Hey guys - new 3rd gen owner here, so please don't crucify me on this one, but...

I'm swapping out my stock 3rd gen fuel tank to a '99 LS1 plastic tank. Did the whole "fuel gauge is not correct" problem ever get figured out? I have read a LOT of discussions, but I can't seem to find a definitive solution. Surely after a decade this was figured out and I'm just missing it, right?

I have the stock LS1 tank, filler neck, sender, in-tank pump, etc... I just want to be able to bolt it up and plug it in. Is there an actual step-by-step writeup anywhere? Everything I see is partial threads and broken links.

Thank you

 

You need a new level sending unit from i believe a 97 grand prix

 

Post #1 of my build thread has links that will answer some of your questions.

https://www.thirdgen.org/forums/ltx-...-qwktrips.html

Orr90RocZ just gave you the right solution.

Somebody is likely to say you can change out resistors in the fuel gage. Doing that will make the needle align with "full", but you'll never get enough sweep of the gage for "empty". Follow the link I gave you above to the info about modifying the fuel gage if you want to know why it doesn't work.

 

Thirdgen fuel gauge is looking for 0-90ohm. I used an aftermarket Grand Prix fuel level sensor assembly but only used the circuit board from it. I did the following:

1. I removed the circuit board from the LS1 sending unit, it is held in by plastic clip, may also have to disconnect wires to get the fuel level assembly parts removed from the sending unit
2. I de-soldered the wires off of the circuit board for the LS1 sending unit
3. Removed the board from the Grand Prix unit and de-soldered the wires off of it (just like the LS1 unit in steps 1 and 2)
4. Soldered in Grand Prix sending unit board to LS1 sending unit wires and re-installed.

Here is the link to the aftermarket Grand Prix fuel level assembly I bought, It's a Herko GFC31 For Fuel Pump Module E3978M: https://www.ebay.com/itm/Herko-Fuel-...72.m2749.l2649

 

That only works in the first/early design sending unit.

 

I'm assuming that Herko GFC31 unit is just about the exact same thing as this one Hawks is trying to sell for $169!?!?
https://www.hawksmotorsports.com/82-...-tank-swap-gm/

That fixed it full sweep @Firebat? It's (mostly) accurate from FULL to E?

Guess I will pull my sending unit from the new tank tonight and keep my fingers crossed it is an early design.

 

?? I was unaware there was any difference in the 99-02 tanks

 

It's normal for Hawks to price items the way that they do. The one that Hawks sells might be a more plug-n-play one. I could make one like that by using both new LS1 and Grand Prix aftermarket fuel level sensors for much less than that.

Yes, new GP sensor is mostly accurate, old LS1 fuel level sensor was stuck on full until a couple gallons were left in the tank.

 

Man! What a pain to get that retaining ring off.

Here's what mine looked like - appears the Herko GFC31 you linked to will fit the same mounting tabs. I should be good-to-go, correct?

 

Not the tank, the sender. GM revised the design later. I think I read about the hat of the sender melting from the current to the fuel pump.


Yes, that is the first design, should be good to go

Point of note, I do remember having to bend the float arm to swing the other way because it was reading full at empty and empty when it was full. Simple fix

 

I'm assuming I can just Ohm test this *before* I put it back in the car

 

Yeah i actually was able to plug the unit into the body harness outside of the tank and key on, move the arm to see gauge move

 

Perfect. Thanks guys. I've got it on the way.

 

That’s how I got my fuel gauge to work. Your instructions are clear and concise.

 

Sorry if this is a dumb question, but why do you need to re-solder the new board? It looks like it will mount right back in place of the old one. Are the connectors different?

I'm pretty experienced at soldering - but the fact this thing sits *in* the gas tank has me a bit worried about a bad solder joint shorting out and starting a fire. Maybe there are some physics here I'm not understanding though.

 

The fuel sensor wires lead to a plug that also includes wires to the fuel pump.

 

I was able to just swap the board over to the plastic holder in the sender from the 4th gen

Also, there is no possibility in the tank for a fire, there is no oxygen available.