mogulmike

I currently have a new sending unit and an pretty full gas tank and reads 87.6 on an ohm meter. I get this reading via the "T" factory plug behind the dash. This would prove from the sending unit to the plug is a complete circuit. With a coat hanger, I have pushed down and raised up the float and observed the OHM reading to change and properly operate between the 0 - 90 range and looks to be accurate. When I plug in the gauge the ohm reading of 37.8. Thinking the gauge was faulty I sent back to the vendor who bench tested the gauge and said the gauge was not faulty and was right on the money.

The gauge has 2 labels an "S" and a "T". If the S is connected to the gauge and the T is disconnected I get an ohm reading of 48.4. If I connect the T side to the gauge and have the s disconnected I get an ohm reading of 87.6.

In all the above test the G is connected and grounded out to the dash.

What started this was my sending unit started leaking at either the S or the T rubber boot under the tank. I bout a new sending unit, installed it and my gas gauge wouldn't read over half a tank.

I have tried the old gauge in the above examples and it now reads a little over a quarter tank, when it full.

So in conclusion I have a vendor telling me the gauge is spot on a sending unit giving me the expected ohms but when I connect the circuit I have a gauge reading half a tank and an ohm reading of 37.8.

Any ideas on where the problem is and how to correct?

EDinPA

http://www.lbfun.com/warehouse/tech_...rFuelGauge.pdf

mrtexas

Original sending unit. I'm having the same problem you are with a repro sender. Reads fine with the original.

mogulmike

Great article and thanks for the link. The article mentions diagrams multiple times but the pdf doesn't show them. Any links to the diagrams would be much appreciated.

EDinPA

Full PDF photos and all....

http://www.lbfun.com/warehouse/tech_...nding_unit.pdf

mogulmike

I have gone through John Hinckley's article and all test out. The only thing is at the ground on the sending unit between the factory connector and the spade on the sending unit I get an ohm reading of 0.5, not 0.0.

So at the gauge wires disconnected the "s" and the "I" I get an ohm reading of 89.6 for a full tank, as mentioned above. when I connect the "I" and "S" to the gauge via jumpers and the gauge is not connected to the dash nor the gauge ground is connected to the dash I get an OHM reading of 48.

With the gauge ground connected to the cluster via a jumper the ohm reading is now 38 ohms.

Turning the key to supply 12 volts to the gauge, the gauge needle registers 1/3 of a tank, which matches the 38 ohms reading with the key off.

So at the plug the ohms reading is correct at 89 with a full tank of gas. connecting these two wired to the gauge gives me a reading of 48 and grounding the gauge (jumper from gauge ground to cluster) gives me 38. Turning the key gives the gauge 12v power and the needle reads the 1/3 tank (which is equal to the 38 ohms). I then did this test with my old gauge and got the same reading.

So any suggestions on how to fix this circuit/ or any other test to run?? I'm all ears!!

EDinPA

So on a bench, everything tests ok but in the car it is reading wrong? Have you checked the body connector for corrosion? I would run external wires from the sender straight to the gage and bypass all of the wires in the car just to confirm that the installed sender and gauge will read correctly then swap in one of the harness wires as a test and then the other harness wire as a test. You should be able to identify what wire is the problem and then either trace the wire to see if you can find a fault or run a replacement wire.

mogulmike

Ok. I have reinstalled the gauge into the cluster and disconnected the "body conn". On the sending unit of the connecter, I get my 89 ohms or full tank (male side).

On the gauge side I get 47 ohms. When I turn the key I get negative 6 Volts. At the fuse panel of the ignition side I get 12 volts. The gauge reads half a tank

When I connect the body connector, I get 33 ohms and with the key I get 4 volts. gauge reads a third.

I have also by passed the factor gauge connector and ran jumper wires to the body connector so the circuit is gauge to jumper wires to body connector to sending unit. I also jumped 12v power to the ignition wire. This gives me the exact some numbers above.

mogulmike

I spoke with a friend of mine who also has a mid-year. He says he had exactly the same issue of the gauge only reading half a tank. He removed the sending unit and noticed the needle on the sending unit didn't make contact after 1/2 tank. He recommended me dropping the unit and looking for that. This means the sega will continue once I burn through 20 plus galllons of gas.

jerhofer

Turn the ignition on. Remove the sender lead at the sending unit and the gauge should read half full. Touch that sender lead to ground and the gauge should read empty. Touch that sender lead to 12V and the gauge should read full. If the gauge reads correctly at each of these tests, you have a defective sending unit.