Air in fuel lines after sitting over night on 6.2

[plugugly]

suddenly, the last two nights, my sons blazer has been getting air trapped in lines wen sitting overnight. I can bleed and get it started, and it will be fine again till it sits overnight.

Anyone have similar issue that may be able to save me some time from tracing the leak down? I guess its probably worth noting the car will start and idle roughly for a few moments, before dying. Does that mean the leak may be further down the system?

 

[backwoodsman]

In my case, it was an old fuel hose that didn't leak fuel, but had become slightly porous to air. So when it sat a while, fuel would drain back toward the tank as air seeped in through the hose. New hose fixed it.

 

[PrairieDrifter]

Yep sounds like old rubber lines. Sucking air. Especially since it fires a little bit

 

[Ricko1966]

suddenly, the last two nights, my sons blazer has been getting air trapped in lines wen sitting overnight. I can bleed and get it started, and it will be fine again till it sits overnight.

Anyone have similar issue that may be able to save me some time from tracing the leak down? I guess its probably worth noting the car will start and idle roughly for a few moments, before dying. Does that mean the leak may be further down the system?

I do not know if this is applicable or not but when the VW Rabbit diesels were popular,the injector pumps would start to get weak and bleed off. We used to put a faucet cube pump by the tank so the faucet pump was the check valve and a lift pump. That arrangement outlived the cars and those little baztards would run forever. I'm going to put one on my 6.2. Doesn't need it at the moment. Just preventing problems in the future.

 

[Rickf]

Mine would do the same. When I loosened the fuel cap and parked down hill it would not loose prime. Turned out to be the "cold start" advance on the injector pump. Your results may differ.

 

[Blue Ox]

What's likely happening is an air bubble is developing because of a leak or drainback issue and it ends up at the highest point which is normally fhe fuel filter. You're starting up on fuel that is in the injection pump, then sucking ths bubble into the system which stalls it.

Needless to say, you're looking for a fuel leak. Also possibly tired check valves in the lift pump. One common spot people overlook is the fuel returns on the injectors. The injection pump has no check valves, despite what some people may tell you, so it will not prevent drainback by itself.

 

[MrMarty51]

On top of the injector pump, short 1/4” hose shaped like an upside down U.
Remove that hose and replace it with a length of 1/4” fuel rated clear plastic hose.
Start the engine and watch for air intrusion. Might appear like a white foamy substance while the engine is running.
If there is air, replace everything that is rubber between the lift fuel pump and the fuel tank.
I imagine it might still have the mechanical lift fuel pump installed.
That should fix the air intrusion.
Also, be sure that the lift pump holds pressure. Install a FP pressure gauge on the IP side of the FP, crank over the engine to build fuel pressure. The diaphragm in the pump should hold pressure. If it does not then replace that fuel pump.
Might consider going to a pre 1993 electric pump. Leroy Diesel dot com has a real nice electric pump/harness system that has a button that energizes the FP and that is mighty handy for bleeding air from the system.
Remove the mechanical pump, make a 1/4” thick plate that matches the shape of the lift pump and block off the mechanical lift pump hole in the engine.
Also, with the clear hose , it is normal to have an air bubble in the top of the U when the engine is not running.
Leave that clear hose in place, to be used for diagnostic purposes later on. Replace it every coupe of years just to be safe.
I mention that site only because none of our vendors in here has such a nice lift pump system installed.
You do want to be careful which electrical system You choose. The electronical injection pump system runs under a higher pressure than the old mechanical system so a call to Leroy might save some confusion.

 

[BKING33]

If you are still running a factory "box style" fuel filter, you could be leaking fuel from the water sensor. I just had to replace mine for that reason.
It would run rough every time I started up my Burb.

 

[plugugly]

i do have air in my clear hose that goes away once running again.

i do have the brick filter. was thinking about replacing with a spin on. trying to find more info about that.

fp is fuel pump?
ip is injection pump?

 

[Blue Ox]

If you are still running a factory "box style" fuel filter, you could be leaking fuel from the water sensor. I just had to replace mine for that reason.
It would run rough every time I started up my Burb.

Right, but it's the vacuum sensor. Just an O-ring. Easy fix.

Don't condemn the box filter itself. It's actually a fairly well thought out piece.

 

[Blue Ox]

fp is fuel pump?
ip is injection pump?

Correct.

 

[plugugly]

Right, but it's the vacuum sensor. Just an O-ring. Easy fix.

Don't condemn the box filter itself. It's actually a fairly well thought out piece.

any idea what O-rings I need? Both the bleeders on it look wet, I should probably replace those too?

 

[squaredeal91]

My 6.2 has had similar problem. Electric fuel pump on firewall. Not a good place. It started fine but on the road would randomly take off a little while cruising from air in the line and do it almost every time after sitting for a bit. A couple days ago I relocated fuel pump to the frame and it hasn't done it again yet. Some of The hoses looked bad and could have been sucking air.

in your case Odds are if it was just fine and now it's changed suddenly its probably a bad fuel hose. Make sure oil level isn't rising from a bad mechanical pump. And check return hoses on the injectors. They don't always drip but will just look and be wet.

 

[MrMarty51]

My 6.2 has had similar problem. Electric fuel pump on firewall. Not a good place. It started fine but on the road would randomly take off a little while cruising from air in the line and do it almost every time after sitting for a bit. A couple days ago I relocated fuel pump to the frame and it hasn't done it again yet. Some of The hoses looked bad and could have been sucking air.

in your case Odds are if it was just fine and now it's changed suddenly its probably a bad fuel hose. Make sure oil level isn't rising from a bad mechanical pump. And check return hoses on the injectors. They don't always drip but will just look and be wet.

The later diesel trucks had the LP (lift pump) located on the frame rail, in about the location at the back cab door or maybe back a slight bit more.
Easy to get to and to maintain (replace).
Also, the integrity of the mechanical pump can be checked by hooking a FP test gauge to the outlet hose, cranking over the engine and then observing the gauge to be sure that pressure holds for quite a long while. If the pressure does not hold then replace that fuel plump.

 

[Blue Ox]

any idea what O-rings I need? Both the bleeders on it look wet, I should probably replace those too?

There are no O-rings on the bleeders. The screws have rubber tips for sealing. I'll get you the info on the vacuum sensor O-ring and the bleeder screws when I get to work on Monday.

BTW, since the fuel filter is pressurized, if there's an issue it will usually leak fuel while the engine is running.