I searched around but im wondering what the stock 3rd gen gauge reads or of what kind of reading at all it gives BEFORE any mods (resistors or sender)? Mines pegged, cant tell if its an open circuit or just the way it acts before modding it. I'm moding it now with resistors but im wondering if the sending unit was DOA/stuck from my work.

 

3rd gen sender or 4th gen?

 

4th gen tank with 4th gen guts, gonna modify gauge with resistors to use stock gauge, trying to decifer if its normal for the gauge to peg with the wrong resistors in there or if my sender is bad, rapped on the tank a few times just to see if the gauge would move, nothin.

 

This is what I did https://www.thirdgen.org/forums/ltx-...s1-fuel-3.html post # 105

The resitor part of the thread confused me. The only benifit that I saw with the resistors would be the guy who wants to retain the stock guages as well as emisions.

 

thanks for the info i actually i read that thread. the issue i have with that is im already driving my car, last thing to "fix" is my gauge and after getting it together, im not ready to rip the tank out again unless i have to. i just finished soldering resistors in so ill go install and see if it works.

 

nope still pegged at full. confused... jacking up car now to check tank wiring.

 

4th gen sender is about 40 Ohms resistance on empty, and 'full' on the 3rd gen gauge is calibrated to about 90 Ohms resistance. I think the original gauge will read around 1/2 full when the 4th gen sender is at empty. And the gauge will not even come off full until there is well less than 1/2 tank left.

 

well i just put in a 47ohm (E) resistor in and a 270 ohm resistor (Full) into the gauge, when the purple wires out back are connected for the sender it pegs to full, i wasnt positive that was the wire so i switched to the pink lead from the tank to the purple 3rd gen sender wire and it drops to 1/8 of a tank, i went to fill, put in 5 gallons, needle didnt move up at all. thoroughly confused here...

 

i dont if this will help someone help me, but the resistors i took out were:

20ohms 5% 2watt

and

120 ohms 5% 2watt

 

The two purple wires from the 4th gen tank are the fuel level sender. Tell us how you have those two wires routed. It seems to be behaving as if you don't have the 2nd purple wire connected to ground.

The pink wire was originally the B+ power supply to your pump. It has nothing to do with the fuel gauge. The gauge didn't move because it is just responding to whatever circuit resistance is on that circuit. I'd be more worried about damaging your cluster with what you did.

 

i dont have 2 purple wires off my 99 LS1 tank, i have one ppl wire, i have the3rd gen ppl and 4th gen ppl connected right now and i just resoldered the resistors in reversed, i think i might have put them in reversed by mistake, going to add gas now, ill post results later.

gauge is currently reading around 3/4... im gonna go see if its accurate.

 

Picture below is a LS1 F-body pump module. Note the 2 purple wires to and from the level sensor. Those go to the 4-pin white connector. 2 of the pins are the level sensor and 2 of the pins are power for the pump.

Resistors are not directional. Doesn't matter which way installed.

 

i see the two ppl, but im telling ya, i used the LS1 bulk head right through the body, i have all the wiring coming into the cab, i have 2 grounds to one 3rd gen ground, pump power to 3rd gen power and one ppl sender to 3rd gen ppl sender, just as jon (pocket stated) i kept the harness complete so theres no missing wires. with the resistors i meant i put the higher ohm'd one on the full side and vice versa. im stumped. must be a bad level sensor in the tank.. really not sure

weird thing is the gauge shows 3/4, even after topping it off...

 

I suspect you have open circuit to the fuel sender (not grounded correctly using 2nd purple wire).

The fuel gauge operates on a trio of resistors with the fuel sender being the center leg with variable resistance depending on level of fuel float. I think the fuel sender is not grounded correctly (2nd purple wire) and is open circuit. The needle is sweeping to whatever the position dictated by the value of the two resistors you soldered into the guage. When you swapped the resistors the needle switched sides with it. Not having the center leg working is also why your fuel gauge never moves.

Maybe I have some details incorrect (I've not done my swap yet), but it sure seems the problem is somewhere in the wiring at the tank.

 

88Formula, what sender do you have? Stock 4th gen or the Grand Prix?

 

well heres the thing, i opted this route from 750 L98's thread, search fuel gauge or something (in this forum), it comes right up about changing the gauges resistors, its only 2 resistors and fairly easy to change them. also, if you check around, searching "fuel tank wiring" you'll find a couple threads on the 4th gen tank wiring, no mentioning of a 2nd purple wire, i do Not have a 2nd purple wire. my next step is to drop the tank and check the sender and maybe even buy a another fuel gauge to modify just incase.

 

stock 4th gen

For QwkTrip:

Post #4 https://www.thirdgen.org/forums/ltx-...ear-brake.html

Thread from 750 L98:

https://www.thirdgen.org/forums/ltx-...auge-40-a.html

 

I think you did like I did originally. The purple wire is supposed to be connected to the purple and then there is another wire (I Believe it was grey) that needed to be grounded from the sender, BUT there are two grey wires from the bulkhead, one is for the pump. Should be easy to identify since the pump wire is a lot thicker.

When I put mine in I screwed up and had a full tank ALL the time too, though I dont remember what I did that was wrong now. I actually ran out of gas and then I realized my mistake.

 

my grounds are white and black and are both grounded to the one 3rd gen wire, if i didnt ground my pump, it wouldnt work... ill have to take a pic, but again, i might drop my tank this weekend and see whats up with it.

 

Pin B is fuel pump 12v, splice this direct from the 3rd gen harness gry to gry

Pins C blk and D blk/wht are grds for the pump and sender respectively. Splice these to the 3rd gen grd wire blk

Pin A ppl is fuel level sender signal. Splice this to the last wire on the 3rd gen pigtail ppl to ppl

One of the purple wires (the ground) from the level sender in the tank, changes color from purple to blk/wht when it exits the top of the sender. I think thats where you two are confusing each other.

88Formula, I still recomend going to the Grand Prix sender and leaving the resistors alone.

 

Yep, you're right.