Is the mechanical fuel pump on the 6.9 capable of sucking through a dual filter setup?

[David Pratt]

The fuel system I had designed for my IDI build plans to use a dual-stage remote mounted filter housing on the frame rail, holding a primary and secondary filter/water separator, bypassing the stock filter/separator between the mechanical pump and injection pump with a hard line.

Does anyone know if the stock mechanical fuel pump is capable of sufficiently sucking through two filters between the tank and itself? The assembly/filters are shown in the attached photo.

The idea is to have a 3/8" pickup tube feeding a -8AN line going, a remote mounted dual-stage filter assembly, then back to -8AN line to the mechanical fuel pump on the engine block.

If needed, I can redesign the system, throw in an electric pump, or order different parts. I figured I'd ask the brain trust here on the forums for some insight before doing so though.

 

[Nero]

I can confirm that I have a fairly large filter on my rail between selector valve and lift pump and my truck runs just fine. As for two, it probably would run fine, but if you start getting high inlet restriction the mechanical pump may struggle.

 

[Clb]

Not a professional but, fluid dynamics (the way stuff flows) says the most restriction free path to the pump is going to give the best performance , but we've got some pretty good guys here.
Wait for it...

 

[The_Josh_Bear]

Clean diesel and clean filters will run just fine. It's the super cold temps or #2 in cold temps or WMO mix you need to worry about. What's the micron rating of the fuel filter? 2 micron will flow. It'll also make any of the above worse.

 

[David Pratt]

Clean diesel and clean filters will run just fine. It's the super cold temps or #2 in cold temps or WMO mix you need to worry about. What's the micron rating of the fuel filter? 2 micron will flow. It'll also make any of the above worse.

The CAT 1R-0749 filter is a 2 micron filter and rated high efficiency. The fuel/water separator I'll run is a CAT 256-8753, also rated as Advanced High Efficiency.

One other concern I had was fuel temp...as the stock top hat mount for the OEM filter between the lift pump and injection pump has a fuel heater and sensor built into it. Currently with my design I'm losing both of those in this setup. I live in Texas, so typically we have warmer weather but I do visit family in Colorado occasionally.

 

[sjwelds]

You won't need the fuel heater. Many of us, myself included, have deleted it with no ill effects.

 

[Booyah45828]

That's a tall filter setup, where are you going to mount that? Can you run the 2 micron after the lift pump? It might take some extra line, but that's how I would do it. I run the bus through a 30 micron racor primary filter/water seperator, then through the stock mechanical lift pump, and then through a 6 micron secondary filter and into the injection pump.

I've read elsewhere that water separators work best under a vacuum. So I would run that before the lift pump. Then run through the lift pump, and then into the 2 micron secondary filter, and then into the injection pump. That way your biggest restriction is after the pump and under pressure so you won't have trouble trying to suck through it. Plus, it's good practice to have a filter as the final thing the fuel passes through to get to the injection pump.

So long as the fuel is pump diesel, you likely won't have an issue this way. Run wmo/wvo, gelled fuel, or something else thick and you'll starve even the best pump setups.

 

[Booyah45828]

Oh, and that filter head, is that the derale dual filter mount? That's used to run 2 filters parallel to one another. I don't think you can use that to run 2 filters in series, like you would with a primary filter/water separator and a secondary filter.

 

[Booyah45828]

Yeah, I'm almost positive that's the derale parallel filter unit you have pictured. If so, those filters paralleled like that is not what you want.

 

[David Pratt]

That's a tall filter setup, where are you going to mount that? Can you run the 2 micron after the lift pump? It might take some extra line, but that's how I would do it. I run the bus through a 30 micron racor primary filter/water seperator, then through the stock mechanical lift pump, and then through a 6 micron secondary filter and into the injection pump.

I've read elsewhere that water separators work best under a vacuum. So I would run that before the lift pump. Then run through the lift pump, and then into the 2 micron secondary filter, and then into the injection pump. That way your biggest restriction is after the pump and under pressure so you won't have trouble trying to suck through it. Plus, it's good practice to have a filter as the final thing the fuel passes through to get to the injection pump.

So long as the fuel is pump diesel, you likely won't have an issue this way. Run wmo/wvo, gelled fuel, or something else thick and you'll starve even the best pump setups.

It is tall, but this isn't a stock setup.

I've swapped a 6.9 idi into a Scout II and I planned to mount this setup on my frame rail in under the cab. Two main reasons, 1) clean the fuel before before it gets to any mechanical/moving pieces to save them and 2) the top mounted filter/separator is too tall to fit under my hood without a body lift.

I've never heard that bit about separators working better under suction, do you have a source for that?

I do like your suggested philosophy of ensuring the final thing before the injection pump be a filter. I may need to reconsider my plan.

 

[David Pratt]

Oh, and that filter head, is that the derale dual filter mount? That's used to run 2 filters parallel to one another. I don't think you can use that to run 2 filters in series, like you would with a primary filter/water separator and a secondary filter.

It isn't the parallel one, also known as a single-stage. This one is machined as a dual-stage, forcing the fuel in/out one before the other.

 

[Kevin 007]

It is tall, but this isn't a stock setup.

I've swapped a 6.9 idi into a Scout II and I planned to mount this setup on my frame rail in under the cab. Two main reasons, 1) clean the fuel before before it gets to any mechanical/moving pieces to save them and 2) the top mounted filter/separator is too tall to fit under my hood without a body lift.

I've never heard that bit about separators working better under suction, do you have a source for that?

I do like your suggested philosophy of ensuring the final thing before the injection pump be a filter. I may need to reconsider my plan.

I don't have a source for that, but it is the consensus on them. Some manufactures of filters who have detailed installation instructions, also state that the primary/water separator filter must be installed on the suction side

 

[The_Josh_Bear]

I've swapped a 6.9 idi into a Scout II

Pics or it didn't happen!

 

[Old Goat]

I don't have a source for that, but it is the consensus on them. Some manufactures of filters who have detailed installation instructions, also state that the primary/water separator filter must be installed on the suction side

Correct. Did some researching and found this on a set of instructions from Racor.
Should be between the Fuel Tank and Lift Pump to work correctly.

https://www.parker.com/content/dam/Parker-com/Literature/Racor/Tech_Install/15332_500FG_Turbine_Series.pdf

Goat

 

[Booyah45828]

It isn't the parallel one, also known as a single-stage. This one is machined as a dual-stage, forcing the fuel in/out one before the other.

Okay, no issues with it then.

You can try it. But I'd have the factory vacuum sensor some where in the system so you will know it's not keeping up. 2 micron is a pretty tight filter to pull through.