I have a 78 Crew with dual tanks and the factory transfer switch in the dash. I recently attempted to switch to the main tank from aux tank and got no gauge reading (gauge reading empty) on the main tank that I had recently filled and no fuel transfer, causing the truck to run the fuel line empty and die. The transfer valve is less than a year old. Is the only other possibility the factory in-dash switch, or could there be other possibilities I have not considered? When the switch is in the aux position, the gauge reads accurate and fuel delivery is good. Any thoughts on this?

 

The fuel transfer switch is a solenoid type operation. With no power to it it is in the main tank position. The only thing that happens when you put the selector switch to the main tank position is the switching of the fuel tank sensor to the main tank. Since it works OK in the aux tank position you must have something plugged in the fuel line to the main tank. The problem with the gauge not registering on the main tank has to be a totally different problem. It could be anything from the switch on the dash, a broken wire somewhere or a bad sending unit in the tank.

The quickest was to test the gauge is to find the sending unit wire on the main tank. Pull it loose and ground it. If the gauge moves up then the sending unit is bad. If not then the wire or switch is bad.

The most common problem with a plugged gas line is the filter sock in the tank. The easiest way to find that is to pull the line loose at the fuel pump and try to blow back into the tank. You will know if it is plugged. I have had two trucks that the sock plugged in. I would never bother to take the tank apart to replace the sock. I just take compressed air at about 90 psi and blow back through the line. This blows the sock off. I then put an external filter near the tank that can be cleaned without taking the darn tank down.

I hope this helps.

 

but i would like to know what others have to say. On my 78' when you switch from main tank to auxilary tank it will get fuel, but my guage is reading 0 also. Im sure its just a wiring issue, but havent looked into it yet.

 

https://www.ford-trucks.com/forums/1...uel-gauge.html

https://www.ford-trucks.com/forums/1...-1-2-mark.html

https://www.ford-trucks.com/forums/1...es-off-the-peg.

 

You need to do a 'search this forum." If you look just to the top of the thread listing on the right hand side you will see the search engine. Just click on it and put in "fuel gauge not working, or fuel transfer switch not working" and you will get dozens of pages of replies to your type of problems. This is usually the best way to use this site. Good luck in your searching.

 

You will get 50 pages of results, from about 20 different threads. Good luck trying to find anything useful quickly.

have a buddy flip the switch while you are under the truck. The solenoid should be near the rear gas tank, just forward of the crossmember. It should buzz and click when the switch is activated.

If you don't want to fool around with trying to blow air into the fuel line, and risk getting bathed in fuel, you can disconnect the line, put it into a bucket, and try to blow a little bit of air into the fuel inlet. (create a seal with a rag around the air nozzle.) If its the sock is clogged, fuel will not come out of the hose, if it isn't, fuel will dump out quickly. I would almost venture a guess however that your problem is not a clog, rather an electrical problem.

Good luck with your repair.

 

He said the thing works fine in the aux position, but not the main tank position. And as I pointed out the fuel transfer switch doesn't have any voltage going to it in the main tank position. (Check the wiring diagram) The solenoid is relaxed (dis-engaged) and lets the fuel from the main tank go through. So even if the switch was bad and the darn thing didn't even have voltage on the entire vehicle fuel would flow through from the main tank. So he has something plugged in the main tank.

As far as getting bathed in gas, you would have to be an idiot to have that happen. The only way you could get bathed in gas would be if you took the gas cap off and stood over it while someone put air pressure into the fuel line. putting the air nozzle over the fuel line before it goes into the fuel pump (where there is no gas) couldn't possibly get you bathed in gas. I know of hundreds of people (search the forum) that have done this and have never been bathed in gas.

But as you suggest putting the air into the filler neck and putting a rag around it to seal it off and putting pressure into a full tank of gas is DANGEROUS. If there is no pressure release as no vent or a plugged sock you are going to pressurize that tank and it is going to blow gas all over you, rag or no rag.

As far as the search function goes; If everyone would do a search for their problem before posting it there would be a lot less clutter on this forum. Virtually every question that has been posted has been asked before numerous times. (as you testified to by you own statement "50 pages") I rest my case..

 

As it turns out, I was not getting power to the sending unit on the main tank due to a break in the 12v lead wire that I couldn't see tucked up above the tank. I guess I should have checked for voltage at the sending unit sooner. I'm not sure how the system is wired, but once I fixed the 12v lead to the sending unit, everything worked fine again. Thanks for all the suggestions and helpful hints. Next time I will do a search on this forum for my specific problem. You know how these dog-gone rookies are.

 

Then you needed to look at the post above yours (Posted 21 Minutes before your search suggestion) ....to note that I had already linked 3 threads with tons of info in them.

I took his "have to search" out of the equation.

That's why I get the big bucks!


Also,Users posting topics that are 73-79 PERTINENT have been posted thousands of time is not clutter.

Clutter is those hundreds of threads that are NOT 73-79 related that get posted in this forum but are "system specific" that relate to numerous years trucks.

They need to be posted or moved to the related forum.

 

The point I was trying to make Dennis was the search engine is there for a reason. I see guys posting on an obvious problem that has been discussed dozens of times. I did see the three links that you posted and you do a great job of helping the guys out here. I am constantly amazed at all of the drawings and diagrams that you come up with. I guess thats why you make the big bucks. I was just trying to help out a rookie to keep him from making the same mistakes that I did when I first came on this site. I always do a search before I post a question and most of the time I get an answer without having to post. That is why I have such a low amount of posts for the time I have been on FTE.

I am still confused about the guy getting 50 pages from 20 different threads. When I do a search on a thread I only get results from that thread. (I think)

P.S. I don't sit at the computer all of the time. I might reply to a thread, get called to the phone, go to the bathroom, do a honeydo or numerous other things. and then come back to the computer and send the reply. So possibly somebody may have sent something in between my typing a reply and sending it without ever knowing that someone else had posted a reply. Thats my story and I am sticking to it.

 

That goes for me too

Every once in a while I search out popular threads copy and paste them into an e-mail message (create a draft) for future events.

Sometimes the search is down and/or very busy.

So I do this just to keep helping people.

I prefer the initial interaction with new users by answering topic and giving them info (redirection) on how to make the most of FTE.

 

Is the maine tank the one in cab or under the truck

 

well according to the owners manuals from front to back it is

In-Cab tank,Aux (mid-ship), and Main tank