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TR2/3/3A Fuel Gauge

Redoakboo

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New starter, works great! Time to check other stuff before it hits the road.

My fuel gauge reads Full all the time. I fished a wire hook down around the float. I can pull it all the way above the gas level, still reads Full.

Does this indicate a bad sending unit, or gauge?

Dick
 

sp53

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If it is the fuel gauge, it might be fixable, kinda easy, maybe. Anyways, there are adjusting screws on the outside back of the gauge for calibration that move these little coils inside the gauge and that could be waked out or over if you are lucky. Plus the connection oxidize easy, so if you have not had the gauge out of the car or loosened cleaned at the connections and retightened the problem could be anywhere in the loop.
 

CJD

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The original TR2 used the steel fuel line to ground the gage. This system depends on having a braided fuel line from the fuel shutoff valve to the engine fuel pump. Most add a ground from the sender to the chassis, since the fuel valve is often removed and the hose changed to plain rubber, thus removing the factory ground. The TR3 used a separate ground from the sender tot he chassis.
 

sp53

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Interesting the Tr2 did not have that little ground wire set up. They must have learned something about the gauge not grounding as they developed the car. It is basically a black wire with a big loop on one end to go under the gas tank strap, and I think the other end on the sender. I could see how with the wrong sealant on the gas tank sender unit, the sender itself could insulant and not work without some extra grounding.
 

Graham H

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It is generally the gauge in the dash that has a poor earth, if it doesn't have one already fit a dedicated earth to the gauge .

Graham
 

sp53

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I believe the tr2 is same as the early tr3 and is plumbed in with metal tubing. The early tr3 and tr2 had a braided line from the shut off to the pump. I have only seen one, but they are probably still listed. Most the time now that small section on the early stuff is rubber from the shut off to the pump. The braided line was probably deleted because of the fittings on the ends; they need to have 2 twistable ends. Most early cars still have metal out of the pump to the carbs on early cars. Around 1959- 60 they changed too more rubber line sections. There is a rubber line under the later cars connecting the 2 large lines together. Early cars are plumed in from tank to the shut off with metal.
 

Sarastro

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I'll ask the obvious question that no one has asked yet: when you say "reads full all the time" does it read full even when the ignition is off? If so, it's the gauge. If only when the ignition is on, it could be either. It also might be that the wire from the gauge to the sensor is shorted to ground.

You can check the sender with an ohmmeter. The gauge is a little harder, but if the sender is OK and the wire is not shorted to ground (check that with an ohmmeter, too), it's gotta be the gauge. You can take it apart and you should see the problem easily.
 

CJD

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Good call Steve. I was waiting for red to respond to the ground before bringing that up...
 

Graham H

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The black wire on the left hand gauge is the earth, you need to make sure it has good contact otherwise when you turn on the ignition the needle will go straight to full and hit the stop pin.

Graham
P1010182.jpg
 
OP
R

Redoakboo

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It has no grounding wire, think I will install one, per your pic. Is there a reason you installed the ground under the oil pressure bracket?
 

CJD

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In that pic it is merely hanging loose at the end by the oil pressure gage. It should be grounded to the grounding stud on the panel.
 

Madflyer

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Grounding is the number one reason. Gas lines are never a good ground as there has to be movement from the motor. TR's use a black wire as ground so grounding at gauges is needed even for one wire gauge lite. A bad sending unit would be one of two things 1 a bad float 2 a open resistor on sending unit. A hot feed through gauge to resistor to ground to get reading. A tap of the gauge as needle may be stuck. Madflyer
 

Graham H

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It was back in 2011 when I did the rebuild so I can't remember all the details. I am sure it was connected to the grounding stud on the panel, it's defiantly not under the oil pressure mounting bracket. You could use a temporary earth wire with an alligator clip on one end clipped to the mounting stud to see if that solves your problem and as Madflyer said tap the gauge with ignition off as the needle may be stuck.

Graham
 
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