please explain how

[genchowford]

Please explain how air in the return line can affect the running of the engine. Not trying to be arguemenative but really need to understand this. My 7.3 is starting hard and this may be the problem according to all the posts but just cant get a grip on it.
thanks

 

[icanfixall]

The fuel system needs to be air tight. Any air getting in displaces the fuel. Then you have a hard starting motor or a ruff running motor. When the injection pump runs dry or gets an air pocket it advances the timing and you get a feeling of unheard of horse power... For just a second... Then the motor dies. Getting all the air out is most of the time very hard to do. Some guys don't have any issues at all when they run out of fuel. They run the electric pump and purge out most of the air but... Getting the air out of the high pressure side of the injection pump can be tuff. Its supposed to get pushed out thru the injector return lines and into the precups on the motor... Sometimes it doesn't do that exactly like its designed to do. so any air in the system is displacing the fuel. Thats the long and short of it...

 

[typ4]

I think what he wants to here is the part about the fuel bleeding out of the filter when air can get in then it is hard to start.
Gary I know you and I are technical but sometime KISS works

 

[icanfixall]

Yeap... Thats me... Long winded with lots to say... I'm so lonely.. I just gotta talk to someone.....

 

[genchowford]

Have electric fuel pump and did bleed the schrader valve----had no air. Hey maybe need to bleed each individual injector?

 

[91ford7.3td1in]

i bled my injectors my loosining all 8 then starting the motor and then tighten oll of them while its running helped me to do it engine ran perfect after to.

 

[MIDNIGHT RIDER]

Air in the return-line system should have absolutely zero effect on the running of the engine.

The catch is, How and where is the air in the return-line coming from; that air could be coming from air that has become trapped in the high pressure side of things.

For all practical purposes, you should be able to clip off the return-lines and let it pour out on the ground with no effect on the running of the engine.

The fuel in the return system is merely finding it's way back into the fuel-tank; it cares not if it is full of air or not.








And, for what it's worth, I NEVER EVER did anything special to "bleed" my old 6.9; all I ever did was crank the engine until it started and let it "bleed" itself.

If you have to do anything different, then your system probably has an issue going on that should be addressed.

 

[typ4]

Running, correct. Hard starting wil be caused by air in the filter, I guess the question is does it clear up after start, if not then there is a leak on the suction side and let me tell you it only takes a tiny intrusion, I had a fuel filter that would not leak but it would let air in the pump side. Took a while to find that one, never assume a new part is perfect.

 

[h2odrx]

Yeap... Thats me... Long winded with lots to say... I'm so lonely.. I just gotta talk to someone.....

Lonely? chat is open?

Running, correct. Hard starting wil be caused by air in the filter, I guess the question is does it clear up after start, if not then there is a leak on the suction side and let me tell you it only takes a tiny intrusion, I had a fuel filter that would not leak but it would let air in the pump side. Took a while to find that one, never assume a new part is perfect.

Been there too, my line was loose at the pump it would start then die...

I've got a few questions for ya...
How old are the return caps and lines? how much fuel is in the tanks?

 

[SHIP4BRAINS]

Question about the return line plumbing...it appears there is a return that goes to the tank, and to the filterhead...true?

 

[Dsl_Dog_Treat]

Question about the return line plumbing...it appears there is a return that goes to the tank, and to the filterhead...true?

Correct. Fuel is retuned to the filter and recycled. Any excesfuel s is then retuned to the tank and varries as the demand changes.

 

[RLDSL]

in simplest terms, air rises to the top of a liquid. There is a line in the return sysem that goes back to the filter and one to the top of the injection pump housing . aif there are no leaks anywhere the liquid is held in place in the lines by the existing vacuum you get from a sealed system ( think dip a straw into a soda with your finger over the top and pull it out, the liquid comes with it, take the finger off, i.e. create an air leak, and the liquid all drains out )
So long as there are no leak points, the fuel stays in the system, but if there is a leak anywhere, the fuel drains out, and when this happens , then physics kicks in again and creates a siphon effect and also draws fuel out of some vital areas of the pump and filter and injectors causing the primary side of the injectors to loose prime and making it difficult to start

 

[mcbg]

Question about the return line plumbing...it appears there is a return that goes to the tank, and to the filterhead...true?

I plugged the line at the filter and ran the return from the injector to a tee in the 3/8 return line.
I was looking at this and it just looked like it would recirculate air.
Its been this way for a couple hundred miles no problems.

 

[MIDNIGHT RIDER]

I plugged the line at the filter and ran the return from the injector to a tee in the 3/8 return line.
I was looking at this and it just looked like it would recirculate air.
Its been this way for a couple hundred miles no problems.

I never did see the wisdom of that return line to the filter.

 

[RLDSL]

I never did see the wisdom of that return line to the filter.

No real wisdom to it. Some systems have that to assist in returning fuel that has been heated back through the system to keep the filter and pump from gelling up when there are no additives in the fuel.
A lot of the veggie kit folks suggest this on systems that never came with the loop from the factory.
Personally, I think it's just a bad idea because it's just a place for an air bubble to set in to a high spot and be a bear to bleed off because it doesn't want to be forced out to the tank since there's a loop.