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Air in Fuel System Causing Stalling

Woody35

Woody35

Active Member
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Location
Chi-Town Suburbs
So my truck has been stalling. When it first happened I thought I had a plugged fuel filter so I installed a new one and it started right up after I bled the system. Went to drive it again and it stalled on me again. Bled the fuel system and it started right up. Next time I started the truck I let it idle for 15 mins because I was wondering if I had not fully bled the fuel system all the way. It never died and I took it on a 40 min drive but it did have some weird cutting out problems at higher rpms while downshifting that I got a video of.

[video=youtube;wqbZo71RxRE]http://www.youtube.com/watch?v=wqbZo71RxRE[/video]

Went to start the truck again and it died again while idling. Bled the fuel system and it started right up and kept going till the next time I wanted to drive it after shutting the truck down. It also has a weird loping/missing idle that occasionally has occurred in the last 8 months. I don't know if my present problem is connected with it but I took a video of it. most of the loping is in the beginning of the video. Black smoke also comes out when it does this.

Whenever I bleed the fuel system a lot of air comes out. I cant see any obvious fuel leaks in the lines and I took the truck down and up hills so I don't think its sucking air through the sending unit in the tank. I did read a post by WarWagon that said that when his tank sock clogged it caused his lift pump to lose prime and stall the engine. Do you guys think that is a possibility here? Any ideas on the loping/missing? Thanks for the help guys.
 
I guess you can only have one video per post so here is the missing/loping video I was talking about

[video=youtube;Iovdu-Dxsfo]http://www.youtube.com/watch?v=Iovdu-Dxsfo[/video]
 
also have you put a clear line on the return line coming out of the IP? check of fuel pressure would be good too
 
Where are you bleeding the fuel system from, Woody? If you're getting air in the system between the tank and the IP, you need to find that one first, and there are lots of places...
 
I use a fuel o vac gauge to test my fuel system. It occurred to me watching the gauge go full vacuum that is was forcing air leaks or boiling the diesel in the fuel line. This happened while the strainer in the lift pump plugged solid. 0 PSI on most gauges that don't read a vacuum do not tell the full story - is it really 0 PSI or is it a full vacuum? We have to stop thinking like the carburetor gas setups and tak into account the transfer pump in the IP that is capable of boiling diesel in a full vacuum. Aka vapor lock. :rolleyes5: Carbs do not have this so 0 PSI is it - there is no vacuum potential in a gas fuel line.

I put a clear line on the IP return and it would go clear when the kinked line ran me out of fuel.

I would check the fuel lines before the FFM for kinks or going soft and failing/plugging internally. O rings before lift pump is suspect. Tank pickup at top for rust pinholes. Plugged sock... Plugged fuel cap vent.

Then if you have to drop the tank, I am sick of doing this myself, I recommend the following:
Remove the tank sock and do not re-install.
Get a new fuel level sensor from Leroy diesel. These are bomb proof and will work in corrosive wet slime that bad biodiesel turns into. Factory sensors simply quit.
Use a external filter water separator before the lift pump or a new lift pump like a Walbro that has a strainer/screen in it. I use a Cat water filter pre-lift pump on my 1995 and it saved the IP and injectors from wet buggy fuel. The 1993 didn't have that and I replaced both IP and Injectors...

Any restriction pre lift pump can cause it to loose prime as the diesel boils in the line. Mainly from the positive displacement rotary vane transfer pump in the IP.
 
JiFaire said:
Where are you bleeding the fuel system from, Woody? If you're getting air in the system between the tank and the IP, you need to find that one first, and there are lots of places...
Click to expand...

At the top of the FFM while the lp runs and while cranking. I think my best bet is to replace all the fuel lines because the truck has been in the rust belt its entire life.

ak diesel driver said:
have you tried a spare pmd?
Click to expand...

No im at college 1000 miles away and thats the one thing for my truck I forgot.

ak diesel driver said:
also have you put a clear line on the return line coming out of the IP? check of fuel pressure would be good too
Click to expand...

I gotta go to one of my buddys house to do that. Would be kinda hard in the parking lot my truck is located now. I read somewhere that possible air leak at the ip would cause the loping/missing so I am going to investigate that. I wonder if I have more than one leak?

WarWagon said:
I use a fuel o vac gauge to test my fuel system. It occurred to me watching the gauge go full vacuum that is was forcing air leaks or boiling the diesel in the fuel line. This happened while the strainer in the lift pump plugged solid. 0 PSI on most gauges that don't read a vacuum do not tell the full story - is it really 0 PSI or is it a full vacuum? We have to stop thinking like the carburetor gas setups and tak into account the transfer pump in the IP that is capable of boiling diesel in a full vacuum. Aka vapor lock. :rolleyes5: Carbs do not have this so 0 PSI is it - there is no vacuum potential in a gas fuel line.

I put a clear line on the IP return and it would go clear when the kinked line ran me out of fuel.

I would check the fuel lines before the FFM for kinks or going soft and failing/plugging internally. O rings before lift pump is suspect. Tank pickup at top for rust pinholes. Plugged sock... Plugged fuel cap vent.

Then if you have to drop the tank, I am sick of doing this myself, I recommend the following:
Remove the tank sock and do not re-install.
Get a new fuel level sensor from Leroy diesel. These are bomb proof and will work in corrosive wet slime that bad biodiesel turns into. Factory sensors simply quit.
Use a external filter water separator before the lift pump or a new lift pump like a Walbro that has a strainer/screen in it. I use a Cat water filter pre-lift pump on my 1995 and it saved the IP and injectors from wet buggy fuel. The 1993 didn't have that and I replaced both IP and Injectors...

Any restriction pre lift pump can cause it to loose prime as the diesel boils in the line. Mainly from the positive displacement rotary vane transfer pump in the IP.
Click to expand...

Thanks for the info and suggestions
 
I've been chasing gremlins like that for about a year now. Problem is, I can't afford to just toss parts at it and hope it goes away. If I could, the whole fuel system would get replaced. I already have a reman IP. Mine first started with a small leak in the line going from the tank to the LP. Then it ran ok for a little while. Then, it started acting up again I figured Id install a new LP this time instead of a used one. Then I found that the repair the garage had made to the line was just a compression fitting and part of it was loose. Tightened it up, new LP and it still does the same thing. ARGH!!
 
Mezmorized said:
I've been chasing gremlins like that for about a year now. Problem is, I can't afford to just toss parts at it and hope it goes away. If I could, the whole fuel system would get replaced. I already have a reman IP. Mine first started with a small leak in the line going from the tank to the LP. Then it ran ok for a little while. Then, it started acting up again I figured Id install a new LP this time instead of a used one. Then I found that the repair the garage had made to the line was just a compression fitting and part of it was loose. Tightened it up, new LP and it still does the same thing. ARGH!!
Click to expand...

have you changed the OPS?
 
Well it turned out to be a rusted hose clamp that broke but still stayed somewhat tight on the outlet of the lift pump. It was barely leaking fuel so I missed it at first but enough of an opening to suck air. New hose clamp and runs like its old self. Still doesn't explain the random missing/loping but I'm gonna check out the return on the IP.
 
lps can fail intermittently, sometimes it works and sometimes it won't. put a pressure guage on it so you can verify fuel pressure while driving and monitor it for awhile.
 
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