Engine/Transmission (1994 - 1998) Fass on a 12V

[zstroken]

who has used a Fass on a 12V?? How did you do the return lines off of the injectors?? Does the stock mechanical liftpump have a return line? Thanks

 

[Kawi600]

Are you replacing the stock lift pump with the FASS or are you using it as a pusher pump?

Id leave the return lines alone. If you are bypassing the stock pump you may want to make sure its removed or that it has something to pump, I dont think it can be run dry.

If youre having fuel pressure problems Id look at the overflow valve and replacing the stock pump first.

 

[Joe G.]

Why? The stock lift pump really moves fuel. If you are having problems with the stock system it is usually pretty cheap to fix, but may be hard to find.

 

[zstroken]

No problems with the stock lift pump, just want the ability to push more fuel, plus it is a good safety feature for a fuel shut off

 

[Joe G.]

Joe Donnelly made 800 HP on the stock lift pump. You need more than that?

 

[zstroken]

As people have mentioned, a dyno run is for probably 3 -5 secs. Truck pulling a run typically lasts 20 secs or so. I would also like to get rid of the tiny banjos on the pump.

 

[bmoeller]

No need to mess with the fuel return lines. it goes back to the filter, then is T'd off of that.



Just replace the fuel supply lines have AN fittings, to get rid of the banjos. Won't be enough room between the pump and block, for the return. Also, will still need to keep the overflow valve anyways. That thing has smaller holes than the supply side.



Do you have a fuel pressure gauge? If not, I'd get one. It doubt itis an issue anyhow.

 

[Joe G.]

Will the FASS keep up with the stock 12 valve lift pump? It might end up being a restriction. The stock system pumps way more than you can burn in the P7100 pump. Try it with a hose directly from a bucket of fuel into the pump and see how fast it empties it. Most of the fuel pumped by the stock lift pump returns to the tank.

 

[zstroken]

I imagine the FASS will keep up. 2. 5GPM is plenty. Considering a hot (like scheid truck) fuel set up a year or so ago was good for 5GPM. I am going to say a FASS unit will out pump the stock lift pump. Pumping into a bucket is pretty much zero head pressure. Anybody able to produce specs for the stock pump? It is also RPM dependent. I just feel the FASS is a better setup for my application, more filtering capacity, no pressure spikes, etc, etc. If the stock system pumps so much then why are so many of the big HP guys replacing them??

 

[Joe G.]

The example was pumping FROM a bucket through the whole fuel system, ie. the line from the tank was suspected so this was a test to see how it worked if a bucket was used instead of the tank. It was connected to the supply line hose before the fuel heater. So it had to overcome the overflow valve so there was plenty of pressure needed to flow a lot of fuel.



I have no idea why the big HP guys are replaceing them. Do you know the GPM of a stock lift pump? That might be something you would want to know before doing anything.



The service manual gives flow test for cranking speed (200 to 400 RPM). It does not say was the expected flow is at competition speed. It does, however, say that fuel flow increases with RPM. That sounds like what you want for competition.

 

[zstroken]

And we still have neglected one of the other reasons for this

plus it is a good safety feature for a fuel shut off

I just don't see anyway possible the stock lift pump can pump as much as a FASS 150. If not the pump the stock filter housing will restrict it.

 

[BPonci]

I run a full fass system and dumped the stock lift pump. I ran new line from the o/f valve and i teed in the injector returns and dump them back to the tank. I run around 42 to 45 psi and it seems to keep up way better than my oem pump and o/f valve shimmed to 52 psi.

 

[Joe G.]

Thanks Brad for the information based on experiments.

 

[bmoeller]

And we still have neglected one of the other reasons for this

plus it is a good safety feature for a fuel shut off

I'd rather kill the juice to the shutdown solenoid than run the pump dry. Maybe wire the solenoid and FASS pump together, so it will kill both.