Fuel Starvation Problem

[qmcdugan]

Im working on a fuel starvation problem. The fuel pump replacement addressed most the the ills. It now runs. However not as it should. I did a search for fuel selector valve and have viewed several of the post here at Fordification.
The engine is a 351M (400 cid) from a 71 Mustang. Because of this fuel problem it runs like a dog not a the fire breathing Mustang that it ought to be.







Assuming that the rubber fuel line ( that runs from the steel line (that exits the frame near the selector valve) and goes up to the top of the PO's re-located fuel tank mounted in the front of the box and protected somewhat by a large handy tool box ) is not the problem. Plan to replace this line very soon.

Question 1 Is it possible that the line that goes down into the fuel tank has a hole in it that now permits air into the system and therefore a loss of fuel pressure at the Carb?

Currently there are two fuel filters in the system. The first is just off the fuel tank ( in the hose that runs down to the steel line that exits the frame ) the second is just before the Carb. Neither of the see-thur filters fill, even half way!

Question 2 What would be normal, 1/2 to 3/4 full filter?

[Dragon]

Are you sure it is a fuel problem????

Ignition, fuel , vacuum many reasons why it is not fast oh and the fact your truck weighs way more than the 71 Mustang. Filters only show full if they are standing on end or the float is stuck open and all the fuel is just shooting through the engine.

[qmcdugan]

True

I spared you guys the whole story. A trusted gearhead friend of mine who has some personal knowledge about my truck ( he has been helping me with it since I got it (not from him) in 07), says to rule out the fuel tank/line/filter issues. The Edelbrock carb and Manifold are okay. He thinks it's (the problem) in the tank. I hope it's not. Also I didn't mean to give you the impression that this daily driver is abused, I know that it's just not putting out what it use to, nor what it is capable of.

Im just getting with my Fordification Bump Heads and getting that perspective. Which is always a smart thing to do, even when I think I know the answer.

[sideoilerfe]

The engine is a 351M (400 cid) from a 71 Mustang. Because of this fuel problem it runs like a dog not a the fire breathing Mustang that it ought to be.
?

The 351M wasn't made until '75. If it came out of a '71 Mustang it's probably a 351 Cleveland. Regardless of that, the fuel problem could be narrowed down by using a 5 gallon gas can and some 5/16 rubber fuel line. Put the can in the bed and drive the truck. If the problem disappears, then the problem is the PO's custom tank.

[fordman]

you can take the gas gauge out fo the tank and remove the fuel cap. shine a flash light down in the filler neck and look inside the tank and see what the condition of it may be. it could be clean it coul dbe rusty. it could have stuff floating in the botom of the tank. it could have a collasped sock on the fuel line at the bottom of the tank. that tube could also have pins holes in it not lettign it suck fuel up properly. it doesnt cost anything but maybe a new gauge gasket. which can be made from cork if you wanted to do that.

[sideoilerfe]

you can take the gas gauge out fo the tank and remove the fuel cap. shine a flash light down in the filler neck and look inside the tank and see what the condition of it may be. it could be clean it coul dbe rusty. it could have stuff floating in the botom of the tank. it could have a collasped sock on the fuel line at the bottom of the tank. that tube could also have pins holes in it not lettign it suck fuel up properly. it doesnt cost anything but maybe a new gauge gasket. which can be made from cork if you wanted to do that.

He's got a custom tank inside the bed and more than likely it doesn't have a sender.

[fordman]

when he said in front of the box i took that as in cab.

[ForingaMex]

take the gas gauge out fo the tank

If he has a guage in the tank than that is the problem.
I'm just pulling your chain Fordman, I'm sure you meant the sending unit.
Jake

[70_F100]

Currently there are two fuel filters in the system. The first is just off the fuel tank ( in the hose that runs down to the steel line that exits the frame ) the second is just before the Carb. Neither of the see-thur filters fill, even half way!

Get rid of the filter near the tank. Those filters are meant to filter under pressure, not suction. That in itself could cause fuel starvation.

Question 2 What would be normal, 1/2 to 3/4 full filter?

The filter near the carb should be near 1/2 full, maybe a little more. It will probably never be totally full.

[Dragon]

Currently there are two fuel filters in the system. The first is just off the fuel tank ( in the hose that runs down to the steel line that exits the frame ) the second is just before the Carb. Neither of the see-thur filters fill, even half way!

Get rid of the filter near the tank. Those filters are meant to filter under pressure, not suction. That in itself could cause fuel starvation.

Only EFI vehicles have a factory frame filter and that is after the pump.

[qmcdugan]

As the weekend nears I'll pull the sending unit out of the tank and see what I can find. The line coming out of the tank looks to be welded inplace from the factory. Im told that the line may have a "sock" screen at the bottom end that has some debris stuck to it... unreachable as I invision it. I suppose that I'll end up pulling the tank and rinsing it out somehow or other, God knows what I find at the bottom. Guys, I don't even want to think about this and a new tank is NOT in the cards. Weekend warriors.... me am talking about. NW weather is milder than almost anywhere else and a little rain won't be that much to contend with. The bitch of it is this, the truck is how I get back and forth to work and can't afford to have it down. The other two vehicles are OOC for the time being, and the 68 C/S is currently torn apart for major clean up.



Is the sending unit gasket that cork / rubber material?

Is there a means of getting the fuel line out of the tank?

Once I get this done, I'll upload pics and let you guys see what came out of all this.

[Dragon]

The sender unit comes out and you can usually reach the line end in the tank.

The sending unit gasket used to be just cork.

[sideoilerfe]

We don't know what kind of tank it is since it is not a factory tank. Post some pics so we can help you easier.

[fordman]

yes the stock factory in cab tank had a cork gasket under the sending unit.

[70_F100]

The first thing I would do is to get rid of that filter, like I suggested previously.

Check all of the rubber lines between the tank and the fuel pump for cracks. You may even do yourself a favor by replacing them, as they may be separating on the inside (not visible from the outside, of course) and blocking the flow of the fuel.

Drain all of the fuel from the tank and look into it through the filler hole, looking for any sort of debris that might be floating around.

I posted this a few weeks ago in a similar thread:

Once upon a time, many years ago, I was working on a GMC 6500 mobile home hauler with a 427 gas engine.

This truck would run BEAUTIFULLY when it ran, but it would totally shut off randomly, and would not start.

Each time it cut off, I found that there was no gas getting to the carb.

I replaced both of the fuel filters, checked the lines, replaced the fuel pump, gave the engine a complete tune up, and inspected everything from the front to the rear of the truck. Of course, being a mobile home hauler, there wasn't a lot of distance between the front and the rear.

I worked on this truck for two days. Twice, on test drives, it shut off completely and had to be towed back to the shop. Other times, it would shut off, and if I let it sit for a few minutes, it would fire back up.

Unfortunately for me, my hair was much longer back then, and I pulled it quite a bit trying to pull it out. I only succeeded in making my head sore!!

Eventually, as a last resort, I drained the fuel tank and pulled it off the truck, thinking that the pickup tube might be cracked.

What I found when I pulled the tank was a leaf that had gotten into the tank somehow, and it would get sucked over the pickup tube at random times, blocking the flow of fuel.

Cleaned the tank out, got rid of the leaf, put the gas back in, and it ran fine. Saw the truck come into the dealership a few other times, but never for a problem with performance.

I had something similar happen a few years later on a Scout that my wife and I raced off-road. Seems that the seal came out of the lid of a gas can I used for refueling, and it got into the tank. Caused us to DNF at a couple of races.

The moral of this story is, check and make absolutely sure you don't have any trash floating around in your fuel tank before you spend a bunch of time and money chasing problems that may not exist. The truck is 38 years old, and there's no telling what you might find.

Your troubles sound just like what I've described.