Fuel tank/Fuel Cap problems
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Fuel tank/Fuel Cap problems
This is my first post and any help would be appreciated. I am a proud owner a mint condition rust free one owner 1986 regular cab F150. The truck has a 4.9L I6 carb. C6 three speed trans 85,000 original miles. This truck is mint and have added about $1500 in new maintenance parts just because this is going to be my daily driver not because anything was broke. This is the problem I am having..... Truck has been running fine then one day the side mount mid fuel tank starting giving me problems. Has dual tanks. The truck starts fine and will idle normal. The truck will drive fine at low RPM (under 15 mph) as soon as you start accelerating to higher RPM (over 15 mph) the truck stalls and runs out of gas. The fuel tank is under pressure and won't run. I can open the gas cap and vent the tank and the truck does the same thing till you accelerate. Now if I run the truck on the rear tank it runs fine no problems. So can I drill out my cap to release the pressure or buy a vented cap? The truck has the evac system and I would assume is working since the truck runs fine on the rear tank and the truck was running fine up until this problem. I could just always use the rear tank but both tanks worked fine till now? Any help?? Thanks.
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From: Virginia
The tank has a vent coming out of it, and it runs over to the passenger side where it tees into the vent running to the rear tank. The other end of the tee runs up front on the pass side frame rail and hooks in the charcoal canister. I would check all this out and make sure it's free and clear.
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Sine the rear tank and side tank vent into the same line going back to the engine your suggesting the problem is the line on top of the tank before the "T" fitting. I was wondering would rust plugged up on the pick-up in the tank cause these symptoms? Basically the main symptoms are lack of fuel and the tank under pressure so when I open the cap it sucks in a huge gulp of air.
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From: Virginia
If you pull fuel out, you have to let air in. The venting system I described did that, and I believe also the fuel cap does have a check valve in it to let air in, but not to let air out(emissions). So you could trade caps front and rear, but what I would do is run it on the front tank till it quits, and then crawl under the truck and pull the small lines loose on top of the tank and see if they let air in or not. The small line goes into a plastic fitting on top of the tank, and these are called roll-over valves. They let air back and forth unless the truck turns over, and then a ball bearing inside plugs the hole so gas won't leak out all over the place.
Lead Driver
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From: Sheffield, AL
If you pull fuel out, you have to let air in. The venting system I described did that, and I believe also the fuel cap does have a check valve in it to let air in, but not to let air out(emissions). So you could trade caps front and rear, but what I would do is run it on the front tank till it quits, and then crawl under the truck and pull the small lines loose on top of the tank and see if they let air in or not. The small line goes into a plastic fitting on top of the tank, and these are called roll-over valves. They let air back and forth unless the truck turns over, and the a ball bearing inside plugs the hole so gas won't leak out all over the place.
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Thanks for the help, my truck is in the shop getting a dent fixed (only one on the whole truck) when I get it back I will check the hoses on the top of the tank. I have one more question, looking at towing a 3,000 pound trailer with brakes. My truck has a stock I6 1B carb 3 speed C6 with 3.08 rear end. Do you see it having a problem going 65 down the highway for 300 miles? I looked at tons of towing posts on here and most people only recommend towing 2,000 pounds with 3.08.
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From: Virginia
Get a aftermarket tranny cooler and mount it in front of the radiator and plumb it in like the instructions tell you to. Then try it. The tranny overheating is the only possible problem you could have. The only other problem may be a deflated ego when everyone is passing you on a hill, but other than that, you should be ok.
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Post Fiend
Joined: Jul 2004
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From: Northern California
Sine the rear tank and side tank vent into the same line going back to the engine your suggesting the problem is the line on top of the tank before the "T" fitting. I was wondering would rust plugged up on the pick-up in the tank cause these symptoms? Basically the main symptoms are lack of fuel and the tank under pressure so when I open the cap it sucks in a huge gulp of air.
The vent line is placed on the top of the tank. It has a special roll over valve to keep fuel from entering the valve if the truck is rolled. If you overfill the tanks, (top them off) it can damage these valves, make them sticky, or get fuel in the vent line.
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Thanks for the information. I will check this roll over valve first. Now that i think of it, this problem did start shortly after I filled up both tanks. Thanks again for the help everyone. Hope to keep the truck on the road for the next ten+ years. The only thing that I am worried about is the carb. Has the feed back system. So far works perfectly but not sure who to take it to if I start having problems. Also, would most mechanics have the appropriate scan tool to get the codes off the computer or would they have no idea what to look at.
Post Fiend
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From: Northern California
A Mechanic should have the tool required, or know how to get the codes. The same tool works for 1981-1995 ford/Lincolin/Mercury vehicles, and there are still a few of those on the road, even in California.
As for the feedback system, it is a good reliable system, and has some refinements over a conventional carb. Self adjustment for different elevations, and fine tuning of the fuel mixture for best possible fuel mileage. However most people do not know how to work on them, or disconnect smog components *****-nilly and cause huge problems. If you don't tamper with the system it should be simple to diagnose problems either by one of us, or by a mechanic.
As for the feedback system, it is a good reliable system, and has some refinements over a conventional carb. Self adjustment for different elevations, and fine tuning of the fuel mixture for best possible fuel mileage. However most people do not know how to work on them, or disconnect smog components *****-nilly and cause huge problems. If you don't tamper with the system it should be simple to diagnose problems either by one of us, or by a mechanic.
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Thanks for the information. I'm a newbie to this site. I have been scanning through the posts for the past few months and have learned so much information about my truck. I'm going to take some pictures of my truck today and put up a hello everyone post. I'm as proud as a peacock to own my truck. When I post pictures try not to drool.
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Ok everyone, I replaced the roll over valve and still same problem. I drive and the tank builds pressure the stalls out. I drove with the gas cap off and still same problem. So my theory that its not venting is wrong. Something else is causing the motor to stall out. And also making a vacuum in the tank. Any suggestions. The next step might be just drop the tank and look inside.
Post Fiend
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From: Northern California
Did you check the line to the vent to see if it was open?
Does your truck have a three port selector valve, or a six port selector valve mounted on the framerail?
With the new information, perhaps the return line is plugged, or the six port valve is malfunctioning and closing the return to the tank when it should be open, causing a vapor lock condition at the engine.
On six port selector valve systems, each tank has a send and return line so the fuel can circulate. If the return is plugged, I can see it causing a vapor lock, or the in-tank fuel pump to be dead headed, unable to pump fuel etc...
Does your truck have a three port selector valve, or a six port selector valve mounted on the framerail?
With the new information, perhaps the return line is plugged, or the six port valve is malfunctioning and closing the return to the tank when it should be open, causing a vapor lock condition at the engine.
On six port selector valve systems, each tank has a send and return line so the fuel can circulate. If the return is plugged, I can see it causing a vapor lock, or the in-tank fuel pump to be dead headed, unable to pump fuel etc...
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From: Virginia
He doesn't have a return line system with the 300 does he?
It might get messy, but you can pull the line off coming from the front tank to the valve, and see if you have fuel when it won't run. If you have fuel, then it must be something with that switching valve. If you don't have fuel, must be something wrong in the tank. You can also hook a short piece of line up and bypass the valve, and run the front tank straight to the fuel pump and see if the problem continues.
It might get messy, but you can pull the line off coming from the front tank to the valve, and see if you have fuel when it won't run. If you have fuel, then it must be something with that switching valve. If you don't have fuel, must be something wrong in the tank. You can also hook a short piece of line up and bypass the valve, and run the front tank straight to the fuel pump and see if the problem continues.
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Joined: Jan 2001
Posts: 57,012
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From: Virginia
He doesn't have a return line system with the 300 does he?
It might get messy, but you can pull the line off coming from the front tank to the valve, and see if you have fuel when it won't run. If you have fuel, then it must be something with that switching valve. If you don't have fuel, must be something wrong in the tank. You can also hook a short piece of line up and bypass the valve, and run the front tank straight to the fuel pump and see if the problem continues.
It might get messy, but you can pull the line off coming from the front tank to the valve, and see if you have fuel when it won't run. If you have fuel, then it must be something with that switching valve. If you don't have fuel, must be something wrong in the tank. You can also hook a short piece of line up and bypass the valve, and run the front tank straight to the fuel pump and see if the problem continues.