Fuel Gauge Failure and Diagnosis

After doing the harness upgrade when I ran the engine to check things out, I noticed that the fuel gauge read zero. Judging from the last fill-up and the number of hours ran, there should be about 1/3 to 1/2 tank. After cleaning up dirty screw on top of the tank sensor, I am getting a resistance reading of 235.5 ohms. The question is, is the reading about normal and if so then my panel fuel gauge is probably shot. When I jump across the sense term to ground the gauge needle goes to full.

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Some ideas on sorting out gauges. Gauge problems can drive you crazy. To trouble shoot them you must remove two possibilities 1. bad ground and 2. bad 12v. On the Catalina panel the 12v comes from the switch. Make sure each gauge is daisy chained to this 12v source. Likewise to the ground. A bad (may look good) connection will give you strange behavior everywhere on the panel. Gauges only have three terminals +, -, and S for sender. To check a gauge short the S terminal to - or ground and you will get a full scale reading if the gauge is good. If this works then the problem is bad sender or bad ground to the sender or bad wire to the sender or bad ground to the gauge. That's it end of story.

Current may feed back through gauges with good grounds to gauges with bad grounds that will result in weird voltage readings and other things related to black magic and witchcraft. If the grounds are good, the 12v is good the thing will work. As soon as good ground and power is established most unexplained symptoms will vanish. The ones left may be replaced because they are the problems.

Sometimes fuel senders wear out on full setting on older boats because they constantly sit with full tanks. Senders for temp and oil pressure are very reliable, but can fail. To test for a bad sender, remove the sending wire on the block and connect it to ground and see if the gauge goes full. If it does, replace the sender. Same with the fuel tank sender. Bad grounds on fuel tanks are extremely common. Clean and tighten em up and at least you know the problem is somewhere else. Suspect all crimp fittings if in doubt, redo them or better yet solder them.

The wiring harness upgrade is wonderful. It is a vast improvement over the connectors that came with the Universal/Catalina configuration. As a matter of preference, I don't like the termstrips. I believe a better way is to go straight to the senders/alternator/starter/gloplugs, but that's just me. Best of luck sorting it out. Watch out for opinions from the dock from people that have fifty different ideas that stray from the facts. 12v/good ground/senders. I have no idea where these people come from. Just imagine how intelligent you will look with all of that stuff disconnected sitting on the back of the boat with a beer cheerfully making your boat safer for everyone aboard. Remember, there is nothing quite like the feeling that comes when you turn the key and nothing happens! Better to fix it now and fix it right. Betcha the problem is the last thing you check! :) If I loose something, I always find it in the last place I look. Ken, Family Affair #876

Here's the gauge troubleshooting procedures:

Teleflex gauge troublshooting Tech_Reference [[1]]

--KWKloeber 04:42, 21 December 2014 (PST)