1987 190D 2.5 fuel gauge tests

[bentrod]

Hey, who recalls how to test the fuel gauge?
I somewhat recall long ago to remove the plug from the sending unit and jump the connectors to see if the gauge itself is okay - but don't remember how its done correctly.
And what other tests can be done to sort it out? Thanks

[jay_bob]

The best thing to do is pull out the sender and try cleaning it out. I've done this on a 123 but I suspect the 124 is similar.

Loosen the big nut and carefully pull the tube up. Wait until it quits dripping before pulling it out all the way. Be ready for fuel to spill out the end.

There is a plastic nut at the bottom of the tube. Remove this nut and carefully slide the tube cover off.

Inside there will be a float and some very fine guide wires. The guide wires are actually resistance wires, when the float slides up and down it shorts the two resistance wires together - less resistance = more fuel. For this reason I don't think you can direct short the leads at the connector without harming the gauge.

The third wire is the low fuel light switch.

Use some mineral spirits to clean everything up and put it back together. Be very gentle with those guide wires, they are quite fragile.

Before inserting the tube in the tank plug it in to the connector. Hold the sensor vertical and you should have empty and low fuel light lit. Slowly rotate the tube past horizontal and you should feel the float start to move up the tube, which will correspond to increasing quantity on the gauge.

[Mxfrank]

At the top of the sender, there are three wires. One is a ground. The other is for the gauge, the third is for the reserve light. I'm not sure of the colors for your particular car, but if you ground them one at a time, the following should happen:

1-Ground wire (probably brown) to ground, nothing happens.
2- Reserve light wire to ground (probably blue green), reserve light glows.
3- Gauge wire to ground (probably blue black), gauge goes to full.

[barry12345]

Dash gas gauge failures are rare in most cars. Odds are always stronger that the sender is presenting the issue. Nothing really hard or firm but just a generality.

[bentrod]

Originally Posted by Mxfrank

At the top of the sender, there are three wires. One is a ground. The other is for the gauge, the third is for the reserve light. I'm not sure of the colors for your particular car, but if you ground them one at a time, the following should happen:

1-Ground wire (probably brown) to ground, nothing happens.
2- Reserve light wire to ground (probably blue green), reserve light glows.
3- Gauge wire to ground (probably blue black), gauge goes to full.

I will give this a try, thank you!

[bentrod]

Originally Posted by Mxfrank

At the top of the sender, there are three wires. One is a ground. The other is for the gauge, the third is for the reserve light. I'm not sure of the colors for your particular car, but if you ground them one at a time, the following should happen:

1-Ground wire (probably brown) to ground, nothing happens.
2- Reserve light wire to ground (probably blue green), reserve light glows.
3- Gauge wire to ground (probably blue black), gauge goes to full.

Your wire colors and test was exact! Thank you!

[jay_bob]

Ok so now that you know the gauge and wiring works it’s time to pull out the sender and clean it. The most likely reason for your issue is that the sender is clogged.