Waterman in a street truck.

[cumminsman315]

Originally Posted by Vincejax

The pressure in the return line from the pump is what counts. The returned fuel is what cools the injection pump. If you are putting 100psi into the ppump and only getting 20psi out you have a lot of restriction on your return and probably not cooling enough. You should read your pressure at the return regulator, not before the injection pump.

I’m just guessing but I believe I’m flowing a lot more fuel through that return line than with a stock style fitting or a torktek orifice fitting. And also psi is not necessarily measuring flow, if I capped that return it would have way higher pressure with no flow. If I left the return how it is and went to a bigger lift pump and it gave me more pressure in the return then yes it would be flowing more

[bateman]

Vince have you ever measured pressure on the inlet side of your pump? Curious what it should be.

[biggy238]

Originally Posted by Vincejax

The pressure in the return line from the pump is what counts. The returned fuel is what cools the injection pump. If you are putting 100psi into the ppump and only getting 20psi out you have a lot of restriction on your return and probably not cooling enough. You should read your pressure at the return regulator, not before the injection pump.

This, something is way off (restricted) if you have 100psi that the injection pump inlet and 20 psi between the IP return and the regulator.

The regulator should determine overall pressure minus small pumping loss at the banjos and case restriction.

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[smoken02]

How much pressure would you expect to see in a return line if the feed is 100psi? Wouldn’t the fuel the engine is consuming reduce what’s getting returned?

[RacinDuallie]

Originally Posted by bateman

Vince have you ever measured pressure on the inlet side of your pump? Curious what it should be.

Feed it and regulate the return.

[jasonc]

I only measured mine pre inj pump, and set it to idle at 25psi, and would ramp up to 50psi at 4k rpm.

And I could set the bypass regulator on the return side to make the inlet side show 100psi, if I wanted to.

The return going back to the tank looks like a water hose at idle 25psi inlet pressure.

[biggy238]

Originally Posted by smoken02

How much pressure would you expect to see in a return line if the feed is 100psi? Wouldn’t the fuel the engine is consuming reduce what’s getting returned?

I would have to see exactly how your system is plumbed, but there are some fundamental hydraulics rules: pressure is the resistance to flow, pressure in the system is equal and constant in the system, and metered out is more accurately controlled than metered in.

With those things being said, the regulator needs to be the last thing the fuel passes through before the tank (excluding the hoses), and the pressure anywhere before the regulator should be the same anywhere between it and the outlet of the pump. If it's not, there is something else restricting the flow, not just your regulator.

Which hose you call the return line dictates whether or not it should have pressure. The return to tank should be as close to zero as possible. Between the IP and reg should be within 5 psi of IP inlet depending on fitting style and hose size and length in my opinion.

Yes the IP metering fuel out of the system will drop some pressure, but I wouldn't expect it to be 80psi worth.

Just an example, 15mpg of fuel is 4 gallons per hour at 60mph metered out on the IP. The transfer pump should be capable of that per minute depending on what it is. I think even a stock 12v pump is over 5 gpm


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[smoken02]

Makes sense. So you will get an accurate reading if your fuel pressure gauge is at the IP inlet and the regulator is in the return line.

[cumminsman315]

Originally Posted by smoken02

Makes sense. So you will get an accurate reading if your fuel pressure gauge is at the IP inlet and the regulator is in the return line.

That is how mine is setup and I see 100+psi on inlet side, 20psi on return line at idle. Return side gauge is just a little mechanical gauge mounted right on the regulator so not sure how accurate it is

[cumminsman315]

Originally Posted by biggy238

I would have to see exactly how your system is plumbed, but there are some fundamental hydraulics rules: pressure is the resistance to flow, pressure in the system is equal and constant in the system, and metered out is more accurately controlled than metered in.

With those things being said, the regulator needs to be the last thing the fuel passes through before the tank (excluding the hoses), and the pressure anywhere before the regulator should be the same anywhere between it and the outlet of the pump. If it's not, there is something else restricting the flow, not just your regulator.

Which hose you call the return line dictates whether or not it should have pressure. The return to tank should be as close to zero as possible. Between the IP and reg should be within 5 psi of IP inlet depending on fitting style and hose size and length in my opinion.

Yes the IP metering fuel out of the system will drop some pressure, but I wouldn't expect it to be 80psi worth.

Just an example, 15mpg of fuel is 4 gallons per hour at 60mph metered out on the IP. The transfer pump should be capable of that per minute depending on what it is. I think even a stock 12v pump is over 5 gpm

I have -8 from lift pump to injection pump, dual feed. -6 on return to regulator mounted on firewall. JIC 90 out of the pump instead of banjo style, -6 after regulator to tank. Injection pump return is separated, no longer ties in with injector return fuel.

As to the 5gpm stock pump, that would be 300gph on stock pump. Don’t see anyone ever going aftermarket if that were the case. Here’s something for you to look at Cummins Fuel Fuel System - The Cummins Lift Pump

[biggy238]

Originally Posted by cumminsman315

I have -8 from lift pump to injection pump, dual feed. -6 on return to regulator mounted on firewall. JIC 90 out of the pump instead of banjo style, -6 after regulator to tank. Injection pump return is separated, no longer ties in with injector return fuel.

As to the 5gpm stock pump, that would be 300gph on stock pump. Don’t see anyone ever going aftermarket if that were the case. Here’s something for you to look at Cummins Fuel Fuel System - The Cummins Lift Pump

Good article, although my memory of mine flowing higher nearly 20 years ago is foggy at best.

What you described for plumbing sounds like how it should be set up. I don't get the low return side pressure. Maybe the case on the IP is that restrictive. I thought that they were a bit more free flowing than that.

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[Vincejax]

Originally Posted by bateman

Vince have you ever measured pressure on the inlet side of your pump? Curious what it should be.

I regulate with an aeromotive regulator and set pressure there but i also have a sensor that I log fuel pressure with on IP dual feed distribution block after my fuel filter. Fuel pressure before IP is same pressure as after at idle, about 20psi lower after IP at WOT. I run a belt driven pump, so it bypasses more fuel as RPM rises.

[smoken02]

Originally Posted by cumminsman315

That is how mine is setup and I see 100+psi on inlet side, 20psi on return line at idle. Return side gauge is just a little mechanical gauge mounted right on the regulator so not sure how accurate it is

If the return line gauge is mounted right on the regulator then it’s probably measuring pressure on the exit side of the regulator. Not the inlet. In a gas application you have the pump then the regulator then the carburetor. A gauge mounted to the regulator tells you how much pressure you have going to the carburetor. Not how much pressure you have coming into the the regulator. This could explain the big difference in pressures between the 2 sides of your IP.

[cumminsman315]

Originally Posted by smoken02

If the return line gauge is mounted right on the regulator then it’s probably measuring pressure on the exit side of the regulator. Not the inlet. In a gas application you have the pump then the regulator then the carburetor. A gauge mounted to the regulator tells you how much pressure you have going to the carburetor. Not how much pressure you have coming into the the regulator. This could explain the big difference in pressures between the 2 sides of your IP.

I agree with you except this regulator is for efi setup and shown to be mounted after injectors with gauge port so you can set your fuel pressure. Also correct way to plumb for carb is to y or t the fuel feed with one leg to the carb and one leg to regulator/tank return

Only way to be sure would to check it with a separate gauge but I most likely never will. Been on there for 10 years and 130k mi. I did just pop the hood and look at it with truck off and lift pump running, gauge read 0 so not working at all now.

[smoken02]

Originally Posted by cumminsman315

I agree with you except this regulator is for efi setup and shown to be mounted after injectors with gauge port so you can set your fuel pressure. Also correct way to plumb for carb is to y or t the fuel feed with one leg to the carb and one leg to regulator/tank return

Only way to be sure would to check it with a separate gauge but I most likely never will. Been on there for 10 years and 130k mi. I did just pop the hood and look at it with truck off and lift pump running, gauge read 0 so not working at all now.

So are you plugging the return port on your regulator? I’ve never had a regulator that had a return port so not sure if that would hurt it.

[cumminsman315]

Originally Posted by smoken02

So are you plugging the return port on your regulator? I’ve never had a regulator that had a return port so not sure if that would hurt it.

Return port is what goes to the tank. 2 port regulator

[smoken02]

Got it.