Tbi swap build thread

[68c10owner]

Can anyone tell me if there is a single external fuel pump that will work wit hthe TBI? I have dual tanks so i would need 2 fuel pumps if I went with internal pumps right? Would I have to change my tanks or just the sending units?

[cjracing15]

Originally Posted by 68c10owner

Can anyone tell me if there is a single external fuel pump that will work wit hthe TBI? I have dual tanks so i would need 2 fuel pumps if I went with internal pumps right? Would I have to change my tanks or just the sending units?

If you use in tank pumps you will have to get a FI tank. The fuel injected tanks have baffels in them to control fuel slosh so the pump will not suck air if the tank is low of gas. Plus you will have to get the sending unit and pump.

I am just going with one tank right now because that is what i have. I will get both tanks working in the futrue.

I have talked with "Dirtylarry" about what he did and it sounds real good.

He swap the one primary tank on his truck with the in tank pump, and then monted a transfer pump so he can just pump gas out of the spare tank when he needs it. It will be cheaper I think than making every thing work like stock. (unless I can find a donor parts truck cheap)

[cjracing15]

Well I got to work on the old truck today. Got a little done before I had to quit.

First I untangeled the harness a litle more. I cut all the tie points on the harness and re soldered them so they are all untangeled, and i can route the harness some time this week hopefully. THe first pic is what you will find with a stock tbi harness with all the tie points. They are crimped and covered with tape from the factory. The pic has a sample of both.

Second I got the oil sending unit and switch fixed. I went to the parts store and got an brass adapter to adapt my oil switch to the tee threads. Problem sloved.

Third I instaled the intake on the motor I to use anouther intake than the one in the pic above because I found a crack in on of the back bolt holes. So I was thankfull that I had a spare. You can see in the last pic of the oil switch and sending unit instaled on the block. Stay tuned.

[68c10owner]

Originally Posted by cjracing15

If you use in tank pumps you will have to get a FI tank. The fuel injected tanks have baffels in them to control fuel slosh so the pump will not suck air if the tank is low of gas. Plus you will have to get the sending unit and pump.

I am just going with one tank right now because that is what i have. I will get both tanks working in the futrue.

I have talked with "Dirtylarry" about what he did and it sounds real good.

He swap the one primary tank on his truck with the in tank pump, and then monted a transfer pump so he can just pump gas out of the spare tank when he needs it. It will be cheaper I think than making every thing work like stock. (unless I can find a donor parts truck cheap)

My truck has dual tanks but I only use one so I guess it doesn`t matter. I`ve only used the other tank when I was running low on gas and was worried if I had enough to get to the station.

[DirtyLarry]

This is going to be a nice and informative thread!

With TBI, I think you guys will probably be fine running a frame mounted pump to pull fuel through the dual tank switch valve however you may need to figure out a way to pause the frame mounted pump while you switch tanks otherwise you will stumble the engine momentarily. As far as the pump, just mount the pump as low as you can below the tanks and switch valve and on the engine side of the switch valve.

The problem I had running a frame mounted pump with my 8.1L was twofold. First, 8.1L requires 60 psi fuel pressure but on my marine controlled 8.1L it only requires 43 psi. None the less, the return side ports on the OEM switch valve are little bitty 5/16 ports and restrict the high pressure fuel return flow back to the tank causing the fuel pressure to run around 100 psi at the fuel rail! Once I bypassed the switch valve the fuel pressure ran normal. This would not be an issue for TBI as TBI only runs around 12 psi and what little fuel goes back to the tank is very small compared the later model sequential EFI engines. GM used that exact switch valve on TBI trucks anyway so again, the fuel return through the switch valve won't be a problem.

The second issue I had with the frame mounted pump was mainly off-road where you are crawling along on the trails at 2 MPH for hours on end without any wind blowing over the pump to keep it cool. Once I would stop for a minute to take break or something then try to restart the truck it would only crank as the fuel pump was too hot and cavitated the fuel inside. The pump would scream like crazy when it was warm too! Being my truck sees more off-road than on, I wasn’t going to be able to live with that so I swapped to a ’87 TBI tank, ’87 TBI sending unit with a Corvette fuel pump to feed the 8.1L the pressure it needs.

GM and AC Delco pn for the switch valve 14029228


Here is how I had my frame pump mounted. Protected by the cross-member from road debris and also shielded from the exhaust. This contraption is gone now that I have converted to an in-tank pump and a transfer pump to move fuel from the secondary tank to the primary.