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

[rweis]

As I try to gain better insight on how to feed the VP44 psi and volume, I picked up on a comment about the VP44 is calibrated at 13. 5 psi on the Bosch calibration machine. Anything outside of the "calibration" psi is degradation to some extent.



What is the rpm that this 13. 5 psi relates to?



Is lesser psi (12 psi) acceptable at idle (850 rpm) when the Vp44 is not running at cruise speed? How critical is this 13. 5 psi?, what is the range of psi where operation is acceptable? ( I have heard this is 13. 5 + - 3, but also get the impression that the cruise rpm is best at 13. 5 psi calibration setting due to internal hydraulic loading / forces that are more pronounced at high rpm (2000) than at low rpm (850))



Is higher psi at higher rpm as in a RASP install acceptable? Should the RASP idle psi be something like 12 psi then rises to 13. 5 psi at 2000 rpm so the high rpm is at the calibration psi?



Is lower psi at higher rpm as in a electric lp install acceptable? Should the lp idle psi be 16 psi and drop to 13. 5 at 2000 rpm? so the high rpm is at calibration psi?



Just exactely how should the VP44 input psi be mapped?



I get the impression that the psi has to do with the internal diaphram fuel chamber feed to the high pressure section and the damage to seals if to high or low a psi. I also gleaned an idea about hydraulic loading on the rotor if the high rpm psi is too high, above ??? 13. 5?



I realize most of us do not know the details of the VP44 and it is my hope that some of the rebuilders will help out here with exactely how we should feed the VP44 and what the psi map should look like.



Most of us push input psi to the VP44 assumeing "more is better" up to some personal assumed limit (14 psi?, 16 psi?, 20 psi?, 25 psi?), volume plays a role, fuel cleanliness plays a role, no free water plays a role, psi plays a role - but exactely what role? and at what rpm? (low rpm?, mid range rpm?, high rpm?)



If you would rather not comment your thoughts on the subject, how about just what the Bosch specs are in fuel psi, engine rpm (I know the VP44 rotates at 1/2 engine rpm like the cam shaft), fuel temperature (I have heard the input fuel temperature upper limit is 160*, what is the lower limit temperature? There is an internal fuel temperature sensor that figures into the injected quantity calculation)



Thanks in advance



Bob Weis

 

[rweis]

TTT



Bob Weis

 

[Froadin]

I really would like to know this one as well.
Good topic!
Hopefully we will get some qualified answers that can truly answer this question.

 

[Gary - K7GLD]

I have this sneaking suspicion that none of the rebuilders have an answer to that one, and FEW engineers at Bosch will agree on the same spec...



My guess is that it will boil down to a "nominal" RPM, sort of an average between the highest PSI at idle, and the lowest ideal/acceptable PSI at full load...



In my case, a near-future fuel supply mod involves a Walbro pump with an automatic bypass valve (to allow fuel flow AROUND the Walbro in case it fails) like I use on the current Carter LP and pusher,



#ad


and then a regulator right at the VP-44. The Walbro will be output controlled by a Pulse Width Modulator (PWM) control in a way that allows lowest Walbro voltage and RPM within the mechanical regulator setting to arrive at as steady a VP-44 PSI at 15 PSI or so as possible under ALL operating conditions and RPM...

 

[BillBrown]

If I am not mistaken (which could be possible) the VP44 has A bypass valve built into it that should be calibrated at aprox 13. 5 psi. Unless You are pumping more volume than this valve can relive You will not go over it's set point on presure but if You are not pumping more volume than the VP is feeding the injectors You would not make that presure. So the short answer is that as long as You can supply enough volume to maintain at least 10 psi at wide open throtle or not enough to go over about 16-17 You should not have any loss of power or negative effects on the VP.

 

[Gary - K7GLD]

If I am not mistaken (which could be possible) the VP44 has A bypass valve built into it that should be calibrated at aprox 13. 5 psi. Unless You are pumping more volume than this valve can relive You will not go over it's set point on presure but if You are not pumping more volume than the VP is feeding the injectors You would not make that presure. So the short answer is that as long as You can supply enough volume to maintain at least 10 psi at wide open throtle or not enough to go over about 16-17 You should not have any loss of power or negative effects on the VP.

That old wives tale keeps resurfacing as one of the most misunderstood of VP-44 features! Many guys ASSUME that "overflow" - or bypass valve, is at the fuel INPUT tract, right as the fuel supply enters the VP-44 - NOT SO!



Perhaps that misconception arises from the fact the bypass valve port sits right next to the incoming fuel flow port - but internal passages quite WIDELY separate those 2 ports for each other, and actual fuel bypassing occurs LOTS further down the VP-44's operating function, and in fact, those 2 ports are pretty much totally isolated from each other in operation.

 

[BillBrown]

Thanks for the reply. I learned something today.

 

[rweis]

Here is the fuel flow diagram from the Bosch book pg 221. The upper right is the outflow valve. It is in the transfer pressure section that is the feed pressure to the solenoid at #3. Same pressure as the advance piston shown under the rotary pump.

 

[rweis]

I get the impression that this section is at 100 - 120 psi. The reason the return flow is not 100 - 120 psi is the throttle valve at the outflow valve is tiny tiny tiny compared to the size of the return line and therefore drops the pressure way way way down, also volume is relatively small.



Light blue = feed the internal vane pump



Medium blue = transfer pressure (Internal functioning of timing solenoid, bleeding air off at the outflow valve, return unused transfer fuel delivered to high pressure solenoid valve to the tank



Dark blue = high pressure



Bob Weis

 

[rweis]

Gary, what about this idea-



Vary the PWM according to the pressure delivered to the VP44. Pressure starts to drop due to demand, PWM increases to run the pump faster and vice versa.



THAT would be the "cats meow". Pretty electrical based, but a self regulating supply based on demand. I get goose bumps thinking about the continuously variable feed based on demand. REAL close to the answer for the electrical pumps, like really really close to the answer.



Bob Weis

 

[rweis]

Back to thinking out loud about the orgional post at #1.



In the old post "pumps, lines and whatnot... " Bill K mentioned that the temperature of the return fuel went up as the input psi to the VP44 went over 20 psi (as I recall the reading). I think I remember he tried 20psi, 25 psi, 30 psi, up to 40 or 50 psi. The VP44 worked harder and harder generating more heat as the input pressure rose (might be the hydraulic loading Brady eluded to). The same amount of fuel returned regardless of the input pressure tends to support the idea that rpm and load are what determine fuel returned and the input fuel and the return fuel are very diferent parts of the internal VP44 as can be see in the diagram.



Thinking about that now in light of better knowledge, it implies there is a psi that the VP44 runs best, and it may well be the calibration psi of 13. 5 psi.



Now how to get 13. 5 psi under ALL conditions.



Bob Weis

 

[Edward]

That old wives tale keeps resurfacing as one of the most misunderstood of VP-44 features! Many guys ASSUME that "overflow" - or bypass valve, is at the fuel INPUT tract, right as the fuel supply enters the VP-44 - NOT SO!



Perhaps that misconception arises from the fact the bypass valve port sits right next to the incoming fuel flow port - but internal passages quite WIDELY separate those 2 ports for each other, and actual fuel bypassing occurs LOTS further down the VP-44's operating function, and in fact, those 2 ports are pretty much totally isolated from each other in operation.

Gary

If the two ports are isolated as you say how then can the air removal process for fuel filter changes take place. If you cycle the pump to remove the air it needs a place to go or you can't remove it. If the air does not go through the bypass how does it get out of the fuel filter? Not trying to be argumentative here but it's the first question that came to mind when I read your post.



Edward

 

[NoSeeUm]

I don't know why I think this, but I had thought I remembered reading some where that the transfer pressure was in the 300 psi range at rated flow. A number of 330 psi seems to stick in my head.



As well as feeding the piston pump isn't transfer pressure what actually rotates the timing assembly with the electric solenoid acting as a pilot?



Jim

 

[rweis]

My Bosch book has a range of like 110 - 320 psi (from memory), but does not say specifically, only that is a range.



In the II post, Brady implied that there is a rebuilders chart of input pressures and transfer pressures. I am trying to find out what that chart says so we can see where 100 - 120 psi transfer pressure is in relation to input pressure. I think if we really KNOW what the transfer target psi in relationship to input psi is we can find a way to hit it exactely.



The advance piston movement back and forth that rotates the timing cam most definitely is a transfer pressure function as is feeding the pump pistons.



Maybe the mechanical pressure balance we are trying to find is in moving the timing cam with authority (ie not even a microscopic non perfect mechanical mating surface) and not deforming the diaphram more than . 5mm so it is not dammaged in the process.



If this is the real objective, then things like lubricity and maintaining a cool temperature range (the temperature range thing (larger mechanical tolerances at cooler running component temperatures) is one of those things in my craw and not necessarily in yours) on all the moving parts becomes even clearer as to why absolutely clean and well lubricated fuel plays such an important part in feeding this thing.



Bob Weis

 

[Gary - K7GLD]

Gary

If the two ports are isolated as you say how then can the air removal process for fuel filter changes take place. If you cycle the pump to remove the air it needs a place to go or you can't remove it. If the air does not go through the bypass how does it get out of the fuel filter? Not trying to be argumentative here but it's the first question that came to mind when I read your post.



Edward

The air removal function takes place elsewhere in the VP-44 fuel routing, and Bosch drawings have been presented in related threads several times displaying that fact and function.



Yeah, I know, old stories die hard (no, Ford DOESN'T own Cummins... ), but there is NO direct path between the VP-44 input and bypass valve. If you have access to a VP-44 that's off a truck, just remove the banjo bolts from both ports and TRY to blow air from one to the other!



Been there, done that with *2* different pumps, and NO direct passage between the 2...



PLUS. I have an empty VP-44 case:



#ad




And while this particular angle doesn't show the related ports, it's quite easy to see the individual ports are NOT connected if you had it in your hand...

 

[rweis]

I TOTALLY agree with Gary.



The input fuel has to go through the vane pump, and then cycle to the solenoid fuel input, then the path to the bypass valve is after the solenoid cycles and is on the opposite side of the solenoid passage.



The physical location of the outflow valve is in the close proximity of the input fitting, but only physically (maybe for manufacturing practices or efficiencies?).



This misconception has been around for quite a while. Sort of "the more input fuel pressure the better" same concept.



Bob Weis

 

[Edward]

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

 

[NoSeeUm]

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 am going to say most of goes out the injectors and some via the overflow valve.



Jim

 

[rweis]

Page 215 Bosch, air venting 3rd paragraph

 

[BradyWilliams]

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