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There have been several postings concerning calibrating the TR3 fuel guage using the MGAGURU method published by them; however there are several comments that the procedure is the same but the resistance is different. The resistance used in the mgaguru procedure is 68 ohms. If this is not the correct resistance, what is? To make matters more confusing, there have also been several comments to the effect that they have used this procedure with these resistances and it has worked fine. Should I consider this procedure to be adequate and go with it or continue to attempt to find the correct resistance for the TR guage?
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TR2/3/3A Fuel Guage
- Thread starter BobbyO
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Earlier this spring I used the instructions you have to a very satisfactory result.
CJD
Yoda
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I used resisters laying around the house. (I know...I need to get a life if I happen to have resistors laying around!?!). I could not get exactly 68 ohms, but did get very close. It worked great.
But...if you are concerned, just put an ohm meter on the tank sender and measure with the float full up and then full down. You will then get the exact numbers you need for calibration.
But...if you are concerned, just put an ohm meter on the tank sender and measure with the float full up and then full down. You will then get the exact numbers you need for calibration.
I'll just attempt to find 68 ohm resistors. Resistors are not as readily available as the use to be. Not in this local anyway. My system is working fine but a friend is having problems. And, I have a couple of spare gauges I thought I'd check. As if there isn't enough to do on these cars anyway. By the way John, up until a couple of years ago I also had resistors laying around. I'm sure I got them in the '70s but got rid of them when I moved.
TR3driver
Great Pumpkin - R.I.P
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That's my suggestion too, measure the sender you have. They aren't all the same.
Check eBay for resistor assortments. But don't forget that each resistor has a tolerance; they are practically never exactly the advertised value. For example, a 1K 5% resistor may be anywhere between 950 ohms and 1050 ohms and still be within spec.
Another route is to use variable resistors and set them with your meter (which hopefully ensures they will match the sender, even if your meter is off a bit). I have lots of them laying around (almost as many as Triumph parts, which in a way, they are); but you should be able to find a couple of cheap ones on flea-bay for not much.
PS it occurs to me that some people might not know: If you connect two resistors end to end ("in series"), the overall resistance is the sum of the two resistor values. So, for example, you could grab this kit from Amazon for $3
https://www.amazon.com/gloednApple-...499375354&sr=8-2&keywords=resistor+assortment
and connect a 22 ohm resistor in series with a 47 ohm resistor to get "close enough" to 68 ohms.
Check eBay for resistor assortments. But don't forget that each resistor has a tolerance; they are practically never exactly the advertised value. For example, a 1K 5% resistor may be anywhere between 950 ohms and 1050 ohms and still be within spec.
Another route is to use variable resistors and set them with your meter (which hopefully ensures they will match the sender, even if your meter is off a bit). I have lots of them laying around (almost as many as Triumph parts, which in a way, they are); but you should be able to find a couple of cheap ones on flea-bay for not much.
PS it occurs to me that some people might not know: If you connect two resistors end to end ("in series"), the overall resistance is the sum of the two resistor values. So, for example, you could grab this kit from Amazon for $3
https://www.amazon.com/gloednApple-...499375354&sr=8-2&keywords=resistor+assortment
and connect a 22 ohm resistor in series with a 47 ohm resistor to get "close enough" to 68 ohms.
6TTR3A
Jedi Warrior
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I found a 0-200 ohm pot years ago. Made up a home-made dial in 5 ohm increments from 0 to 95 and it covers the resistance values for the scores of Smiths sidescreen tank units that I've checked over the years. Most Smiths FT 3331/02 units go from 2-5 ohms empty to 88-93 ohms full. Aftermarket ones seem to be lower range (10-80 Ω)
Frank
Frank