Gas gauge/sending unit-yes another one

Hi Everyone,

I got a new WEMA fuel sending unit and a new gas gauge from a discount marine store. When hooked up the fuel gauge pegged all the way past full. Since we had filled the boat up on the way to the ramp I figured it was just reading full. After running around for a couple of hours the fuel gauge is still reading past full. After reading all the posts on this site I figured there had to be a short in the ground.

I grounded the sending unit directly to the battery with new wire and connections and still the gauge was pegged past full. I then grounded the fuel gauge directly to the battery as well and the results are still the same, fuel gauge pegged at full?

I have read all the posts on this site regarding fuel sending units and guages and am stumped?

Thanks in advance for your responses.

Re: Gas gauge/sending unit-yes another one

The answer is simple -- you did something wrong! Let's start at the beginning. 1) Did this boat have a gas gauge before and you elected to replace both items because you had nothing better to do or 2) did this boat not have a gas gauge and you decided to add one? If it had a gas gauge before what made you determine it needed replacing? If it didn't have a gas gauge before, then let's look at how the system works. When you installed the sending unit, it is very possible you stuffed it into the hole and the float arm is too long for the tank so it is stuck in the full (up) position. So the test will be to pull the sender but leave it connected electrically. Then slowly move the float arm up and down while watching the gauge (key on of course). If the gauge doesn't register at all or is pegged, then you have a wiring issue or the sender is bad. To verify the sender, measure its open circuit resistance. 30 - 240 ohms should be measured as you measure resistance with the float arm up and down. About 109 ohms at 1/2. If that checks out, then go back to the wiring. Most people make this way harder than it has to be. Any gauge except the speedometer has a +12 volt connection on it that is active when the key is on. That terminal is usually labeled "+" or "I". Connect the same terminal on your new fuel gauge to the same terminal on any other gauge. Same for the ground which is labeled GND or "-". The gauge lite wire is connected in the same manner. The metal shell of the sender must be connected to any ground point in the boat which can be the negative terminal of the battery, the engine block, a ground terminal on the engine or any of the ground terminals on the fuse panel. The only connection left is the sender connection which goes to the "S" (SENDER) terminal on the gauge. Here is how things should look. If the sender measures ok, you know the gauge is ok because it moves so it reacts to voltage. The job of the sender is to vary that voltage so it is translated into fuel level. If you've followed the diagram it will work.. If not -- it won't. In my picture I show the feed from the battery to the ignition switch then to the gauge. That is just one wire that makes up the bundle that runs from the battery POS post through the engine harness to the ignition switch. All you need to make certain of is that the +12V connection on the gauge is active when the key is on.

Re: Gas gauge/sending unit-yes another one

Although I blew right past the WEMA sending unit -- all of the troubleshooting tips remain the same. Instead of the float arm being stuck, the float mechanism on the sender may be stuck. Or it is entirely possible that when you measure resistance, you find that you were sent an International sending unit rather than a Universal. The resistance for the two units are different and because of that they take different gauges.

Re: Gas gauge/sending unit-yes another one

The boat sat on the side of my brother in laws house for 2 years uncovered so the gauges were all faded out and the volt & fuel gauges were not working.

I removed the old sending from the gas tank and it was a reed type sending unit 4?? deep. I measured the tank from the bottom of the tank to the top and it was 4?? deep. After researching I realized that the bottom of the sending unit can not sit on the bottom of the tank. I ordered a WEMA reed type sending unit 4? deep since the tank is 4?? deep.
I purchased a new fuel gauge from a discount marine warehouse since the old one was faded out and not working.

I installed the new sending unit following the manufactures directions ?pink wire to ground and black wire to S on the gauge, I know its reverse of what it normally is but its what the manufacture calls for? and then installed the fuel gauge ?purple wire from the ignition to the I, black wire from sending unit to S and the pink wire to the G ?remember the pink and black wire are opposite of what they normally are?.

We filled the gas tank up and put the boat in the water. The gas gauge was pegged at F but since we had just filled the tank I thought nothing of it. After running around for several hours the gauge was still pegged at F. After researching the posts on this site I realized that if there was a short in the ground it would show the gauge as being on F.

I ran a new ground from the sending unit directly to the battery using new wire and connector and from the gauge directly to the battery.

I?m thinking since I purchased the gauge from a discount marine supply warehouse I could have gotten a bad gauge?

Re: Gas gauge/sending unit-yes another one

Doubt it -- gauges either work or they don't. It takes 12 volts to peg the gauge so I seriously doubt it's the problem. There is a situation however, that the sender and the gauge are not compatible, or that the sender itself is bad. The gauge can only work on resistance so measuring the resistance of the sender as you slide the float up and down will validate its operation. I would also question reversal of wires. This doesn't make any difference on a standard float arm style sender but it may on the WEMA sender.

Re: Gas gauge/sending unit-yes another one

Thanks for your replies!

I?m going to test the sending unit tomorrow and see if it?s any good. It?s covered under warranty since it?s only a week or so old.

Re: Gas gauge/sending unit-yes another one

Just wanted to post an update

I tested both the gauge and sending unit and both tested out good. I then ran new wires from the sending unit to the gauge and it worked! I must have had a break in one of the wires?

I can?t believe how sensitive the new sending unit is. The only way I can get an accurate reading is if the boat has been sitting perfectly still other wise the needle on the gauge is bouncing up and down as the gas in the tank sloshes up and down.

Re: Gas gauge/sending unit-yes another one

What size and kind of tank do you have? I have a 92 gallon and a 47 gallon aluminum tanks and neither of them cause the sensor to bounce much at all. Even when under way.

Re: Gas gauge/sending unit-yes another one

WEMA's are still a float style sender and therefore measure fluid "level" not volume. Any change in level -- as in sloshing -- will register on the gauge. On odd shaped tanks "V" styles or wide, long and flat styles can have a great deal of fuel movement so it very hard to create a sender that isn't sensitive to this movement. Baffles in the tank is the only way to limit fluid sloshing.