Truck wouldn't run???
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Truck wouldn't run???
Hi all, new here today. Didn't know you existed, but glad I found you.
Looking for a little bit of help with a quandry I encountered this morning and would appreciate any thoughts you guys might be able to share. Thanks in advance...
I just received word from a mechanic that was looking at why my 1994 F-250 (7.5 litre V-8) wouldn't start.
He's telling me that with dual tanks, I have to have gas in both tanks, or the truck won't start and run. (Apparently, my father-in-law ran the back tank dry when he borrowed it.)
Now I may be thinking old school, prior to all of this computerized junk they use these days, but this just isn't computing with my brain.
Why would the truck care whether or not one tank has fuel if you're trying to run the truck off of the other tank and it's full?
Anyone out there know anything about this topic?
Looking for a little bit of help with a quandry I encountered this morning and would appreciate any thoughts you guys might be able to share. Thanks in advance...
I just received word from a mechanic that was looking at why my 1994 F-250 (7.5 litre V-8) wouldn't start.
He's telling me that with dual tanks, I have to have gas in both tanks, or the truck won't start and run. (Apparently, my father-in-law ran the back tank dry when he borrowed it.)
Now I may be thinking old school, prior to all of this computerized junk they use these days, but this just isn't computing with my brain.
Why would the truck care whether or not one tank has fuel if you're trying to run the truck off of the other tank and it's full?
Anyone out there know anything about this topic?
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Subford,
Thanks for the quick reply. That's exactly what I would have thought, but what I've outlined, is what I'm being told, and it just didn't make sense.
I thought perhaps, it was somehow tied into the emission control system and the computer or something?
By the way, what is an FDM?
Thanks for the quick reply. That's exactly what I would have thought, but what I've outlined, is what I'm being told, and it just didn't make sense.
I thought perhaps, it was somehow tied into the emission control system and the computer or something?
By the way, what is an FDM?
Fleet Owner
Joined: Aug 2005
Posts: 23,667
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From: Easton,Ks
All the Computer does is ground the coil of the fuel pump relay, then check on its output (the relays) and does not know if you have fuel in the tank or what tank you have selected.
The only connection of the emission control system is the tank vents and they vent to a carbon canister.
The FDM is the Fuel Delivery Module, Here is a diagram of it:
http://i54.photobucket.com/albums/g91/subford/Fuel/FuelDeliveryAssembly2.gif
The only connection of the emission control system is the tank vents and they vent to a carbon canister.
The FDM is the Fuel Delivery Module, Here is a diagram of it:
http://i54.photobucket.com/albums/g91/subford/Fuel/FuelDeliveryAssembly2.gif
Post Fiend
Joined: May 2004
Posts: 11,289
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From: Lakewood, Ohio
i have run my rear tank in my 94 dry and it ran off the front tank with no problem.
you never say if truck now starts or does not start.
you never say if truck now starts or does not start.
Last edited by quicklook2; Aug 30, 2006 at 06:14 PM.
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Quicklook,
The truck is running again. I'm not sure I entirely understand the cause even after discussing it face-to-face with the mechanic, but I'll try.
Apparently, there is some type of check valve between the two fuel pumps and tanks. If you run either of the tanks dry and try to switch tanks, the valve can become dry and as a result get stuck.
If I understood him correctly, in this scenario, it continues to try and pull gas from the empty tank, as the valve having been stuck in place is blocking access to the full tank.
They claim they put gas in the rear tank messed with it enough to get the gas up to and moisten the valve. After they were able to accomplish that, the truck started and has been running good ever since.
Who'd have thunk???
The truck is running again. I'm not sure I entirely understand the cause even after discussing it face-to-face with the mechanic, but I'll try.
Apparently, there is some type of check valve between the two fuel pumps and tanks. If you run either of the tanks dry and try to switch tanks, the valve can become dry and as a result get stuck.
If I understood him correctly, in this scenario, it continues to try and pull gas from the empty tank, as the valve having been stuck in place is blocking access to the full tank.
They claim they put gas in the rear tank messed with it enough to get the gas up to and moisten the valve. After they were able to accomplish that, the truck started and has been running good ever since.
Who'd have thunk???
Fleet Owner
Joined: Aug 2005
Posts: 23,667
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From: Easton,Ks
Originally Posted by Jed 16265
Apparently, there is some type of check valve between the two fuel pumps and tanks. If you run either of the tanks dry and try to switch tanks, the valve can become dry and as a result get stuck.
Originally Posted by Jed 16265
If I understood him correctly, in this scenario, it continues to try and pull gas from the empty tank, as the valve having been stuck in place is blocking access to the full tank.
Originally Posted by Jed 16265
They claim they put gas in the rear tank messed with it enough to get the gas up to and moisten the valve. After they were able to accomplish that, the truck started and has been running good ever since.
Who'd have thunk???
Who'd have thunk???
Did they charge you anything for all of this BS.
I think I would find another mechanic, as these mechanics do not know what they are talking about.
Here is a diagram of your fuel system.
http://i54.photobucket.com/albums/g91/subford/Fuel/FielSystem.jpg
Last edited by subford; Aug 31, 2006 at 07:55 AM.
