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Fuel return lines

Fuel pressure regulator? Holley efi uses it on the return side. Or am I thinking something different?
 
If I'm reading what you're writing correctly........I'm going to say no, that can't work.

Are you wanting to take what's being bypassed out of a regulator and dump it back into the supply line?

What is bypassed by a regulator can only flow into something at a lower pressure than what's in the bypass line.
 
The only way i see loosing a return line working is having a fuel pump control.
 
gt1guy said:
If I'm reading what you're writing correctly........I'm going to say no, that can't work.

Are you wanting to take what's being bypassed out of a regulator and dump it back into the supply line?

What is bypassed by a regulator can only flow into something at a lower pressure than what's in the bypass line.
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I totally missed his point.
 
Austin said:
… seem dumb. Is there some sort of tee, with a check valve or something, that can be added to the supply line by the block to create a smaller loop?
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You can absolutely install a pressure regulator close to the tank and avoid having to run a feed and return line all the way to the engine.

The only problem with that is that you need a pump capable of supplying and maintain fuel volume in a container that is many times the volume of the original fuel rail. Not a problem at all with modern fuel pumps. As already stated by Pb Foot, the LS1 corvettes are built this way from the factory.

This is not the best solution for high HP engines or hot engine compartments, but under 500hp N/A, I've been successful in implementing a very short return loop.
 
gt1guy said:
I was taking a wild guess at what his point actually was. You'd think the owner of the site would be better at this whole forum thing.:lmao:
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I mean ... I can draw you a picture :flipoff2:

Diesel goes from the tank, to the injection pump, to an injector and all the injectors are connected with fuel return line. Why does that have to run all the way back to the tank?

The 'use a fuel filter that has a return' got me looking all weekend on diesel filtration.
 
Austin said:
Diesel goes from the tank, to the injection pump, to an injector and all the injectors are connected with fuel return line. Why does that have to run all the way back to the tank?
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Draw a little diagram and think about what you're saying.

My previous post doesn't apply for a diesel vehicle with a mechanical pump.
 
Austin said:
I mean ... I can draw you a picture :flipoff2:

Diesel goes from the tank, to the injection pump, to an injector and all the injectors are connected with fuel return line. Why does that have to run all the way back to the tank?

The 'use a fuel filter that has a return' got me looking all weekend on diesel filtration.
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We need more info than this bull shit "line over here instead of over there" :lmao:
 
Austin said:
Diesel goes from the tank, to the injection pump, to an injector and all the injectors are connected with fuel return line. Why does that have to run all the way back to the tank?
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Generally cooling and air separation.
There is also the situation of pump volume and effectively "dead heading" the pump for no benefit other than not wanting to run the return line.
 
CarterKraft said:
We need more info than this bull shit "line over here instead of over there" :lmao:
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This diagram is from a diffrent model vehicle than my motor came from, so ignore the heat exchanger part. The mechanical fuel pump pulls right from the tank as shown by the green line.
Screenshot 2023-04-24 at 2.21.26 PM.png

I was wondering why the 3 return lines that merge to 1 (circled), can't just merge back to the supply side with a one way valve or something .....
 
I certainly wasn't thinking diesel earlier.

Are there any air bubbles in the fuel when it exits the return line? That would be one reason not to do it.

Not 100% sure on this next one but, could it cause the mechanical pump to lose it's prime by pushing fuel up stream towards the tank?
 
gt1guy said:
Are there any air bubbles in the fuel when it exits the return line? That would be one reason not to do it.
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I wouldn't think the system would intentionally cause them.

This was more of a general 'Why' question for my own curiosity. To your point of air I was looking at a FASS pump/filter and they do a good job of removing air from the fuel. So I was wondering why, if the air is filtered out already, would you dump the return back into the tank where it's going to slosh around and get more air back in it.
 
gt1guy said:
I certainly wasn't thinking diesel earlier.

Are there any air bubbles in the fuel when it exits the return line? That would be one reason not to do it.

Not 100% sure on this next one but, could it cause the mechanical pump to lose it's prime by pushing fuel up stream towards the tank?
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Yeah air has to get back to the tank. return fuel from injectors is hot and needs to shed heat at the tank as well.
 
Austin said:
I wouldn't think the system would intentionally cause them.

This was more of a general 'Why' question for my own curiosity. To your point of air I was looking at a FASS pump/filter and they do a good job of removing air from the fuel. So I was wondering why, if the air is filtered out already, would you dump the return back into the tank where it's going to slosh around and get more air back in it.
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Biggest reason I dont think it would work is because, like someone mentioned, you are deadheading the pump. Any extra fuel that isnt used, needs to go somewhere. Lets throw some numbers out here. Your pump sends 100 GPH, injectors only use 30GPH. If you have it plumbed the way you show, that extra 70 GPH is being added to the supply, with no where for the fuel to go. Its basically like hydrolocking an engine. Engine is trying to compress the water like the fuel pump is. Think about the return line as a pressure relief line, rather than a return line where the unused fuel returns to the tank, so that the full 100GPH from the pump is able to take up the volume that its needs to not over pressurize the pump.
 
Austin said:
I wouldn't think the system would intentionally cause them.

This was more of a general 'Why' question for my own curiosity. To your point of air I was looking at a FASS pump/filter and they do a good job of removing air from the fuel. So I was wondering why, if the air is filtered out already, would you dump the return back into the tank where it's going to slosh around and get more air back in it.
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It removes the air from returning it to the tank. I would think strongly about a FASS, IMO they are not the most reliable and parts are very specific to it.
 
I would not want my fuel pump potentially pulling a vacuum on my return line.
 
It has nothing to with aeration. It's about relieving the injection pump pressure. Youre around 6k psi at idle and it runs up into the 20k range under throttle. When you let out, the pressure needs to be relieved or the injector poppets would stay open because the injection pump can't dump the pressure. It dumps that fuel to the tank.

The return line is under the fuel level in the tank to prevent aeration.

You could have a fuel filter on the draw side before the lift pump where the return line terminates but, you will be pushing warm fuel into that filter. It's generally better to have a line that goes to the tank.
 
Austin said:
Tell me more .... whats a better alternative for removing air from diesel and filtering?
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The filter arrangement on the engine in the diagram you posted is doing that air separation/filtering job.
I am not a fan of a unfiltered/screened lift pump inlet as you show but the system you posted is plenty adequate.

A racor PS120 pre filter gets you a easily serviceable suction screen with clear housing for inspection.

A rear mounted electric lift pump is fine, even excellent but IMO their reliability in the aftermarket has not been stellar IMO.
We switched to a stone simple solenoid lift pump on our skid steers and it has been the biggest piece of shit we have ever seen.
We have had similar failure from the gearotor pump that replaced the solenoid pump.

This is all after having had multiple personal FASS pump failures, they just repeatedly blow the fuse.
 
There are a few things 'they say' about the mechanical lift pump on these OM617's:
  • Once rebuilt, they are good for 100k mi
  • They will supply more fuel that the engine needs
  • Their sole job is to keep 1psi at the injection pump intake
  • they are better than any electric pump

I've got bigger injectors, bigger turbo and a modified performance injection pump. How can that that same lift supply enough fuel from the same cam setup as stock?

Going electric means adding more shit to the system, but ...
  • With the modified pump, the lift primer does not work. I'm sure I could figure a way to rig it.
  • If that primer worked, it's in a super PIA spot to reach once the cab is sitting back around the motor.
  • People with electric pumps don't need to prime their and they say they run a lot smoother

I feel like the small factory filter is 70s tech which Is why I'm leaning towards FASS for better air removal and filtering. CarterKraft that pre-filter is awesome if using the existing setup, but I want to replace that stock mount/filter completely. Are there better options as far as a stand alone filter and stand alone air separator?

gt1guy said:
You'd think the owner of the site would be better at this whole forum thing.:lmao:
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So .. I've taken my general Tuesday question asked on a Saturday and changed course to talk about my setup specifically .....See I know how forums work :flipoff2:
 
Austin said:
There are a few things 'they say' about the mechanical lift pump on these OM617's:
  • Once rebuilt, they are good for 100k mi
  • They will supply more fuel that the engine needs
  • Their sole job is to keep 1psi at the injection pump intake
  • they are better than any electric pump

I've got bigger injectors, bigger turbo and a modified performance injection pump. How can that that same lift supply enough fuel from the same cam setup as stock?

Going electric means adding more shit to the system, but ...
  • With the modified pump, the lift primer does not work. I'm sure I could figure a way to rig it.
  • If that primer worked, it's in a super PIA spot to reach once the cab is sitting back around the motor.
  • People with electric pumps don't need to prime their and they say they run a lot smoother

I feel like the small factory filter is 70s tech which Is why I'm leaning towards FASS for better air removal and filtering. CarterKraft that pre-filter is awesome if using the existing setup, but I want to replace that stock mount/filter completely. Are there better options as far as a stand alone filter and stand alone air separator?


So .. I've taken my general Tuesday question asked on a Saturday and changed course to talk about my setup specifically .....See I know how forums work :flipoff2:
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Is this 12v or 24v system?
 
I'd probably just get a $20-120 12v diesel fuel pump to put near the tank, like a 3-5psi job, to feed the mechanical lift pump

Before installing it, make sure you can blow thru the inlet/ suck the outlet, then throw a $20 spare in the toolbag


And run your return to tank
 
Projectjunkie said:
I'd probably just get a $20-120 12v diesel fuel pump to put near the tank, like a 3-5psi job, to feed the mechanical lift pump
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You think the mechanical lifts are superior? I don't know much about diesel fuel injection pumps, so I'm wondering how the upgraded 7.5mm elements are supplied enough fuel from the same cam driven mechanical pump as stock. Are they just pumping a overkill amount that the larger elements are not affected?

One of the biggest advantages of an electric I see (aside from my unique situation where I need to save the space of the mechanical pump) is the fuel filtering before hitting the lift. The stock setup has the filter after the lift.
 
500 hp is around 30 ish gallons per hour.
I'm sure we could figure out the pumps flow if we knew what it was.
 
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