Would a fuel pressure regulator help the OEM LP?

[rweis]

I have poured through lots of threads on LP's. Seems ONE of the main failures is the internal bypass spring and ball system.



I only know what I have read. If I have something wrong please correct me.



If the internal bypass system is one of the main failure points of the LP would a fuel bypass regulator post LP help?



If the internal bypass operates when the VP is not demanding what the LP can output, if the bypass is set at a value below when the LP bypass operates (14psi?) would it stop the internal LP bypass from operating?



Still providing the VP with a steady 14 psi but bypassing anything over 14 psi. The VP still gets pleanty of fuel, but the LP bypass does not become unseated and subject itself to wear and failure.



The LP would never see a output pressure higher than what the bypass is set and would run with less head pressure and therefore less strain.



I watch my LP pre and post filter. When at a stop light the pressures waver slightly when I think the internal LP bypass is functioning. When at 65 mph (higher VP demand) and the LP is outputing a steady 14 psi the pressures are stable for hours until we slow down and lessen the demand.



Please chime in and toss your . 02. Idea good or bad idea? Do they make them for diesel?



Bob Weis

 

[illflem]

Not real familiar with the VP but doesn't it have a bypass to the return line in it already?

 

[rweis]

Bill,



I think so, but I think it functions based on rpm of the VP. I read threads of fp and it typically is 16 psi at idle, 14 psi at 65 mph unloaded, 12 psi 65 loaded. From what I read the LP bypass is set so that when the LP is putting out more than the VP is taking it bypasses in the LP. When the LP bypasses is when the little spring / ball / ball seat get into the picture.



What I was thinking is to keep the spring / ball / ball seat from getting into the picture. A lot of the threads seem to have three areas of failure in the LP. Not in any order of occurrance:



1. the spring / ball / ball seat failure

2. the motor itself (commutator, brushes)

3. the nylon connector from the motor shaft to the pump head



#3 seems to be when the fuel is cold / some state of gell. Many threads cite #3 mainly in winter conditions.



If I can remove:



#1 with a pressure regulator. In a couple of threads some have drilled and tapped the LP and put a set screw in to hold the bypass valve closed. Wouldn't this approach put more stress on the LP motor? Apparently you can't get it out without damageing the LP.



#3 with a fuel additive (lubricity, pour point, etc (Stanadyne Performance Formula)) or a LP pre filter with a fuel heater (RACOR 690).



then deal with #2 as the motor wears out, which if the pressures can be kept lower without sacrificing flow to the VP, might be extended.



Just tossing an idea around.



Bob Weis

 

[15w40]

I believe that most of the lift pump failures are due to the internal spillover valve dieing. The pumps I have dissected all had the spring or valve ball seat damage causing fuel pressure to drop or fluctuate.

(The following is my opinion and is not proven by any measurement. ) The problem with the lift pump is caused by the VP44 fuel flow. Its internal rotary pump pressurizes the internal pump structure and incorporates a spillback valve just as the lift pump does. The problem comes from the variation in pressure when the VP is injecting fuel or spilling it back to the input port. This causes the fuel flow from the lift pump to start and stop as the VP sucks and blocks flow. One way to model this is with this example: using a garden hose with a pistol grip nozzle that you are continually squeezing and releasing will cause the water in the hose to speed up as the nozzle is opened and stop abruptly when the nozzle is closed. If you were to measure the pressure in the hose, it drops when the nozzle is open and will spike up when the nozzle closes. Now if the water in the hose were supplied by the Carter lift pump, The output port on the lift pump would see a cyclic pressure drop and an abrupt pressure spike up. The lift pump spill back spring and ball seat don’t stand a chance of having a long life with the constant pounding.



An interesting side thought about this is if the Cummins engine is never at idle and is always running at high RPM, the lift pump will be at a lower pressure and will not open its spillback valve. The VP will not be pounding the lift pump as badly since it is always injecting fuel and drawing from its input port. So the answer to long lift pump life is to always rum at WOT!



rwies, I am not sure a pressure regulator between the lift pump and VP will help. The fuel will still start and stop as the VP does its thing, but it may help attenuate some of the spikes.

 

[rweis]

How do you get the VP spikes out of the system?



Some of you design folks that do buffering for fluid systems ought to throw in an idea here.



A fuel buffer tank between the LP and VP?, but isn't the OEM filter sort of that? Maybe a second fuel filter to filter but more importantly buffer the LP from the VP?



The water hose example. A water well has a storage tank so when the well pump is running the pressure goes up in the tank, but there is a regulated output to the house that stays within a fairly narrow range. Valid parallel?



Longer fuel lines between the LP and VP?, like mounting it on the frame?



A fuel regulator set at something below the LP spill over valve setting so the LP spill over valve never actuates?



Change the LP to one that does not have the internal design problem?



Just a thought, was a try to think of the LP problem from a different end.



Maybe just carrying a spare LP and tools is the real answer.



Probably cheaper too.



Bob Weis

 

[radar doctor]

Nice Theory

Very Nice Article. Has anyone seen any Posts on the 03 having Lift Pump Troubles? Bob why don't you Team up with some designers and lick this fuel pump Problem. . Do you have any Idea what Money might be in it . . ?????

 

[rweis]

LONG -----------------



I am willing to test a plan for the lp.



I agree with 15w40 that the VP has an over pressure valve that inputs BACK to the lp. Why do I agree? I agree because I have pre and post fp and when you accelerate quickly you can see the vp demand pull both fp down to ~14. When you let off the go pedal the post fp spikes to about 16 -18 for 1-3 seconds then both pre and post stabilize at ~16.



It appears that the OEM filter buffers the spike because I see some rise pre fp but not as much or as quickly.



BUT, when I am under higher VP demand (faster unloaded) the fp both slowly fall from ~16 to ~14 and stabilize. If I am pulling a load they fall from ~16 to ~12 and stabilize.



BUT, when I am at slower speeds or at a stop light and both are at ~16 you can see the psi flutter a bit. As you accelerate they slowly start to fall and the fluttering slowly smooths out, but still have a slight flutter until ~14 psi. Once at ~14 psi they stop fluttering. I think this is the lp bypass functioning.



The plan:



Put a bypass regulator pre (incase the bypass self destroys) OEM filter set at ~14 psi (maybe ~13 psi).



IF the VP bypass spills back into the feed line the bypass SHOULD not allow the line to go over ~14 and with the buffer of the filter the lp SHOULD not see the over pressure.



When the VP is not demanding enough fuel and the lp bypass would normally open, it will not because the fuel bypass looks like a constant (VP or bypass) demand to the lp. Might also be easier on the lp if the psi were steady state.



I think the problem is two fold:

1. VP spikes to the lp

2. Lp bypass functioning



I would like to collect some data:



1. I would like to hear what psi indications that others that have pre & post fp see at low speeds and high speeds.



2. I would like to hear what psi indications that others that have 2 filters post lp see. Does the second filter cut out VP spikes to the lp? You still have the lp bypass problem though.



3. I remember someone that has the tank in the bed and gravity feeds the lp. I would like to hear what psi indications they have and what psi are they monitoring. Does positive feeding the lp make ie less suseptiable to VP spikes? You still have the lp bypass problem though.



4. Has anyone disabled the lp bypass? If so how did it then function? How did the psi function?



5. Has anyone that has added a pusher pump put in a bypass so the VP does not get too high a pressure? You used a bypass to keep the psi "~ factory"



Thinking out loud:



Would a buffer tank post lp (1 gallon, 2 gallons, ?) with a regulated return to the tank do the same thing and maybe simpler?



Would a second LARGE filter cut the spikes to the lp? Still have the lp bypass problem though.



If you replace the OEM lp with XXX lp does it have a bypass or did you do a bypass regulator?, or did you just take the output however it came?



Should be interesting,



Bob Weis

 

[illflem]

The Watts Regulator Co. makes a water hammer arrestor that would work better than a filter to smooth out pluses, p/n 150A. What it is is a fist sized tank similar to a well pressure tank with a rubber diaphragm that you charge to your normal operating pressure, the air chamber absorbs pressure spikes. You would have to check that the diaphragm material is compatible with diesel, Watts phone is 978/688-1811.

All of my ag sprayer pumps have what is called an air dome built into them that serves the same purpose, to smooth out spikes. Air pressure is obtained though a tire valve same as the Watts. Without a charge in the air dome the sprayer's pressure regulator goes into noisy spasms, very hard on the pump. Same thing is probably happening to your lift pumps you just can't hear it over the noise of the Cummins. .

Here's more info

 

[daveshoe]

Noticed the same thing

I also noticed the same thing and thought that a steady resistance value would be a better thing. I have also thought some sort of accumulator might be a good thing - IF that is what is causing the problem. However, another area of concern is the fact that the lift pump rapidly cycles on and off when the key is first turned to start the truck at 7 psi and then goes to high pressure when the beast fires up. [VP does not like start up pressure more than 7 psi]

It seems to me that this event would also cause ''pressure slams'' in the lift pump. The only way to test this would be to make the pump run 100% duty and dump it into an accumulator set to 7 psi all the time. You would have plenty of flow to the VP, but then would have to worry if a higher flow also needs higher pressure than 7 psi. In any case ,you would have to flow test the output frequently if you wanted to run at such low pressure.

I am not offering any solutions here -- so shoot holes in this all you want

 

[rweis]

Bill,



Called Watts, the 150A diaphram material is Butal (sp) rubber. Petroleum fluids OK, NOT for brake fluid or regular gasoline. Does that check with what you know about Butal rubber?



Daveshoe,



Not sure I would want to run 7 psi all the time. Miles of threads on it though. One camp is any psi, one camp is strong psi. VP cooling issues? Risk to the VP? Bypass in lp would stay closed though.



15w40,



Do you know what psi the lp bypass is set? If I do a bypass regulator I want to use a value to make sure the lp bypass doesn't open.



Bob Weis

 

[mediccummin]

Bob?

I have been reading up on all this fuel system stuff and was wondering if the Carter 4601HP can be used in place of the OE lift pump?? I have been reading but can't find that answer. It is probably slapping me right in the face. I want to move my pump back by the tank and was wondering if this pump (4601) could be used in place of the oe pump. I was thinking of leaving the oe pump in place for a back up ( got some ideas but to hard to post). I plan to change to 6 or 8 an fittings and hoses. I pull down to 6psi wot right now with dd2's and va. But im upgrading to DDUFM or Comp and dd2's. How is your current set up working? Did you add the Stanadyne set up you mentioned prior? Also thanks for the email of your list. Any input would be great thanks... . Dwayne

 

[illflem]

According to this chart butyl is compatible with diesel. If I'm not mistaken the o-rings used on our fuel systems are butyl. The Watts 150a is a nice heavy duty unit, it would have no problem under the hood. I've used them a few times in homes where the fast closing valves on a washing machine cause a water hammer that feels like it going to shake the pipes out of the walls. Works great.

 

[rweis]

Mediccummin,



The Stanadyne Fuel Manager went back to the supplier. The mounting bracket was not even close, but it is an aftermarket bracket not made by Stanadyne. The lift pump option was rated at 40 gph at 10 psi. Which is probably enough for a fail safe, but I was concerned it would limit the 75 gph oem system. Might not, but. The chance you would ever use 75 gph is zero, but I use that as a "not smaller than" design factor. The filter was not a water block like RACOR uses. Decided to do a RACOR 690 instead and carry a spare lp.



I am going to put the RACOR pre lp so the lp gets the absolutely the best clean 10 micron water free fuel it can. Stanadyne Performance Formula every tank for water, lubricity, pour point, etc and if I ever go north put in a fuel heater in the RACOR so the lp gets warm fuel. That should take care of the nylon coupling in the lp.



Now I am working on the spike psi's.



For the project I used AN-6 fittings. Some like AN-8. AN-6 works fine for me.



I have a question on the Carter 4601. It puts out constant psi? or is bypassed?, or is ... ?



What happens to the fuel the VP doesn't take?



Bob Weis

 

[WadePatton]

spikes and flutters

I'm running an electric FP gauge and don't see all this spiking and fluttering. My 35,000 mile old LP puts out 12-13 idle and 7-8 WOT and spends 90% of the time above 10psi.



Maybe my sender is soaking up the fluctuations. I'll watch it more carefully for a day or two. I've quit looking at it after my last upgrade.



I have upgraded to all 3/8 line and AN-8 fittings. Search for "Wildcat Max Flow" for more on that.

 

[Hemiless]

Tigerloop

rweis



I'm not real sure from reading your post what all your looking for and truth be known I've never even looked closely at our trucks fuel system yet as I'm a relitivly new CTD owner. But you might look at a tigerloop to take away some of the pulsation and it might even help the lift pump not work as hard. The Tiger loop is used in home oil heating systems to eliminate the oil return line and make the tank seem closer then it is. I'm not sure if it would even work in your application but you might check it out. I know Dad won't install a oil boiler with out one because they work that good. Might even be an application for it before the lift pump? Not sure as stated before I've never even looked at a lift pump. Do a search for Tigerloop on google and you will find all the info on it.



Hope this helps

 

[cap-n-cray]

I have read so many threads about the lift pump, I need to ask some basic questions.



1. Does moving the lift pump closer to the fuel tank help and why? I know that it push rather pulls. Is the shock less by distance?



2. Did Cummins want to put the lift pump back at the fuel tank, but Dodge did not want the extra work in the engine install?



3. Where does Cummins put the lift pump in other applications?



4. I have read that some members have moved the lift pump back by the fuel tank. Has that helped?



5. When the lift pump fails it can take out the VP. But does the VP pump work for a time without the lift pump? If so does it pull fuel through the failed lift pump.



6. Has anyone ever installed a second stock lift pump by the fuel tank in combination with a stock lift pump in its original location? It would be like a back up pump. Both pumps working and if one failed the other would still work.



I am seeing 12 PSI at idle, and as low as 7 PSI at WOT with stock injectors. I do have Rays banjo bolts which I have been told lower the pressure with better flow.



Sorry for the basic questions, but I am confused.



Thanks,



Cary

 

[WadePatton]

wildcat maxflow kit, stock LP in stock location, no fuel supply probs under 500ponies.

 

[15w40]

The stock Carter lift pump will recirculate fuel at about 15 or 16 psi. One problem is it will be at a lower number if there is a restriction before the lift pump. If you add a filter before the lift pump and it starts to clog, the spillback valve will open at a lower pump output pressure. Another way to think about this is the lift pump will supply a differential pressure of 16 psi, and the differential pressure is the difference between the output and input pressures.



Sorry for the long delay to respond but a storm partially crippled the AC power to my house and my line voltage went to about 200 volts and fried the power supply in my computer.

 

[rweis]

I've decided to do a Mallory external fuel bypass after the lp and set it at about 14 psi to return anything over 14 psi to the tank. The VP gets a steady 14 psi and if the VP draws below 14 psi the bypass will close and deliver all the fuel to the VP.



I will have to maybe adjust it for the RACOR pre lp filter a little, but this is the way I am going.



I'll report back every so often on how it is going.



Thanks for ALL the ideas. IF I am right then I have 2 of the 3 lp failures fixed. And you can put in ANY lp and nothing changes. Mallory makes a nice gerator 110 gph pump too when the current lp and the spare lp die if ever.



Bob Weis

 

[Un-Hemi]

Have a look at this. It may be what is required... . or not.



http://www.matronics.com/fuelchec/dampener.html



No connection with the mfr. I'm considering it myself.



Tom