Edit 11/27/06: Moved pictures on to the thirdgen server. See attached pictures in this post and on my next few replies.

*Trumpet Fanfare*

Ladies and Gentlemen,
It is with great pleasure that I present this guide on how to modify your LS1 fuel level sending unit for 0-90 ohm use with your stock gas gauge. Enjoy.





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When doing the LS1 swap, one has two main options for a gas gauge when using a LS1 gas tank: 1) Keep the stock LS1 fuel sender and accept that the gas gauge will be inaccurate, or 2) Modify the LS1 fuel pump assembly to accept a 3rd gen fuel level sender. Since 3rd gens use the more common 0-90 ohm gas gauge, the fuel level reading will be incorrect when using the LS1 fuel sender, which is 40 ohms empty and 250 ohms full. The following is how to modify a 2002 LS1 fuel sender to give a 0-90 ohm reading. Thanks to "jeromio" over at LS1Tech for the idea of using a 100 ohm resistor. He is the only one that I know of who has performed this modification.

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Here is the LS1 fuel pump assembly next to a stock 3rd gen fuel level sender from the junkyard. I couldn't figure out a way to modify the sender to fit on the fuel pump bucket to my satisfaction, so I started looking at the LS1 sending unit.

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The LS1 resistor assembly.

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Here is the LS1 resistor, after I had scraped on it a few times. The black coating seems to be a conductor, and when I scraped a little off, the resistance increased. The upper contact is where the resistance changes, and the lower contact is where the 2nd brush touches to give current to the left side wire.

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This is the heart of our new fuel level sender, a 100 ohm wire wound resistor, available from Radio Shack (come in packs of 2, 10W, 10% tolerance). Be careful that you don't nick the resistor when you chip the ceramic coating off of it. I found that softly tapping on the resistor with a hammer will do a good job. You will then need to rob off any little particles that are left.

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After bending the resistor to match the upper curve on the LS1 PCB resistor, I took the Dremel and carved out a section for it to sit in, as well as drilling two holes for the leads to go through. You cannot use any glue to hold the resistor in place, as the gas will eat it up. Bend the resistor leads back towards the front to hold the resistor in place.

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The factory brush pickups could not be used due to being bent and broken while I was trying to figure out how to sender worked. So, I took a strand of copper from a 1.5 inch section of 10-gauge primary wire (bought from Napa) and pulled it through two holes that I poked through the plastic "head", and then bent the ends over to keep tension. I then took a small piece of 0.005" brass, bent it in a smooth arch, and soldered both ends to the copper strand. The brass sheet is made by K&S Engineering, and is available from any good hobby shop.

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You can vary the ohm reading by about 10 ohms, depending on which end of the head you place the bump that touches the resistor. With the brush bump in the factory/LS1 position (left side), I could get 90-8.8 ohms, left-to-right, full-to-empty. With the bump on the right side of the head, it measured 78.8-0.4 ohms. I opted for a more accurate empty. Be smooth when tapping the brass pin in to hold the head to the plate, and test the movement when you get to the end. There is a tiny bit of play between the head and the brass pin (to allow it to move) and my bump would loose contact with the resistor if I moved the head "out". I had to adjust the bump height to stay in contact with the resistor throughout the movement and play of the head.

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Here is the finished LS1 fuel sender; all that is left to do is wire it. There are two purple wires on the LS1 resistor. The right side wire is "D" on the fuel pump connector, which is from the PCM and is Low Reference. This connects to C405A (rear bulkhead connector behind back seats) as a 20 awg Black/White wire. The left side wire is "A" on the fuel tank connector, which changes into a 20 awg Purple wire on the way to C405A. This wire is the 5V Fuel Level Sensor Signal, which goes to the PCM, and which you should connect to the gas gauge. Solder the right side (0-ohm) resistor lead to the Low Reference wire, and then solder the 5V Fuel Level Sensor wire to the copper strand on the head. Do not worry about the left side lead, since we don't want a constant 100 ohms.



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I have proofread this several times, making edits for clarity, but let me know if there are any errors. How do I submit this for a tech article?

 

Have you tired it yet??? Looks pretty complicated Not sure if i want to take that on. Dont want to break more things

 

What do you mean tried it? I did all the work, as well as ohm measurements with an ohm meter... so it works if that's what you are asking.

 

Have you put it back into the tank and filled it up with gas and see that the gauge reads right? Thats what i was asking lol

 

I tested it with an ohm meter by moving the brush head. It is exactly what will happen when you fill up the gas tank... the plastic float moves the head, which changes the resistance. There is no way that I would modify this, install it in the tank, and fill it up with gas only to find out that it doesn't work.

 

thats alot of work...and confusion

how about i give you $100 plus parts and modify mine for me ???

 

Here's an update for you. I installed the sending unit in the tank and into the car today. Final readings before I installed the sender in the tank (after soldering the wires and a little more tweaking) were 0.3 ohms empty, 79.8 ohms full. A 10 ohm resistor needs to be added in series to the 5V fuel level sending wire (to the gauge/PCM) to give me 0-89.8 (0-90) ohms.

You can do this... you're a thirdgen'er after all. I had no idea what I was doing when I first started, especially since I had no instructions or pictures to go by. I've practically written out a whole tech article on how to do this along with pictures for you to follow.

Possibly. How long can you live without it (i.e., turn around time)?

 

I will give you $100 too... Sound good??? How lond do you think it would take for you to do it bro?? SOrry to confusing you lol. So put in a 10ohm resistor in series with the purple wire coming from our fuel gauge?

 

I just thought about it again, and no, a 10 ohm resistor will no do anything. It will increase the resistance a 0 ohms to 10, so it will mess with the reading across the board. It was a good idea though.

I've found a source for 90 ohm resistors online (instead of 100 ohm) so I will look at those next, and see if I can get 0-85 ohms instead of 0-80. It's not so much the resistor that is the problem as it is the head's limited travel. I'm not sure what the gauge reading is at 80 ohms, but I'm guessing it will be around 90% (.9 x 90 ohms is 81, which is close to the 80 ohms on the modified one). I am looking at having a company design a PCB replacement, so all you would have to do is pull out the stock PCB resistor, cut the wires, and solder them to the new 0-90 ohm resistor board. I wouldn't mind modifying your sending units to work, but I haven't finished the wiring or tested mine with a full tank, and I wouldn't feel comfortable modifying anyone's without testing mine first, in case I forgot something.

 

lol, hell if you guys are willing to pay $100 plus parts for it, i might get into it... LOL!

seriously though, super_kev.. nice writeup... you might want to post it in the conversions section of LS1tech too.. give them the same info.

 

Thanks. Yes, I was thinking of doing that.

 

Well bro, I will wait till you test it out fully. But as soon as you do and it works, Im going to need your address lol.... That would be great if some company could make this. Wouldnt be to much work at all.

$100 per unit, you would make a killer bro....

Joey

 

Well I'm working on getting the factory-style 0-90 ohm PCB resistors made as a direct drop-in, so that is my ultimate goal. I'm sending the OEM board in to get re-designed. Hopefully I'll have something in a month or two.

 

I cant wait for that!!! Thanks bro, you just made the swap even more fun.... Finaly going to get my gauge to read right

 

Solid! Nice work Kev!

I have been working on this too and rumour has ir that the 98+ V6 cars used a 90 ohm sender for some reason so i bought one at a flea market for 2 bucks and was gonna try it just havent got that far I dont even know if its gonna fit. I am taking this week off work and my goal is to have the car running by Friday so i will likely be posting/searching/questioning like MAD to get it all done so if any y'all see a post or two from me this week please help where you can.

I cant wait to hear that thing run... Its been a year and a half out of comission

 

YAHOO!!!!!

Drama over. V6 sender is 80 ohms. Snaps right in place all plugs the same. I took a bunch of pics with my cel phone and no way to load them right now but its was pretty easy to get it in there. The sender I got wasn't even from a Camaro so I had to snap it the LS1 tanks float arm but very simple.

Nice effort Kev I wish I could have verifed this sooner and saved you the hassle. I'm on the road for starting this biatch on Friday so I gotta get back to work...

 

80 ohms? So it still doesn't give us a full full. Once the 0-90 ohm PCB resistors are done, it'd be pretty simple to install, and you would have a true empty and a true full.

 

Maybe my meter is sketchy cuz my stocker read 80 ohms too and the Ls1 ohm'd out at 233 so that would make sense.

Regardless the sender I put ohm'd out EXACTLY the same as the stocker. Only odd thing was the offset of the V6 unit was a little different where the tabs are that hold it locked in place so i had to reverse the locking slider in from the top. It fits fine no intereference and holds well. Heres a couple of pics. Apologies for the poor quality. Phone cam

 

the 4th gen pump reads 0-250 empty-full. instead of pulling sender apart and redoing it why not just put your 100 ohm +-10ohms inline with the sender signal wire and be done with it? but thats just my opinion.

 

Look up on how resistors work. If you added a 100 ohm resistor, you would get a 100-350 ohm signal (0+100 to 250+100).

 

so what kind of car did that v6 sender come out of? 4th gen?

 

Yes.

 

There wouldnt be a part number on that V6 sending unit would there? I would like to change mine before I put the tank into my car and this would save me a little money and I wont have to put another gauge in my car. I would look it up but my other computer is dead right now and I dont have the parts book on this one. Thanks

 

yes there is a parts number i can get it for you monday night. i work at a dealership lucky me i can get them for 60 bucks but i think your cost is like 130ish. so ill get you the part number.

ryan

 

I usually order from Dal so I wouldnt have to pay full price for it but $130 is a little much. Ill see if I can find the CD I have with the part numbers. If not I would appreciate it if you can get the number

 

I found the CD parts book I have. The gauge sender isnt listed seperately so if you can find it please let me know. I would rather not buy a whole fuel can unit, GM Parts Direct say list is $500, $260 their price. For that much I would modify myself or ty to find a V6 car and get it out or just buy a gauge. So please let me know if available seperately

 

To my knowledge, it's not available seperately. A junkyard would be your best bet.

 

Been outta the loop for a week or so but I have no pn for that unit I used. I bought it off a GM parts man at a flea market who had TONS of stuff that was sitting collecting dust as he put it. He didnt know what year it came from and it had no pn on hence the two bucks price.

Those prices above seem pretty steep to me. Try a gas tank rebuild shop maybe if they didint have it they could point you in a better direction

 

there is a part number for the sender. i can get it for you all come monday night.

so now with that said are we even sure that it is a v6 4th gen sending unit that is the correct reading? 0-90ohms?

 

No, we aren't positive what year it is, but I do know that it is not '99-'02 LS1 or V6. I will find out middle of the week when my '98 V6 sender gets here, so let us know the PN for that.

 

what the crap? this is the only thing holding me up on my swap.

 

No so hopefully someone orders one in and bench tests it right there at the dealer( anyone friendly with their dealer could do this )

The float arm on mine was WAY different than the ls1 unit so dont let that scare you the sender was practically identical aside from the color and the arm just snaps in place. At least we're on the right track

 

okay so ill order one monday and test it at work. hopefully its correct cus they thend to complain if i order something and then dont buy it. haha

 

You couldn't have posted this up before I put that tank in my car?? ARRG, now that thing is going to have to come back out. Do you know how much that sucked for me? Great info, better late than never!!

 

Well, someone had to do it, and I wasn't going without a stock functional gas gauge like the rest of you suckers.

FWIW, I've removed and installed the LS1 tank twice now. I've gotten it down to 10 minutes out, 10 minutes in. Hopefully I'll do it just one more time (if the V6 sender I'm getting is correct).

 

Do those 10 mins include removing the rear suspension/ exhaust?? or just the tank? If everything, you have to come over and help me out!! Even the tank itself seemed to take the better part of 1/2 an hour.

 

dude its not that hard to remove the panhard rod and the drive shaft disconnect 1 brake line and everything swings down. but thats off topic who cares this is about the sending unit.

 

I know that it's not tha hard, it's the removal/install (esp the install) of the tank that's the time eater. more a hassle than anything.

 

*Anxiously waiting* Any word on that part number?

 

ok folks ill have part numbers tomorrow night. i dont want to release any part numbers if the sender does not read 0-90ohms.

 

Ok, the '98 V6 unit came in, and it is the same reading as the '99-'02's, so we now know that it's not:

'99-02 LS1
'99-02 V6
'98 V6

I've spent over $120 getting fuel pump units from junkyards to measure the ohms, and I've decided to take a break right now. I'm guessing the elusive part # is going to be from a '93-'97 f-body.

 

haha i see you have come to the same conclusion as me. i spent the better part of today in the parts room of my dealer measureing senders of all kinds. haha no luck. i agree with the 93-97 lt1's. i was talking with a tech today he said they didnt switch over to the 30-250ohms til obd2 so if we search for obd1 hints early lt1's we might have something. so yeah who wants to order a sender? hahahahaha

 

LMAO what have I started. All this for a freakin fuel gauge. Go figure

Wish I had a pn for you guys

 

seriously dude. you should have a p/n they are usually right below the variable resister board on those things.

 

Its installed and in the car now and I have little to no spare time hence the year and a half its taken to get the swap this far. I am lucky to get one day every three weeks to work on it and I have the diff, exhaust, heat shields, fuel system all installed so yanking out the tank now is just not an option.

I reviewed all the pics I took and the numbers are illegible but it looks like the first two are 24. Better call Columbo now cuz I'm tapped. Wish I had more info for you guys

 

Thats what I was thinking when I asked a few days ago. Where do you live? Ill come drop the dank get the P/N and put it all back together, lol.

 

well ive pretty much got my whole shop thinking about this whole fuel sender ordeal. some are saying jbodys others s10's but i believe we need to search years 96-97 because that is when they really did the sender crossover. this is so complicated. i wish someone new this stuff my ohms and not just part numbers.
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you know looking at those pictures. im almost tempted to mount the stock 3rd gen sender on the plastic assembly of the 4th gen. maybe some screws or super glue

 

I agree, but what else has that type of plastic unit? I would think it's a recent GM design... maybe 'vette as well, but I thought they had a different pump/bowl setup than the f-bodies.

I tried that, and wasn't happy with how the sender fit. It's not an easy glue-on solution, especially since gasoline dissolves glue and other things like that.

 

dang no glue huh? bummer. haha screws? no corvettes have a sattle bag type tank due to the torque tube. yeah i dought they have a 0-90ohm being gm's flagship and all. i honestly think though its gotta be in those sunfires/cavaliers or s10s because think about it. how long did that bodystyle last they were seriously like the redheaded step child of gm no upgrades or anything. im betting its gotta be one or the other. and im going to go with 96-97. but idk. im almost to the point of being over it and just putting a radio shack resister in it and finish my swap.

 

i have the solution