Changing signal from sender to gauge to make gauge read correctly

Thread Starter

rgadsby2013

Joined Mar 5, 2022
20
Good evening all
im trying to control an input signal from a sender to make it stronger or weaker
im using some fairly generic electronic gauges for fuel which is reading low from fuel sender compared to original sender (the sender that comes with gauge doesn’t fit the fuel tank) and also a temperature sender that is reading high from from engine sender (again the sender that comes with the gauge doesn’t fit the engine)
im thinking of adding voltage with potentiometer for the fuel and turning it down for the temperture. Is this likely to work?
many thanks in adva Richard
 

Reloadron

Joined Jan 15, 2015
6,584
Really depends on the sensors involved. Gas tank senders are usually just a variable resistor but linearity comes into play. Replaced the pump on wife's little 99 Tahoe and it just used a variable resistor. Really need to know exactly what you have for sensors. Engine temp sensors are also just resistive devices. Again, need to know what you previously had and what you have gone to.

Ron
 

Thread Starter

rgadsby2013

Joined Mar 5, 2022
20
Really depends on the sensors involved. Gas tank senders are usually just a variable resistor but linearity comes into play. Replaced the pump on wife's little 99 Tahoe and it just used a variable resistor. Really need to know exactly what you have for sensors. Engine temp sensors are also just resistive devices. Again, need to know what you previously had and what you have gone to.

Ron
Yes it’s just the original old stlye variable resistor on the fuel sender and a resistive heat sender.
the new senders are the same in that they work the same way they just won’t fit the engine/fuel tank
so when attached the fuel gauge reads low on new gauge old sender
the temp reads high again new gauge old sender.
so I need to add power to fuel and lower power to temp gauges from senders if that makes sense?
many thanks in advance
 

Ian0

Joined Aug 7, 2020
5,091
First, make a spreadsheet of the resistance of the sensor at various fuel levels, and the reading on the display.
When you have that you will know how much it has to be adjusted. If the readings are linear, the task is relatively easy.
You will also need the resistance of the meter, and the voltage driving the meter (usually it is a regulated to a lower voltage than the battery, so that the meter reading doesn't vary as the battery voltage varies), but those are just one-off measurements.
 

crutschow

Joined Mar 14, 2008
29,779
A simple resistor and/or voltage addition will likely not work, since the gauges would probably be inaccurate at either the high or low end, which we assume is not desired.
That's why we need more detailed info to recommend a proper solution.
There have been several posts on these forums that provided such circuits, but they all required knowledge of the resistance and voltage values involved.
 

MisterBill2

Joined Jan 23, 2018
11,877
For the temperature sensor, they are usually some kind of thermistor, either increasing resistance with temperature or decreasing with temperature. Both kinds are used in different places. Fuel level sensors usually use a wire-wound resistance that is often lowest when the tank is full. But not always. One end of the resistance is usually tied to vehicle body ground.
Running over things that pushes the tank bottom up often results in never reading empty, and less tank capacity, as well.
So adding a series resistance will result in a change, possibly better, probably not.
For coolant temperature the area around boiling is most interesting and that temperature is simple to produce. Just put the sensor in a pot of boiling water with an ohm meter connected. And watch the resistance as it heats..
 
Last edited:

Alec_t

Joined Sep 17, 2013
12,807
For coolant temperature the area around boiling is most interesting and that temperature is simple to produce. Just put the sensor in a pot of boiing water.
That gives you a 100°C point, but the gauge scale needs to go above that, allowing for the coolant being under pressure and having a higher boiling point.
 

MisterBill2

Joined Jan 23, 2018
11,877
100 C is a handy check point, and observing the behavior as it is approached and passed will provide a hint about how the sensor works. I did not suggest that it was for a calibration. That check will show the sensor response in the area of interest. It will also reveal when it is a thermostat in series with a resistor.
 

bassbindevil

Joined Jan 23, 2014
419
There should be a way to make the new sender fit the engine. Maybe drill out and tap an old sender, or get a reducing bushing, or some creative combination of sender, bushing, filing, drilling, and brazing.
Or maybe if you can identify the type of temperature sender the new gauge uses, some equivalent can be found that will fit the engine. Or, carefully disassemble the new sender and fit the guts into the housing from an old sender.
 

MisterBill2

Joined Jan 23, 2018
11,877
The resources to do any of those processes in a way that would stand up to the average automobile environment and use are far from what most of us have accessible, even when we have the skill sets to use them. At east that is my situation. And a cobbled effort that falls apart at an inconvenient time is really bad news. Mapping one response curve to a required response output is far easier, but seldom as simple as just adjusting gain and offset..
 

Thread Starter

rgadsby2013

Joined Mar 5, 2022
20
Hi thanks for all replys
the sender works on a range of 0-2900 ohms
the gauge has a working range of 0-190 ohms!
is it possible to step the sender signal down to work the gauge correctly?
thanks in advance richard
 
I went down this road at one time on a 1978 truck. I don't know how much things have changed in the years since, but I did find out the old analog gauge senders are not even close to being linear. Even the specs for the GM temp sensor that I went with that was designed for ECU use was not linear. On top of that the fuel tank was not a perfect shape which added more work. Luckily I wasn't making it compatible with updated gauges and could handle all the conversions in software, but even then it was a good deal of trial and error getting the math correct.
 
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