I need help with fuel tanks on my 87 dual tank

[Nutro]

I've got my 87 dual tank TBI that has the 4.3L V6 and I put all new parts in it and I cannot get the drivers side tank to fire. The pump primes with the key on and it will crank but I'm not getting fuel in the throttle body. I've checked grounds etc. All new stuff.

New tanks
New pumps/sending unit assemblies etc
New selector valve
New dash tank selector switch
New fuel filter


The passenger side works perfectly. I can key it on the DR side and I hear it prime but will not fire when cranking. Every now and then, it seems like it wants to start but it just cranks. I did find that the previous owner installed a "Kill switch" toggle switch mounted to the dr side kick panel. They basically cut one wire behind the dash selector switch and routed to the toggle then out of the toggle and back to the cut wire on the body side.

I removed the toggle and it still won't fire but works perfect on the pass side.

I'm lost.

 

[chengny]

I've got my 87 dual tank TBI that has the 4.3L V6 and I put all new parts in it and I cannot get the drivers side tank to fire. The pump primes with the key on and it will crank but I'm not getting fuel in the throttle body. I've checked grounds etc. All new stuff.

New tanks
New pumps/sending unit assemblies etc
New selector valve
New dash tank selector switch
New fuel filter


The passenger side works perfectly. I can key it on the DR side and I hear it prime but will not fire when cranking. Every now and then, it seems like it wants to start but it just cranks. I did find that the previous owner installed a "Kill switch" toggle switch mounted to the dr side kick panel. They basically cut one wire behind the dash selector switch and routed to the toggle then out of the toggle and back to the cut wire on the body side.

I removed the toggle and it still won't fire but works perfect on the pass side.

I'm lost.

Does the gas gauge seem to indicate the level of the selected tank? If switching tanks (and the tanks have significantly different levels) does not cause a noticeable change in the gauge reading, it may indicate that only the pumps are being switched.

There are only two leads coming out of the select switch - a gray and a tan. Somewhere between the switch and the Pollak valve each lead splits into two legs. One goes directly to the in-tank pump, and the other continues on to the tank switch valve.

This is pure conjecture, but consider what would happen if the splice in the tan lead (to the production tank) failed. Depending on how it failed, it's possible that power to the pumps would shift, but the branch to the valve would not.

So, you'd get a situation where the desired pump is running, but when the fuel tries to pass through the valve it can't - because the valve is still lined up to the auxiliary tank.

The contacts for switching the gas gauge sensing legs are mechanically coupled to the valve. That's why it is a good way to tell if the valve is actually shuttling - along with the pumps being switched.

Just a thought.

Like this:

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[Nutro]

Hmm I need to check that this evening. I started with 5 gallons in each and when I changed tanks it seemed the levels were the same (As they should've been) but now that I've been driving the truck on the passenger tank, I haven't checked level in the other one. So you're saying the pump might come on but it's not shuttling the fuel to the dead tank. If I remember correctly, I had 12v key on at the selector valve for that passenger tank but that only tells me the pump is working, not that its shuttling.

I do recall when I bought that Pollak valve it came with 3 rubber plugs but I removed the caps and can see the diverter rod Inside the housing so I had assumed it would work.

 

[chengny]

Hmm I need to check that this evening. I started with 5 gallons in each and when I changed tanks it seemed the levels were the same (As they should've been) but now that I've been driving the truck on the passenger tank, I haven't checked level in the other one. So you're saying the pump might come on but it's not shuttling the fuel to the dead tank. If I remember correctly, I had 12v key on at the selector valve for that passenger tank but that only tells me the pump is working, not that its shuttling.

I do recall when I bought that Pollak valve it came with 3 rubber plugs but I removed the caps and can see the diverter rod Inside the housing so I had assumed it would work.

So you're saying the pump might come on but it's not shuttling the fuel to the dead tank.

Kind of like that.

When you toggle the switch on the dash to the LH tank, power is applied to the tan lead. That is supposed to do three things:

1. Start the production (LH) tank pump

2. Shift the valve internals so that the ports to and from the LH tank are opened - and the RH ports are closed.

3. Switch a set of contacts which determine which sending unit is connected to the gas gauge.

But if the tan lead has an open at - or after - the splice, no power goes to the valve. Consequently, the valve ports remain lined up to the RH tank (and the gas gauge continues to read that tank as well).

So, even though the pump is running - and trying to supply the engine - the flow is dead-ended at the transfer valve. And tank level indication remains on the RH tank.

This is all a WAG. It could be any number of other things. Maybe the best thing to do first is disconnect the supply hose from the LH pump to the valve and verify proper flow/pressure. If you confirm that - and since the other pump is able to run the engine - then it would kind of suggest that the valve isn't switching correctly. But since it is brand new - rather than the actual valve being the problem, you might next want to verify that power is getting to it.

 

[Rusty Nail]

Kind of like that.


This is all a WAG. It could be any number of other things.

Merry Christmas @chengny .

 

[chengny]

Merry Christmas @chengny .

Tks Rusty, and same to you and yours.

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[MrMarty51]

Remove the hose from the inoperable tank, at the diverter valve, shove on a different piece of hose, remove the hose to the TBI at the valve, switch to inoptank then blow into the hose, that`ll tell You if the valve is going to full on mode for that tank.
If You also remove the hose that goes to the operating tank, when You blow into the hose, if You can feel air coming through the other port, then You will know that the valve is bypassing fuel to the other tank.
I once did have to repair a in tank pump on a brand new Dodge van, when they put it together at the factory, they did not get the hose clamp all the way onto the nipple, inside of the tank and the hose was mostly popped off the nipple, it would act like it wanted to start but just not enough pressure to feed the fuel to the TBI.
Might possibly be what happened inside the inop tank.

 

[Nutro]

I crawled under the truck last night and pulled the inop tank hose off at the valve and had my father key that tank and I am getting fuel so the pump is sending it. I also get 12v key on at the valve wiring so something is screwy

 

[MrMarty51]

I crawled under the truck last night and pulled the inop tank hose off at the valve and had my father key that tank and I am getting fuel so the pump is sending it. I also get 12v key on at the valve wiring so something is screwy

But is there fuel coming through to the out port to the TBI ?

 

[chengny]

I crawled under the truck last night and pulled the inop tank hose off at the valve and had my father key that tank and I am getting fuel so the pump is sending it. I also get 12v key on at the valve wiring so something is screwy

By any chance, when your father toggled the dash switch left to right - did you verify that power shifted between the TAN & GRA leads?

If so, you have proven; the switch is good, the wiring to the pumps/valve is good and both pumps will deliver gas to the transfer valve.

The output from the RH pump is able to pass through the valve and supply the engine normally. However, the output from the LH pump is blocked by the valve and can't supply the engine.

If you didn't check that the power to the valve - on the TAN/GRA leads - is alternating as expected when the switch is toggled...I would certainly do that before you blame the valve. I say blame the valve, because that is the only thing that hasn't been proven good - if the switching of control power to it has been checked.

But, at this point it seems that the valve is not shifting. So the plumbing always stays lined up to the RH tank - regardless of which pump is operating.

 

[Jppr26]

Man I got the same problem with my 87. It had rotted out tanks when I got it so I put new tanks, sending units, and filter. Both tanks worked fine for a while till one day running on left tank truck instantly died, I switched to the right side and fired up fine, switched left, instantly dies everytime. Everything but the wire harnesses is new now and same thing.

 

[Ron Sebastian]

Following. This has happened twice to me so far. Truck just dies. I switch tanks, and the truck runs. I switch tanks again and the truck runs. Weeks go by and the same thing occurs again.

 

[Wildjoe330]

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What your looking for is the power to the (AUX tank)
solenoid switch (that nut connector in the picture) that
changes fuel from one tank to the other When the drivers
side tank or custom, or Aux tank side, of the switch is not
getting power to the solenoid fuel switch it will default to the
passenger factory tank and you will only run on the factory
tank passenger side of the truck.

When the fuse to the turn signals is blown on my square body
it shuts down the custom tank too, the Aux, tank Drivers side
tank for the 77 and then it only runs on the Factory tank or
passenger side tank, and you better have fuel in it or your not
going anywhere. ha always run out the Drivers / Aux side fuel
tank first so you can run on the factory tank later.

It happens to me on my 1977 it originally only had one factory
tank on the passenger side no extra right left switch in the cab
NO EXTRA PARTS HERE AND THERE SO IT helped me figure it out.

 

[chengny]

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What your looking for is the power to the (AUX tank)
solenoid switch (that nut connector in the picture) that
changes fuel from one tank to the other When the drivers
side tank or custom, or Aux tank side, of the switch is not
getting power to the solenoid fuel switch it will default to the
passenger factory tank and you will only run on the factory
tank passenger side of the truck.

When the fuse to the turn signals is blown on my square body
it shuts down the custom tank too, the Aux, tank Drivers side
tank for the 77 and then it only runs on the Factory tank or
passenger side tank, and you better have fuel in it or your not
going anywhere. ha always run out the Drivers / Aux side fuel
tank first so you can run on the factory tank later.

It happens to me on my 1977 it originally only had one factory
tank on the passenger side no extra right left switch in the cab
NO EXTRA PARTS HERE AND THERE SO IT helped me figure it out.

I think the posts above are in reference to TBI systems, with in tank pumps and transfer valves using a 5 wire control circuit. Like this:

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[Nutro]

Okay! So I finally had some decent weather and crawled under the truck and removed the selector valve to possibly replace it again with another new one. I pulled the valve but decided to have my father key it with all the lines disconnected and holding the valve in my hand. The passenger side that was working, sprayed fuel. I had him select the LH tank and key it. The pump humms and primes but NO fuel is coming out.

For a recap. All brand new:

LH and RH tanks
New pumps/sending unit assemblies
New selector valve
New fuel filter
New dash selector switch
Rebuilt TBI throttle body

I either got a bad brand new pump that primes but does not pump or I have a kinked line coming from that tank. What sayeth the hive?