Fuel tank selector switch....!!!!!

[ochavez86]

My V30 tbi with dual tanks has a jumper wire in the fuel tank selector switch harness. I bought a new switch in place of the jumper and when I put it in it would stay on either tank. I have to hold the button on either left or right tank for the truck to stay running. If I let off the engine dies. Ive tried several switches, Im not sure what else could be the problem or if I have the wrong switch. It is switching from either tanks and reading correctly. I cant drive while holding the switch and tring to shift gears and stear with only two hands.lol Any suggestions?

[INSIDIOUS '86]

Glue...

What year and pin style is the switch?
Posted via Mobile Device

[wyattglock]

Sounds like you got the momentary switch. You need the switch that stays on either left or right tank. The tbi trucks need the current going to the pollak valve and the sending units constantly. Otherwise, the sending units lose voltage and shut down. I went through the same thing a couple times before I finally went to NAPA and got the right switch.

[hatzie]

You don't have the correct switch.

The 82-91 tank switch should be the same part. Many parts houses sell an incorrect 3 position polarity reversing Double Pole (Momentary ON)-OFF-(Momentary ON) switch. It's the wrong part. You can get away with it on the 82-86 dual tank motorized valve system but it's still the wrong part.

The correct switch for all dual tank 82-85 CK & 86-91 RV models is a 2 position polarity reversing Double Pole ON-ON switch. Meaning the contacts stay closed in each position and it does not spring back to a center OFF position.

[kustomrust82]

i have a question too, i changed both sending units, valve, switch. and everything worked fine for a while. now i have no gas gauge and im not sure if its switching tanks? ive been only on the left tank for sometime. i just asumed it was the wiring? could it be the switch on my truck doing this too? mines an 82. any help would be appriciated. sorry to post this on someone elses question. just wanted input while were on the topic!

[hatzie]

Originally Posted by kustomrust82

i have a question too, i changed both sending units, valve, switch. and everything worked fine for a while. now i have no gas gauge and im not sure if its switching tanks? ive been only on the left tank for sometime. i just asumed it was the wiring? could it be the switch on my truck doing this too? mines an 82. any help would be appriciated. sorry to post this on someone elses question. just wanted input while were on the topic!

82 is a transition year.
Do you have the single wire valve or the motorized valve with the 6 tower WeatherPak?

[kustomrust82]

Originally Posted by hatzie

82 is a transition year.
Do you have the single wire valve or the motorized valve with the 6 tower WeatherPak?

ill have to look at it tomorrow to tell you i dont remember, i believe it had a plug with mutiple wires. so probably the 6 wire. ? so switchs from 81-85 are different from 86-91? because of carb vs. tbi?

[hatzie]

Originally Posted by kustomrust82

ill have to look at it tomorrow to tell you i dont remember, i believe it had a plug with mutiple wires. so probably the 6 wire. ? so switchs from 81-85 are different from 86-91? because of carb vs. tbi?

The same maintained position polarity reversing switch should be used from 81-91. Even though you can get away with using a momentary switch on the 81-86 you'll have to hold it down long enough for the valve shuttle to make a complete transit. If the valve shuttle is not traveling all the way to the stop the gauge will not switch.

[Desert1957]

Originally Posted by hatzie

The same maintained position polarity reversing switch should be used from 81-91. Even though you can get away with using a momentary switch on the 81-86 you'll have to hold it down long enough for the valve shuttle to make a complete transit. If the valve shuttle is not traveling all the way to the stop the gauge will not switch.

OK, I have a question, If the switch is NOT momentary doesn't the motor see a constant 12 volts holding it in that position? I wouldn't think any motor would like being pushed to its stop and held there. Help me to understand my 83 setup. Do I have the wrong switch(Momentary)?

Desert

[ochavez86]

cool thanks Ill have to wait till monday morning but Ill try it out. Our good parts stores close half day saturdays and sundays. I thought that was my problem but Oreilly advance and auto zone all said this was the correct switch. Ill look for the maintained switch if not Im gonna have to rigg it up some how.

[hatzie]

Originally Posted by Desert1957

OK, I have a question, If the switch is NOT momentary doesn't the motor see a constant 12 volts holding it in that position? I wouldn't think any motor would like being pushed to its stop and held there. Help me to understand my 83 setup. Do I have the wrong switch(Momentary)?

Desert

Normally that would be a problem. However the 81-91 motorized fuel valve system is a clever little piece of engineering. It works because it has two SPDT micro-switches inside the valve combined with the polarity reversing switch on the dash.

Grab the '82 GMC Service Manual from the link in my signature. On the bottom panel of page 1364 you'll find the gasoline engine dual tanks wiring diagram for 1982.
Any of the '81-'91 wiring diagrams gas or diesel will show the same selector valve internal electrical detail as they all use the same valve...

Look at the "Fuel Tank Selector Valve & Meter Switch" internal detail box. I attached a quick drawing I made of just this detail.

• The 6 position WeatherPak has pins labeled A-F. Pin F has no wire.
• Internal to the valve you see 2 SPDT switches that are moved when the valve shuttle reaches either extreme end of its' travel.
• The top switch selects one of two opposite facing diodes that feed one leg of the shuttle motor from Pin E. Diodes are in very simple terms an electron valve that only allow electrons to flow in one direction. When this switch is activated it shuts off the motor. The Dash switch reverses the polarity of Pins D & E allowing electrons to flow through the selected diode again. The valve shuttle kicks the switch to the opposite diode when it reaches the end of it's travel. Electrons will not flow till the polarity of pins D & E are reversed again.
• The bottom switch selects which sender wire on pins A or C feeds the gauge on pin B.
  

[Desert1957]

Thanks again, Great explanation.

Desert

[ochavez86]

Thanks guys the maintained switch worked! It switches from left to right fuel tank great. Now all I need is state inspection, for now. Then Paint, new custom flatbed,motor overhaul, pipes , interior,etc.... This project has just begun.