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Discussion Starter · #1 ·
Hey guys,
Love this site although I don't post much. Have an 04 and just did the blue spring kit, pressure had been bouncing between 38 WOT and 55 idle. Unfortunately forgot to put the o-ring on the plastic valve seat part (found out on this site) the first go around yesterday and had to tear everything apart again today because pressure was not holding. Nothing like speeding up the job second go around, what a PITA! Now holding at 62! Nice.

OK, so FASS into HFCM help. I have searched far and wide but have not found an answer. Backstory, I bought this truck from a friend 3 years ago. First thing was to change all the filters including ones in the fass system. After changing the filters and fluids on the truck I realized pump on the fass was not working. I found the power lead and hooked it up directly to the battery and it started working. However it was not wired to come on with the key so I just left it alone the last couple years with no issues. I actually helped him put this system on the truck way back in 2006 when we were college kids. It is the original FASS 150 system, red housing. Looking at how we plumbed it, the outlet of the FASS feeds the inlet of the HFCM. The return lines from the engine are in stock configuration, going back through the HFCM. So basically HFCM is working as it should but pulling fuel through the fass filters and pushing fuel through the stock filters. Probably not good for life of the HFCM pump, but good filtration of course.

That being said I just pulled up the manual for the new fass system and see that it completely bypasses the HFCM. I know these titanium series are better than the original pump on this truck, however IS THERE A PROBLEM WITH ME HOOKING THE FASS BACK UP THE WAY IT IS PLUMBED NOW? Is there an issue having it pump into the HFCM? Will I blow seals in it? He ran the truck like this for a long time. We lost touch and so I have not clue why the pump was disconnected? Maybe he didn't even know it has been. There are wires all over the darn place with all the crap that was added over the years. Before I call FASS wanted to hear from the pros!

Thanks!
 

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Discussion Starter · #2 ·
Bump?? I guess this must be something no one has had issues with in the past?
 

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if you do not need to beef up the fuel supply for any injectors or other specialty items i would not add the complication of the FASS

now i would wonder if it would even supply fuel pushing thru a dead HFCM
I would probably test that if it was mine and if it did not work as a back up I would remove it all together
 

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Discussion Starter · #4 ·
I was thinking the same thing. I plan on getting tunes for the X3 that came with the truck but my goal is fuel mileage so I don't plan on putting my foot into it very often. The fuel mileage is much worse than I thought a diesel truck should get. Guys with V10 are getting better mileage that me, and lets not get started on Cummins folks and their mileage.

I don't think the fass would be able to push fuel through a dead stock pump. The FASS is not also capable of producing enough pressure to run directly to the engine, at least I do not think so. Not sure if the stock pump uses gears to pump fuel like a hydraulic gear pump or some other way.

Truck works fine the way it is so I am thinking I leave well enough alone. I will just extend my stock fuel filter change intervals since fuel is going through the fass filters as well.

Thanks for the help.

Anyone else run into this issue?
 

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I was thinking the same thing. I plan on getting tunes for the X3 that came with the truck but my goal is fuel mileage so I don't plan on putting my foot into it very often. The fuel mileage is much worse than I thought a diesel truck should get. Guys with V10 are getting better mileage that me, and lets not get started on Cummins folks and their mileage.

I don't think the fass would be able to push fuel through a dead stock pump. The FASS is not also capable of producing enough pressure to run directly to the engine, at least I do not think so. Not sure if the stock pump uses gears to pump fuel like a hydraulic gear pump or some other way.

Truck works fine the way it is so I am thinking I leave well enough alone. I will just extend my stock fuel filter change intervals since fuel is going through the fass filters as well.

Thanks for the help.

Anyone else run into this issue?
I agree with ZMANN though - the OEM fuel pump is fairly reliable and is capable of supporting some reasonably strong tunes. My OEM fuel pump is fine with the Gearhead SRL+ tune. I replaced the original pump at around 200k miles - pretty good lifespan IMO.
 

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FASS seems overkill to feed the HFCM, most people do the 6.7L pump if they are wanting to go that route. My guess it would work but OP (rather previous owner) should've used a LP high volume version of the pump (like for the duramax guys) and not the high pressure 55psi one he has.
 

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Discussion Starter · #7 ·
FASS seems overkill to feed the HFCM, most people do the 6.7L pump if they are wanting to go that route. My guess it would work but OP (rather previous owner) should've used a LP high volume version of the pump (like for the duramax guys) and not the high pressure 55psi one he has.

It did work, that's how FASS instructions had us plumb the thing back in 06 if I remember correctly. You won't see that in the instructions now. Not sure if they even made a low pressure pump back then. It does not matter anyway as i am leaving it alone. Just getting mentally prepared for possible egr and oil cooler replacement after 10K miles on new replaced units shop put on for previous owner before he sold it.
 

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It did work, that's how FASS instructions had us plumb the thing back in 06 if I remember correctly. You won't see that in the instructions now. Not sure if they even made a low pressure pump back then. It does not matter anyway as i am leaving it alone. Just getting mentally prepared for possible egr and oil cooler replacement after 10K miles on new replaced units shop put on for previous owner before he sold it.
all you have to do is turn the regulator down on the fass to drop the PSI and that's probably all that was done, maybe not down to 14 psi or something "low" but probably not 55psi wide open either. If it's working keep on keeping on.
 
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