1987 Sierra classic fuel sending unit

nascarmikeb · April 28, 2018

I have pulled the original 305 FBI & have put in a 350 mechanical fuel pump.. I have pulled the electric fuel pump assembly and want to go back with a fuel sending unit only.

Trying to figure out which sending unit to use that will plug into my existing 87 wiring so my fuel gauge reads correctly

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txab · April 28, 2018

Couldn't you keep the original assembly, remove the pump and re-plumb the pick-up tube/filter, then just use it.

Or buy the same sending unit and plumb the new pick-up assembly

Edited April 28, 2018 by txab

nascarmikeb · May 1, 2018

thx for the reply.

My first thought was to just purchase a new sending unit but just don't install the pump portion and the eletrical connections will work. My only concern, and it may not be a valid concern, is if I don't use the pump, then I have a pigtail connector disconnected inside the fuel tank. I wasn't sure if this would be a safety issue. You know, open electrical connection inside a fuel tank. I have been trying to find research on if there are any safety concerns with the pump wire not being connected inside the tank. Any feed back would be appreciated.

Mike

txab · May 1, 2018

Couldn't you clip the wire outside the tank?

sdeeter19555 · May 1, 2018

thx for the reply.

My first thought was to just purchase a new sending unit but just don't install the pump portion and the eletrical connections will work. My only concern, and it may not be a valid concern, is if I don't use the pump, then I have a pigtail connector disconnected inside the fuel tank. I wasn't sure if this would be a safety issue. You know, open electrical connection inside a fuel tank. I have been trying to find research on if there are any safety concerns with the pump wire not being connected inside the tank. Any feed back would be appreciated.

Mike

The upper explosive limit (UEL) is exceeded inside the fuel tank, too much vapor, not enough oxygen. That's why electric pumps are safe inside a fuel-filled tank in the first place. As long as the electrical connector isn't shorting out, should pose no issue.

2012 2500hd 6.0l CCSB 4wd

nascarmikeb · May 1, 2018

4 hours ago, sdeeter19555 said:

The upper explosive limit (UEL) is exceeded inside the fuel tank, too much vapor, not enough oxygen. That's why electric pumps are safe inside a fuel-filled tank in the first place. As long as the electrical connector isn't shorting out, should pose no issue.

2012 2500hd 6.0l CCSB 4wd

That is very good info. Thanks for the UEL. My plan I believe is to use the '87 sending unit/pup assembly, this way the factory electrical connections are made and I get a reading to the gauge. I have the wiring diagram and I know which wire at the truck harness is power to the pump. My plan is to disconnect it at the connector. I'm wondering if by disconnecting the power to the pump, will this break the circuit and the gauge not work. Or does the gauge work without the pump wired up.