Fuel flow
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Junior User
Joined: Dec 2003
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From: Maryland
Fuel flow
I hope I am not wearing out my welcome here, but since my recent problem took a different direction, I thought I would start a new thread. When I run my truck on the front tank it is hard starting and runs rough intermittenly. I switch to the rear tank, which has been replaced, it runs fine. The supply line from the tank switck to the lift pump have been repalced. When I pulled the fuel filter off yesterday (after running the frt tank) it was only 1/3 full. Any suggestions would be much appreciated. Thanks Bill.
Fleet Owner
Joined: Jun 2004
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From: Rio Rico, AZ.
Well it sounds like you are sucking air somewhere. Do these earlier Fords use the same crappy quick connects that my 99 does? I had to eliminate those and substitute high quality fuel line with screw clamps to get rid of the air in my fuel.
Also your pickup tube might be cracked, clogged, etc.
Also your pickup tube might be cracked, clogged, etc.
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Junior User
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From: Maryland
Kwik, I replaced the quick connects on the tank switch on the supply and return lines as well as the lines. I also replaced all the other return lines on top of the motor and the orings and fittings.
PLC, the tank is full. But if it makes any difference, when I first started having problems the tank was low, maybe less than a 1/4.
If I am sucking air someplace is there any test I can perform or meter that would help pin point the leak? Also, if it is only happening when I am using the front tank, does that mean if it is an air leak it would be from the tank switch back towards the tank?
PLC, the tank is full. But if it makes any difference, when I first started having problems the tank was low, maybe less than a 1/4.
If I am sucking air someplace is there any test I can perform or meter that would help pin point the leak? Also, if it is only happening when I am using the front tank, does that mean if it is an air leak it would be from the tank switch back towards the tank?
Fleet Owner
Joined: Jun 2004
Posts: 25,090
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From: Rio Rico, AZ.
Please remember that I have never looked at the fuel system on the earlier trucks....
You could substitute some of that fuel line temporarily with some of that clear vinyl stuff so you have a "sight glass" and see what's up.
I agree that if the problem is with the front tank only than you need to look there, not discounting a possible leak at the switching valve itself. If you have already replaced all the quick connects with nice tight connections secured with screw clamps, well now it's time to look into the tank, etc.
You could substitute some of that fuel line temporarily with some of that clear vinyl stuff so you have a "sight glass" and see what's up.
I agree that if the problem is with the front tank only than you need to look there, not discounting a possible leak at the switching valve itself. If you have already replaced all the quick connects with nice tight connections secured with screw clamps, well now it's time to look into the tank, etc.
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Junior User
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From: Maryland
Thanks for your input. I'm not sure but, from the search I did and from other related threads I have read I may have to pull the bed back to access the top of the tank. From what I understand this is easier esecially with the skid plate and the fact that the tank is full. I will look at it again tonight and go from there.
Post Fiend
Joined: Nov 2004
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From: Manitoba
Because the lines are so small if you use screw clamps they simetimes do not seal in a complete circle. You could use some RTV around the connection to see if it seals any air intrusion but this is not the real fix.......try to find Hduty clamps like the ones on the return lines on the engine which clamp in a circle.
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Fleet Owner
Joined: Jun 2004
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From: Rio Rico, AZ.
What works best is to get a hose that is small enough in diameter so that it fits tight on the steel line before you even clamp it down. If it just "falls on" or feels sloppy at all then the hose is too large of diameter. Then there is virtually no chance of anything getting in or out.
Last edited by Kwikkordead; Oct 6, 2005 at 10:15 PM.
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Post Fiend
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From: Nutter Fort, WV
Usually the less than 1/3 tank is the fuel pickup tube is broken.
Tank sending unit and fuel pickup tube is a one piece deal.
Replace it and your problem will probably go away.
Over the years I notice my front tank has more problems with the pickup tube than the rear one does. But then when you look at how long and skinny the tank is, and think about all the braking and acceleration with the fuel sloshing around in the tank from front to back I guess it is kinda to be expected.
Tank sending unit and fuel pickup tube is a one piece deal.
Replace it and your problem will probably go away.
Over the years I notice my front tank has more problems with the pickup tube than the rear one does. But then when you look at how long and skinny the tank is, and think about all the braking and acceleration with the fuel sloshing around in the tank from front to back I guess it is kinda to be expected.
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Junior User
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From: Maryland
For the supply and return lines that I replaced so far I have used factory parts from the dealer, The return lines(on top of the engine) were bulk stuff, but I reused the original clamps that are all in good shape.
I crawled under the truck last night and was able to get my head between the bed of the truck and the frame rail. The top of the sending unit was looks to be a possibility as to the problem. It is pretty dirty, kind of greasy, which could be an accumulation of fuel over a period of time. It didn't have a convincing smelll of diesel though. Also the two steel tubes going down into the tank are rusty. I am going to replace the lines from the sending unit to the tank switching valve next ( I'm tring to rule out everything before pulling the bed off. I have a sleeper that connects to the cab with a gasket and a tool box under the sleeper. They both will have to be removed to move the bed). I think I am on the right track though. My gut tells me that it is the sending unit. I really appreciate everyones help. Bill
I crawled under the truck last night and was able to get my head between the bed of the truck and the frame rail. The top of the sending unit was looks to be a possibility as to the problem. It is pretty dirty, kind of greasy, which could be an accumulation of fuel over a period of time. It didn't have a convincing smelll of diesel though. Also the two steel tubes going down into the tank are rusty. I am going to replace the lines from the sending unit to the tank switching valve next ( I'm tring to rule out everything before pulling the bed off. I have a sleeper that connects to the cab with a gasket and a tool box under the sleeper. They both will have to be removed to move the bed). I think I am on the right track though. My gut tells me that it is the sending unit. I really appreciate everyones help. Bill
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From: Maryland
I picked up the new lines that run from the sending unit to the tank switch valve and before I get to far I have a question. The connectors on the existing lines at the SU are the same as all the rest. They are plastice with a white u-shabed piece that locks the fitting in place. The new lines (100 friggin dollars) are serious looking covered steel braided and the connectors on the SU end are metal with look to have locking springs inside. Are these right? The parts guys said that those are the ones listed for my truck. I didn't want to mess them up if they aren't right.
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Joined: Nov 2000
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From: central NY,near Syracuse
Just been reading, and have noticed no one mentioned the possibility of plugged lines. older tank,possible rust, work on the lines to shake it free,and a 1/3 full filter. all point to the possibility of gunk in the lines, stopping fuel flow. I'm not sure if the pick-up has a screen,but it might. Just a look from a different angle. Best of luck Phil
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Junior User
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From: Maryland
Phil, I have been thinking the same thing. If these new lines don't change anything (they need to be replaced regardless) I will pull the sending unit out and am wondering if I don't find it clogged. I will let you know what I find.
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