Superduty

I've installed an 05 Cummins in my Ford SD. It starts and idles. I am supplying it with fuel from a Walbro GS392 inline pump with no pressure relief. I used the same system on the SD when it had a Powerstroke in it.

Everything works fine except that I was testing the APPS circuits with the key on and fuel pump running and it started blowing fuel out the filter lid ! So I disconnected the fuel pump and ran the engine and it ran fine. I was just idling it so every now and then I momentarily turned on the fuel pump.

However, the engine started to surge a bit so I shut it off. Turning the fuel pump on at that point would not make the surge go away.

Where is all this backpressure coming from ? The CP3 ? This is the same tank, line, pump and return line I ran on my PSD. The only thing that has changed is that we now have the Cummins filter canister and the CP3. Is the CP3 that restrictive ? Or is it the filter ? I can't imagine an orifice small enough to create this kind of backpressure at only 255L/hr.

fahlguy

Again....I am still no expert...but I think you need to regulate the pressure to under 20 psi......your restriction is at the CP3.......




Bill

BigBlue

All you really need is 15psi. A constant 15psi would be perfect but we don't live in a perfect world. What kind of pressures are you putting out right now?

WhiteSport600

I told you so.... Just get a regulator and keep it under 20psi. I've been there and done this.

Haulin_in_Dixie

After a few months of settling in on the new spring, mine sits on 18, just about all the time. Real low on fuel it may get to 17 wot. It starts fine, runs fine. Looks like under 20 and all is ok.

Superduty

I did some mods and now I have the full GS392 output going to the CP3. I don't have a regulator on it. My pressures are low, 5PSI at the CP3, but all 255L/hr go to the CP3.

I kept my pressure low so that I could put a low pressure 2 micron filter between the stock filter housing and the CP3.

The CP3 has a gear pump that feeds the main pump and the cooling flow and the return flow. It isn't like another pump whereby you can flow as much fuel through it as you want. The gear pump sets the volume the CP3 will take. If you pump more than that the pressure skyrockets. It is a fixed displacement gear pump with no overflow route.

CP3s do not need a lift pump theoretically. Just get a high volume of fuel to them so that the gear pump is always fed and that is all you need. The problem with using a lift pump is that it is fine until the CP3 wants more fuel, whereby then it becomes a restriction to the CP3's gear pump sucking more fuel. Duramaxes don't use a lift pump and they do fine. I think Dodge trucks have CP3 pump problems because once the lift pumps get weak they serve as a hindrance to the CP3 sucking fuel itself.

CP3s have a valve in them called the cascade overflow valve. It prioritizes the useage of the fuel the pump gets. First it feeds the pumping chamber. Then it feeds the pump coolant fuel. If there is any fuel left after that, it feeds the return line.

I fear that some of these gages that read 0 PSI for FP should actually be showing suction. I think the CP3 is getting starved in trucks with weak lift pumps.

BTW: My SD is running with an 05 Cummins in it. I'm waiting for the ******* to get me a new filter lid.

coobie

FASS system

Superduty

You'd have to convince me that the FASS did something that my present system isn't doing. I don't see any need for a 95 GPH flow rate, I don't believe in all this "air in fuel" BS and I don't think a pump and filter should cost $400. I've got a clear piece of line in the return on my truck (temporary). I was watching it today and I didn't see any air.

coobie

How about 2-3 mpg,s more per gallon than the stock lift pump?Thats about what I have averaged since my FASS install.coobie

MR4WLR

The way I understand it the air is not going to be "visible" but it is there.