Fuel gauge off 1/2 tank

[Marty D]

When I had my new motor installed, Suzuki 250 with all new Suzuki gauges. I ran out of gas gauge was reading 1/2 tank. Suzuki dealer replaced the gauge. It was still off 1/2 tank. I replaced the sending unit. It got better, now only off 1/4 tank. Yesterday I saw the bulb not working. I took the bulb out and when I did that the gas gauge dropped 1/4 more. Now it's right on. I pull the sending unit and its 7 inch of gas on a 15 inch tank. The gas gauge is on the money. Why would the bulb out do that? Bad ground? I wanted to test the volts but can't find my volt meter. Need some help!!!

[Moonlighter]

When you say "the bulb was not working" what do you mean? Had it sucked flat? Is it positioned vertically with the arrow pointing upwards? (eg high end towards the motor)

It seems hard to explain what possible influence the primer bulb could have had on the fuel sender unit, or the gauge, for that matter. I would be looking at the wiring from the sender unit up to the dash where it connects to the fuel gauge. Perhaps in the process of changing gauges, the installer has damaged a wire or moved a dodgy wire??

At best, those electric fuel gauges based on floats are not very reliable indicators of fuel level, and nobody I know relies on them.

It shouldnt take long for you to know the average mpg of your boat with your new Suzuki - most GPS units tell you trip distances so if you start with a full tank, do a trip, check the distance travelled then refill, it isnt hard to work out an approximate range given the quantify of fuel your tank holds. Even though this is a rough calculation, there is no way you will be out by half a tank.

What gauges did you get with your motor? All anaologue?

With any of the digital engine displays (eg the old SMIS displays or the new C-10's), or even just setting up a simple NMEA2000 network and connecting to a suitable GPS combo, you will get a serious range of engine data that you cant get on analogue gauges, plus you will get very accurate fuel flow, mpg, fuel used, and fuel remaining data. This data is so good, many people, myself included, never look at our old analogue fuel gauges any more. Mine is always within 1-2%.

Might be worth talking to your dealer about, as per our other discussions on other threads.

[Marty D]

I was talking about the light bulb in the fuel gauge. When I took the bulb out, the gauge dropped. I just don't want a elect short, in my gas tank.

[Harper]

Not sure that the bulb is indicative of a bad ground, but it's a possibility, I guess. If the bulb was burned out, removing it should not have done anything. Whether a burned out bulb is in or out of a socket shouldn't change anything, since the bulb circuit was open in either case. But if the bulb was somehow shorting the circuit, that might make a difference. Have you tried putting in a known good bulb?

[Marty D]

This is a new Suzuki gas gauge I got from browns point two days ago. I done a new gas sending unit and now the gauge. The bulb is good. My gas gauge is spot on now. Without the bulb in or I can just pull off the jumper wire going to bulb. I pulled the sending unit out today to check everything. All good. I have 7 inch of gas in a 15 inch tank. It's reading 1/2 tank now. If I plug in the bulb, the gauge goes up to 3/4. Never have I saw this happen. I need to find my volt meter. Maybe I have low volts? Bad ground? Who knows. I use my MPG chart. I go 250 miles, I know I have 1/2 tank. I just like to know why this is happening.

[RayBersch]

Who knows. I use my MPG chart. I go 250 miles, I know I have 1/2 tank. I just like to know why this is happening.

Oh, please don't use MPG charts to estimate your fuel usage - so many, many things impact fuel usage, including rough seas - Long Island Sound.

You may want to learn Gallons Per Hour usage for your normal cruising RPM and make estimates from that - or just carry a six gallon spare tank for awhile.

When you were checking the light bulb, you may have been changing the ground connection and that will impact the gauge reading. Often ground wires (black) for gauges are daisy chained from one gauge to another - and these are all newly installed - so check them all, I mean actually tighten them all. The blue wire to the bulbs may also be daisy chained, but will have no impact on gauge readings. Be sure the pink wire is tight at both ends as well. If you did not use a DVM when you checked the sending unit then you don't really know if it is (reasonably) accurate but if you are satisfied with it then leave it alone. Also, be sure the sending unit gasket is sealing properly, I know you said the unit was just replaced but re-compressing a gasket could lead to leakage - fuel out, water in.

[Marty D]

I do have a GPH. I know a 4000 rpm is a great speed. 30 knots. I filled this boat 5 X at 250 miles and take 100 gall max. Most times its 92 gall. That leaves me with 50 gall. It's a 150 gall tank. The jumper wire is a red wire from Suzuki harness. That's the wire that I have off. I will check that wire to make sure it's hot. 12 volts. Your saying it may be a ground and that is why this is happening? If it is a ground, where would the dealer of screwed up.

[RayBersch]

Perhaps I am going where I shouldn't with you, but ABCY wiring standards applicable to gauges call for black = ground, pink = fuel sender, dark blue = lights and purple = power when ignition switch is on. So, to my knowledge, no red wire should be present on the back of a fuel gauge - is this a multi-function gauge? If so, then I will shut up - that is out of my league for troubleshooting. If not, my suggestion about the ground wire possibly being the culprit is because it is not unusual for one or more of the daisy chained wires to loosen as gauges are manipulated during installation and a good ground is needed to make gauges perform correctly.

The common failure for analog fuel gauges is to read either full or empty and trouble shooting is meant to determine if it is the gauge or sender that has failed.

You can test the sender accuracy by removing it from the tank, connect a digital multimeter on the ohms setting and manipulate the float up and down to see if the reading correspond to the specs for the sender.

[Marty D]

Yes, it's the multi-function gauge. I'm sorry I bought it. It come with a harness with 10 wires. The wire for the light is red. I'm going to bring it in to the dealer because the oil light came on yesterday. It's time for a oil change. I'm done trying to get this working.