old thread: https://www.ford-trucks.com/forums/1...et-issues.html

The truck has had no real issues for the past few months; it's driven really well. Then, about a week and a half ago, I had some issues. For context, I live in the southwest desert, so the truck's body/frame has never been exposed to salt. It's in great shape except for a bit of minor rust here and there. So, I was driving down a long dusty road on the way home, and I heard a "THUD" The truck ahead of me was a dump truck hauling rock. I keep a good follow distance between cars and give a ton of room for trucks; that stuff could fall out, but it was not enough. It looked like landscape material about 1-2 inches in range; it bounced under the truck and tore a hole in the front tank. When I parked it gas soaked my parking spot. I opened the hood immediately and unhooked the negative battery terminal and took out the fire extinguisher from inside the cab, if anything happened, it would be on hand. The truck smelled of gas, so I put some tape on the hole on the tank, then hosed down the belly of the truck. I have had carb issues with the fuel jelling in the tank, and my fuel filters usually clog. So, I brought the air compressor over and disconnected the fuel pump gas line and shot air into my lines for both tanks because i had some line clogging issues. Because my back tank is fine, just old and beaten up (and original), the idea is to replace both because I'm going to be working on them anyway.

I ordered the tanks from AutoZone; I also got the fuel sender units. The front tank is long, and the back tank is square. I was able to get the correct fuel sender unit for the front tank, but the back tank, while I was on the site ordering, the description said the part would fit, but it does not. So, 1 out of 2, I guess, is really not bad. The tanks have three total holes: a large hole so I can place the fuel sending unit in, then connect to the electrical, and a line to connect to the fuel pump. I also have two other holes: one to fill the tank and the third seems to do with emissions. I plan on just reusing all my old hoses. I could take out the old fuel sending unit from the back tank and just drop it into the new tank because it's not broken. I think it's not an extremely difficult project; it will just take a lot of time and cleaning before I put the tanks back in.and the third seems to do with emissions. I plan on just reusing all my old hoses and straps. I could take out the old fuel sending unit from the back tank and just drop it into the new tank because its not broken, i heard the newer fuel sender units have reliability issues.

 

The older ones had reliability issues and the original ones also. They used paint for the resistance material on the sender, and the wiper wears it off after awhile. It was probably fortunate you got a hole in the tank if you were having other issues. New tanks will be a great addition to your old truck. A clean fuel system makes a reliable truck.

 

I removed both fuel tanks, fixed the issues with nasty rotten lines it was so bad, i am just glad i caught it. I painted the fuel tanks to give extra protection and the front tank was powder coated so it looks like it has good resistance to rust.

So i put on a new carb its a single barrel like ND5607 (ill need to recheck model number odds are its wrong) but i am having some adjustment issues. I had the idle mix screws too lean so my rpms were too low and the engine turns off especially if im at a stop sign ahaha. I adjusted the mix a bit richer and the rpms increased. Now i have these 2 screws, one is in direct contact to a stainless steel arm i think its the curb idle screws. the other screw because they are about half an inch apart sets the depth of contact away from the adjustment plate and the carb. Ill need to grab a picture but it seems if i back off the screw that is in contact with this arm the rps increase. I can move the arm up and down and it seems though trial and error it adjusts the butterfly valve airflow settings. If i move the arm to the lowest angle the butterfly valve is completely open and usually the engine stalls. i think its called a fast idle cam. i can reset the arm by pulling on the throttle or just moving the arm up or down and i can actually kill or increase engine rpm from this arm i have found.



this video i found was helpful:

https://imgur.com/lM03Eh0
https://imgur.com/25p0bXG
https://imgur.com/6AHevbz
https://imgur.com/7Zb84CR
https://imgur.com/necLbsd
https://imgur.com/TJmaCJ6

ill see if i can upload a video. but in the photos check if anything is clearly wrong like OH NO why is that hose in that plug ect ect

 

With the engine off, hold the throttle open slightly with one hand, and take the other hand and use a finger to mess with the choke door on top of the carb. Move this door open and shut while looking at those adjustment screws. You will see the fast idle cam moving as you move the choke door in the top of the carb. That is what that one adjustment is for. It is supposed to do nothing when the choke door is straight up and open. When the choke door is closed, that screw adjusts the fast idle for warm up. It will hit the fast idle cam, and hold the throttle open.

I am thinking if you play with this a little bit, it will become more clear how it works. It's just like a weedeater or old lawnmower. The engine has to be choked for it to start, especially in colder weather. And the idle has to be fast to keep the engine running while it's cold till it warms up.

 

alright i got that fixed but i found other problems.

1. The fuel tank fuel sender unit for the back tank is not showing fuel level. I bought 3 fuel sender units in total - 2 of them were broken out of the box. My older fuel sender unit i might have to just drop the fuel tank and put the old one back in. I never buying stuff from autozone again the quality is crap.
2. the fuel tank selector valve seems to be frozen and only works for the bank tank.

the fuel selector valve this is the closest match https://www.summitracing.com/parts/tnk-sov
the wiring has a switch that does not seem like it will work ill need to get a picture. i tested the electrical with a working fuel sending unit and both lines front/back do work.

 

Is getting both fuel tanks working a high priority? All of the Ford trucks I have owned were dual tank, I ran the first one on just the front tank all the time I had it, the rear tank was no good.

The 2nd truck I have now had two working fuel tanks and valve, but I never could afford to fill both tanks and had no reason to. I used it one time when going on a long trip, which was nice. Other than that, I would just fill the rear tank, use it, then fill the front tank when the rear tank go low and kept alternating front to rear when going to the station. Then the switching valve went bad, and I just went back to the front tank. A few years later the front tank developed a leak so now I am just using the rear tank.

You can run a rubber line around the switching valve and just use one tank. If the sending unit in the front tank works,, just use the front tank.

 

If you have that 3 port fuel valve you have a easy system to work on.

As you most likely know the dash switch to the right of the HVAC control sends power to the valve and switches what sending unit is used.

The valve defaults to the rear tank of no power is sent to the valve.
First check the fuse, if blown no power to valve.
Then using a test light check to see if you have power to the valve.
Remember when on the rear tank no power so switch it a few times to make sure you get power.
No power with the switch you will have to back trace why.

If you do have power but you dont hear the valve "click" (key on motor off) then valve it no good.
You can find the valve on Ebay and think Amazon. Any valve you get will most likely have a different wire connection.

To see if the fuel gauge works put the switch to a tank then with the key on ground out the wire for the sender.
The gauge should go to full. Do not leave on full for a long time as you can hurt the gauge. I would say if you see it go to 1/2 tank then everything from tank to gauge is good.
You can also test with a test light. When the switch is on that tank put the test light to the sender wire the light should blink.
If gauge dose not move or no blinking test light you will have to back trace that wire.

For both power and the 2 sender wires (front & rear tanks) there is a harness plug kind of under the brake power booster that plugs into the frame rail harness.
You can unplug it and test if you have power or blinking light on the truck side of the harness plug.
Or you can ohm out the wires from that plug to the senders or the valve plug.
If you have blinking light(s) you can ground that wire and the gauge should move if everything is good from that point to the gauge.

If the truck has been sitting the switch could have a funk on the contacts.
Sometimes moving the switch a bunch of times will kind of clean it.
If you can get to the switch you can use electrical contact cleaner & lube and work the switch a bunch and it may start working.
Good luck
Dave ----

 

I like to use both tanks because i live 45 minutes from town and the truck is fuel hungry so its always best to have backup fuel.

I dropped the back tank again today and pulled the failed fuel sender unit out and put in the old one. The older fuel sending unit is not oem but an original ford part from 98 i was very impressed it was in nearly perfect condition and still working. Now both front and back tanks are new, new fuel lines, new inline fuel filter next to carb, new vents plugs on both tanks, fixed the inner fuel vent pipe on both tanks also i have working duel fuel sending units that detect fuel amounts so thats very good. as of now both tanks are working in all respects. I dont know if the fuel selector valve is stuck in the default (back tank) position. The back tank has less then 1 gallon in it yet the truck is running fine so i guess its pulling from the font tank since i have it in the front tank position on the switch.

I found the harness for the fuel switching unit but it looks different ill need to get a picture. It looks like a plug like key that you insert into the switch. I unplugged it cleaned it off and tapped it with a wrench for a few minutes then switched between tanks about 20 ish times while the engine was running. Then again if it was clogged im just going to plug my inline filter that goes to the carb.

Ill need to go test drive it. If the fuel selector switch is bad ill run the back tank dry and stall. If i am able to come home ill know that im draining the front tank. ill take a can of gas with me that if the selector switch is still stuck in the back tank ill just fill it and come home and buy another switch.

As for the test light maybe this will work :

 

The Amazon link no workie after the internet issues the other day.
My web site is also messed up

You can get the test light from HF or any parts store just dont get one that uses a LED bulb.
If you have a volt meter you can use it but a light you can see if it lights or not.
A meter you have to see if the needle moved or not and why I dont like to use it if a light will work.

With that said you can use the volt meter on the wire to the switch valve.
On the front tank you should get 12 volts or close to it.
Rear tank no volts.

You may also want to check the valve for markings from the 2 tanks.
1 should have a "F" for front the other "R" for rear.
It has also been posted early valve defaulted to the front tank with out power so maybe you have one of them valves and running off the front tank?

Again motor off key on have someone flip the switch and see if you give can hear it click and with hand on it if you can feel it click.
Dave ----

 

I rechecked the truck today by doing a cold start. The fuel selector was going to the almost empty back tank. The engine started then stopped because the truck was out of gas. I flipped the switch to the front tank and that is half full. I predicted it would not start and the truck failed to start. So the selector valve is stuck open for the back tank.

*The back tank is empty because its new and freshly installed so thats why its empty.

I ordered the fuel tank switcher from amazon and i noticed it has a different plug for the electrical. I am going to cut mine and still keep the old plug and Y branch from the old to the new switch with a terminal plug.

 

I dont remember what was different between the factory valve?
Think it may have had a 90* push on like the oil psi switch and the new valve had threads and a nut?
Without getting under and looking I think the 90* just pushed on the threaded part and worked.
Then again maybe I cut the end and crimped on a ring?
All new valves have threads so changing is not a big deal for me.
Dave ----

 

Is that a typo above? A 1998 fuel sender will not work with a 1986-dwn fuel sending gauge setup. 1986 is the last year, 1987 they changed the way the gauges work.

 

no no its not a typo i think i did not give the context sorry, its a fuel sending unit manufactured in 1998.

I installed the fuel switch valve this morning it was not that complicated. I cut the wire, stripped it then crimped on a terminal connector. I can now detect the amount of fuel in both tanks.

I cut the fuel vent hose about one inch shorter then the one in the tank and i noticed it was spurting a bit of gas while filling the tank. Ill snake a camera into the gas tank again to get a better look but its working you have to fill it slowly. I put my new vent hose and the old vent hose and the new one is only 1 inch shorter and yes i installed it where it has a seat on the fuel tank.

I still dont know if the switch actually moves the valve to switch between tanks. I went under the truck and put my hand on the switch as the internal switch was moved from forward to back in the cab and i felt nothing move. I can see the fuel in the tank via the fuel sending unit but it could be stuck in the default back tank.

So i took the truck out first around my block because its the desert im not going to hit anyone if the truck stalls and it ran fantastic, with that bit of encouragement i took it local area shops to pick up some cookies as a reward for the effort. (new fuel tanks, fuel lines, switch, cleaning under the truck)

well the celebration cookies was premature. I started to have problems with speed control mainly with my gas pedal. I think the choke tension is wrong because i feel the gas pedal stop moving then the truck starts to slow down, it feels like the gas peddle is stuck. I mean this is a good reaction in that i dont have to kill the engine because i cant control the acceleration. The engine does not turn off it will idle fine, if i put it into park it seems to reset the issue with the peddle and i have full range of motion in that i can press it all the way down.

My guess is that the issue is not enough choke chain tension. I did have to pull over about four times to get the peddle working, other then that the engine and everything else worked. oh and the curb idle feels correctly set along with the fuel enrichment valve to control idle speed.

 

i snaked the camera into the fuel tank and found the vent hose was bent so i pulled out the outer tube and was able to fit it back in without a kink. I then readjusted the throttle linkage to make it looser so i wont have that "peddle sticking" because driving with that is really not fun.

i tuned down the engine by lowering the curb idle and the fuel mix valve. I found 1 1/2 makes the engine run stable but still shake it must be a factor setting, while 2 1/4 turns makes it really smooth - i was adjusting the enrichment valve. I did see a bit of dark smoke in the exhaust when starting it up it was very mild. its probably not an enrichment issue but the fact the engine is cold. so i am not running over rich and burning too much fuel or adding excess carbon deposits to my exhaust system.


the main problem is the fuel selector switch does not work at all. i can view fuel tank volume via the fuel sender unit but for what ever reason i cant make the valve move. I put gas in both tanks, the front has 1/2 tank while the back has 1/4 tank. i looked at both tanks and only the back tank is feeding the engine so the fuel selector valve is stuck in the default back tank configuration so it never moved im now down to 1/8 on the back tank. my guess is that the issue is with grounding.

so to solve the problem why not have a manual valve;
I could have two holes in the cab and snake the fuel lines with the manual switch or i can put a two 90 degree angle bends into the tube so the valve hangs below where i would mount under the truck frame so the switch dangles maybe 1-2 inches past the trucks body panel.

I have another bigger problem the pedal is sticking i cant accelerate at all. I switched the choke change from loose to tight then loose again i cant figure out what is wrong.

 

Are you sure the valve is getting power?
Test light in hand key on see if you get power to the stud if not then that is why you cant pull from the front tank.

There is a fuse for the axu tank in the fuse block see if you have power to it.
I had that blow as the wire shorted out, my fault. I run the front tank first and it did not drop so switched to the rear and found it had dropped as it is the default for the valve.

Now I believe the fuse sends power to the switch then to the valve.
So if the fuse is good but no power to the valve try running a jumper to the valve and see if it works.
Dave ----

ps thsi was a new switch right?
Could switch the feed hoses to the valve to see if the front tank will pull fuel thru the pick up and hose and use some of that 1/2 tank.