1987 GMC fuel sending unit

[nascarmikeb]

I have a 87 gmc pickup original engine was 305 tbi. I now have a 350 carburated I am going to install. I'm trying to figure out the best way to make this conversion. A 1985 sending unit has a completely different connector than does the '87. I am using the standard fuel pump mounted to the engine block. I have removed the in tank pump. I want to be able to use existing truck sending unit wiring with a sending unit that doesn't have an in tank pump like those from 1985 and earlier.
Is this possible?

Thanks

Mike

[nascarmikeb]

I'm wondering if I use a sending unit for a 1987 GMC extend the strainer to the correct length and not use the pump. This way the electrical connection for the sending unit it self is made and the signal will be sent to the gauge. My only concern is leaving the connector for the pump disconnected in the tank if this is a safety concern. Thoughts?

Mike

[cadillac_al]

I have no experience with the 87 tbi fuel sender. If I had it apart i could make it work. Like you said, extend the pickup strainer. I would try to isolate the fuel pump wires from the gas gauge wire and disconnect them. When I removed a fuel pump from the sender of my Caddy, I bought a sending unit from a 69 Chevy truck and cut the tube and filter sock off it and connected it to my Caddy sender.

[nascarmikeb]

Originally Posted by cadillac_al

I would try to isolate the fuel pump wires from the gas gauge wire and disconnect them. When I removed a fuel pump from the sender of my Caddy, I bought a sending unit from a 69 Chevy truck and cut the tube and filter sock off it and connected it to my Caddy sender.

I have located the '87 sierra fuel system wiring diagram. I have located and isolated the sending unit wire and the pump wire on the truck harness connector.

I basically have 2 options here:

1. Use a pre-87 sender and splice into the truck harness sending unit wire to get a signal to the sender.
2. Or I can use a '87 sender/pump assembly and disconnect the pump power wire at the truck harness connector. This way there is no power going into the tank for the pump.

Just not sure which is the best option. I'm wondering if I use option 2 and I disconnect the power to the pump, would I lose power to the sender by breaking the circuit.

Thoughts?

Mike

[kipps]

The fuel gauge/sender circuit looks something like this.

12v battery source >>> fuel gauge >>> fuel sender >>> ground.

The only connections you need at the fuel sender are the wire going to the gauge and a decent ground. Your fuel sender unit should be grounded to the frame or to the harness. Leave that ground connection intact, and leave the wire intact going to the gauge, and you'll be fine.

To clarify, you should have three wires coming away from the fuel sender. One is for the gauge, one is the pump hot, one is ground for both functions. I only found two wires on my hacked-up '87 sender. I had to improvise a ground to get the tbi pump running with full voltage.

[nascarmikeb]

Ok I believe I got it. This is what I did.
Ordered a '87 sending unit only, no pump; this way my electrical connection will work. Isolated the fuel pump power wire on my factory harness & snipped it at the factory side connection. On the old sending unit, I cut off the pick up tube that the pump hooked to. I then used the supplied heavy duty rubber hose and clamps that came with the new unit and attached the "extension" tube to the new pickup tube, so the tube extends to the bottom of the tank. It ended up being the exact length
Now hopefully when I install everything, my gauge will work.

[nascarmikeb]

Now all I have to do is figure out how to convert the 5/16" & 3/8" fittings at the end of the factory steel TBI fuel & return lines, so I can connect braided steel fuel lines to my pump. Any suggestion on the correct fittings? I have read to use 6AN fittings
there are so many options on summit and other websites.

Thanks for all of the help everyone.

Mike

[kipps]

Originally Posted by nascarmikeb

Now all I have to do is figure out how to convert the 5/16" & 3/8" fittings at the end of the factory steel TBI fuel & return lines, so I can connect braided steel fuel lines to my pump. Any suggestion on the correct fittings?

Browse through the "LS swaps" section under "Engine and Drivetrain." Using braided hose and AN fittings is pretty common for those swaps.

Personally, I don't see any point. It doesn't add any durability over common fuel injection rated hose, it's under the vehicle where no one can admire it, it costs a lot more, and it will be nearly impossible to find replacement hoses or fittings outside of mail-order sources.

[nascarmikeb]

Thx for the reply. I wasn't clear. I'm keeping my steel lines from the tank to the engine compartment. Now, I need to get those fuel supply and return to my pump mounted on the block. This is where I need the correct fitting on this end of the steel lines. I don't intend to change the entire fuel lines, not right now at least. I just need to supply the engine with fuel, so it will run and be safe (no fuel leaks.)

[kipps]

Originally Posted by nascarmikeb

Thx for the reply. I wasn't clear. I'm keeping my steel lines from the tank to the engine compartment. Now, I need to get those fuel supply and return to my pump mounted on the block. This is where I need the correct fitting on this end of the steel lines. I don't intend to change the entire fuel lines, not right now at least. I just need to supply the engine with fuel, so it will run and be safe (no fuel leaks.)

The line from the tank to the pump is not under pressure, since the pump is sucking fuel from the tank. If it were me doing it--

Pick a spot where the two steel lines(supply and return) leave the frame rail and begin to go up to the tbi unit, and cut the supply line there with a hacksaw. Slide common 3/8" fuel hose over the sliced steel tube, and secure with little pipe clamps. Use fuel injection clamps if you're really particular. Use several cushion clamps or zip ties to support the fuel hose within the frame rail for those last three feet to the fuel pump. Optionally, protect the fuel hose against any chafing with 5/8" split wire loom.