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1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks Discuss the Early Eighties Bullnose Ford Truck

Engine Dying and Vacuume in Tanks

 
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Old 03-15-2019, 07:50 PM
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Engine Dying and Vacuume in Tanks

And yet another post asking questions. I appreciate everyone's answers, even if my questions are stupid sometimes. So I got my 351m finally running and took it for a test drive. It was cut rather short, as the engine died after driving about 300 yards. I kinda messed with the car for about 15 minutes and somehow got it to start up again and drove it home. I poured some gas into the vent tube of the carb and it started right up, which led me to believe that the carb is just not getting fuel. Since I checked all the lines when I changed my fuel pump and carb I am pretty sure that the problem lies somewhere behind the fuel tank selector valve. I also noticed that the fuel was a disgusting brown color so I got a see through fuel filter and bypassed the selector valve with it. It accumulated quite a bit of rust in the short time the engine was running.
When I have the engine running with the fuel from the bowl, I can hear the gas tank building up a vacuum as it actually contracts so much that it pulls in the walls of the tank. So I ran it without a gas cap, which went better, but it still seems like it is just not getting enough fuel.
I have the suspicion that is a combination of the vacuum buildup and maybe rust in the fuel tank clogging up the intake line?
I am tempted to drop the tanks to clean them a bit and get the most of the rust out. The external fuel filter seems to do a good job of protecting the fuel pump. What do yall think>
 
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Old 03-15-2019, 08:08 PM
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I know money is tight sometimes, but a new tank is the best way to go. If there is that much rust in the tank, it won't be long till it starts leaking. A clean fuel system makes for a reliable vehicle. You didn't say, but since you have a 351m I am guessing you have around a 1981 f150. I looked on rockauto and they have tanks for about $80.00.
 
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Old 03-15-2019, 08:11 PM
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I don't care how much you clean the tank and even seal the inside with a DYI kit it will still cause issues down the road.
Now there is a shop that can coat the inside but a new tank is cheaper than doing this.
I say go for a new tank, cap and maybe the sender / pick up assy. and new rubber hoses and never have to look back at the tank again.

Now not knowing the year of the truck and what size tank and where it is bolted in at, if at the rear you may want to look into a larger 38 gal rear tank but you will need to move the spare tire from under the factory tank.
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Old 03-15-2019, 09:27 PM
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I have a 1981 F250 with dual tanks. One is 19 gallons and the other one 16 I think. If I am going to replace the fuel tanks, replacing everything in them seems like a good idea. Having it off once, I should probably just renew everything.
 
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Old 03-15-2019, 10:36 PM
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There seem to be a few different gas tanks available for the F-250. Do you know if there are any part numbers on the fuel tanks, and if so where?
 
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Old 03-16-2019, 07:57 AM
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Originally Posted by BlueWhiteFord View Post
I have a 1981 F250 with dual tanks. One is 19 gallons and the other one 16 I think. If I am going to replace the fuel tanks, replacing everything in them seems like a good idea. Having it off once, I should probably just renew everything.
Originally Posted by BlueWhiteFord View Post
There seem to be a few different gas tanks available for the F-250. Do you know if there are any part numbers on the fuel tanks, and if so where?
Ok duel tanks, long bed or shout bed (did they make a short bed 250?) because the short bed trucks use a 16 gal side tank and the long bed a 19 gal tank.
What motor doe it have if that make a difference. Being an 81 take it no electric pumps.

I also know you have to watch the side tank senders as I want to say most list the same sender for both size tanks and that in not right.
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Old 03-16-2019, 08:01 AM
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You should have two 19 gallon tanks. Since you have the earlier truck, you will have the small sending unit hole. Other than that, there should be no choice in tanks.

Do you actually need and use two tanks? Both trucks I have and have had before had dual tanks, and as I was driving them I never filled both tanks at once. I did once though, and that was on a long road trip. Other than that I never used both tanks, so when things went south and I needed new tanks, I just replaced one and did not use the other.
 
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Old 03-16-2019, 09:46 AM
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Yeah, I don't think I have electric fuel pumps. I looked on rock auto parts and they seem to find the tanks you need pretty well. It says tanks for 1980-1984 trucks, so I am guessing those are the ones I will need. If I get the tanks and the sending units, is there anything else I need to get everything hooked back up?
I want to keep both tanks since I need to keep the truck original for import.
 
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Old 03-16-2019, 10:16 AM
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You may want to replace the duel tank switching valve being the system is down.
The only other thing is to replace all the rubber fuel lines.
Oh just thought of the tank vent/roll over valves & grommets. Sometimes the plastic valve nipple will break off or the rubber gromit could be bad and you would then need to wait for them.
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Old 03-16-2019, 12:18 PM
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I can't seem to find a switching valve that looks like the one that is on my truck. What are the other parts you mentioned? I might as well just order everything and get it all replaced and then not have to worry about it again.
 
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Old 03-16-2019, 03:36 PM
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Originally Posted by BlueWhiteFord View Post
I can't seem to find a switching valve that looks like the one that is on my truck. What are the other parts you mentioned? I might as well just order everything and get it all replaced and then not have to worry about it again.
If you follow the outlet of each tank it should go to the switching valve unless someone removed it.
Could also start at the fuel pump and work your way back to the tanks. Should come to the switch valve before you get to any tank.
Do you have the duel tank switch to the right of the heat / AC controls?

As for the other parts look at numbers 4, 5 & 6 they call it a vent.
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Old 03-16-2019, 03:54 PM
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Originally Posted by BlueWhiteFord View Post
When I have the engine running with the fuel from the bowl, I can hear the gas tank building up a vacuum as it actually contracts so much that it pulls in the walls of the tank. So I ran it without a gas cap, which went better
The correct fuel caps are vented & (under normal circumstances) allow air into the tank, but block it from exiting......... so any vapor & pressure build-up exits forward to the charcoal canister, in the engine bay, to later be burnt. If an excessive pressure build-up occurs in the tank, there is a relief valve in the cap.

But it's possible someone has installed a non-vented cap to your tank, which isn't allowing air in, as gas is used.
 
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Old 03-16-2019, 04:00 PM
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I have seen the switching valve and have the switch in the cab, I just can't really find a replacement part that looks like the switching valve that I have.
I found a replacement valve in the national parts depot. It looks wider than what is illustrated on the picture you send. Pretty sure that's what they look like for the 90s truck. I think I am going to go ahead and order the fuel tanks, sending units, new tank straps, gas caps, and those ventilation valves. They look like the right size for the tanks at rock.
 
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Old 03-16-2019, 07:56 PM
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Here's the valve you need. You will have to cut the Ford wiring connector off and put a ring terminal on it, but it should functionally work the same as the original.

https://www.ebay.com/itm/Universal-D...75.c100623.m-1
 

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