Notes From PAUL
Rochester Fuel Senders: - Instrument Rebuild is now licensed by the FAA to REBUILD and refurbish your ROCHESTER FUEL SENDERS. This is good news and a license that we alone hold.
Cessna Fuel Gauge System
Don't let your customers become glider pilots
Make sure they know how much gas is in their tanks. Fuel gauge accuracy is essential and can be achieved. Too many pilots fly by their watches only to find out too late that they should have trusted their fuel gauges when they registered empty.
The fuel sender gives the greatest problem due to wear that occurs with the wiper. To check operation, take ohmmeter readings between stops. These readings should be about 20 to 235 ohms with no intermitents. Stops on body of sender must be nearly vertical, as their main function is to prevent wiper from running off resistive strip and grounding out or jumping off to opposite side of strip. Fuel gauge accuracy must be checked with a good sender. If you go from stop to stop and the gauge goes from E to F, this indicates that the electrical parameters are OK. However, if the arm wire has been incorrectly bent, then the in-tank reading will be affected. The thing to remember is that it takes approximately 1 1/2" of fuel to lift the float before any readings take place, so the arm should be at rest 1 1/2" above the tank bottom, which is the empty point. If the gauge still reads incorrectly, it may require instrument shop bench calibration of coils.
Cleaning and Installing Fuel Systems
The fuel gauge actually has three connections on its back: the two threaded studs you normally see, and a brass strip that is most important. It is your ground return to the sender body. Corrosion or tarnish on this ground return will cause false readings or occasional needle pegging. Contact with normal airborne moisture and dirt over the years causes a hard brown tarnish to form on this small brass strip, which slows or interrupts current flow. Symptoms of poor grounding are slow or inconsistent gauge readings and occasionally the meter needle will peg.
To remedy this gauge problem, remove the gauge and clean the brass strip and the instrument mounting with #600 wet or dry grit and electrical cleaner. Polishing and cleanng these contacts will clear electrical paths. It is very important to understand the electrical paths in the actual fuel gauges. For instance, when removing the gauge, there will be insulating fiber or plastic washers on the studs. Failure to install these washers, or ignorance as to their importance, can result in burnt out meter coils by causing short circuits. A strong light source and a large mirror will help during removal and installation of the gauge.
We welcome your calls and your questions. We are here to help you. 480-888-955