[erik49051]

How does air get into the fuel system? I thinking someware between the fuel tank and filter. After the filter if there was a leak wouldnt fuel leak out not air in?

Thanks,

 

[chuckster57]

There are a number of places air can get into the fuel system on the IDI. Most often air is allowed into the system after you shut down. The return system has "O" rings and the plastic caps can get distorted over time. When you shut the engine off, if there is any breach in the itegrity of the return system, fuel will "drain back" into the tank and the void will be filled with air. Air can GET IN WHERE FUEL CAN'T get out. Another spot for this is the supply line from the filter header to the back of the IP. Fuel will drain onto the valley pan and you might not see it, and once again the void is filled with air.

While your running, air can be sucked into the fuel system from a failed "O" ring on the tank connection or the selector valve. In rare cases the flex line from the frame to the inlet side of the lift pump can get cracked.

 

[erik49051]

I have a rough idle, if a leak is comming from "While your running, air can be sucked into the fuel system from a failed "O" ring on the tank connection or the selector valve", would this be visible in a clear line running from the return rail up to the filter head?

Thanks

 

[chuckster57]

I have a rough idle, if a leak is comming from "While your running, air can be sucked into the fuel system from a failed "O" ring on the tank connection or the selector valve", would this be visible in a clear line running from the return rail up to the filter head?

Thanks

The clear line test will positivley identify air in the system. If you make a loop, then yeah you can tell which direction it's coming from. I don't have the specifics handy but I know it's been posted a few times under "clear line test".

 

[erik49051]

great, I read though the post for clear line test but wasn't clear wether it would indicate where the air is comming from.

Thanks for the help!

 

[tmracing]

hey guys I have a 93 7.3 idi 4x4 truck with an auto trans. 152k I just bought this truck and i like it, it has enough power for what i want it to do!

the prob.. the truck runs great! but every morning i have to purg air out of the srader valve on top of the fuel filter. after it cracks for about 5 to 10 sec's it will push fuel out.
then i crank it on the floor it starts and has a rough idle or a short min. i know that the air is making the prob but where is it coming from!!

 

[drinkypoo]

http://www.thedieselstop.com/forums/f30/clear-line-test-but-where-air-coming-292428/
Ford diesel 6.9 7.3 IDI (from thread http://www.thedieselstop.com/forums/f30/hard-starting-283547/)

 

[SteveBdogs]

fuel drain back problem

I need help.
I have a 1989 Ford 1 ton with a 7.3 liter diesel, 180,000 miles runs perfect. Now the problem, for some reason when the truck has been shut off for 10 or more hours the fuel has drained back to the tank. I’ve changed all lines between injectors with a new kit, new fuel pump and it still seems to be getting air back into the system to let it drain.
Forgot to add that it has 2 tanks so could the selector valve be my problem?
Thanks for your help.

 

[leyrret]

If the truck runs fine otherwise it's likely bleeding in through the filter head. Try removing bleed line on filter head and plug fitting. No need to plug hose. The next morning remove plug and replace hose. If it starts and runs ok installing a cheap vacuum check valve in the hose shouldl eliminate the problem.

 

[SteveBdogs]

Fuel draining back to tank

Found the problem, it was the continuous vent with check valve located on the filter head. Starts right up with no problems and it runs great.
Thanks for your help.
Steve

 

[mjacks]

I have found a couple times on different trucks that when the was shut off and the next time you when to start up and engine ran like it had got air into the system, I have found that the air bleed off on top of filter housing was the culprit. Put a good metal cap with an o-ring on valve and problem solved(use to get them from tire store or a good bicycle)