there is a 2psi difference between empty and loaded (ie lots of return flow and less return flow) and we can center it on 13. 5 +- 1 then find a spring / shim combination that will give us +- 1 for a total of +- 2 we will have hit a home run out of the park (spring training is starting up here in FL).



Bob Weis

 

[NoSeeUm]

Does anyone actually know how the overflow valve functions?



I know that it acts more or less as a back pressure regulator, that is not what I mean. I also know that as RPM is raised and more fuel is passed supplied pressure will drop. But at the same time transfer pressure (vane pump) will rise. This makes sense because as things happen faster and faster in the VP it would require a higher and higher transfer pressure to ensure that the pistons are completely filled for each stroke of the high pressure pump. This is because the time to fill gets shorter and shorter. It is a balancing act and that part I think I get.



Is the overflow operated sort of like a pilot valve so that as transfer pressure rises it is held closed more? But that I mean as transfer pressure increases less fuel is released via the overflow back to the fuel tank. The purpose being to provide cooling lubrication during idle / low fuel flow condtions when the transfer pressure is the lowest?



Thinking with words.....

Jim

 

[rweis]

This is also thinking in words.



As the rpm's go up the VP44 pump cycles go up (VP44 gear shaft turns at 1/2 of engine rpm just like the camshaft).



As the pump cycles go up the injection events go up and the solenoid needle functions more the amount of fuel that comes out of the overflow valve goes up. BK's old post measured it at miniscule at idle, ~ 30 gph at ??rpm.



I know (by testing) that unloaded VP44 heat addition to the input fuel goes up as the rpm's go up. I also know (Gary was right) that loaded VP44 heat addition to the input fuel goes up a greater amount as the rpm's go up. Empty the VP44 adds about 15* to the input fuel temp. Loaded (13k 5er, same rpm's) the VP44 adds about 20* - 25* to the input fuel temp. Conclusion I think is that rpm's are NOT the only thing that effect VP44 heat buildup, it seems to be rpm's AND load.



From Brady's comments & BK's old post that excessive input fuel pressure will increase the VP44's output fuel temp (meaning something is working harder at higher input fuel pressures than at nominal input fuel pressures).



At low rpm's very very little fuel flows through the overflow valve. At high rpm's a lot (~30 gph) of fuel flows through the overflow valve. Like you say about the transfer pressure, low rpm - lower pressure (but from Brady's post still about 100 psi) higher rpm - higher pressure (but from Brady's post still about 120 psi).



Still fuzzy about exactely how all this goes together.



Bob Weis



For the temp measurements I measure the input fuel actual liquid temp, the EBC with a contact sensor, the output (return) fuel with a contact sensor on the fuel line (goint toward a liquid contact sensor here also), all fuel lines in the engine compartment are heat shield wrapped.

 

[NoSeeUm]

Well Hmm, still thinking out loud.....



It would make more sense to me to recirc move via the overflow circuit at lower RPM than higher RPM. Typically that is how most pumps would do it for cooling at low flow. In this case for lubrication also as diesel would likely even be a poorer lubricant as its temperature rises.



If the overflow valve opens maximum at high RPM it would seem to me that its purpose is to control the maximum supply pressure to the piston pump. But it would seem to me that higher lubricant pressure would be better to prevent film break down.



-OR-



Mostly likely I need to get back over the fence and back onto right field. :-laf



Jim