$750 L98

So I have a spare 3rd gen firebird gauge I took apart. Now, since some one has already made the in tank sender work, I figure why not try the reverse route?

I have the gauge sitting in front of my with what looks like 2 resistors on it.

Empty (left side): 22 ohm, 5%, 2 watt green resistor
Full (right side): 82 ohm, 5%, 2 watt green resistor

Now, going by that would it be as simple as replacing each resistor with a corresponding resistor for the new sender? (though 22-82 ohm seems a little off to me). Any electrical gurus out there? This is really just experimental, but I'd like to be able to just swap the LS1 style pump assemblies in and out with ease, using factory parts.



Edit TESTING ONE NOW:
Finished my gauge and put it in the car, going to road test it tomorrow. This is a simple, and probably incorrect as far as electricians and the like are concerned - but it gets the point across.

Firebat

iTrader: (7)

Why not just buy a 97 grand prix sending unit?

#25319676. Sender out of a '97 Grand Prix.

https://www.thirdgen.org/forums/ltx-...s1-fuel-2.html

$750 L98

I read that, my issue is, a gauge is much easier to work on in the apartment and bench test. I can't have open gasoline containers/smell in the garage or the house. Plus being able to go with an off the shelf LS1 pump assembly would be nice.

Not to mention $1 for 2 resistors is a lot less than $160 for that sender.

It looks like I can modify the stock gauge very easily to accommodate the difference in the ohm reading. It looks really simple from what I see:

The two resistors on the gauge if replaced should turn it into a 40-250 Ohm gauge, at a cost of about $1 for the resistors. I'm not certain how this gauge works is the only problem. I believe part of the circuit involves the board on the back of the gauge housing (green sheet with contacts). I couldn't find anything on the site that covers how the gauge circuit works, at least not with any more detail than the wiring diagrams.

It's really just the fact that modifying a spare gauge that I have lying around is MUCH easier. Honestly it looks like it gets the same treatment as the fuel sender in the tank. Solder in new resistors, stick it back in and you are good to go.

The only real question I have is, the two resistors on the gauge, 22 & 82 - they should be replaced with a 40 & 250 respectively correct? Or is there another function in the gauge that i'm not seeing?

3.1EyeCandy

iTrader: (3)

Have a source for in-tank pump setups? Our favorite shop drilled holes in the bucket and removed the sock on mine...

$750 L98

Christ...all the more reason for me to check mine sooner than later. I bought a pump/tank locally for $100. It's a LS1 tank with the stock 40-250 Ohm sender, so I am working out a way to make the stock gauge work with a 40-250 Ohm sender. I'll let you know how bad I screw it up tomorrow.

Can't believe they did that to you! We need to get a group together with owners who had work done there as a therapy session LOL. You won't believe what I found. 3/4 of my trunk pan was removed for a fuel pump door. I kid you not, they cut out almost all of my rear floorpan, in PIECES - then welded it back in. No wonder it smells like fuel in there now. Our poor cars, did they tell you without the sock that pump was rated to 700rwhp? LOL

$750 L98

Ok, well I hacked off the 22 Ohm resistor, spliced in a temporary 680 Ohm and had it reading right. Maybe I figured it out. I'm new to wiring, and even newer to trying to mess with gauges and resistors lol

However I assume that the resistances just need to match up on the gauge and sender in the tank. Meaning I should be able to put a 40 Ohm and 250 Ohm resistor on the stock gauge and have it work just fine with the LS1 tank. That would bypass the need to do anything to the tank or sender itself.

I know it's late so forgive me if I missed something simple, and once some one with experience and knowledge on the subject gets in here. I'd appreciate help and clarification if I've got something wrong here.

3.1EyeCandy

iTrader: (3)

Yeah - they replaced my pump with a walbro and claimed it was necessary to put holes in the bucket/remove the sock or else the pump would starve. Luckily (compared to yours), they only removed enough to access the pump on mine (already a ls1 tank). If you've got a stock ls1 sender, I've got an extra (brand new) grand prix sender. I'm going to need the ls1 sender for the new speedhut gauges (adjustable but preset to the ls1 setting).

Now to find a complete bucket with sock...

$750 L98

well If I don't get this thing worked out we could definitely swap senders if you need a LS1 sender lol, I can't believe they trash the cars they work on like that though. Oh well, gotta do the work ourselves I guess - can't trust a shop to do anything but butcher them.

Ramair21

iTrader: (3)

Hey L98, You make a lot of sence. You might be on to something here bro! I really believe your on the right track here man. Im so excited about this cause i still need to fix my gauge to read right. and the only fix i thought was to replace the sender unit with the correct 0-90ohm one. I so excited i cant even type. you got it man. Keep working on it. Please ask me any question you have about resistance or circuits.

Joey J.

screeminchicken

iTrader: (2)

post up some photos on how u disassebled the gauge to get to the resistors and what they look like

Ramair21

iTrader: (3)

i just saw that this is for a firebird. Which is way different for a camaro. Still good to find out what you did

ghettocruiser

iTrader: (4)

Great thinking!!!

The only thing is...does the gauge swing in the correct direction? If so..you should be able to dial this in.

This could be as easy as having the LS1 sender out of the tank, and hooked up to the gauge. Move the float to the full mark, and adjust the resistence to show full. Move it down to empty, and adjust the other resistor to show empty.

however...Im not sure this is how it works. Those two resistors might just be there to balance out the voltage to help keep the needle from moving too much? I dont know...

This is quite a good idea though.

J.

Firebat

iTrader: (7)

My background is in electronics and electrical. Ditto on getting pics of the back of the sender - just to show where the resistors are going, how and what they are hooked up. I would bet that one resistor is not for empty and one is not for full when there is only one sending unit wire going to the gauge. One resistor is probably to add resistance in-line for a 0-90 ohm sender, because 0 ohms would be a short causing a fuse to blow. The other resistor could be in parallel to adjust the meter in the gauge. Or both could be working together somehow.

Without even touching the gauge cluster, a 140ohm resistor could be added in parallel going from ground to the sending unit wire to make the gauge read better but not perfectly.

Using the formula for resistance in parallel = RTotal=1/(1/R1=RX)
RT=90ohms(0-90 sender at max, what thirdgen gauge is looking for at max).
R1=250ohms(40-250 sender at max, what LS1 gauge is looking for at max).
RX=?(Resistance needed to change total resistance to 90)
Use algebra and solve for RX...
RT=1/(1/R1+1/RX)
=1/RT=(1/R1+1/RX)
=1/RT-1/R1=1/RX
=1/(1/RT-1/R1)=RX
=1/(1/90-1/250)=RX
=1/(.01111-.004)=RX
=1/(.007111)=RX
=140.625 =RX

The problem is if you run this formula and solve for RT instead, for the empty side with 140=RX and R1=40ohms(empty for LS1 sender), it comes out to 31ohms instead of zero. This means your gas gauge wouldn't ever show below 1/3 tank, gauge will only read from about 1/3 full to full.

If had a better idea of what those resistors on the back of the gauge go to, then could possibly calculate the gauge to read better than 1/3 to full by calculating somehow those resistors.

$750 L98

I know the gauge is a small electromagnet type on the firebird. With the resistor on the left (empty side) being a 22 Ohm I am guessing that like you said it prevents it from being a "short" or fully grounded, but at the same time will cause anything below 22 Ohm to read empty. That is likely the reason that I've had my gauge read below empty on a hard stop.

The full side is a 82 Ohm, probably to allow a bit of variance in factory senders and aging or wear and tear on it. The circuit looks simple, there are only 3 wires on it, power, ground, and signal. So I'm guessing that :

22 Ohm = empty
If signal is less than or equal to 22 Ohm it will show empty

82 Ohm = full
If signal is greater than or equal to it will show full, which explains why the gauge pegs full if it is disconnected from the sender (infinite resistance). However if you ground it, it will peg empty (NO resistance).

If that is correct, I should be able to replace the resistors and having it working on the LS1 range. I have been working OT and haven't had time to tinker yet, but it looks promising. I will get pics.

$750 L98

Also, each resistor has a pedestal attached to it, the signal wire also has a pedestal (magnetized with voltage), that comes very close to the copper windings around the gauge needle. That is what makes me think that it's a "greater or less than" kind of operation.

$750 L98

Found a schematic that shows the power/ground/signal. It works just like I thought: http://www.austinthirdgen.org/mkport...uges_part2.gif

Basically the needle is free floating and influenced by the signal coming from the sender. Both the 22 Ohm and 82 Ohm poles are charged, and canceled out by the signal depending on how full/empty the tank is. Correct me if I'm wrong, like I said I'm really new to this stuff, but if I can make it work - It sure would be easy on us when we swap LSx into these things lol

techrunner

this sounds great. way cheaper than a $100 sender unit. would love to see pics, i might just tackle this once i figure my other problem out. thanks, great thinkin!

screeminchicken

iTrader: (2)

Instead of using 2 resistors ......why to use that little adjustable resistor you get at the shack......i think its called a potentiometer

I am guessing u dont have a camera....try phone photos ......this thing is too intresting not to see what ur talking about

$750 L98

The potentiometer would be good for testing it out, I may grab one while I'm out. The two resistors are just replacing the stock resistors though - solder them in, and plug the gauge back in. I will get pics of the parts tonight. It will be late though lol, just been too busy to mess with the car for the most part.

LBC_camaro91

iTrader: (1)

wow that sounds like a lot of work. I was trying to get my 3rd gen gauges to work but said hell with it since some of my 3rd gen gauges didn't work. So i pretty much modified my 3rd gen dash to fit a 99 z28 cluster fits pretty good in there and got all the gauges to work like they should be. I also used the 99 z28 gas tank and fuel lines.

Here some pictures.

Thats my friend in the picture

LBC_camaro91

iTrader: (1)

LBC_camaro91

iTrader: (1)

LBC_camaro91

iTrader: (1)

Let me know what you guys think. Ill try to take some more better pictures i took these pictures with my cell phone. Ill try to take some pictures of the gauges working.

$750 L98

Not bad, that cluster fits pretty well in the camaro. I doubt firebird owners can get away with that though. I did modifiy one of my stock gauges. All you have to do is pull the cluster. (i've done this several dozen times experimenting with the lights)

You just need to pull the white gauge "bucket" out and pull the volt/fuel gauge. On the left side of the gauge you have a 22 Ohm resistor, and on the right you have a 82 Ohm resistor. I replaced them with a 47 Ohm resistor and a 220 Ohm resistor respectively.

After that you just bolt the gauge back into the bucket, pop the cluster back in and you are done.

Pics:

$750 L98

well I put it in the car and it seems to read right, I am still using the 0-90 Ohm sender right now, but I want to test the functinality and range of the gauge in the car. I will plug in a LS1 sender shortly to test it with one of those.

The new gauge has a range of 47-220 Ohm (173 Ohm sweep), so with a full tank, it should show roughly half. If it works out tomorrow morning it looks like all went well. Would anyone care for a write up and a few lovely MS Paint pictures illustrating this? Maybe a write up as an alternative to the sender method?

ghettocruiser

iTrader: (4)

Great work man! If this works...I would MUCH rather do this than goof with the tank sender. Ide rather the thing submersed in gasoline to be GM certified engineering haha. Also keeps replacement parts easy to figure out.

I was going to mention trying a potentiometer...basically making your gauge adjustable for fine tuning. Looks like you are on your way to some testing though. Im very interested in what you find! Ill never ditch my autometers, but this is GREAT info for any future projects I MIGHT have

J.

techrunner

YES! more info and pics would be great. I think i will try this, but having never pulled the cluster, i would feel a lot better about it if i could see more pics.

RED_DRAGON_85

wouldnt it be easier to just go to a junkyard, pull a fuel gauge from the appropriate car and measure the resistor values?
you could then put it back together and only pay the entrance fee to the junkyard.
and we would all know for sure the correct resistors to use.

$750 L98

I am going to test it with a potentiometer, but testing a 4th gen gauge would be nice. Unfortunately the nearest parts yard is about an hour away and I am working OT all week. Maybe this weekend. Until then I have to tinker with what I have, unless some one is willing to disect their 4th gen gauge and let me know what the values are.

Regardless, it works with my current 3rd gen sender, pegs empty when the tank is empty, and reads about half with a full tank. Going to fry's tonight to see if I can find a potentiometer, then I will make a video of an in car test with the potentiometer, and a small tutorial on removal of a Firebird cluster and how it comes apart.

Ramair21

iTrader: (3)

Hey LBC_camaro91, that looks pretty clean. Would you mind if i pick your brain about this?

LBC_camaro91

iTrader: (1)

Thanks man and no i don't mind go for it.


-Mike

$750 L98

Found some useful info on tech, a guy was gracious enough to Ohm out his stock gauge resistance values from full to empty.

His finding was:

33 ohm = empty tank = 0.57V

68 ohm = empty tank = 1.05V

100 ohm = 1/16 tank = 1.40V

150 ohm = 3/8 tank = 1.84V

220 ohm = 7/8 tank = 2.30V

270 ohm = Full tank = 2.56V

And I wired my mine like so:

33 ohm = empty tank = 0.57V (I used a 47 Ohm here)

68 ohm = empty tank = 1.05V

100 ohm = 1/16 tank = 1.40V

150 ohm = 3/8 tank = 1.84V

220 ohm = 7/8 tank = 2.30V

270 ohm = Full tank = 2.56V (I used a 220 Ohm here)

This ought to help some on get a bit closer than I did on the full side, but Like I said Fry's didn't have anything about 220 Ohm that was close enough. Anyway, If the mods feel this thread is worthy of being added to the conversion sticky as an alternative method of handling the gauge sender problem, I would appreciate it. I'll try to get some more clear and concise info together over the weekend when I'm not working oddball hours.

$750 L98

Just wanted to update every, I've been daily driving with this gauge for about 3 weeks. It works like a charm. As long as you stay semi-close to the values listed above it will be much more accurate than the 3rd gen gauge ever was.

If nothing else, I still just love the fact that ALL of my factory gauges work with the LSx like they were meant too now.

KNBlazer

any updates?

$750 L98

Yeah I've run it from full to empty months on end, it works just fine, and is more accurate than the factory gauge IMO. When it hits E I usually have about 3 or so gallons left, I prefer it this way because when it hits E, I am immediately looking for a gas station, but still have roughly at least 60 miles or so to do that.

I still need to get a camaro gauge to modify and test out. Modding the bird gauge I super easy though, if you are using a 4th gen tank, it is MUCH easier than taking the 4th gen sending unit apart (not to mention messing with electronics plus gas makes me nervous).

Anything in particular you wanted to know about it?

KNBlazer

I'll be replacing the resistors with a 50 and a 240 setup... this way I have at least a few gallons after hitting "E" and roughly about the same above "F" when full .... I have two 3rd gen Bird clusters, so I'll try it out on my old 80mph cluster and then apply it to my 120mph cluster...

$750 L98

Sounds like a plan, let me know how it works out for you. I may eventually use a 250-270 resistor for my full, but of course I was more worried about E being accurate and Fry's seemed to be lacking anything about 220 Ohm sadly.

luvmy64

did you ever get to pull apart a Camaro gauge and try this? Great thread, and needs to be "stickied"

$750 L98

I have not been back out to the parts yard yet for a camaro cluster. Doesn't seem like too many people prefer the method, but if I get some spare time I may run and get one to tinker with. Most camaro swappers seem to prefer the precut Autometer panels/clusters.

gpingu87

I am currently doing a ls1 swap into my 86 Firebird and i am going this route. So i just need to make a trip to radio shack and get 2 resistors, 1 as close to 33 ohm as possible. Better to be higher than lower if you cant get 33, so you think your out but in reality you have some left. And for the other as close to 270 ohm as i can get. Would it be better to go just above or just bellow this ohm for more accurate reading?

also dose the watt ratting or the resistors matter? A quick look at the autozone site showed me the exact right ohm resistors butt the watts was 1/2 and on the gause resistors its 2. Not verry good with electronics(pocket doing my harness) but i know basics.

Was looking at these:
http://www.radioshack.com/product/in...ductId=2062312
http://www.radioshack.com/product/in...ductId=2062318

Pocket

iTrader: (24)

1/4 or 1/2 watt will work fine. The wattage is the amount of power they're rated for

$750 L98

For full, get as close as you can to a 270ohm resistor, and for empty, I like the 47ohm, it seems like I still have a good few gallons or more before the tank is empty when it's on E, so as soon as it hits less than 1/4 tank I start looking for a gas station, but unlike the original cluster, I can actually make it on that much gas.

iansane

iTrader: (1)

Just wanted to throw up a thank you. I'm gathering parts to swap a 4thgen plastic tank in because my filler neck has cracked and I was dreading figuring out how to make the factory sender work. This seems mucho easier, plus the idea that I can get any parts store pump later on and just drop it straight in. Awesome. Thanks a lot.

82Camaroguy

What a great idea and write up! I am going this route myself, seems like it will be much easier than messing with the sending unit!

$750 L98

Glad it has helped some people out! I did find it much easier than fiddling with in-tank components, and in my case it was much cheaper, a few bucks in resistors beats buying a sending unit any day!

88FormulaKiller

iTrader: (8)

750, just so im postive on this, the lower ohm resistor is for empty and vice versa?

$750 L98

Yes sir, the 47ohm I used is for empty. I saw your post in the other thread and it seems like you are having ground or signal issues. I've been using my cluster up until I cracked my oil pan. Car is getting parted out now though. Did you get the wiring sorted out?

88FormulaKiller

iTrader: (8)

yeah the wiring is all set, i think one of two things happened, either i fried the gauge (which i found one local to replace the whole cluster, thankfully) or the float is stuck, I might drop the tank first and crack'er open. thanks for the info and great thread btw.

Zipacna

This thread is a little old, but I wanted to fire back saying my Firebird had a gauge with a 20ohm and a 120 ohm resistor. Although it looks the same as OP's. Now I'm wondering if I need to keep the ratio correct on mine or go with his setup...

After putting it on the volt meter, it looks like mine is actually outputting 70.65 on the 'high' side and 21 on the low side, so it looks like his setup is the way to go.

88FormulaKiller

iTrader: (8)

im wondering if i got the wrong resistors, i got the correct values, but the ones i got from the shack were mini compared to the fat green OEM resistors i cut off...? i never did fix the gauge, its stuck on 3/4 and hasnt moved with the resistors in, again might be a stuck float but i had the gauge moving at one point....