has anyone successfully tried or at all..... trying to put a modern day fuel level sender in their thirdgen gas tank? i think it would be great to have those newer senders that had an internal delay so your gas gauge wouldn't instantly react when you went downhill or uphill and gave you false readings cuz of gravity also wouldbe great to have those senders that have internal switches to hook up to an led and get that yellow light when your running low on gas. has this been done yet?

That's a good idea but I'm thinking is it worth the trouble to do it.
Wouldn't it have to be correctly calibrated or 3rd gen specific?

i would think....all you would have to do.... if you want to use your stock fuel gauge

find a modern fuel sender that matches the ohm readings of our stock fuel sender.

like at 160ohms our gauge reads full you would have to find a sender that reads 160ohms when the fuel tank is full

just a simple example i have no idea what the ohm readings are

or i guess you could gut a modern day car and take the fuel gauge and fuel sender and do some homework on how everything is wired up.

and install in the thirdgen.


personally i want the low fuel light and im tired of the fuel gauge always moving cuz of gravity on a hill

i would love to get a professional opinion on this.

my car is my baby and runs fine i dont want to do such an operation unless i was darn sure it would work

anyone else have any thoughts on this?

I'm sure there's a way of turning on a warning at a specific resistance then IF that's what you're getting at.
I might just research this and come up with something.
I'm a member at 12volt and the guys there are really helpful.
I'm sure they got just the thing.

Edit: I've posted it up and should get a reply soon.
I'm thinking we can just wire something into the wiring behind the dash to help us out on this. Like a small circuit of transistors.
I'll get back about it when I get results.
Maybe someone else has a quicker solution here though.

The only thing that bother me about my gauge is....

3/4 tank = 160 miles
.Empty = 200 miles

WTF???? Our gas gauges are SO inaccurate, it isn't even funny.

great thanks astro surfer this would be awesome if it can be done.

another thing you can ask is maybe something we can put in the circuit with our stock!!! fuel sender

like a delay circuit so our gauges don't react as quickly for when we go uphill or down hill like modern day cars

also maybe something we can put in the circuit like a resistance switch that will turn on a yellow led when the tank is almost empty


that would be great if we coudl just add something to what we already have.

that way we dont have to drop the gas tank.

just a thought

another thing that would be neat is the little digital display that calculates your MPG but hey one can dream

Those gadgets were popular in the 80's. They used a magnetic pickup on the driveshaft and a transducer in the gas line to the carb. I have a British made unit I'm hoping to transfer to my present car this summer.

There's lots of silly & sloppy things about gas tanks. Why for example is the pickup usually in the front of the tank when you need gas the most when going uphill? One should also think it's important that the float should be located in the middle of the tank to give the most consistent readings up/down hill. Senders are incredibly simple & inaccurate wire-wound potentiometers. The length & angle of the arm to the float is important for its calibration.

interesting so any suggestions on how to upgrade our older vehicles?

I'm guessing that the actual age of our senders would account for the ever so inaccurate readings we get.
I'll also assume that more in tank baffles, or better designed baffles are used in more modern cars. making the gauge less reactive.
I've had a very busy day and not had time to check out 12volt yet.
I'll check in a minute and see if the guys have replied with any ideas yet.
Tracking mpg on our old cars would require 2 measurement units I'd imagine. 1 for feed and 1 for return and some sort of logical calculator to decifer actual usage. Very feasible if someone wanted to spend that kind of time figuring it out.
I'll say that the warning light will be the easiest to do. May require installing a new sender unit to make it function correctly tho.
If your gauge reads zero before actual zero then the warning would be way too premature.
I have a whole bunch of 555 timers I bought a while back.
I'm sure I can come up with a circuit that functions as we are trying to accomplish here.
No one has answered on 12volt yet but 28 views so far.
Someone knows what to do.

ok sounds good. lets stay on this.

it would awesome if we can come up with something that everyone can use if they wanted to.

To make a tank gage accurate requires some tedious work if you can't get parts that are known fixes. The way I see it you'll have to make a kind of "jig" or an open model of the tank if you will. Remove the sender from the tank, inspect it for obvious defects and mount it on the model, then hook it up to the gage in the car. Moving the float will show you what's happening & what needs to be done. You may need to bend the rod to the float up or down, "shorten" or "lenghten" it, & finally make sure the float becomes as close to the middle as possible (when back in the real tank).

An empty tank light could be made in two ways. One is simply tapping the voltage from the sender and feeding it to a simple transistor circuit that turns on a light. This of course requires a correctly adjusted sender. The original 80's circuits consists of only 1 transistor and 2 resistors. The other is mounting an extra device in the tank independent of the float.

As for mpg displays - it would be sad to have to reinvent the wheel - there were dozens of models made in the 80's. But maybe most of them were scrapped along with the cars they were mounted in, and so hard to get hold of now.. FI has made the market small. If the return line comes from the fuel pump then you only need one flow transducer. They are simply an impeller in the flow, being magnetically or optically detected, but you basically need nothing less than a one-chip computer to make an mpg display.

The thing about a 24 yr old sender is that it is most probably worn out at the half to quarter tank due to that being probably the most used place of the float position on the variable resistor that is actually sending the signal to the dash. It is after all metal against metal with no lubrication. A new unit would overcome this I'd imagine. It's merely a resistance value sent to the gauge and can easily be tapped to turn on a light at the right time, but like I stated before if you have a bad sender it won't work right. I know I can do this with a transistor. I have lots and lots of these since I dabble in electronics. I am currently working on sequential tail lights that don't cost an arm and a leg to do. Components are cheap. But I keep having issues with my 555's. I'll get there.
I'll dabble in the light at the weekend when I got time.

im really excited to see if you guys come up with soemthing, i would REALLY like an accurate reading fuel gauge. im really not smart at all with this stuff so ill sit back and just watch

I know the late 80's Chrysler Lebarons had an mpg display, among others. I owned one a few years ago. Is there anyways to adapt the components from one of them to make an mpg guage for us? Or at least salvage the flow transducers? What does the transducer look like anyways?

As for guage accuracy, as long the needle is one needle width under the red line or higher, I've got enough fuel to get to the station. :P

i had an 89 buick riviera that was ALL digitial and even had a stock touch screen radio/climate control/EVERYTHING. also had an 88 Cadillac (Huge effin car) and it had digital fuel milage and that thing where it tells you how much farther you can go on your fuel in the tank. very handy.

Bobby_80s, that does sound a like a great idea. For a moment, I thought my fuel gauage was broke (seeing how sometimes I would drive up or down hill and it would play tricks with me). Now I'm much releived to hear that these things are just inaccurate.

I know I don't know much about the subject, but what about something from the 4th gens? Were those ever accurate, or are they just like ours?
If not, I know this may sound funny, but maybe something from an import instead of domestic (seeing how the majority of the time, those seem to be ALOT more accurate, rather than playing guessing games).

yea i was curious to see if anyone knew if the late 4thgens were more up to date in this area.

and if anyone knew if the 4thgen tanks fit under our cars. might make life easier if it was a direct swap with a sender insdie much more accurate and already has teh wiring for the low gas light i would imagine


and it would be cool if someone can scrap a mpg gauge or parts from those buicks or cadilacs and seee if we can rig something together

4th gen tanks into 3rd gen cars are a VERY common thing, especially with the LS1 swap crowd. Since the LS1 needs a higher fuel pressure, it is much easier to just toss in a 4th gen tank with the higher pressure pump, than to find a high pressure pump to fit in our 3rd gen tanks (unless they go external pump) but even with an external pump, you still hafta pull the stock tank and remove the 3rd gen pump, (i believe) to prevent it from being a "restriction" to the higher pressure pump.

As for accuracy...I dunno if it is any better or worse, but I do know the signal is different, so that needs to be addressed to get our gas gauge to read correctly.

I've even seen TPI cars switch to a 4th gen tank & install their stock pump inside it.

The mpg displays I was referring to were aftermarket gadgets for carb engines. I see now you're FI of course. FI mpg displays would use the information that's already inside the ECM. It only needs a "few" lines of code extra in the ECM to make a display. An external add-on display would instead have to measure the injector and speedo pulses and make a calculation.
I would expect factory displays to be inherent to their respective ECM; that is you couldn't extract & adapt the display into another car (without some serious programming feats).

does anyone know of current kits or old parts that we can put together to work for our cars as far as the mpg display is concerned,

and yes i have 305 TPI FI engine

well if anybody does do this, whether its for carb, TPI, or TBI, make a sticky for it so the rest of us can do it to.

My friend has a 95 Trans Am and its fuel gauge fluctuates on hills and under acceleration and braking. If I recall correctly, it's quite as bad, but it's not fixed. Maybe the LS1s were better.

any follow ups on this guys?

how is this done??? im going carb (thank god) and id love to do it.. how much is this gonna cost me?

I did a quick search on eBay and came up with only one Driving Computer.
That one'll set you back around $190.-
I don't think they were as expensive back then as I was able to afford one even as a student. But like I said most people that had them most likely ditched them along with the car, and nowadays I guess the market for them is too small for them to be produced. But they could be home-made from just a one-chip puter w display, a flow sensor, a speedo pickup, and some relatively simple programming. Anyone dare ask the DIY PROM guys?

thanks for the ebay link now at lesast we know the name of the item from the 80s its a start a bit steap but might be worth 190

anyone else find any other products? im looking right now. illl post if i find anything

any one know if this zemco item is ok with fuel injection or does it matter?

Anyone figure out anything about the dummy light theory, it seems like it would be a relatively simple light to wire. Any inputs on what can be put before a 12V bulb to get it to turn on at a good range? Like out of the 0-90Ωs (empty to full respectively), is there something that can turn a light on at say 20Ωs?

yea if anything this would be a good simple mod if someone can figure it out.

im not too good with the calculations my only concern is if we feed off the fuel signal for ohms would it change the value that hits the gauge and give false readings?

probably impossible or dumb question, just want to make sure

it's not a dumb question, and it is a possibility, but if we branch a wire out in parallel a little ways before the guages, i don't think that it will affect the guages that adversely if at all, but with a wire and guage that depends strictly on a specific resistance range, i guess it could affect it. Something for someone to chime in about, but it isn't a bad or stupid question.

The computer I linked to was made for carbed engines. It won't work on FI if there's a return line from the fuel rail, just like it wouldn't work with a carb if the return line was coming out of the carb itself.
You can't put a lamp directly on the sender wire, that would screw up the reading, you need a properly designed IC/transistor circuit in between that won't load the gauge circuit. You can make the circuit light the lamp at any voltage (resistance) you desire, but you'll need to know if the sender is 0 or 90 Ohms when the tank is empty.

If I get a chance this weekend I'll see what I can figure out.
I'm thinking I can include a 555 timer to trigger at a specific resistance and flash the actual fuel gauge illumination.
Though now I'm thinking how I can do it in the daytime. I guess I got to go with some sort of LED setup for this.
I will figure this out.
You cannot patch off of the feed wire straight to a light...like above was stated...it has to be done with a separate circuit.
Still won't work on an old faulty sender though.

Interesting discussion. I have 3 thirdgens and they all have the "Waving" fuel needle.

I can confirm that the fuel gauge is 0-90Ωs (empty to full respectively). I tested my float while i had the sending unit out to replace the pump. There might be slightly higher by one or two ohms at full, but as you get down, it does go to zero. Is this something simple to wire together? Like how many parts would i need outside of a circuit board to make this happen?

My fuel gauge in my 92 would never go above 1/2 a tank. I know the dash had issues tach was WAY off along with other guages reading in accurately. I have ordered a new gauge to install in my custom dash to see if the issue goes away...

Anythings possable. With technology the skies the limit. Being an electronic engineer alot of this stuff could be done fairly easily with radio chack parts. As for the discussion at hand. Now ill have to take a look at the schematic for the circuit but im sure something can be worked out. Having a warning light for low fuel wouldnt be too bad i wouldnt imagin if designed correctly could even be adjustable. Although the wide needle fluctuations are usually the result of a bad sender this could be applied to an electronic filter to smooth out the fluctuations a bit. Also with the guage inacuracies a circuit could be designed to allow you to adjust the range of the readings. So the user could actually drain the tank and set a minimum resistance and then fill the tank and set the maximum resistance. This means as long as the sender is linear it will be accurate within the tolerance of the sender itself (and fluctuations in level). A fuel milage gauge could be done but would require conciderable more costs than the above ideas but heres a cheap ballpark alternative. A cars fuel consumption is related to engin vacuum less vaccum less MPGs. It would be possable to "tune" a vaccume gauge to your car to give you a pretty desent approximation of MPG for the cost of a $20 vacuum gauge.

I would like to just stop the fluctuations while driving... Maybe a schematic?

Well if all you guys wanted to do is to reduce the fluctuations this would be about how youde want to go about it. To clear up how this circuit works because there seems to be a bit of a missunderstanding the gauge actls like a tug of war between the maximum and minimum reading on the guage. The deciding factor is the voltage at the connection associated with the fuel sender. When the fuel sender is at 0 ohms it essentially shorts out one half of the gauge's "tug of war" sides and the gauge pegs to the empt side. With the maximum 90 ohms the circuit pegs to the full side. The objective of this circuit adds a bank of capacitors that will by nature resist any change in voltage at the fuel sender. Much like the perpose of large capacitors used in high power sound systems to keep adaquit power without voltage fluctuations. If you have enough capacitors you can essentially make the gauge not fluctuate at all. However if you have too much capacitance the gauges responciveness will be less than the rate at which gas is being burned. This means the gauge will always be trying to catch up and never be right. Thats where the addition of a variable resistor comes into play. By increasing or decreasing the value of this resistor you can controll the responciveness of the gauge. The lower the resistance the lower the respocniveness the less prone to needle fluctuations. The amount of capacitors hooked up in parralel and there values is not really critical but the higher the value and the more in parralel the greater ability this circuite will have in dampaning the fluctuations. Due to a lack of information on the gauge itself i cannont say how much capacitance would be needed or what value of resistance would work best for the disscharge resistor but this is where alittle trial and error comes into play. I would guess a potenciometer of 0-10k ohms for the disscharge rate resistor would work and again the more capacitors the better. Too few will not allow this circuit to work too many is ok. If done correctly this circuit should work but as with any mod you attempt this at your own risk.

ok good we're getting somewhere,

now who wants to be the ginny-pig haha

Yea i cant wait to hear the results as to how much capacitance/ resistance is needed. However i cannot stress enough proper installation caution some capacitors will explode if hooked up backwards and aside from that do it correctly so wires dont short out against the body of the car (although it will not harm the gauge as the fuel sender is designed to go to 0 ohms anyways). So basically installed with alittle common sence this will work. Anyways i cant wait to hear the results. Also i recomend etching your own PC board (supplies can be bought at radioshack for less than $20) for a very profetional job. Also if someone has there car in a position they can make some measurements, other circuites can be designed to do things like the low fuel warning light. Ide do it myself but sadly its about 10 degrees here and without a garage makes auto projects very difficult.

what kind of measurements are you looking for exactly? I'm interested in the low fuel light so that i have an idea of the range of fuel i have. I haven't experienced this fluxuation everyone's talking about, but then again i haven't driven my car but a few times.

I've got some components on the way for the light...some thing I did not have.
Will be making the circuit shortly.
However I am unable to road test this, at the moment.
I need to be absolutely certain that the sender is definitely 0/90 ohms.
parts stores list them as another value.
So before I go making these...I need to be certain.
As a side note.
Would people be interested in purchasing these as a self install into the dash or would they want it to hook up to somewhere else.
Not everyone is capable of removing and installing things.
I have the schematic I need and if successful I would fabricate these upon request.
Where would folks like the light to be?

Well what ide really like to have is a mathamatical modle for how the gauge works. That way i can determine what voltage across the sender corrosponds with what fuel level. To do this what i need is data from 3 points 1/4 tank, 1/2 tank, and 3/4 tank. I need the voltage measured across the fuel sensor with respect to ground (with the gauge hooked up) and the exact resistance of the sensor itself also with respect to ground and with the fuel gauge dissconnected. From this information i can come up with an equation that describes how this circuit functions. Without this information it makes it rather makeing a low fuel light circuit is possable but it would have to be adjusted by the user to turn on at the right fuel level. If i had a mathamatical modle for how the guage worked then i could get this circuit operational without any tuneing required (allthough i still think it would be nice to be able to adjust the on/off points for the light)

id be willing to purchase one for a reasonable price and instructions lol. i think id like to have mine in replace of one of my dummy lights. or maybe screwed into the bottom of the dash pad. just make a "prototype" and we can go from there.

I personally was going to see if i can put into one of the unused dummy light locations on my dash, so that it looks nearly stock until i'm low on fuel, and either way, i gotta look over for the gas guage so seeing the light would catch my eye. Anyways, it might be 0-100Ωs, because if i remember correctly, it went slightly above 90 when i forced it up. 0-90 was something i've seen a few times on this website, and thats how i tested it when i had it out of my tank.

what I will be making has to be user adjusted for each vehicle.
Easily done with a potentiometer.
When the parts arrive I will make the prototype.
I too was thinking about using one of my dummy lights...like my shift light or something.
I was also thinking about making the fuel gauge Illumination lamp blink but that would be useless during the daytime.

Well according to my 83 factory manual these cars use a 0-90 ohm sensor. Later years may used different sensors. Although i highly doubt it maby the 91-92 but beond that im confident most of them if not all are 0-90 ohm. Granted thats all theroretical ideal numbers.

OK.
Off sick today but I feel better and put myself to good use.
Pulled out the dash again and got to testing around.
0-90 ohms across the fuel gauge is the correct operation range...thanks also for the info above.
I have noted the extra bulb hole and light lens below the check engine light.
Hmm.
Useful I say. I scraped the black ink from it and low and behold it's clear.
Temporarily I have drawn on the back with sharpie...a little fuel symbol.
On the back of the cluster the bulb holder was blocked out...so I cut this and bared the connection to the copper circuit board which the bulb will plug in and connect to.
This will be used for my low fuel light.
I'm not sure if the same set up is in all dashes but mines is a 84 trans am.
I can post up some pics later if anyone wants a write up.
Meantime I'll work on the mod and how we can integrate into the dash flawlessly.

Pictures are always nice. Keep us up to date!