doug60

I am in the process of finishing my half scotty half custom installation. New 1/2 line (bulkhead fitting in tank) to a high flow holley filter (60 micron screen) to the new holley gerotor 12-150 pump. Also the system will feature a check valve , in case of pump failure the CP3 will be able to pull fuel through the bypass check valve. The front end is all Scotty smart fuel. doug

CTDHokie

Looks like a great idea, I have always thought about using a powerstroke style fuel pump on my truck. I've got a couple questions for you.

Do you have a fuel pressure sensor between the stock filter and the inlet to the CP3? If so what does it typically read?

Do you know what flowrate and pressure the stock filter is rated for? We don't want to go blowing that filter apart with to much flow.

I've thought about doing a similar setup to yours, but having a fuel pressure regulator installed before the stock filter bowl set at around 10psi so we don't pump more fuel then needed through the filter.

This method would put a constant 10psi at the CP3 inlet and may not need the external bypass right at the CP3 you installed.

Again great write up, I'm going to need to redo my fuel system real soon so this definitley helps

Superduty

"Do you have a fuel pressure sensor between the stock filter and the inlet to the CP3? If so what does it typically read?"

I had one temporarily hooked up when I first plumbed in the bypass. The pressure read 3 PSI with the engine idle. That pressure is the result of the backpressure created by the restriction of the bypass and return line, which isn't much. People need to understand that. Being that the supply volume (255L/hour) is much, much greater than the CP3 usage, that pressure is likely to stay where it is even under WOT conditions.

Furthermore, even if that pressure would drop to zero, my CP3 isn't going to starve. As long as my pump puts out 255L/hour and the CP3 only uses 150 L/hr, there is lots of fuel to keep it fed. Remember that all of the fuel from my pump goes by the CP3. None is going back to the tank by any other means.

CP3s DO NOT need to be fed with a big positive pressure supply. With no other route to the tank other than via the CP3 bypass, my CP3 is free to draw as much fuel as it needs from the 255L/hour flowing past it continuously. At WOT that might be 150 L/Hr.

"Do you know what flowrate and pressure the stock filter is rated for? We don't want to go blowing that filter apart with to much flow."

Nope. I know that my filter housing lid cracked at about 60 PSI. The filter presents very little backpressure unless it starts plugging. I didn't write about it, but I was thinking of putting a fuel pressure indicator (like the air filter indicator) upstream of the fuel filter to warn me of an impending dirty fuel filter.

"I've thought about doing a similar setup to yours, but having a fuel pressure regulator installed before the stock filter bowl set at around 10psi so we don't pump more fuel then needed through the filter."

You are missing the point. First, if you look at commercial installations of diesel engines (combines, trucks, etc.) that use an electric lift pump, all the fuel goes through the filter, just like my setup does. You want to feed the CP3 with all the clean fuel the pump produces so it never starves.

"This method would put a constant 10psi at the CP3 inlet and may not need the external bypass right at the CP3 you installed."

No it doesn't. It would feed the fuel filter with 10PSI and how much fuel/pressure gets to the CP3 depends on how much filter and line restriction is between the regulator and the CP3. See the difference ?

Here is another way to think of it. Pretend you have an P7100 on your truck with no mechanical pump and you are going to feed it with an electric fuel pump. What does the route the fuel takes look like ? It goes tank-> pump-> filter-> P7100-> tank. The pressure relief is in the P7100 housing and it is only a few PSI at most.

Now think about the CP3. We can't feed fuel through the CP3 like we can with the P7100, but the CP3 is capable of sucking whatever it needs for fuel from the line nearby, so instead of running the fuel through the CP3, we run it right by it and let it take what it wants.

When you start fooling around with pre filter regulators what inevitably happens is that only half of the flow gets to the CP3 (the rest goes through the regulator) and then under WOT throttle conditions it starves.

BTW: lets say we are running a stock 05/325/600 engine. It has a WOT BSFC of 0.390 lbs/hphr. At WOT, the amount of fuel it uses is:

325 x 0.390 lbs/hphr = 126.75 lbs/hr. Fuel weighs 7 lbs per gallon so...

126.75 lbs/hr / 7 lb/gallon = 18.1 gallons per hour. 1 gallon = 3.785 litres, so

18.1 gallons x 3.785 litres/gallon = 68.5 litres per hour.

This is the amount of fuel going into the combustion chambers. Extra fuel must be pumped to the CP3 to allow pump cooling/lubrication as well as injector leakage, etc. Even if it was 50% of the engine useage, the total supply requirements to the CP3 would be about 100 L/hr, which incidentally is the spec Dodge dealers use when testing lift pumps. I used 150 L/hr for worst case bombing situations.

Remember that the Walbro GS392 supplies 255L/hr at low pressures (< 20 PSI).

MadFrog

so, is there a concern that the FASS pump would over pressurize the CP3? It is a 95gph pump (what's that, about 350l/hr?) so it definitely has the flow for it.

Maybe someone with the FASS could add in the bypass line that you came up with and thus provide some added peace of mind?
I don't know if the FASS is internally relieved?

Superduty

I don't know anything about FASS systems.

I do know that thousands and thousands of highway trucks run without any sort of a fuel/air separator. If you look back in the Diesel Stop forums, for a while everyone was convinced that there was air in the fuel on Superduties. My Cummins runs beautifully with the stock tank and fuel pickup. There was nothing wrong with the fuel system on the Superduties other than the engine using the fuel...

DR3500

They remove the pump from the fuel filter housing during the retrofit. you should see around 25 psi since the in-tank pump puts out close to 10 psi and the holley raises it 15 more. The only disadvantage of the two pumps is that if one fails the other can't push/pull thru it.

CTDHokie

I don't see a huge difference between your method and my idea of putting a regulator before the filter. The only way the CP3 would be starved with fuel is if the stock filter becomes so clogged that it+the line losses have a 10psi drop.

I guess I just don't see the point of filtering a whole lot of fuel you are not using.

One another topic, have you ever thought of putting a check valve on the return line to keep the CP3 from sucking in air from that line? I guess it is most likely not needed because you will always have more fuel then needed at the inlet to the CP3.

wannadiesel

It's all gotta be filtered at some point. What difference does it make if it gets filtered 200 times instead of once? It's not gonna plug the filter any faster.

DR3500

Superduty, with your fuel bypass wouldn't the CP3 pull fuel from the return if the lift pump couldn't keep up or the fuel filter is dirty? I think it would at least momentarily until it pulled all the fuel from the return line and start sucking air? did you put a check valve it the line?

Superduty

There is no checkvalve in the return line.

With my pump setup, if the filter blocks enough to starve the CP3, there will be 60+ PSI of pressure in the filter housing and it will blow the lid off. (Like it did before I put the bypass in the system...)

I am going to put a pressure telltale on the supply line to the filter housing someday.

JDGnut

Tweeter.. When you stack pumps that have an internal regulator, you will add the pressure setting of each pumps to each other... because they are returning their fuel back to the inlet... If you use an external regulator, you can return the fuel back to the tank.. this will limit the total pressure...
Bryan

CTDHokie

The difference is if the filter is not rated for the increased flow it may blow apart and cause all sorts of issues. Now I do not know what the flow rating is of the stock filter, so I don't know if this is even an issue.

Superduty

There is no problem flowing 255 litres/hour through the stock filter when it is clean. When it is plugged, that will be a different matter, thus the need for a filter minder.

ckennedy

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ckennedy

Superduty

whats your take on the growing concern and "use" of finer filtering. Have you thought about adding in your setup??