Engine/Transmission (1994 - 1998) stock transfer pump limit? switch to FASS?

[AMendes]

heavy loads injection pump seems to wimper out, pulling and racing, wont tack out. im thinking it is not getting enough fuel, psi stays around 20 at filter, but who knows what the gpm's are? i just dont trust those 1/4" stock fuel lines. thinking about the FASS, i love it on my 24v. or maybe just replace stock lines with 1/2" just thinking out loud. thanks brothers

 

[tp0d]

First, Welcome to the TDR! Good to have ya!



If you only have 20psi at the inj pump, you may have an overflow valve problem. Try stretching the spring for a temp fix, you should only have 20psi at idle, to a max of 50-60psi at high rpms. You can pinch the return line partially for a test.



The fuel lines are 3/8" ID supply, 5/16" return for 96+ 94/95's are both 5/16" i believe... . If you still have flow issues, you could have a partially clogged pickup in the tank.



As for the fass, you would need the newest high pressure, high flow fass, i`m unsure of the model, but you want the highest pressure model they have to bypass the lift pump... How many miles are on the lift pump? Over 150k, you probably have leakage thru the check valves, lowering pressure. .



good luck



-j

 

[Joe G.]

I seriously doubt that the lift pump is the problem. As far as miles are concerned 150K is nothing. Mine has 243K on it. There are milliion mile trucks on the road that still have the original lift pump. My idle fuel pressure is in the mid 30s. Running on the road pressure pegs my 40 PSI gauge. If you have low pressure and it runs ok otherwise then you probably need a new overflow valve. If you have a starting problem them look for an air leak.



One thing to remember is that with a mechanical lift pump fuel flow increases with engine speed. With an electrical lift pump fuel flow does NOT increase with engine speed.

 

[AMendes]

great info thanks, shes got 255k miles, did some hot laps up and down the road today, psi drops to 12 from launch to 3rd gear then goes back up to 18 but never over 25 even just cruising. i did not realize the psi needed to be that high, my 24v would have a harder time starting with any thing over 20 psi.

i wont to put a separte suction pipe into the tank with larger fuel lines, know of anybody with a tank kit. thanks again

 

[tp0d]

Only tank refits i've seen are for 24v's... Probably because the lift pump doesnt have enough arse to move that much fuel. . The mechanical lift pump can really move some fuel. . i could be wrong tho, theres probably something for the 12v.



I bet its your overflow valve. Take out the spring and stretch it to about . 55" (. 5 is typical). I bet you`ll see better numbers then. If you dont know that its been replaced, its probably a good time to do it. Also. . what is the condition of your rubber fuel lines? If you are sucking in air at all, your pressure will go to crap. Might want to swap in a new fuel filter just to be sure also.



good luck



-j

 

[Joe G.]

AMendes,



What year is your truck?



Nothing you know about your 24 valve fuel system applies to a 12 valve except the fuel tank module. From what I have read on here about the in tank lift pump mod for a 24 valve you don't want it. If you would like a write up about the 12 valve fuel supply system , how it works and how to fix it e-mail me at -- email address removed -- and I'll send it to you.



The overflow valve controls fuel pressure. If the spring gets tired (common problem), fuel pressure is low. There is still plenty of fuel flow in that situation because of how the fuel system works. If the overflow valve is weak the fuel just goes through the injection pump to the return line to the tank with little restriction. When my overflow finally gave it up I had 6 PSI. It still ran ok, but would not start when I got it home.

 

[AMendes]

thanks for all the help. wish i found this sight years ago, you guys are great

fuels lines are OK prob should replace them, but no visual cracks or hard spots

just changed the filter with last oil change

that fuel tank module is what i am afraid of, i had to gut it out on the 24v cuz it sucked air, im thinking this might be doing the same, thats why im looking for a new siphone systom to install when i drop the tank out

you guys think i will be wasting time/$ if i change out stock lines with 1/2 hose from tank to filter

and also both my 12v fuel guages only work when they feel like it, is it common for them to devlope dead stots in the sending unit, or something else i havent heard about, or just my luck

 

[Joe G.]

fuels lines are OK prob should replace them, but no visual cracks or hard spots

You CAN'T see an air leak! The fuel hoses can be completely shot and still look good. The supply line hose is in the suction side of the fuel system. If it leaks there will be no sign of fuel. The stock hoses generally leak from the ends instead of the sides.