air in fuel system

babbler · #1 (**permalink**) 11-01-2009, 09:03 PM

i have a 1990 7.3 and starts up and dies and then you have to crank it and then she will fire up, but even when its warm it can be hard to start? so where is the best place to start looking for air leaks in the fuel sysstem? any pictures or diagrams would be great!!! the motor onec running will run fine and then once in a while spit and sputter and if you rev it up it will come out of it, and when you drive it down the road it will surge once and awhile? thanks

rupejosh · #2 (**permalink**) 11-01-2009, 09:07 PM

im gonna have to say fuel filter.you might try a new filter and filling it with diesel kleen to clean up the ip and injectors

babbler · #3 (**permalink**) 11-01-2009, 10:12 PM

thanks i will try a new one, whats the line coming out of the bottom of the fuel filter?

JHoffman93 · #4 (**permalink**) 11-01-2009, 10:16 PM

It is a water drain.

joe f350 · #5 (**permalink**) 11-01-2009, 10:25 PM

what i do is unhook the fuel line at the lift pump hook it up to a fuel can that will tell u if the air leak is at the motor or in the hose or at the tanks

stangfas · #6 (**permalink**) 11-02-2009, 04:52 PM

You just described the same exact problem I'm having with my 92idi. I tried doing the filter change along with diesel 911 in the filter as well as sea foam in the tank. No luck though. So, I'm leaning towards an air leak. The only think I can think right now is that I removed the rear tank due to it was leaking and I didn't plug the lines. If you come up with a solution, please share.

babbler · #7 (**permalink**) 11-02-2009, 09:24 PM

okay heres the deal i changed the filter and and added diesel clean, still does it a lil bit and i forgot to add doesn't stat very well when warmed up? never had that problem before , i did notice that after i shut it off i had no pressure at the schrader valve on top of fuel filter? when i rev it up a lil bit it and let it fall back to idle it will kill?

FORDF250HDXLT · #8 (**permalink**) 11-02-2009, 11:08 PM

sounds like the lift pump might be getting worn out.
how many miles on the engine,and has the mechanical lift pump ever been changed?
(fuel pump bolted to engine under the fuel filter)
these luckily are only 40 bucks or so.

vacuum test the fuel pump.
remove the fuel line from the pump that goes back to the tank and plug it so nothing gets in.
hook a short tube to the pump with a vacuum gauge on it.
start the motor and read your gauge.
if you have less than 12 inches HG then you need a new pump.
don't worry,these are only $40 or so.unlike the ip pump.

if you dont have a vacuum gauge,you can just remove the line that goes to the filter and see if it pumps into a bucket with good flow.not the best way,but if its real bad,and hardly flowing,you would know for sure that she's tired.
but be sure to check for leaks on both sides of the line connected to the lift pump first.dont get hurt around that fan!!!!

if it does test bad.now is a good time to bring the fuel system up to speed a little bit.research electric fuel pump conversion.
switching to electric would eliminate a lot of hard starting problems.the electric pump would push,not suck,from the tanks(well very close to them)up to the fuel filter.this means,air leaks from tanks to fuel filter are no more problem-ever!
and free up a small amount of power as well.all extra power is good.

babbler · #9 (**permalink**) 11-03-2009, 01:17 AM

update just came in from working the truck and found the fuel in to the lift pump had a good size crack in it and was leaking fuel, starts a heck of alot better, thanks for all the advice,the electric pumps sounds like a good idea, i seen them on older tractors and work really well.