13 replies to this topic

[Rana101]

Afternoon all 

     Have just fitted new sender unit to lh as gauge not working . Have put about 15 ltrs of fuel in a gauge now moves but only very slightly where as with my calculations should be reading between 1/4 and 1/2 

 any productive solutions appreciated  Thanks 😊 

[Shiney005]

Factory sender or aftermarket?

[Uncle Chop Chop]

Also double check your electrical connections.

[Rana101]

After market rare spares , what voltage should at connection wire ?

[Uncle Chop Chop]

If you have the factory fuel guage in the dash, then they should have +5V as an input. GMH use a regulator, but I can't remember if it's inside the guage unit, or somewhere else in the wiring loom.

 

There are multiple different sender units that have a different ohms range. If the wrong unit is in there, then the wrong reading will be given.

[Rockoz]

The 5 volt regulator is a tin can device located on the back of the dash.

If he is getting a low reading, and other gauges are working okay I would suggest that it is okay.

 

Short out the wire at the sender to the chassis while someone is watching the needle.

Dont leave it connected for too long.

If the needle goes full scale the gauge is likely okay.

That means you likely have the wrong resistance range sender for the gauge.

 

With the wire off the sender and the ignition turned on, the voltage on the wire should be 5 volts or thereabouts.

You could also try a separate grounding wire from the body of the sender to the chassis to see if that changes things.

 

Cheers

 

Rob

[Rana101]

Thanks guys for comments will try these things and see how I go  appreciate the input

 Derek 

[axistr]

The wire going to your fuel tank sender is the earth side of the circuit. Earthing out this wire will cause the gauge to move with the ignition on. You won't get a correct voltage reading from this wire as the gauge has a resistance winding also. Yes the gauges other than the volt gauge all use a crude 5v system circuit. I ditched my original 5v GMH regulator and fitted a small electronic adjustable regulator from J-car $12.00 from memory and set the output to 5 volts.

 

The electronic voltage regulator is much better and the gauges don't fluctuate anymore. Earthing out the sender wire for more than 10-20 seconds can damage the fuel gauge, so don't do this test for to long. I use a resistance wheel, you can pick them up at J-car for around $15.00  I cant remember what the sender resistance range is on a Torana but 10-70 ohms is common. If you are serious about an accurate fuel reading use this resistance wheel and set it on 30 ohms. Connect one end of the resistance wheel wire to the sender wire and the other wire of the resistance wheel to a good earth. Turn on the ignition switch and the gauge should travel to 1/2 tank of fuel. If your sender is 10-150 ohms set the resistance wheel between the min and max range example 75 ohms would be close enough. You can leave the ignition for as long as you like and it won't damage the gauge when using the resistance wheel. I always set the gauge to read smack on empty when I still have at least 10% of fuel in the tank as a slight buffer from running out of fuel. 

[Cook]

Hi Derek. I had the same problem with my LX. I was told that the Rares senders are calibrated as per factory and I don't doubt that. The resistance from factory (as per advice from my auto elec) should be 73ohms - empty, 25ohms - half, and 10 ohms - full. I suspected the grounding wasn't great given the tank and straps were both painted. I got the auto elec to run another ground from the sender to the chassis (which I was told numerous times by him was a real PITA. anyway, filled the tank as full as possible and it now works. I don't think it is overly accurate but sufficient that I can live with. The reason I filled the tank was because the auto elec said given the it is only 15ohms from full back to half and it takes 48ohms from half to empty it means that it takes 3 times more resistance to go from E to 1/2 than from 1/2 to F. Which is what happens in my case. Hope that helps. Cheers Ron 

[Rockoz]

Lenny.

 

I will back my 40 years of electrical knowledge against yours on the voltage reading. lol

 

Cheers

 

Rob

[axistr]

Lenny.

 

I will back my 40 years of electrical knowledge against yours on the voltage reading. lol

 

Cheers

 

Rob

 

Rob it wouldn't be the first time I have gotten something wrong and please correct me if so, however I wouldn't think you would get a 5 volt reading on the sender wire. I can't ever remember having to check for a positive volt reading on the tank sender wire but would expect closer to millivolts.  

[Dr Terry]

I'm with Rob. With sender wire not connected I believe you would get the full 5 volts because it's a 'floating" open circuit.

 

You would get a much lower reading with the sender connected.

 

The best method of diagnosis here would be to substitute the 73, 25 & 10 ohm values for the sender & see if the gauge reads empty, half & full.

 

Dr Terry

[Rockoz]

Need a continuous circuit with some current flowing to get a voltage drop across any resistance in a circuit.

A multimeter having an extremely high input impedance would cause virtually no current to flow, so no voltage drop.

Little bits of knowledge like that help with diagnosing problems.

Think of it like a hydraulic system.

You get a higher line pressure with nothing working than you do when you are running or pushing something.

Hydraulics and electrics share some similar principles.

 

Cheers

 

Rob

[Dr Terry]

^^^^ What he said.

 

Dr Terry