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FASS Fuel Systems


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It has been suggested to me that I look into the Fass Air Separation System for Macks.

Has anyone any experience with these?

Their website states some great things but would like to know if anyone has actually tried one of these and would they pass on some comments.



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Pittsburgh Power has some good products, and they seem to know what they're talking about.

A good friend of mine runs a Pittsburgh Power Box on a 475 Cat and loves it, he hauls lumber from the family sawmill to upstate New York and New Jersey. He's usually over gross on weight and says it makes his W900L KW a pleasure to drive. I don't know if he has the FASS or not, but i'll ask him.

I knew another guy that rebuilt his own engine with Pittsburgh Power parts. It was a 315 Cummins originally, in a W900 daycab. He used to haul pulp wood to Covington with us. None of our company trucks with 500hp. N14s could keep up with him on the mountain. He was an excellent mechanic, I always said he could put a Cummins engine together in the dark, but I don't know if he had the FASS system either and he's no longer with us to ask.

Producer of poorly photo-chopped pictures since 1999.

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I'm actually a dealer for FASS pumps at my shop. Im going to be putting one on my E9 powered CL real soon. You really aren't going to see any fuel mileage difference or increased power on a stock engine (unless your factory lift pump is weak). Once you turn your key on its sending fuel to the motor so starting can be easier. I have only ever had one comeback for a failure and that was due to a fried electric motor and it was warrantied no problem. They make a good product and its made in the USA too!

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Unless U got a problem

me dun believe in fixn stuff th@ aint broke

If u got an unreliable fuel supply ...like pump n out of dirty drums etc

why bother

the biggest problem wiff fuel supply is a build up of water (Condensation) in tanks

best to try n keep the tanks near full n dun get in the habit of runn n on MT

n the existing fuel filters do fine AZ IZ

Q:? Have U drained off the water @ D bottom of your fuel tanks L8lee ??

there B only so much power u can get from a gallon of juice

Jist me 2 cents worth tax FREE today



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Thanks for your insight guys.

My inquiry on this product is related to the problem I have starting my E7400 Mechanical in the morning as in the tread I have also running here in "Engine and Transmission" forum called

E7 400 Mechanical - Won't start in morning without priming

The saga thickens .....................

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mate if your engine runs fine and holds prime when running but looses prime when it is turned off the problem is not in the supply of fuel to the pump the simple fact that it runs fine should tell you that

It only leaves one other spot for air to enter the return line when it syphones fuel back when not running !!

so the problem is in the return line to the tank or the tube inside the tank has a crack in it

you can put all the non return valves in the delivery line you like it wont make any difference

this do dah aint gunna fix it either you gotta fix the problem not the symptom

I can draw picture to explain whats happening if you like


ps Im not trying to be a smart ass if I am coming across that way I apologise


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We have a few FASS fuel systems here and love em. What im reading here seems a little misleading. The FASS system is not designed to replace your transfer pump. The main "goal" is to remove air from the fuel system. And to better filter it. I have one on my N14 and im here to tell you it makes a difference! I gained .06 mpg BUT more importantly the engine starts better, idles smoother, and the best part is I gained 3lbs of boost. The first yr or so I had wiring trouble with the system. Walking up to the truck I could tell if it was working or not just by sound of the engine. Ill tell ya a story that happened down in Fl 1 night. Coming up Hwy 27 From Lake Wales, Fl going to Ocala There are traffic lights. It was late at night and I was running with a WAlly world truck. He took me at 3 lights. Something was wrong cuz that aint suppose to happen!! I could tell when shifting. The engine wasn't responding as usual. Pull over fix the wiring get the FASS system working caught to Wally world around Haines city and put him in his place! You will notice a difference. Your engine will appreciate it.

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Remember if it's got a hood it's no good!

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this the way I under stand it but as always I could be wrong

First pic is with motor running as you can see the fuel comes from the tank thru the primary filter then to the lift pump the it goes to the secondary filter to the injector pump through the the motor uses what it needs whats not used goes out thru a Tee to the puff limiter and air start if fitted are supplied under pressure and the left over fuel returns to the tankscan0001_zps8l7zvwao.jpg

now when the motor is off (second pic) the fuel siphons back down to the tank and it is meant to drain back thru the lift pump and siphons the fuel up from the tank thru the return line as the return line reach's to the bottom of the tank thru a tube inside the tank

now what is most likely happening is there is a slite leak in the return system somewhere most likely thru a fuel line or perhaps thru the air start puff limiter but one thing I think for certain is it is in the return side of the fuel system

The fact it runs fine eliminates the supply side of things as all you have looked at is the supply of fuel and it all checks out it has to be the return I have learnt this by going down the same path as you it wasnt till someone explained it like this that I fixed the problem


mate I hope all this waffle helps and one thing to remember tens of thousands of these trucks run fin every day with out any fancy fuel supply system

seeya and good luck


remember its a Mack enjoy the ride

hey Dave what part of this wide brown land are you at brother ?

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Paul - Thanks for the diagrams.

The differences I have are

1. The pump is a full Bosch not an Ambac therefore there is no Puff Limiter

2. I have an air start which I put a tap on before the lubricator too eliminate any possible leaks here. It made no difference. I had this problem on a previous V8.

3. There is no tube in the tank for the return line. Fuel just goes into the tank through an elbow and splashes into the tank.

I have taken the return line off the pressure relief value on the pump overnight and placed a funnel and cup underneath - nothing was captured - I assume from this that nothing was leaking or draining back through the pressure relief valve back to the tank.

In what your saying, I don't know if it will suck back through the pressure relief value back into the pump in the opposite direction. Though this direction may need more investigation. Maybe I could put a one way valve (I have here) in that line to stop any possible sucking of air back through the pressure relief valve.

Working today the truck was stopped for 2.5 hours and it wouldn't fire without priming. It is Pissssssssssssssing me off.


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Ok Dave all I know is this is fairly standard across all diesel motors

as to taking the return line off the pressure relief valve you wont catch an fuel there because the fuel is running back down the supply line to the tank so it will be trying to suck fuel in

perhaps you could screw the return line into the bottom of the tank for a few days and see what happens or maybe remove it and put it in a bucket of fuel when you stop to see if it then starts ok you would have to remove it with the motor running

but I think that missing bit of line in the tank might hint towards a possible problem

good luck


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Paul my return on the rw doesn't have a dip tube either. I've fixed this issue before and its been either supply check valves at the filter base, hole rubbed in a fuel line or cracked dip tube in the tank. Don't know without seeing the truck but there are plenty of good guesses on this thread for sure.

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