Won't start using aux tank

[Bronco808]

Aloha all, wifey was driving her 1973 Bronco with a 2 bbl carb and ran out of gas in her main tank. She switched to the aux tank which shows full and I'm sure there is fuel in it but it would not start. I pulled the fuel line from the carb and had her crank it and no fuel was getting pumped out of the hose. I got her a gallon of gas for the main tank and after a few cranks/pumps she started right up. Any ideas?

 

[nvrstuk]

Check what blubuckaroo said and if that isn't it there are several other possibilities.

A crack in the aux fuel line could cause it too. Seals when sitting but when a vacuum is put on it from the fuel pump it creates a small gap that sucks air instead of fuel. Won't leak so you can't see the problem. Yeah, this happened 800 miles from home a long time ago...

 

[75MIKE]

If you didn't catch the tank swap when it started sputtering, it can take quite a bit of cranking to get fuel back to the carb. If the fuel line was run dry it will take a bit.

 

[blubuckaroo]

I've got to ask...
Did you only switch the gauge to the aux tank, without switching the tank selector valve?
Our Bronco gets used by the whole family. Because of this "FORD booboo" I've had to go out to rescue them on the side of the road too many times.
I finally replaced the aux valve with an electric that's powered from the gauge switch. Problem fixed!

I've actually got a good story about this...
In '76 I was test driving a new Bronco. I was on a dirt road and it ran out of gas on the main tank. Not knowing there was a separate valve, the Bronco wouldn't start.
I called the dealer and they sent out a mechanic. He didn't know about the aux valve either. He pulled the air cleaner, checked for fuel, and slammed the hood on the air cleaner making a big dent on the hood.
He took me back and came back with a tow truck, but in the mean time the Bronco was stolen. The police called me at home that night and questioned me.
Eleven years later, a friend showed up with an 11 year old Bronco with just over 400 miles on it. And it still had the dent on the hood.
Turns out the Bronco got stashed in a shed, where it was found years later.
My friend bought it from the original Ford dealer.

 

[Broncobowsher]

Seeing the very low post count, guessing you are new to the Bronco?

Did you just flip the switch on the dash? All that changes is what the gauge reads.
Under the drivers seat there is a lever. That actually is what changes the fuel tank.
This is my first guess as the issue.

Round 2, if the valve was actually changed. Fuel line has an air leak. Think of sucking on a straw that has a pin hole in it. A slow sip, you get nothing but air. A hard sip you get air and drink. At cranking speeds it is a super slow sip.

I should step back, round 1½. If you ran out of gas, the fuel line is also out of gas. If the valve was switched it may be connected to a full tank of fuel, but the line, the pump, filter, carburetor are all empty. Takes a lot of cranking (which is very slow on the fuel pump) to fill everything so there is actually fuel getting to the engine. This is where people will often put a shot of fuel into the engine just to start it. Runs for a few seconds, fuel pump gets a lot of cycles in those few seconds and gets fuel up to the engine so it will run.

 

[SHX669]

I've also seen people turn the tank selector valve only 90* - to off - vs to Aux tank . Switching tanks to us " experienced and well used gear heads " -lol - who learned to drive on a '49 Studebaker pickup /double clutch / starter on the floor / vacuum wipers - switching tanks is no issue - to some of the younger generation it seems to be.

 

[Bronco808]

We have the electronic valve so I'm guessing it may have gone bad. Any tips on checking it, such as volt or ohm reading?

 

[DirtDonk]

Might depend on which type of electric was installed after the fact. There are the standard "solenoid" type with just one wire, and there are the "motorized" type with a larger body and more wires. Often six ports too, instead of the typical three ports of a standard.

Rather than an ohm reading, you could verify it's working at all first by having someone flip the switch with the key on (or just flip the switch to aux and then turn the key on and off) to see if you hear/feel a click in the valve.

Additionally, once it's verified that you're at least getting the valve to switch, you can remove the hoses and blow through it (using compressed air is best of course) to make sure that both inlet hoses are allowing flow through the outlet.
If one is blocked, then the valve is stuck/broken/defective and needs to be replaced.

Good luck.

Paul

 

[Broncobowsher]

If you have the 1-wire solenoid electric valve it may be an issue of how it was wired.

Where does the switch that controls the solenoid get the power from? Is that hot while the key is in the start position? Say it is on the accessory circuit. The accessory circuit powers down when the key is in start. Not a fault of the solenoid, a fault of the person who wired it in.

 

[Bronco808]

If you have the 1-wire solenoid electric valve it may be an issue of how it was wired.

Where does the switch that controls the solenoid get the power from? Is that hot while the key is in the start position? Say it is on the accessory circuit. The accessory circuit powers down when the key is in start. Not a fault of the solenoid, a fault of the person who wired it in.

I bought the Bronco from a friend who was 90% done with a Painless wiring kit, so you may be correct. When I test the wire that goes to the solenoid I get no power. Guess I'll have to check the switch wiring if he has a hot wire going to it.

Thanks!

 

[Bronco808]

Might depend on which type of electric was installed after the fact. There are the standard "solenoid" type with just one wire, and there are the "motorized" type with a larger body and more wires. Often six ports too, instead of the typical three ports of a standard.

Rather than an ohm reading, you could verify it's working at all first by having someone flip the switch with the key on (or just flip the switch to aux and then turn the key on and off) to see if you hear/feel a click in the valve.

Additionally, once it's verified that you're at least getting the valve to switch, you can remove the hoses and blow through it (using compressed air is best of course) to make sure that both inlet hoses are allowing flow through the outlet.
If one is blocked, then the valve is stuck/broken/defective and needs to be replaced.

Good luck.

Paul

Thanks Paul, I'm not getting power at the solenoid so I'm working my way back to the switch.

 

[SHX669]

Just in case you don't know - when the fuel lines are connected properly and the solenoid is wired correctly ; in the aux tank position the solenoid is receiving power to keep/allow the valve to draw fuel from the aux tank . When in the main tank position there is no power to the solenoid and obviously pulls fuel from the main tank . The side effect of this is if you lose power to the solenoid it defaults to the main tank.

 

[Bronco808]

Just in case you don't know - when the fuel lines are connected properly and the solenoid is wired correctly ; in the aux tank position the solenoid is receiving power to keep/allow the valve to draw fuel from the aux tank . When in the main tank position there is no power to the solenoid and obviously pulls fuel from the main tank . The side effect of this is if you lose power to the solenoid it defaults to the main tank.

Thanks good info to know. I'm gonna trace the wires back to the switch today and see if it has a hot line.

 

[DirtDonk]

And make sure to check with the key on. You would normally be able to check with the key in the ACC position, which is where most auxiliary circuits get their power from the ignition switch, but if the installer tapped into one of the ON-only circuits, you would not get any power in ACC.

Just don't leave the key in the ON position for more than a few moments at a time. Ignition systems (at least the older ones) don't like having power run through them without the engine running. You can damage things.

If your wiring harness is a new aftermarket replacement, it's possible that the gauges work on ON only anyway.

Paul

 

[Bronco808]

And make sure to check with the key on. You would normally be able to check with the key in the ACC position, which is where most auxiliary circuits get their power from the ignition switch, but if the installer tapped into one of the ON-only circuits, you would not get any power in ACC.

Just don't leave the key in the ON position for more than a few moments at a time. Ignition systems (at least the older ones) don't like having power run through them without the engine running. You can damage things.

If your wiring harness is a new aftermarket replacement, it's possible that the gauges work on ON only anyway.

Paul

Thanks Paul et al

So I traced the wire back to the switch and it wasn't attached. Also, the PO didn't have a hot wire to the switch to supply power to the solenoid. I found one in the painless wire kit he used and verified its getting power to the solenoid when it on aux. To be safe I also put in a new electric valve. Now I just have to drive it around the block a few times with the main tank hose disconnected and plugged to ensue its feeding from the aux tank.

 

[blubuckaroo]

I wired mine to an on only circuit. There's no reason to energize the solenoid when the engine isn't running.

 

[Wes harden]

Wow this story is so familiar to me. My wife would flip the switch and not the mechanical valve, and run out of gas. Numerous phone calls, pre cell phones.
I finally modded mine with the 1 wire electric solenoid. Mine would crank and hold the valve open at the same time. Only a problem if we ran out of gas on the normally open. We started using the normally closed side then switch to the normally open.

 

[bronco t]

Just curious... will the Main/Aux switch on the dash handle the amperage draw of a one wire fuel solenoid valve, or would one have to wire in a relay?

 

[BOBS 2 68S]

Just curious... will the Main/Aux switch on the dash handle the amperage draw of a one wire fuel solenoid valve, or would one have to wire in a relay?

Yes. I have had no problems on 2 Broncos over 40 years

 

[DirtDonk]

Those switches are failure prone even when just running the gauges alone. So while they can handle the added load of the solenoid, you might still be replacing one or two of them over your life of the vehicle.
Not necessarily caused by the extra load on the switch. Just the design I guess.

I bet there are still a few originals running around still working, but far more of them needed to be replaced. I got about 11 years out of my original, five years out of my second and the third was still going strong using it to switch a motorized valve and gauge.