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Discussion Starter · #1 ·
Last year my fuel guage wasnt working so I sent it to get fixed. mechanic said it was a bad gauge and replaced it along with a new sending unit and wiring, however the new system didnt work correctly all season so now I am trying to fix it myself. I think i need to replace the sending unit but wanted a second opinion..Tell me what you guys think?

1.When i turn the key the fuel gauge reads just under 1/4 tank, however, I just filled the entire tank.
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2. My next step was to test the wires at the sending unit, I removed the deck plate and touched the (+) and (-) wires together, when doing this the gauge went to full
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3.Next I reconnected the sending unit wires back to the unit and pulled the gauge itself out. There was a purple wire going to the ignition, a black ground wire, and a pink wire going to the sending unit. I checked with a mulitmeter for voltage between the purple and black wire, had the needed 12v there. So next i disconnected the pink wire an connected it to the ground wire, with the ground still attached to the ground terminal. The gauge did not move at all.
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4.When I connect the pink wire back to the sending unit terminal and remove the ground wire from the ground terminal, the gauge reads full.
 

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I'm having an issue with my sending unit as well, problem is I haven't gotten a new one yet or had a professional look at it. My gauge works because when I grounded out the needle it went from empty to full (on step 4 it looks like you did that). My problem was that my wire connections from my gauge to the sending unit came off (the wire is in a bad spot under the console and putting things under there and taking them out broke the wires off the connections on the unit) I tried to reconnect them but still no proper reading. Unfortunately I don't have a solution for you but I did find some helpful info via the internet
 

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Call the company in Texas that is the sole US distributor for this gauges. There is usualy a stainless float rod that must be trimmed precisely for the depth of the tank you have. Get them to send you the instruction sheet. It will have the excact trim length for every depth tank based on 1/2 inch increments.
 

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Your sending unit works off resistance, the gauge uses 12V in (red wire) from the ignition switch and passes it through you sender (pink wire) and on to the battery ground (black wire). As the float moves the resistance changes which is interpreted by the sender. You can test your sender with a multimeter across the leads and moving the float, you check that against the specs for the sender which should tell you the resistance range from low to high.

It seems your gauge works by the lower the resistance the higher it reads. If disconnecting the ground sends the unit to full you could just be shorting it out. I would test the wires out, check resistance on the pink wire from the gauge to the sender, use an extension cable so you can reach the wire for the meter. Test the ground as well as this might be your problem, the sender may already be grounded but you need to check all the wires.





bump for advice
 

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That is by far one the best most coherent images describing an electrical system I have seen in quite a long time. Way to help the guy out.
 

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Last year my fuel guage wasnt working so I sent it to get fixed. mechanic said it was a bad gauge and replaced it along with a new sending unit and wiring, however the new system didnt work correctly all season so now I am trying to fix it myself. I think i need to replace the sending unit but wanted a second opinion..Tell me what you guys think?
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Rule #1 when dealing with a mechanic, coming from an ex-mechanic: Just because they said they replaced this or that doesn't mean they did. IF it was warranty work, "padding" the work order is very common. Warranty doesn't pay the same as cash, so techs like to embellish to make up some of the difference. If you paid cash......hmm

Common sense says if the sending unit, gauge AND wiring was replaced it should work like new. Sure, sometimes brand new parts are bad, so will give the tech the benefit of the doubt.

1.When i turn the key the fuel gauge reads just under 1/4 tank, however, I just filled the entire tank.
View attachment 126698
2. My next step was to test the wires at the sending unit, I removed the deck plate and touched the (+) and (-) wires together, when doing this the gauge went to full
View attachment 126714 View attachment 126722
Lets assume "full" on the gauge would correspond to a complete short (0 ohms) coming from the sensor...which is about right. Empty would read as an "open" circuit coming from the sender. By shorting the pink and black wires together you told the gauge to read full, and it did...good. With the pink wire not touching anything (open) the gauge should read empty...did it?

The sender is nothing more than a variable resistor. It takes the full ground from the black wire and grounds the pink wire to a varying degree. When the float is at the bottom of the tank there is high or no resistance (open, pink wire "disconnected") and when at the top there is very little resistance ( a short, like when you connected the wires). Obviously as the float moves through the center of it's stroke the resistance between the two terminals should vary accordingly. Your multimeter should have an Ohms setting.....use it on the terminals while moving the float through it's stroke. Of course, also make sure the float FLOATS through it's entire sweep...make sure it is not hanging up on anything.

3.Next I reconnected the sending unit wires back to the unit and pulled the gauge itself out. There was a purple wire going to the ignition, a black ground wire, and a pink wire going to the sending unit. I checked with a mulitmeter for voltage between the purple and black wire, had the needed 12v there. So next i disconnected the pink wire an connected it to the ground wire, with the ground still attached to the ground terminal. The gauge did not move at all.
View attachment 126746 View attachment 126754
Black is ground and constant. Purple is positive 12v and constant with the ign switch on. Pink is a varying degree of ground as I said above, and the important wire in this troubleshooting obviously, especially since you have the B+ voltage you should from the other two. So, taking the semi grounded pink wire and touching the ground terminal at the gauge won't and can't tell you a thing. They are both grounds, and the pink wire terminal on the gauge is the only one that should have an affect on the gauge reading which is disconnected in your test. Shorting the pink terminal to the black/ground terminal here should give you the same full reading as when you shorted the two back at the sender....IF the ground wire here is good.

If you hook up your ohm meter from the pink wire here to the black wire you should get "near" a short if your tank is full. If you do, your sender is good and suspect a bad gauge. If you don't, you can suspect the sender or wiring, which can be narrowed down if tested at the sender itself.

4.When I connect the pink wire back to the sending unit terminal and remove the ground wire from the ground terminal, the gauge reads full.
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Don't do that :D. Your gauge is fed 12v + through a very small winding just looking for a ground to use to complete the circuit. When no real ground is present it will find another way. In this case the other way is through the pink wire and sending unit. Hard to explain...just don't do it....sending amperage through sending units is an easy way to blow them out. Never remove a ground wire to something that is getting power...and has another way of finding ground with that power. That is how most car computers get fried...luckily this circuit should be more forgiving.


Anyway...from what you described above my money would be on the sending unit. Your step 2 told a lot. But I would still do a few simple tests with an ohm meter to be sure...it'll take less than 2 minutes. Good luck.
 

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Stop beating your head on a rock... Just install a mechanical gauge on the tank. Then use that hole in your dash for a useful gauge like engine temp or water pressure. Moeller Marine or Tempo both sell them. Just measure how deep your tank is and order the right one. Get yourself a clear plastic cover for the deck access plate over the sender.

http://www.moellermarine.com/aftermarket/fuel_systems/fuel_senders/ Down the page a bit...
 

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Can you post a pic of the sending unit and the hookup with the wires? I suspect like bayrat said the sender may be getting hung up if your gauge goes full when you short and 0 when you disconnect an when connected it goes to 1/4 tank. If you can pull the sender and hook up and move the float through various stages to see how the gauge responds, while you do that see if the float sticks along the way.

After reading your post, if you shorted the wires at the sending unit and the gauge went to full I suspect the sending unit is bad or getting hung up. I cannot believe the mech replaced all that and it still did not work, no way all those parts (if new) failed again.
 

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Discussion Starter · #10 ·
Wow..what a lot of helpful info from everyone,wanted to first off say thanks to everyone for the responses. I will be working on the boat again this week and will Ohms everything out and check to make sure nothings stuck. Dunk, if the sending unit is in fact bad i just may replace it with the mechanical gauge and get a clear cover as you have suggested.
 

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Discussion Starter · #11 ·
well I pulled the sending unit out and messed around with it, heres the results. When I pulled it out and had the float in the down (empty position) the gauge read full
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when i moved the float into the full position the gauge read empty.
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As you can tell the gauge seems to be working in reverse.
 

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Don't know too much about this one, but I do know that your sending unit has to "pair" with the gauge, the pic looks like you have a new gauge, but can't clearly see if your sender is new- does it look like that? You may just need to get a unit that works with your gauge.
 

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Discussion Starter · #14 ·
tank is from 2003, im assuming that the sending unit is from that time period too. I bought the boat in 2009.
 

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In your initial post you said your mechanic replaced: gauge,unit,and wiring: does the unit appear to be new, as said before - your unit must match the gauge- it doesn't sound like it does.
 

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Discussion Starter · #16 ·
In your initial post you said your mechanic replaced: gauge,unit,and wiring: does the unit appear to be new, as said before - your unit must match the gauge- it doesn't sound like it does.
No the seal looks corroded and the top of the sender looks somewhat corroded also, the mechanics invoice said everything was replaced. I'll have to look around on the gauge to find out what brand it is to see about matching the unit
 

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Did they ever work right together? If yes then something went bad. If not, my guess is the rheostat on the sender (the switch that the float is attached to) is upside down. It could have been correct for your old gauge but reversed for this one. Take the sender back out and you should be able to flip the rheostat....they are made to go on either way.
 

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Discussion Starter · #19 ·
Did they ever work right together? If yes then something went bad. If not, my guess is the rheostat on the sender (the switch that the float is attached to) is upside down. It could have been correct for your old gauge but reversed for this one. Take the sender back out and you should be able to flip the rheostat....they are made to go on either way.
NO they never worked toegther, i''l give it a try tomorrow. Thanks
 

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NO they never worked toegther, i''l give it a try tomorrow. Thanks
I just re-read it's a Moller sender...not all of them have reversible rheostats...teleflexes normally do. I can't tell if yours is or not from the pics. If it's not your best bet is to buy a new Teleflex sender as it seems your gauge and wiring are working correctly.

This style should be reversible: http://www.amazon.com/Moeller-Marin..._sbs_sg_5?ie=UTF8&refRID=0RYY9CZQK5Z2T16ET2M0

This style, probably not: http://www.amazon.com/Moeller-Marin..._sbs_sg_1?ie=UTF8&refRID=0RYY9CZQK5Z2T16ET2M0
 
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