So, basically what the title says. I'm interested in mixing and matching bits from a later gen sending unit, in my 2nd gen's.  I'm not running any power mods, and lately my fass drp has had intermittent defueling at highway speed. Continued after changing fuel filters.

Truck has 370k+ miles on it, big stock, the most recent 150k have been mostly highway. 

I'm getting good flow at 5 psi at idle with a brand new cummins overflow valve... same flow and psi as the old one I just removed. I need to check further me thinks.. 

2 hours ago, wil440 said:

I'm getting good flow at 5 psi at idle with a brand new cummins overflow valve... same flow and psi as the old one I just removed. I need to check further me thinks.. 

 

I don't think that there is any mystery here.  To my knowledge the lift pump feeds directly into the inlet of the fixed displacement vane pump inside the VP44.  The discharge flow of the vane pump is regulated at over 100 psi.  The 14 psi overflow valve is one of many components is in the path of the internal vane pump discharge, consequently there is always return flow through the 14 psi overflow valve - even when there is only 5 psi lift pump pressure.

 

- John

On 8/11/2020 at 8:01 AM, wil440 said:

I'm getting good flow at 5 psi at idle with a brand new cummins overflow valve... same flow and psi as the old one I just removed. I need to check further me thinks.. 

what is good flow? for me good flow would be more fuel through the vp back to tank than what is used by the engine. some would say a steady small stream is good flow...   not enough fuel through the vp back to the tank is not sufficient to cool the vp.

Typically it was only the 12V with overflow problems because the bolt was soft steel and the ball would beat the seat out. 24V overflow valves typically don't fail. 

 

I know you have the belt driven lift pump.

 

Heck I just did a 16 hour day, ran my truck over 414 miles doing a injection pump job in Anatone, WA. The entire day was cool out and truck was kept running most of the day with driving. I had temps ranging from about 65*F to a high of 80*F in Lewiston. Climbing 3 different grades and a few good twisting roads. I even had to go back to Lewiston for a special tool to pull injectors and back to Anatone, WA in the back country. Fuel temp never over 120*F the entire day, 414 miles, 5am to 9pm... Long day...

 

Edited August 13, 20204 yr by Mopar1973Man

On 8/11/2020 at 3:41 PM, Tractorman said:

 

I don't think that there is any mystery here.  To my knowledge the lift pump feeds directly into the inlet of the fixed displacement vane pump inside the VP44.  The discharge flow of the vane pump is regulated at over 100 psi.  The 14 psi overflow valve is one of many components is in the path of the internal vane pump discharge, consequently there is always return flow through the 14 psi overflow valve - even when there is only 5 psi lift pump pressure.

 

- John

Surely if the internal vane pump is regulated at 100 psi but the 14psi overflow valve is in the vane pump discharge the vane pump pressure will be 14 psi ? More likely the overflow valve is in the vane pump inlet and the 100psi regulated pressure is in the vane pump outlet or high pressure inlet section. ?

10 hours ago, CUMMINSDIESELPWR said:

what is good flow? for me good flow would be more fuel through the vp back to tank than what is used by the engine. some would say a steady small stream is good flow...   not enough fuel through the vp back to the tank is not sufficient to cool the vp.

My fuel temps don't got over 120f so while I haven't measured return flow It is full 3/8th rubber line wide when put into the tank neck, I fitted a Fleetguard FF5319 last night, at least 25% longer than the cat 1R0750 I took off. No change.

 

10 hours ago, Mopar1973Man said:

Typically it was only the 12V with overflow problems because the bolt was soft steel and the ball would beat the seat out. 24V overflow valves typically don't fail. 

 

I know you have the belt driven lift pump.

 

Heck I just did a 16 hour day, ran my truck over 414 miles doing a injection pump job in Anatone, WA. The entire day was cool out and truck was kept running most of the day with driving. I had temps ranging from about 65*F to a high of 80*F in Lewiston. Climbing 3 different grades and a few good twisting roads. I even had to go back to Lewiston for a special tool to pull injectors and back to Anatone, WA in the back country. Fuel temp never over 120*F the entire day, 414 miles, 5am to 9pm... Long day...

 

I checked the overflow and it looked ok but as they are cheap here I changed it anyway.

Yes I have mechanical LP. I can use the higher gearing and idle pressure is 10 to 12 ish but I'm curious as to why I have to use high gearing, I feel something is or might not be right. My next step is to test with another gauge then I'm going to strip the pump and check it as it has been on high gearing since new.

Well, my truck hasn't had defueling issues for a month now, nor has it thrown soft death codes. I'll check my idle pressure and unloaded high rpm pressures when I get a chance.

 

Regardless of which way I go pump wise, this has convinced me I need to invest in gauges and an a pillar mount.

I'm running the ISSPro EV2 programmable gauges. I've set my fuel pressure for 13 PSI and below for red warning lamp. 

 

 

Boost is set for >45 PSI warning light

Fuel pressure is set for <13 PSI warning light

EGT's is set for >1200F warning light

Transmission temp is set for >220F warning light.

Edited August 16, 20204 yr by Mopar1973Man

On 8/13/2020 at 10:46 PM, wil440 said:

Surely if the internal vane pump is regulated at 100 psi but the 14psi overflow valve is in the vane pump discharge the vane pump pressure will be 14 psi ?

 

It would seem that it should be that simple.  I am trying to find my source of information regarding the internal workings of the VP44.  It was posted around 2007 in the Turbo Diesel Register.  From what I understand, the internal vane pump displaces more fuel than can be used by the injectors and all the internal working components of the VP44, including the 14 psi overflow valve.  As fuel is metered into the inlet area of the high pressure pump the fuel becomes common with the 14 psi overflow valve.  I believe it is because the inlet flow into the high pressure pump being metered is why the vane pump will send the portion of the unused fuel flow over its own relief (over 100 psi) and the overflow valve will operate at the lower pressure of 14 psi.

 

I will find this information and post it here.  It may take awhile.

 

On 8/13/2020 at 10:46 PM, wil440 said:

More likely the overflow valve is in the vane pump inlet and the 100psi regulated pressure is in the vane pump outlet or high pressure inlet section. ?

 

The photo below clearly shows that the overflow valve is not in the vane pump inlet.  

 

- John

 

T'man,

 

Here you go.  I think everything is covered here. at about 10:45 mark is where he starts talking and showing the internal vane pump.  The excess flow from the vane pump is returned to the inlet of the vane.  At the 15 minute or so mark he is showing the lift pump flow and return. 

 

 

@Haggar, thanks for the reply and the video information.  I have watched this video a few years ago.  I would really like to hear what the narrator has to say in English.  I think it would be very informative.

 

Some people were seriously trying to figure out the mystery of the VP44 back in 2001 (before I even bought my truck).  The return flow testing that Mopar-Muscle did in 2001 supports my belief that the internal vane pump provides the fuel flow for the 14 psi overflow valve.  The lift pump only ensures that there is a positive pressure at the inlet of the VP44 - a positive pressure means adequate flow.  Part of my factory fix from the dealer when my VP44 failed at 87,000 miles was to install an in-tank pump that operated at 6 psi (idle) and 3 psi (WOT).  I currently have 257,000  miles on that VP44.   @wil440, you may be interested in the following read, as well.

 

 

Test # 1

1. well some of you guys ain't gonna like this , especially those led to believe (and those that believe it) ... the bigger is a MUST theory .
   
   spent a couple minutes running some tests with a DIGITAL/mechnical flow meter and a MECHNICAL fuel pressure gauge , items under test ... 2000 RAM , DD2's , DD TTPM on level 2 (??) and a HOT PE , ( all levels tested the same at WOT)factory pickup , factory lift pump , factory fuel filter housing unmodified , all banjo bolts intact and unmodified except the banjo to the input of the lift pump is replaced with a 90* swept areoquip type -6AN hose end , the bolt at the lift pump had the schrader cut off and drilled and tapped to a 1/8 npt ( for the gauge) and the banjo fittings between the lift pump and the fitler housing have been drilled to 9/32nd . again all banjo bolts are not drilled out as i have on my ram ( test conducted on the DTT RAM ) .
   
   we installed ( LaserBob is helping me and getting #2 fuel poured on his head ) a Sonnex digital flow meter ( inside ID is 5/16") in the return line back to the tank , cut in right at the trans crossmember . gph numbers are fuel returned to the tank .
   
   
   DD2 , DD TTPM (True Torque Power Module)
   FP volume
   idle 11 psi 18gph
   
   cruise 8 psi 24gph
   
   WOT 2 psi 30gph
   
   
   DD2 , TTPM , HOT PE ANY LEVEL
   FP volume
   idle 11 psi 18gph
   
   cruise 8psi 24gph
   
   WOT 0 psi 30gph
   
   
   yes you read that correctly , fuel pressure went to 0 and the fuel volume back to the tank did not change from WOT with 2 psi . the truck did NOT stumble , buck , spit , fart , fall on it's face , nothing , ran like all heck at 0 psi , i will note , my truck ran the same at 0 psi with the DD3's , EZ and a HOT PE .
   
   tomorrow we will install -8 lines and an HP carter pump , take flow readings in exact same spot and see what the results are .

 

Mopar-muscle, Apr 24, 2001 Report

 

Test # 2

 

1. well , here we go again , todays test was interesting to say the least , and we believe we have it figured out .
   
   added the carter HP 15psi 110gph pump on the frame rail next to the tank , -8 bulkhead in the bottom center of the tank , -8 line to the pump , -6 line from this pump to the inlet of an unmodified factory 2000 fuel filter housing , the rest of the system is as delievered from the factory except for a banjo bolt that had the schrader cut off and tapped to 1/8 npt for the gauge , the digital flow meter in the exact same location reading flow back to tank after the tee on the engine .
   
   with DD2 , DDTM (True Torque Power Module)
   
   psi volume
   idle 11. 5psi 18gph
   
   cruise 9psi 24gph
   
   WOT 6 psi 30gph
   
   
   with the HOT PE on any level
   
   idle 11. 5psi 18gph
   
   cruise 9psi 24gph
   
   WOT 4psi 30gph
   
   with the addition of the new pump and larger gravity fed pickup point the flow to the tank did not change , though pressure was up , the carter having an internal bypass is living with the backpressure on its output .
   
   the concenus is the VP44 is the restriction . the return line from the pump is only returning the excess fuel from the VP44's own internal pump , the more you feed it the higher the backpressure on the line to the pump .
   
   the guys with the large pumps , bigger lines and regulator mounted as close to the VP44 as possible have a large amount of the excess flow returned directly to the tank , this is not a bad thing ,( except that at a low fuel level it is possible to foam the fuel in the tank with the large amount of fuel dumping back into it from 2 sources ) but is really overkill as the vp44 uses a set amount of fuel and this is proved by the higher pressure seen with no increase in flow back to the tank .
   
   again , the higher the pressure , the lower the flow , BillW explained it perfectly on the prime loc bashing thread and no one ( including myself) understood it or tryed to test it to see if it was true .
   
   someone asked if there was a pump that was between 60 and 100 gph , again carter to the rescue , there street pump , 15 psi , about 70 gph , this pump mounted as close to the tank as possible is the best scenerio .
   
   the factory designed the system to have the least amount of restriction with the most flow given the flow characteristics of the VP44 .
   
   i have not seen the info on HVAC's 34 hp increase with fuel system mod , i will be talking to him to find out the poop on that .
   
   we also felt what happens when you have no flow , we had a low fuel level in the tank and under the bulkhead at the botom of the tank , the engine cutout , if the 0psi had no flow , we would have experienced this same bucking .
   
   next we will move the factory lift pump back in place of the carter hp pump
   
   [This message has been edited by Mopar-muscle (edited 04-26-2001). ]

 

Mopar-muscle, Apr 25, 2001 Report

 

 

 

 

 

 

On 8/20/2020 at 4:20 PM, Tractorman said:

 

It would seem that it should be that simple.  I am trying to find my source of information regarding the internal workings of the VP44.  It was posted around 2007 in the Turbo Diesel Register.  From what I understand, the internal vane pump displaces more fuel than can be used by the injectors and all the internal working components of the VP44, including the 14 psi overflow valve.  As fuel is metered into the inlet area of the high pressure pump the fuel becomes common with the 14 psi overflow valve.  I believe it is because the inlet flow into the high pressure pump being metered is why the vane pump will send the portion of the unused fuel flow over its own relief (over 100 psi) and the overflow valve will operate at the lower pressure of 14 psi.

 

I will find this information and post it here.  It may take awhile.

 

 

The photo below clearly shows that the overflow valve is not in the vane pump inlet.  

 

- John

 

Thanks for posting this Tractorman... gives me some idea of whats going on, I'm still not sure if I have a problem or not, I have low fp at idle coming up damn fast with rpm, to the point of my fp regulator cannot get it back to tank fast enough, only thing I can see that would cause excess return flow is a broken spring just to the right of centre on this picture.... OR as you say in your next post that it is flow not psi that matters

 

5 hours ago, Tractorman said:

@Haggar, thanks for the reply and the video information.  I have watched this video a few years ago.  I would really like to hear what the narrator has to say in English.  I think it would be very informative.

 

Some people were seriously trying to figure out the mystery of the VP44 back in 2001 (before I even bought my truck).  The return flow testing that Mopar-Muscle did in 2001 supports my belief that the internal vane pump provides the fuel flow for the 14 psi overflow valve.  The lift pump only ensures that there is a positive pressure at the inlet of the VP44 - a positive pressure means adequate flow.  Part of my factory fix from the dealer when my VP44 failed at 87,000 miles was to install an in-tank pump that operated at 6 psi (idle) and 3 psi (WOT).  I currently have 257,000  miles on that VP44.   @wil440, you may be interested in the following read, as well.

 

 

Test # 1

1. well some of you guys ain't gonna like this , especially those led to believe (and those that believe it) ... the bigger is a MUST theory .
   
   spent a couple minutes running some tests with a DIGITAL/mechnical flow meter and a MECHNICAL fuel pressure gauge , items under test ... 2000 RAM , DD2's , DD TTPM on level 2 (??) and a HOT PE , ( all levels tested the same at WOT)factory pickup , factory lift pump , factory fuel filter housing unmodified , all banjo bolts intact and unmodified except the banjo to the input of the lift pump is replaced with a 90* swept areoquip type -6AN hose end , the bolt at the lift pump had the schrader cut off and drilled and tapped to a 1/8 npt ( for the gauge) and the banjo fittings between the lift pump and the fitler housing have been drilled to 9/32nd . again all banjo bolts are not drilled out as i have on my ram ( test conducted on the DTT RAM ) .
   
   we installed ( LaserBob is helping me and getting #2 fuel poured on his head ) a Sonnex digital flow meter ( inside ID is 5/16") in the return line back to the tank , cut in right at the trans crossmember . gph numbers are fuel returned to the tank .
   
   
   DD2 , DD TTPM (True Torque Power Module)
   FP volume
   idle 11 psi 18gph
   
   cruise 8 psi 24gph
   
   WOT 2 psi 30gph
   
   
   DD2 , TTPM , HOT PE ANY LEVEL
   FP volume
   idle 11 psi 18gph
   
   cruise 8psi 24gph
   
   WOT 0 psi 30gph
   
   
   yes you read that correctly , fuel pressure went to 0 and the fuel volume back to the tank did not change from WOT with 2 psi . the truck did NOT stumble , buck , spit , fart , fall on it's face , nothing , ran like all heck at 0 psi , i will note , my truck ran the same at 0 psi with the DD3's , EZ and a HOT PE .
   
   tomorrow we will install -8 lines and an HP carter pump , take flow readings in exact same spot and see what the results are .

 

Mopar-muscle, Apr 24, 2001 Report

 

Test # 2

 

1. well , here we go again , todays test was interesting to say the least , and we believe we have it figured out .
   
   added the carter HP 15psi 110gph pump on the frame rail next to the tank , -8 bulkhead in the bottom center of the tank , -8 line to the pump , -6 line from this pump to the inlet of an unmodified factory 2000 fuel filter housing , the rest of the system is as delievered from the factory except for a banjo bolt that had the schrader cut off and tapped to 1/8 npt for the gauge , the digital flow meter in the exact same location reading flow back to tank after the tee on the engine .
   
   with DD2 , DDTM (True Torque Power Module)
   
   psi volume
   idle 11. 5psi 18gph
   
   cruise 9psi 24gph
   
   WOT 6 psi 30gph
   
   
   with the HOT PE on any level
   
   idle 11. 5psi 18gph
   
   cruise 9psi 24gph
   
   WOT 4psi 30gph
   
   with the addition of the new pump and larger gravity fed pickup point the flow to the tank did not change , though pressure was up , the carter having an internal bypass is living with the backpressure on its output .
   
   the concenus is the VP44 is the restriction . the return line from the pump is only returning the excess fuel from the VP44's own internal pump , the more you feed it the higher the backpressure on the line to the pump .
   
   the guys with the large pumps , bigger lines and regulator mounted as close to the VP44 as possible have a large amount of the excess flow returned directly to the tank , this is not a bad thing ,( except that at a low fuel level it is possible to foam the fuel in the tank with the large amount of fuel dumping back into it from 2 sources ) but is really overkill as the vp44 uses a set amount of fuel and this is proved by the higher pressure seen with no increase in flow back to the tank .
   
   again , the higher the pressure , the lower the flow , BillW explained it perfectly on the prime loc bashing thread and no one ( including myself) understood it or tryed to test it to see if it was true .
   
   someone asked if there was a pump that was between 60 and 100 gph , again carter to the rescue , there street pump , 15 psi , about 70 gph , this pump mounted as close to the tank as possible is the best scenerio .
   
   the factory designed the system to have the least amount of restriction with the most flow given the flow characteristics of the VP44 .
   
   i have not seen the info on HVAC's 34 hp increase with fuel system mod , i will be talking to him to find out the poop on that .
   
   we also felt what happens when you have no flow , we had a low fuel level in the tank and under the bulkhead at the botom of the tank , the engine cutout , if the 0psi had no flow , we would have experienced this same bucking .
   
   next we will move the factory lift pump back in place of the carter hp pump
   
   [This message has been edited by Mopar-muscle (edited 04-26-2001). ]

 

Mopar-muscle, Apr 25, 2001 Report

 

 

 

 

 

 

Now that is one interesting read, my low pressure fuel system is really bucking the "required".... I think I need a flow gauge as well as a fuel pressure gauge, I could blow the face off of my fuel pressure gauge by clamping off the return from the T at idle easily, now I would then be in the "ok"  fuel pressure club..... would there be any cooling flow back to tank... no

 

One thing I will again say I have tested MY return flow and checked my fuel temps and my lift pump is mechanical and my basket and draw straw is clean and not blocked so please don't compare your carter in tank sucking through the bottom of a pond and think it will be ok cos it won't

5 hours ago, wil440 said:

One thing I will again say I have tested MY return flow and checked my fuel temps and my lift pump is mechanical and my basket and draw straw is clean and not blocked so please don't compare your carter in tank sucking through the bottom of a pond and think it will be ok cos it won't

 

Not comparing the supply system in my truck to the supply system in your truck at all.  Just pointing out that regardless of which fuel supply system is used,  if a positive pressure is present at the inlet of the VP44, I believe there will always be flow over the 14 psi overflow valve because the internal vane pump dictates that flow by engine rpm at a higher pressure (over 100 psi).

 

One thing for sure.  Lift pumps cannot push more fuel flow through the internal vane pump than the internal vane pump is displacing at any given moment because the internal vane pump is a fixed displacement pump.  Simply stated, the lift pump and the VP44 internal vane pump are plumbed in a series circuit.  The outlet pressure for each unit can be different, but the flow is the same while they are both operating in a series circuit. 

 

Of course, nothing is ever simple.  Example:  At a given moment the lift pump may have a flow rate of 30 gph, and let's just say it is returning 5 gph to the tank.  This would mean that the VP44 internal vane pump would be flowing 25 gph in that same moment (matching the actual flow from the lift pump (30 gph - 5 gph (return fuel) equal 25 gph).  The fuel pressure could  be10 psi at the lift pump outlet at that moment, but the VP44 internal vane pressure could be 120 psi if that is what the relief valve is set for.  The actual relief valve pressure setting for the internal vane pump is still a mystery, but I believe it is somewhere around 120 psi.

 

Also, my VP44 replacement and in-tank lift pump conversion covered under warranty was done at 87,000 miles on the odometer.  Lift pump pressure was 6 psi at idle and 3 psi at WOT with the new system.  The original engine mounted lift pump acutually never failed.  At 250,000 miles on the odometer (over 4 years ago) I removed the in-tank lift pump and installed a used FASS lift pump on the frame.  The in-tank pump was still working fine, I just wanted an easy roadside repair in case the lift pump left me stranded.   The FASS lift pump  shows 12 psi at idle and 6 psi at WOT.  The current odometer is  now 344,000 miles.  The current VP44 has never seen any inlet pressure higher than 12 psi and that is only at idle, but I believe that the 14 psi overflow valve is always operating and returning adequate fuel flow to the tank for the above stated reasons..

 

- John

 

 

9 hours ago, wil440 said:

 

One thing I will again say I have tested MY return flow and checked my fuel temps and my lift pump is mechanical and my basket and draw straw is clean and not blocked so please don't compare your carter in tank sucking through the bottom of a pond and think it will be ok cos it won't

The above wasn't directed at you or your truck, apologies if thats how it seemed more to people that get low pressure  alongside next to no flow through the return and think their vp will be ok