Understanding Return Style Fuel Systems

[Flapjack]

For my twin turbo 5.4L build, I chose the Lethal Performance triple walbro return style system. I've heard nothing but good things about it, and the team at Lethal has been awesome.

My question is in regards to the actual benefits of a return style system. I thought there were two (PLEASE, correct me if I'm wrong):

- Less "lag" in response to a pressure drop
- Reduces risk of running high pressure due to route back to tank

So I've read and re-read the instructions Lethal provided and they only utilize one end of the fuel rails. I was under the impression that fuel actually flowed through the rails before going back to the tank. Am I completely wrong here?

I attached a crappy drawing (and even crappier scan) of how I understand the stock vs return style systems (as in the Lethal kit).

 

[dysan]

I believe you still have a cross-over tube between the 2 fuel rails so it would flow from one, to the other, and then back. But after looking at your drawing I guess not in that config. I'd recommend sending a message to Lito since he has a return system on his car and definately knows his stuff.

 

[Flapjack]

I believe you still have a cross-over tube between the 2 fuel rails so it would flow from one, to the other, and then back. But after looking at your drawing I guess not in that config. I'd recommend sending a message to Lito since he has a return system on his car and definately knows his stuff.

My drawing was the result of reading the instructions. I may not be understanding it correctly, but I doubt it.

 

[dysan]

After looking at some fuel rails on vendor sites most say

"Optional block-off available for return style systems."

So I'm thinking your drawing is correct. I was under the same assumption as you that the fuel would flow through the 2 rails and then back.

 

[05yellowgt]

The block off plate is for the FRPS.

 

[Flapjack]

Yes, that would be if you were using aftermarket fuel rails that originally had a provision for the FRPS, but then you switched to an return style setup.

Hey... that's me. I need a block-off plate for the Fore rails.

 

[gil_t2]

You don't want the return line to close to the injectors, it could cause pressure flux

 

[Flapjack]

You don't want the return line to close to the injectors, it could cause pressure flux

Not sure what you're getting at. But from what I've gathered, the way Lethal is instructing to install it is correct.

The whole pressure drop thing is mitigated by having more than the 40psi (full pump pressure) at the regulator, in case the pressure in the rails drop rapidly, you have a lot of differential pressure there ready to fill in... as opposed to an FPDM having signaling a pump to generate more pressure. The pressure is already there waiting.

Have I got it right?

 

[lito]

If using stock PCM why remove the FRPS?

 

[Flapjack]

If using stock PCM why remove the FRPS?

True. I was planning to run a fuel pressure gauge inside, but there are other ports on the rail I could use for that.

By any chance, is there a standard size gauge that'll read output from the FRPS?

 

[SherrodMustang]

Do you remove/block off the FRPS in the return system?

 

[Flapjack]

Do you remove/block off the FRPS in the return system?

No. Up until I started the build last weekend, I was running the stock system.

The only thing changed so far is the 105lb injectors are now installed. I'm doing most of the turbo install before I do the fuel system.

 

[SherrodMustang]

Yeah, I have the stock system currently too. But, going to the return style with the KB install. Seen the block off plate and really would just like to get rid of it if I don't need it with my fore rails. Already have 1/8 ports on the rail for pressure.

 

[lito]

Do you remove/block off the FRPS in the return system?

You can but if using an stock PCM I wouldn't.

No. Up until I started the build last weekend, I was running the stock system.

The only thing changed so far is the 105lb injectors are now installed. I'm doing most of the turbo install before I do the fuel system.

Are you using an aftermarket ECM?

 

[xxxcobraxxx]

I've never installed a Lethal Kit and seen the instructions but the first way you have it setup will work if you were supplied with a Four Port Regulator. I've talked to Fore and they recommend to run it in either configurations. The more traditional way you see it done is the fuel flows through the rails and then into the regulator and then back to the tank. I have attached two diagrams I made when doing my return system and ended up going with the fuel flowing through the rails with the regulator since its more widely used and accepted. I also left my FRPS in the fuel system so I could datalog with it and the PCM still has a way to see pressure. I would definately make sure with your tuner which way to go with the FRPS. Good luck.

 

[SherrodMustang]

What effects does it have with the stock pcm? Why sell it then, what would it be used for? Aftermarket pcm systems? They say it is marketed for return systems?

Just questions tring to understand. Thanks for the help.

 

[lito]

What effects does it have with the stock pcm? Why sell it then, what would it be used for? Aftermarket pcm systems? They say it is marketed for return systems?

Just questions tring to understand. Thanks for the help.

The stock PCM will compensate injector PW with the deltaP read at the FRPS.

If you use an aftermarket ECM you usually do not have a use for that so you can block it out. It depends on what system you would use.

 

[SherrodMustang]

The stock PCM will compensate injector PW with the deltaP read at the FRPS.

If you use an aftermarket ECM you usually do not have a use for that so you can block it out. It depends on what system you would use.

Gotcha, my system is stock pcm,return triple pump and ID1600 injectors.

So best just to leave hook-up to keep the stock computer from going crazy to adjust?

 

[Flapjack]

You can but if using an stock PCM I wouldn't.

Are you using an aftermarket ECM?

Nope. Stock PCM.

I've never installed a Lethal Kit and seen the instructions but the first way you have it setup will work if you were supplied with a Four Port Regulator. I've talked to Fore and they recommend to run it in either configurations. The more traditional way you see it done is the fuel flows through the rails and then into the regulator and then back to the tank. I have attached two diagrams I made when doing my return system and ended up going with the fuel flowing through the rails with the regulator since its more widely used and accepted. I also left my FRPS in the fuel system so I could datalog with it and the PCM still has a way to see pressure. I would definately make sure with your tuner which way to go with the FRPS. Good luck.

I like the 2nd way better. It goes along with how I understood a return style system to work and also seems to make more sense in my head. I worked for 10 years in fuel systems for the USAF. We had to design and modify a lot of fuel control valves. The 2nd method seems like it would correct a pressure drop a lot quicker.

The stock PCM will compensate injector PW with the deltaP read at the FRPS.

If you use an aftermarket ECM you usually do not have a use for that so you can block it out. It depends on what system you would use.

This is good to know. So even though the PCM will not be controlling the FPDM, there are still other functions that rely on (at least) the FRPS.

 

[lito]

Gotcha, my system is stock pcm,return triple pump and ID1600 injectors.

So best just to leave hook-up to keep the stock computer from going crazy to adjust?

With a proper tune, PCM will have nothing to do with the pump itself (even that you can still use your inertia switch for protection and FPDM to control power on priming) but will still have control of PW correction upon deltaP changes, that can save you an engine in case of an small mishap.

I like the 2nd way better. It goes along with how I understood a return style system to work and also seems to make more sense in my head. I worked for 10 years in fuel systems for the USAF. We had to design and modify a lot of fuel control valves. The 2nd method seems like it would correct a pressure drop a lot quicker.

This is good to know. So even though the PCM will not be controlling the FPDM, there are still other functions that rely on (at least) the FRPS.

I've tried both ways with different rail and different FI configs and ended with a pre-rail regulator configuration and using a single line to feed bank2 and a crossover to bank1 where the FRPS sits so the PCM will closest to the end of the line where I capped with a plug.

Response is quite similar as post regulated system, you have a lot of pressure and volume ready to fill with a triple pump, all my test where done with just two pumps and gasoline and it works great that way even with a PD blower that will sweep MAP from -10inHg to +18psi almost instantly and there are no ill consequences in deltaP, having a turbo even better.

Word of advise, one of the problems of a return system is fuel heating, I personally would not recommend it for a street car, still dealing with this myself as how to cool fuel down, have parts to test but have not found time (or will power to keep messing with the car) to do it. There is also a temp sensor in the FRPTS (as it is really named)

The deltaP correction works out as long as proper tables are used by the tuner within the calibration.