Fuel pressures and flows - lift pump, etc.
02-28-2007, 10:56 PM
#16
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Hi all this imformation is great but I just have a few questions. Why did you go with the nylon and not the fuel grade hose. I know the nylon is good hose but I didn"t know it was diesel rated. Anyway I am getting ready to put A kit on my truck so this is all good.
03-01-2007, 01:18 AM
#17
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Nylon is the material used for lining the inside of pressure rated diesel hose. Nylon-11 is a bit more advanced than regular: not brittle down to -100F and withstands up to +400F, good for wet conditions and better for abrasion resistance than Nylon 6/6, yet more flexible. It is very easy to work with, cuts with a knife but is rigid enough to perform very well with high quality compression fittings like Swagelok. The tubing I used is rated to 580 psi working pressure, yet has fairly large inside diameter (0.275"). Plus, it is very cheap, $0.77 per foot. I sheathed the section in the engine compartment with a 1/2" water hose but that was more to follow the design of the stock lines than really necessary.
I wanted to use compression fittings because I knew I may want to bring pressures up to 100+ psi on the high side of the regulator, so hose clamps were not on the list. So I needed either to buy pre-assembled pressure hose - expensive! - or make my own with quality parts. I chose the latter.
I initially thought of using PTFE but it is expensive ($4 per foot or so), and the level of chemical inertness Teflon provides is not really called for. Once I realized that the regular cheap Nylon-11 is compatible, my mind was made up.
-P
I wanted to use compression fittings because I knew I may want to bring pressures up to 100+ psi on the high side of the regulator, so hose clamps were not on the list. So I needed either to buy pre-assembled pressure hose - expensive! - or make my own with quality parts. I chose the latter.
I initially thought of using PTFE but it is expensive ($4 per foot or so), and the level of chemical inertness Teflon provides is not really called for. Once I realized that the regular cheap Nylon-11 is compatible, my mind was made up.
-P
07-12-2007, 02:12 PM
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I have been running my homebrew Pulse Width Modulation circuit with the Aeromotive pump for about 3 years. The picture in this post shows a 100uM screen filter in red, before the pump and a bypass regulator after the pump. The only reason I decided to use a regulator was in case of an electrical failure with the pressure sensor or PWM controller. This would allow me to run the pump wide open and limit pressure to about 22 PSI. Normally the regulator bypasses nothing so plumbing it from the pump output back to the input is not a problem.
Another advantage of the PWM controller is the pump is just loafing along creating 10 PSI. I measured a supply current of only about 2 amps instead of 9 when running all out. The slow pump speed will prevent cavitation, entrained air in the fuel and runs cool. Motor brushes, bearings and the gerotor should last longer.
A few years after I designed my controller, I found a company that sells a kit with a PC board that looks like a promising and cheap solution to the PWM. I had intended to buy one and try it out before I post my treatise on lift pumps. I don’t think anyone would go to the trouble of building a circuit like I did.
Another advantage of the PWM controller is the pump is just loafing along creating 10 PSI. I measured a supply current of only about 2 amps instead of 9 when running all out. The slow pump speed will prevent cavitation, entrained air in the fuel and runs cool. Motor brushes, bearings and the gerotor should last longer.
A few years after I designed my controller, I found a company that sells a kit with a PC board that looks like a promising and cheap solution to the PWM. I had intended to buy one and try it out before I post my treatise on lift pumps. I don’t think anyone would go to the trouble of building a circuit like I did.
Can you elaborate on your PWM setup? I see that Aeromotive makes a controller, but it's major $$.
Also, how is the pressure-sensing feedback loop configured?
Justin
07-22-2007, 04:17 PM
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OMG...I am glad I found this post before I bought my Walbro and big line kit! If I understand all I have read, if I put the Walbro pump in I need to put a pressure regulator on it also AND a return line?
I was under the impression that the VP has it's own return line so all I would have to do is replace my lp and be done. I can do mechanical and light electrical work, but all this I have been reading is way beyond me. Can someone please help me figure out what I need to do to solve my lp problem? I just replaced my lp and vp in Feb and my lp just dropped to 3# the other day, so i have my truck parked until i can resolve my problem. I am tight on funds and need an inexpensive solution that will last longer than putting another standard lp in. I appreciate anyone's help. This truck is my business and i run 50k miles a year in it...needless to say, i need it running. Thanks.
I was under the impression that the VP has it's own return line so all I would have to do is replace my lp and be done. I can do mechanical and light electrical work, but all this I have been reading is way beyond me. Can someone please help me figure out what I need to do to solve my lp problem? I just replaced my lp and vp in Feb and my lp just dropped to 3# the other day, so i have my truck parked until i can resolve my problem. I am tight on funds and need an inexpensive solution that will last longer than putting another standard lp in. I appreciate anyone's help. This truck is my business and i run 50k miles a year in it...needless to say, i need it running. Thanks.
07-23-2007, 07:26 PM
#20
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Wow, this is an old thread. I’ll try and fill in some of the details.
I am running a Westach electronic pressure sender that samples fuel pressure from the input of the VP. It is connected by a hose and snubber the same way a fuel pressure gauge is connected. I tried to get on the Westach site but they seem to be making changes right now, so I don’t have the part number handy.
The PWM circuit I built is too difficult unless you know someone who wears thick glasses with adhesive tape on the bridge. A much simpler solution is the PWM kit I found for about $25. It will have to have some simple modifications to power the sensor but anyone who knows which side of a soldering iron to pick up should have no problems. This circuit will adjust the pump speed to match the set point on a potentiometer, any where from 0 to 45 psi. At 45 psi, I think this is where to pumps will fry. My dash fuel gauge is the most boring gauge I have, only moving to and from 0 psi when the engine is started and stopped. At all other times from idle to WOT it is at the set point.
An Aeromotive of Walbro pump should work well because they both do not have an internal spill back valve and can both flow way more fuel than anyone will need. I would not hesitate to mount a new Walbro. The PWM circuit can be added later.
I had hoped to have the PWM kit tried out by now but building a house has sapped my time. Before the end of summer I will try to have something posted with info on the kits and wiring. I am not interested in selling these so the info will be for all.
I am running a Westach electronic pressure sender that samples fuel pressure from the input of the VP. It is connected by a hose and snubber the same way a fuel pressure gauge is connected. I tried to get on the Westach site but they seem to be making changes right now, so I don’t have the part number handy.
The PWM circuit I built is too difficult unless you know someone who wears thick glasses with adhesive tape on the bridge. A much simpler solution is the PWM kit I found for about $25. It will have to have some simple modifications to power the sensor but anyone who knows which side of a soldering iron to pick up should have no problems. This circuit will adjust the pump speed to match the set point on a potentiometer, any where from 0 to 45 psi. At 45 psi, I think this is where to pumps will fry. My dash fuel gauge is the most boring gauge I have, only moving to and from 0 psi when the engine is started and stopped. At all other times from idle to WOT it is at the set point.
An Aeromotive of Walbro pump should work well because they both do not have an internal spill back valve and can both flow way more fuel than anyone will need. I would not hesitate to mount a new Walbro. The PWM circuit can be added later.
I had hoped to have the PWM kit tried out by now but building a house has sapped my time. Before the end of summer I will try to have something posted with info on the kits and wiring. I am not interested in selling these so the info will be for all.
07-24-2007, 10:53 PM
#21
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OMG...I am glad I found this post before I bought my Walbro and big line kit! If I understand all I have read, if I put the Walbro pump in I need to put a pressure regulator on it also AND a return line?
I was under the impression that the VP has it's own return line so all I would have to do is replace my lp and be done.
I was under the impression that the VP has it's own return line so all I would have to do is replace my lp and be done.
The built in ball valve on the VP44 does not allow free flow of excess fuel, the pump will immediately overpressurize on the inlet side. Trust me, I tried (briefly).
But having said this, the entire setup is very simple. If you changed spark plugs on a van before you can do this, too. And you do not have to spec the components yourself like I did, you can get a kit like a Glacier (albeit a bit more expensive) and all parts will come in it, including pressure regulator and detailed instructions.
-P
07-24-2007, 11:46 PM
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I, for one am happy, you revived this old thread. There were some very interesting and informative discussion. I had been looking for a fuel pressure regulator for my system and presto...Mt hckbry mentioned the swagelok check valve. So simple I thought i would try it. I have been trying to avoid mounting anything electrical or intricate on the inner frame rail behind the front wheel. Five months of cruddy roads with salt and 3/4 inch sand plays havoc on the undercarriage. I have decided to use a high volume carter pump 100gph in the stock location, with the GDP big line kit and a regulator (adjustable check valve) off a tee in the pressure line that runs back through a 3/8 line to the auxilliary fuel nipple on the sender. It is open and runs down the side of the fuel module in the tank. Most of the negative stuff I have read about the carter pumps leads me to believe they fail due to "deadheading" . There is a small sticker on the side of the pump stating a part number for the pressure regulator to be used, so common sense says use one. I have gathered my parts except for the big line kit, that should be here Friday, so this weekend I'll put this idea together. Got fuel pressure guages to install as well. Have been using my diagnostic guage just to find out whats been happening while I have been driving. With my mods and a heavy foot the fuel pressure does drop fairly low but not quite to zero. This lead me to take steps to improve the fuel flow before I went trailer pulling.I am going to install the "big line kit" first to see what changes this alone makes to the pressure from the intank update pump. I still think they are a good idea
Just not fully thought out before being forced on the consumer.
Just not fully thought out before being forced on the consumer.
08-08-2007, 02:00 AM
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Well, I know I will be saving this post as it is quite informative... For now, since my finances suddenly took a leap off some cliff somewhere, I exchanged my faulty lp for a new one under warranty and invested in the big line relocation kit from Genos Garage. A week of waiting and i finally got my kit in and it was short the most important pieces...LOL. So they were very helpful and overnighted the rest of the parts and I was up and running the next day. I never knew how loud my lp was till i put it UNDER my truck...LOL. I can actually hear it OVER the loud rattling ofmy engine...LOL. Anyway, the big line kit was great...very easy to install. My pressures are 12 at idle, 11 @ 2200rpm, and 9 at WOT. Dont know if it's my imagination, but my truck seems to have a little more giddyup than it did the last time I changed the pump. Anyway, thanks to everyone for their help and all their hard work to research and share this valuable information.
12-20-2007, 11:43 PM
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Wow, this is an old thread. I’ll try and fill in some of the details.
I am running a Westach electronic pressure sender that samples fuel pressure from the input of the VP. It is connected by a hose and snubber the same way a fuel pressure gauge is connected. I tried to get on the Westach site but they seem to be making changes right now, so I don’t have the part number handy.
The PWM circuit I built is too difficult unless you know someone who wears thick glasses with adhesive tape on the bridge. A much simpler solution is the PWM kit I found for about $25. It will have to have some simple modifications to power the sensor but anyone who knows which side of a soldering iron to pick up should have no problems. This circuit will adjust the pump speed to match the set point on a potentiometer, any where from 0 to 45 psi. At 45 psi, I think this is where to pumps will fry. My dash fuel gauge is the most boring gauge I have, only moving to and from 0 psi when the engine is started and stopped. At all other times from idle to WOT it is at the set point.
An Aeromotive of Walbro pump should work well because they both do not have an internal spill back valve and can both flow way more fuel than anyone will need. I would not hesitate to mount a new Walbro. The PWM circuit can be added later.
I had hoped to have the PWM kit tried out by now but building a house has sapped my time. Before the end of summer I will try to have something posted with info on the kits and wiring. I am not interested in selling these so the info will be for all.
I am running a Westach electronic pressure sender that samples fuel pressure from the input of the VP. It is connected by a hose and snubber the same way a fuel pressure gauge is connected. I tried to get on the Westach site but they seem to be making changes right now, so I don’t have the part number handy.
The PWM circuit I built is too difficult unless you know someone who wears thick glasses with adhesive tape on the bridge. A much simpler solution is the PWM kit I found for about $25. It will have to have some simple modifications to power the sensor but anyone who knows which side of a soldering iron to pick up should have no problems. This circuit will adjust the pump speed to match the set point on a potentiometer, any where from 0 to 45 psi. At 45 psi, I think this is where to pumps will fry. My dash fuel gauge is the most boring gauge I have, only moving to and from 0 psi when the engine is started and stopped. At all other times from idle to WOT it is at the set point.
An Aeromotive of Walbro pump should work well because they both do not have an internal spill back valve and can both flow way more fuel than anyone will need. I would not hesitate to mount a new Walbro. The PWM circuit can be added later.
I had hoped to have the PWM kit tried out by now but building a house has sapped my time. Before the end of summer I will try to have something posted with info on the kits and wiring. I am not interested in selling these so the info will be for all.
Here is an update on the DC to Pulse Width Modulator kit, K8004.
The intent of using this kit is to control the lift pump speed to adjust the fuel pressure to a set point you choose. To do this a pressure sender is used to modify the duty-cycle of the voltage to the pump. The kit I chose has all the things needed to do this and I had assumed it could be modified to lower the duty-cycle with a rising pressure. This negative feedback is needed to keep the pump from running at full speed all the time. The IC chip has both positive and negative inputs, which I assumed could be used for this application. Unfortunately this is not the case. After building the kit I found the SG3525 IC chip cannot be run in this way.
I got looking around for an easy answer and came across another chip, SG3537. This is a direct replacement for the SG3525 but has the correct sense to lower the duty-cycle with an increasing fuel pressure. This will be the answer for an easy PWM circuit to control the lift pump. The only problem I have now is trying to buy a small quantity of these chips. Most places only want to sell them in 1000s. But I will not give up easily; just add a few more weeks to my quest for a cheap and easy PWM circuit.
The intent of using this kit is to control the lift pump speed to adjust the fuel pressure to a set point you choose. To do this a pressure sender is used to modify the duty-cycle of the voltage to the pump. The kit I chose has all the things needed to do this and I had assumed it could be modified to lower the duty-cycle with a rising pressure. This negative feedback is needed to keep the pump from running at full speed all the time. The IC chip has both positive and negative inputs, which I assumed could be used for this application. Unfortunately this is not the case. After building the kit I found the SG3525 IC chip cannot be run in this way.
I got looking around for an easy answer and came across another chip, SG3537. This is a direct replacement for the SG3525 but has the correct sense to lower the duty-cycle with an increasing fuel pressure. This will be the answer for an easy PWM circuit to control the lift pump. The only problem I have now is trying to buy a small quantity of these chips. Most places only want to sell them in 1000s. But I will not give up easily; just add a few more weeks to my quest for a cheap and easy PWM circuit.
Any more info about an easy to build PWM kit? I really like the looks and function of your set-up.
12-21-2007, 09:33 AM
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Excellent thread - should be in a sticky in a TECH section - glad it's revived again - SEARCH just doesn't seem to work for me
IMO - the air bubbles are probably due to
1. cavitation resulting from the pump's distance from the tank - a mounting positon close to the tank would reduce inlet restriction - gearotor pumps are pusher-type, not intended for draw-type service, and must be close to the liquid source to prevent cavitation
2. fuel aeration in the pump resulting from a.) cavitation and b.) Diesel fuel's inherent tendency to foaming, which easily occurs when pump output exceeds system flowthru capability - even minor dead-heading from plumbing, regulators, etc will cause aeration - it is not a problem encountered in gasoline systems.
The pwm\pressure scheme simulates the mechanical lp on the 12v's - low volume at low rpm, volume increasing with rpm to high volume at high rpm, maintaining sufficient and relatively constant pressure required to flow thru the resistance\restriction of the fuel filter.
This would help reduce both cavitation and aeration, considerably.
And, remember: 70gph @ 70mph = 1mpg
So, 12gph @ idle, stopped = ???
IMO - the air bubbles are probably due to
1. cavitation resulting from the pump's distance from the tank - a mounting positon close to the tank would reduce inlet restriction - gearotor pumps are pusher-type, not intended for draw-type service, and must be close to the liquid source to prevent cavitation
2. fuel aeration in the pump resulting from a.) cavitation and b.) Diesel fuel's inherent tendency to foaming, which easily occurs when pump output exceeds system flowthru capability - even minor dead-heading from plumbing, regulators, etc will cause aeration - it is not a problem encountered in gasoline systems.
The pwm\pressure scheme simulates the mechanical lp on the 12v's - low volume at low rpm, volume increasing with rpm to high volume at high rpm, maintaining sufficient and relatively constant pressure required to flow thru the resistance\restriction of the fuel filter.
This would help reduce both cavitation and aeration, considerably.
And, remember: 70gph @ 70mph = 1mpg
So, 12gph @ idle, stopped = ???
12-21-2007, 05:31 PM
#26
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Well, its not the consumption (burn) rate, it is a flow rate. Most of that fuel is returned back to the fuel tank from the VP44. One could derive the consumption rate from the pressure drop at different loads on the engine, but it is not very simple. I actually toyed with this idea and pulled out a bunch of viscous flow equations in tubing, but got distracted onto household chores 
and later forgot. I am sure this has never happened to anybody else here 
Any time you hear the "XXX GPH flow" either on the fuel lines, or Walbro pumps, or anything else on these trucks, you gotta think: 35 gal tank, 35/XXX=Hours of run time. Clearly, even the trucks with most HP do not run down a tank full in half an hour, so the high flow figures are in fact "high overflow" figures that are good for "feel good" and bragging rights, although to a degree: more HP will cause more pressure drop, and higher flowing lines will reduce the pressure drop and provide better fuel delivery for the conventional overflow designs (Glacier kits, FASS etc.), which all seem to overflow from the lift pump itself, wasting most of the pump's ability to deliver constant flow to the VP44.
But to summarize, I said nothing that Superduty hasn't said before: if the high-performance lift pump pressure is regulated at the VP44, any line will deliver the necessary fuel, even the stock ones. In this case there is a risk to blow the lid off the filter, though, so care needs to be taken to avoid that.
-P
and later forgot. I am sure this has never happened to anybody else here Any time you hear the "XXX GPH flow" either on the fuel lines, or Walbro pumps, or anything else on these trucks, you gotta think: 35 gal tank, 35/XXX=Hours of run time. Clearly, even the trucks with most HP do not run down a tank full in half an hour, so the high flow figures are in fact "high overflow" figures that are good for "feel good" and bragging rights, although to a degree: more HP will cause more pressure drop, and higher flowing lines will reduce the pressure drop and provide better fuel delivery for the conventional overflow designs (Glacier kits, FASS etc.), which all seem to overflow from the lift pump itself, wasting most of the pump's ability to deliver constant flow to the VP44.
But to summarize, I said nothing that Superduty hasn't said before: if the high-performance lift pump pressure is regulated at the VP44, any line will deliver the necessary fuel, even the stock ones. In this case there is a risk to blow the lid off the filter, though, so care needs to be taken to avoid that.
-P
12-21-2007, 09:26 PM
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Good input, as was your opening post - intent was not to question you, but to confirm the necessity(?) of 150gph pumps, or 100psi pumps - even 35psi can punch holes right thru a plugged 2micron filter - imagine the surge from a 100psi pump.
I've posted links to your thread in several other sections where lift pump questions often pop up - should be food for thought, help everyone start on the same page
BTW - I've been posting the benefits of staying with the oem '05^ in-tank setup for the stock or mildly improved trucks, and promoting the oem upgrade for the VP44 trucks, but which is not intended as condemnation of any add-on system - it is to ensure that everyone is starting from the same basic page, also.
I've posted links to your thread in several other sections where lift pump questions often pop up - should be food for thought, help everyone start on the same page
BTW - I've been posting the benefits of staying with the oem '05^ in-tank setup for the stock or mildly improved trucks, and promoting the oem upgrade for the VP44 trucks, but which is not intended as condemnation of any add-on system - it is to ensure that everyone is starting from the same basic page, also.
12-22-2007, 09:37 PM
#28
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Gmctd, any and all constructive input is welcome here - this is the whole idea of this forum. Everyone chooses the system they feel best about for their truck - be it OEM, p-pump, FASS, Glacier, Hlley Blue or generic Walbro. So anything you can add that helps folks choose is good input.
Regarding 150 gph and 100 psi pumps. It just so happens that Walbros, commonly considered reliable, happen to be capable of delivering both the high flow and high pressure. You are totally correct that excessive pressure will damage the low pressure side of the fuel system, and Walbros should not be allowed to develop high pressure. Two ways of doing that: limiting power to the pump, or relieving the excess flow. Bent_Valves did the former; more simple designs do the latter.
As far as if this capacities are "necessary" - definitely no, not at all. But we are not talking about an "ideal" pump, but about a real one. My choice was, to use some pump that might be more compatible with unmodified stock fuel system, or adapting excessively powerful, but proven reliable, Walbro. I chose the latter.
Now one thing you have accomplished by bringing this thread back Gmctd, is set me again onto thinking that a Walbro based system needs to be made that is a drop in replacement for a stocker. I just may have an idea on this... went and gutted my own old Carter. It just MAY work out. Once I trash mine completely, I might ask folks here to send me a couple of dead stockers for experiments.
-P
Regarding 150 gph and 100 psi pumps. It just so happens that Walbros, commonly considered reliable, happen to be capable of delivering both the high flow and high pressure. You are totally correct that excessive pressure will damage the low pressure side of the fuel system, and Walbros should not be allowed to develop high pressure. Two ways of doing that: limiting power to the pump, or relieving the excess flow. Bent_Valves did the former; more simple designs do the latter.
As far as if this capacities are "necessary" - definitely no, not at all. But we are not talking about an "ideal" pump, but about a real one. My choice was, to use some pump that might be more compatible with unmodified stock fuel system, or adapting excessively powerful, but proven reliable, Walbro. I chose the latter.
Now one thing you have accomplished by bringing this thread back Gmctd, is set me again onto thinking that a Walbro based system needs to be made that is a drop in replacement for a stocker. I just may have an idea on this... went and gutted my own old Carter. It just MAY work out. Once I trash mine completely, I might ask folks here to send me a couple of dead stockers for experiments.
-P
12-22-2007, 10:06 PM
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Any failure indication on the Carter?
You're not talking mounting another lift pump on the filter, far from the tank and higher than tank level? That's what causes the Carters to fail - only diaphragm and piston-type pumps are designed for draw service.
You're not talking mounting another lift pump on the filter, far from the tank and higher than tank level? That's what causes the Carters to fail - only diaphragm and piston-type pumps are designed for draw service.
12-22-2007, 11:00 PM
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I revived this thread because my friend's newly acquired '02 HO truck's lift pump died the other day in a bad part of town. I went to rescue him with a new NAPA pump I had purchased as a spare days after I bought my own truck. This left me with no spare pump, and also motivated me to get my Walbro system installed that has been sitting in a box.
I disassembled the failed Carter from the '02 to determine why it failed. I was rather astonished to see that it looked brand new inside (unknown mileage) and the vanes looked perfect. The plastic drive slot was also intact and the motor was working (we could obviously hear it running) but got no fuel through an open fuel filter top. Swapped pumps after I installed a new filter element and he was good to go.
What happened was the pump's internal bypass check valve died and caused the pump to suck from the internal cavity vs the inlet because is was the path of least resistance.
It appears like the OEM Carter installation in the CTDs is bypassing (or recirculating) A LOT of fuel within the pump when the engine is at idle. When the fuel pressure drops below the bypass threshold (15 psi?), the bypass shuts off and delivers enough volume to the VP44 to keep the LP from recirculating it's own fuel--which heats and aerates it.
This makes me think that simply idling the engine does the most damage to the LP and possibly the VP44 by shoving all that areated fuel into the fuel filter. I am not sure if the filter can remove all the areation, but I doubt it.
Relocating the Carter down next to the fuel tank helps a bunch with cavitation, but the pump will still bypass internally when the engine is not consuming much fuel. The Dodge fix of the intank pumps help, but they are still problematic from what I have read here and elsewhere.
It appears like the best set-ups (LP) are the ones that aerate or heat the fuel the least ammount possible. Walbro or other high flow pumps (insert favorite LP here) with an external pressure regulator located at the VP44 inlet, set-up to dump excess fuel back to the tank (not into the inlet of the pump!) seems like the easiest route to gaining a constant 13.5 psi of fuel supplied to the VP44 under all conditions, but they do recirculate a bunch of fuel.
The RASP pump or other mechanical pump (I'm not picking on RASP here--just an example) is closer to providing variable fueling based on engine RPM, but as HOHN pointed out, a Cummins will use FAR LESS fuel at 2,000 RPM while in neutral vs 2,000 RPM under a heavy load, but the RASP will provide exactly the same volume in either case because it is RPM dependent.
The system Bent_Valves has looks like the ultimate set-up. Run the Walbro (or other LP) with a PWM regulator and feed the engine exactly what it needs when it needs it. The bypass would be there incase of PWM failure. It would not use it otherwise as most systems (internal or external bypass) need to do.
Now if there was only a ready made PWM kit with a harness to connect the LP and a pressure transducer, we would be set!
I disassembled the failed Carter from the '02 to determine why it failed. I was rather astonished to see that it looked brand new inside (unknown mileage) and the vanes looked perfect. The plastic drive slot was also intact and the motor was working (we could obviously hear it running) but got no fuel through an open fuel filter top. Swapped pumps after I installed a new filter element and he was good to go.
What happened was the pump's internal bypass check valve died and caused the pump to suck from the internal cavity vs the inlet because is was the path of least resistance.
It appears like the OEM Carter installation in the CTDs is bypassing (or recirculating) A LOT of fuel within the pump when the engine is at idle. When the fuel pressure drops below the bypass threshold (15 psi?), the bypass shuts off and delivers enough volume to the VP44 to keep the LP from recirculating it's own fuel--which heats and aerates it.
This makes me think that simply idling the engine does the most damage to the LP and possibly the VP44 by shoving all that areated fuel into the fuel filter. I am not sure if the filter can remove all the areation, but I doubt it.Relocating the Carter down next to the fuel tank helps a bunch with cavitation, but the pump will still bypass internally when the engine is not consuming much fuel. The Dodge fix of the intank pumps help, but they are still problematic from what I have read here and elsewhere.
It appears like the best set-ups (LP) are the ones that aerate or heat the fuel the least ammount possible. Walbro or other high flow pumps (insert favorite LP here) with an external pressure regulator located at the VP44 inlet, set-up to dump excess fuel back to the tank (not into the inlet of the pump!) seems like the easiest route to gaining a constant 13.5 psi of fuel supplied to the VP44 under all conditions, but they do recirculate a bunch of fuel.
The RASP pump or other mechanical pump (I'm not picking on RASP here--just an example) is closer to providing variable fueling based on engine RPM, but as HOHN pointed out, a Cummins will use FAR LESS fuel at 2,000 RPM while in neutral vs 2,000 RPM under a heavy load, but the RASP will provide exactly the same volume in either case because it is RPM dependent.
The system Bent_Valves has looks like the ultimate set-up. Run the Walbro (or other LP) with a PWM regulator and feed the engine exactly what it needs when it needs it. The bypass would be there incase of PWM failure. It would not use it otherwise as most systems (internal or external bypass) need to do.
Now if there was only a ready made PWM kit with a harness to connect the LP and a pressure transducer, we would be set!