Fuel Gauge Experiment

Replaced several of the burned out light bulbs.  The right turn indicator sometimes will stay on without permission, so something in that circuit will need further attention in the future.

Sunroof does not open.  At least it is closed so I can roll the 325i outside.

After reconnecting the white left and right fuel level sensors plugs it was possible to reach behind me into the back seat and manually raise and lower the floats to see the dashboard fuel gauge increase or decrease.  I have been warned not to reconnect the black plug (to the fuel pump) or a “thermal event” (i.e. FIRE) may occur as it burns out.  The fuel pump can draw 5 amps and it is normally cooled by the flow of the gas thru the pump itself.

When the floats were positioned in what the mechanism would have considered to be nearly “empty”, the warning fuel empty light illuminated on the fuel gauge.  The service manual indicates that the sensors are in series, and when both tank floats were positioned as “empty”, the circuit resistance is about 20 ohms, and when both tank floats were positioned as “full”, the resistance is about 500 ohms.  Check out the picture of the wiper resistor in the fuel float sensor.

The picture shows the potentiometer wiper arm of the fuel pump.  The  fuel pump assembly is on its side and when the float is raised in service, the brown plastic arm rotates upward and to the right.

After the EV mileage range is determined it would be great to add a small circuit that would cause the existing dashboard fuel gauge to output useful data about the batteries.  The circuit should allow the fuel warning light to illuminate as the discharge of the batteries approaches the usable limit and at the point that the gauge is solid on “Empty”, then further battery discharge might be expected to cause degradation of the battery pack.

Builders Note:  The engine weighed in at 188.6 kg and the fuel expansion tank weighed in at 10.4 kg.

Kinkos was able to scan the outline drawing of the transmission and put the file on a USB.  If I can figure out (or get some help from a blog reader?) how to post the drawing on the blog, I will do so.  This last weekend a metric transfer punch set was purchased from McMaster Carr (8962A41) to help refine the traced outline drawing and locate the center of each transmission bolt hole.  It turns out that each of the bolt holes actually has two diameters depending upon which direction it is approached, with a step hidden within the casting.  This makes the determination of the exact center of the hole more sporty.