Fuel pressure question

[RVerdu]

I installed a low fuel pressure (idiot) light from Genos.

After installing it and running it at idle = no light.

Driving the truck on the highway 40-65 mph I noticed the 5PSI light just started to flicker.

Now I became really concerned and really watched the light.

Starting at a mild load from a red light and flooring it, I get the light to come on pretty steady.

I have NO mods on the truck, its stock from the factory, with a new fuel filter. ( 2005 Quad Cab CTD, auto, 70k)



Should I be concerned?



My truck leads a pretty easy life, with only occaisonal towing, hence the reason for no mods, but I didn't expect to have low pressure, YET.



Opinions?

 

[TCDiesel]

Need more info on the installation point?

 

[sag2]

I have never paid attention to the fuel inlet on factory installed in tank pump setup. Does your truck have an adapter block where the old engine mounted fuel pumps used to be? If so, pull it off and make sure the holes are drilled all the way through. The holes go through the block like a Z so make sure they intersect.

 

[HWestfall]

I don't know what the pressure on a common rail should be or what the light senser is set at as I have a 02. But my gauge reads at 12psi except when the fuel filter is plugging on. I would change the filter and see if that helps. H Westfall



02 HO 6-sp. 3500 Laramie Pat. Blue

 

[RVerdu]

The first thing I did when I giot home was change the fuel filter.

The old one looked good, but I replaced it anyway.



As per the instructions, here: http://www.genosgarage.com/Installation_Instructions/BD1081130-3 Cummins Low Fuel Pressure Alarm.pdf

I installed the banjo bolt on the side of the CP3 pump.



I will take the banjo bolt and double check it today.

 

[CKelley1]

the idiot lite was intended to be used with the vp44 the cr is half the pressure of the vp44 . go back to genos and buy the taped banjo bolt # bf-tapped, gasket #bf-3963983, and gauge # mrg1561 next get a oil pressure gauge install kit at one of the auto parts places for about $10 get the copper tube one. it will have six feet of copper tube and all of the fittings needed. we have mounted them every where in the trucks. the quickest is down by the shifter. you will see about 8psi idle. make sure you install the banjo bolt on the cp3 or bottom of filter not pre filter. do not change filter until it drops to around 2 or 3 psi this is where the filter is most efficient. the cr needs better filtering than the filter is capable of some time in the future consider adding a 2 micron cat filter. we install most of them just forward of the fuel tank from two bolts for the back seat. the last three we did we used a 10 micron napa 4347 filter then the 2 micron napa 3377 filter mounted on the same bracket this spot is just inches away from the fuel line. and yes i can read that the gauge is for test only but it is 10x better gauge than the expensive ones in his catalogue and price is the reason

 

[TCDiesel]

. You may need to purchase the billet cap, Also if you use the cap for the sensor you may need to modify the cap for the new style filter which is about a 1/4 taller and will touch the bottom of the cap causing no fuel to be measured. Do this or CKelley Method.

 

[RVerdu]

I went out and re-installed the pressure switch at the CP3 pump.

I double checked that none of the teflon tape was blocking holes, etc.

I got the same light flickering results going up a nearby grade.



Based on what CKelley1 and TWest are saying, I am going to measure the pressure with a guage.



Does it matter if I use the billet cap on the filter or the tapped banjo bolt on the CP3 to measure pressure?





CKelley1

do not change filter until it drops to around 2 or 3 psi this is where the filter is most efficient

I'm confused. I thought I was watching the fuel pressure to prevent damage below 5 PSI. Are you saying I shouldn't change my filter until I show some blockage with 3 PSI fuel pressure?

 

[TCDiesel]

Genos has the gauge and everything you need. the light does not work well on 3gen factory Pumps,its possible to drop below 5psi and run fine,Factory cp3 will work on or below 5psi,it only concern is adequate volume.

 

[RVerdu]

Checked fuel pressure with a guage

I "pirated" the guage and hardware from another car, and tested.



I have 9 1/2 - 10 PSI at idle,

4 1/2 - 5 PSI at heavy load, full throttle,

6-8 PSI at highway speeds up to 65 mph.



I can live with the flickering light as long as I know I'm not hurting it.



If the above pressures are OK, at what PSI do I become concerned? (besides zero )

 

[cerberusiam]

I "pirated" the guage and hardware from another car, and tested.



I have 9 1/2 - 10 PSI at idle,

4 1/2 - 5 PSI at heavy load, full throttle,

6-8 PSI at highway speeds up to 65 mph.



I can live with the flickering light as long as I know I'm not hurting it.



If the above pressures are OK, at what PSI do I become concerned? (besides zero )

Minimum 3-4 psi is all the lower you want to see.

 

[CKelley1]

ok first things first. do not use the billet cap it only measures the pre filter fuel and is worthless. only use the banjo bolt and only on the bottom of filter or cp3, the cp3 is easer to get to but with some attachments it is used or hard to get to. the cp3 does not require fuel for lube or cooling and a lot of stationary engines do not have lift pumps. think of the cp3 like a gear pump it lift's the pressure 22,000 pounds it does not care if it pulls a vacuum or has 100 lbs into it the only thing with vacuum it is asking for trouble with air until we started using other filter set ups we ran the oem to 0 psi under load before changing filter the cr needs better filtration than the oem can provide and some time in the future you should add a 2 micron cat filter. the last item. having 10 inches of vacuum or 100 lbs of pressure on the input will make no difference on volume or pressure on the rail

 

[cerberusiam]

the cp3 does not require fuel for lube or cooling and a lot of stationary engines do not have lift pumps.

That is a very dangerous assumption. By design the CP-3 needs adequate fuel supply to meet cooling and lube needs, about 3-4 psi to make sure it will maintain 75 psi case pressure and keep the COV open. Drop under that and fuel is prioritized to rail and robbed from the cooling circuit. Same as any of the internal lube\cooled pumps, you rob too much for to long and they eat themselves up, frequently with expensive results.



Comparing stationary engines to the what we have in the trucks is apples to oranges, same as comparing the chevy fuel systems. The gensets generally run less HP at a constant rpm so they don't see the constant up and down of rail pressure, plus, the fuel lines are usually larger and a lot of times its gravity feed. Huge difference from uphill long distance battle on the truck tanks and lines.



Have a little chat with a Bosch fuel system tech sometimes that has worked on these systems for a while. To make the 325 HP and the range of rpm's in these trucks the 3-4 psi is required to flow enough fuel to suppl rail and cooling\lube.

 

[RVerdu]

Thank you to all who replied.