I'm putting a '99 plastic tank with internal fuel pump into my LS1 swap car. I have read several threads on the subject, and still I have a couple questions.

So far my plan is as follows:

Connect the hot wire that I have been using on my external fuel pump (controlled by the PCM) to the solid gray wire at the fuel tank.

Connect the purple wire from the tank to my existing pink wire for fuel level (I am not addressing the sender unit discrepancy in this thread, just want to make sure these wires are correctly paired).

Splice the black w/white wire and the all black wire at the tank and connect these to my 3rd gen ground wire.

My understanding is this will cause the pump to operate, and will send my fuel level information to the front of the car (to be dealt with separately).

I'd like to know how the system will operate with these connections. This plan leaves at least 4 wires on the plastic tank unused.

My questions:

1. Is my understanding correct on the wires listed above?
2. If my tank builds excess pressure, how will it be released?
3. Is my tank vented in such a way that it will not create a vacuum. Can air get in?

Any help would be great. Thanks for reading.

 

I don't remember wire colors but you only need to use the 4 wires on the 4th gen tank that go down into the fuel bucket assembly.

The two smaller wires are the pair for the fuel gauge. One side connects to your fuel gauge wire at the bulkhead connector behind the rear seat. Tie the other to body/chassis ground somewhere. It makes no difference which order you connect the wires. The two larger wires are the pair for the fuel pump, power and ground.

• Ground goes to a really solid point on the body or chassis. Ground somewhere close to the tank to minimize length of wire and associated voltage drop that will reduce performance of the pump.
• Power for the pump comes from a constant battery source or alternator, but has to pass through a relay so there is a means for the engine controller to turn the pump on and off. Terminal R9 is the wire from engine controller that has to go to the field coil (control side) of relay. Be sure to protect the battery wire with a 20 Amp fuse located close to battery, before the relay.

If your car was originally fuel injected then it already has a fuel pump relay in the engine bay and a pair of wires for the fuel pump located at the connector behind the rear seat. I wouldn't use any of that. The relay is a hazard with common failure mode of leads shorting out at the connector. The wires are undersized and you'll get low voltage at pump and reduced pump performance.

 

Here is how I plan to do my fuel system wiring. See post #59. Keep in mind that I have not seen it successfully work yet.

https://www.thirdgen.org/forums/ltx-...wktrips-2.html

Basically I'm adding an upgraded power supply for the fuel pump just like I suggested you do, and repurposing the car's original pump wires for the relay control and fuel gauge ground. This minimizes the number of wires running under the car and makes for a clean install. You don't need to have the relay in the back like I do, but it ends up being that way if you use a Racetronix hot wire kit for 4th gen cars.

 

Those are for tank pressure sensor and evap canister. Not used

 

Thank you both for your replies.

Regarding power to the pump, Pocket actually provided that supply when he built my harness. So far it has been providing power to my external fuel pump. And the pump only operates for 2 seconds with the engine off which I believe is correct. I plan to connect that wire to the gray one on the new pump so all should be good there.

1. Since the tank pressure sensor and evap will be disabled, will the tank always be at atmospheric pressure?
2. Are there mechanical tank pressure relief valves?
3. Do I need a vented gas cap?
4. Am I really supposed to submerge the sender resistance board and all the fuel pump wiring in gasoline? (call me old fashioned...)

 

1) if the tank is sealed, it will be under vacuum. Hook a vent to the EVAP line, the one from your 3rd gen tank will work or use a vented gas cap

4) much line fuel line, wires can come with submersible jackets. The board and wiring were submerged, it won't explode or anything

 

No need for a vented gas cap. Just use the existing evaporative emissions system on the tank for the vent. Leave the charcoal canister open to atmosphere.

Wires in the tank... I don't need to know how old or old fashioned you are, but I'd wager that EVERY vehicle you've ever driven has had wiring in the tank. In-tank wiring has been used for longer than you've been alive! You don't even need a sealed system in the tank - exposed metal is OK (even for wires with current flow). Even a short in the tank poses nearly no risk as gasoline is not flammable, and an empty tank is usually too rich for combustion.

 

Thanks for both the clarifications and the reassurance.

Some things you just don't want to learn the hard way.

 

I was under the impression that the charcoal canister has a native state of open vent if the wiring is not connected. If so, then it is a great filtered vent that will keep the car from smelling like gas.

 

Yes, I remember reading the same thing once, but I haven't seen anything to confirm it.

Hopefully that's the case, I think that would probably work alright.

 

I notice you're from Oregon. Ckeck out cascadecrew.org for a local group of people with thirdgens. Some have LS swaps too.

 

I didn't know about them.

Thanks for the link!