Fuel Gauge problem?

[bderks]

I'm trying to figure out if I have a problem with my sending units or the gauge. I have a 91 Yamaha Pro V 200hp, with dual 12 gallon tanks. There is only one fuel gauge, it's digital and has a switch to read from either the port or starboard tank. <br /><br />Both tanks when full only show 3/4 tank on the gauge. I put in new sending units this winter, both floats reach within 1 inch of the bottom of the tanks, and their movement is not restricted at all. Just to test them, I removed the units but left them hooked up, and moved the float arms manually. With both floats all the way up, the gauge still only shows 3/4 full on both tanks. I ran another test that I read in a post here, and shorted the positive and negative wires out on each sending unit, and the gauge then shows full. Not sure if this is an accurate test though. <br /><br />Since I experience the exact same problem with both tanks, would this indicate a problem with the gauge, or are both sending units bad? The parts guy at the dealer said that sending units are universal, is this true? Any help would be appreciated. THANKS!

 

[Yepblaze]

Re: Fuel Gauge problem?

remove the sender(s)<br /><br />I am assuming these are a float on a wire type sending units.<br /><br />Now with the guage on, pivot the float up and down while noteing the response on the guage.<br /><br />If you see full deflection in the guage it will require that you bend the wire as needed to maintain the full stroke throughout the range of levels in the tank.

 

[bderks]

Re: Fuel Gauge problem?

Correct, it is the type of sending unit that has a plastic float on a wire that pivots. I've moved the float through it's full range of motion, and the gauge will only show from empty to 3/4 of a tank, even with the sending unit topped out.

 

[sparkroost]

Re: Fuel Gauge problem?

Sounds to me like you have the wrong sending units. In order to find the resistance range of full to empty of your gauge you will have to do some experimenting with some resistors, or find the specs on your gauge. I think most gauges are 68-240 ohms(I am trying to remember from brain). In order to find the range you are looking for you will have to get some resistors from radio shack and perform some tests. Those sending units are nothing more than a potentiometer. when the sending unit is all the way one direction will read approx 240 ohms and the other 60 ohms. You will have to find out if a 60 ohm resistor will read full on the gauge. If not... get a 40 ohm resistor, disconnect sending unit. Use resistor in place of sending unit. power up and check gauge. Get a 250 ohm resistor and check the other way. If the gauge does not move far enough in either direction get a larger or smaller resistor to see the desired results. Now that you know what the low and high resistance is.. try and find a sending unit that has the low and high value you require.<br /><br />I would think that full tank is not as important as empty..... If you move the float all the way down, what reading do you get on the gauge? If empty.. I would be happy with it.<br /><br />what it sounds like to me is that you have the wrong sending unit. You need one to match your sending unit with the proper gauge. Your gauge may be a 0-240 ohm sending unit and not 60-240, which is what I think you bought.<br /><br />Does your gauge, since it's digital, have a "zero" function, or adjustment screw? (grabbing at straws on this one)

 

[Boatin Bob]

Re: Fuel Gauge problem?

Agree with sparkroost, sounds like you a compatibility problem with the senders not matching the guage. You have proven the guage out by shorting the sender terminal to groud which causes it to read full. This link has some additinal info on fuel senders which may help you out. Fuel Sender Info

 

[sparkroost]

Re: Fuel Gauge problem?

On another note.. You could possibly have a bad ground! The sender needs to be grounded to battery ground. Alot of senders ground to the chassis. If the chassis is not grounded to the tank, it will not work right.

 

[bderks]

Re: Fuel Gauge problem?

Thanks for all of your help guys! I plan on trying a different sending unit, and then going from there. I'll post my results here for future reference.

 

[roscoe]

Re: Fuel Gauge problem?

Could the wire/float be too long, so that when it floats up, it hits the sidewall or other obstruction inside the tank? Maybe just have to bend/twist/shorten.

 

[bderks]

Re: Fuel Gauge problem?

roscoe,<br />Good idea, but that is one of the things I checked first...besides, even with the unit out of the tank, the gauge still only reads 3/4 full even with the float arm all the way up.<br /><br />I was just researching sending units (slow day here at work), and found this one by teleflex:<br /><br /> Teleflex Sending Unit <br /><br />It's design looks like it might be more accurate than what I currently have:<br /><br /> Current Sending Unit <br /><br />Anyone have any experience with these?

 

[bderks]

Re: Fuel Gauge problem?

Okay, I bought 2 new Teleflex sending units, and am still having the same problem - when tanks are full, the gauge reads 3/4 of a tank, and when tanks are half full, gauge is reading empty. Both the old and new sending units I have are 240-33 ohm ranges. All tests have been verified with the sending units out of the tanks, by manually moving the floater arm, so float movement restrictions is not an issue. I still don't think it's the gauge, since I shorted out the leads on the sending unit and the gauge then reads full as it should. Is it possible that my guage requires a different ohm range? Any ideas? This is driving me nuts!!!!

 

[sparkroost]

Re: Fuel Gauge problem?

ok, you tested out of tank. Where is the ground connected when making this test? ALSO... you could have a bad switch or mis-wired switch that changes from 1 tank to the other. <br /><br />Start with the basics. Bypass the switch. Connect a ground directly to the sending unit to the gauge. some sending units don't have a pole for the ground so you will have to connect it to the sending units housing that mounts to the tank.<br /><br />You have the right sending units.. want to check the gauge.. get a 33 ohm resistor and a 240 ohm resistor, 1/4 watt. connect the 33 ohm to the "S" on the sending unit and to the ground on the sending unit. power up, should read full. Remove 33 ohm and put in 240 ohm.. should read empty. If this works, you have some bad wiring.

 

[bderks]

Re: Fuel Gauge problem?

Sparkroost - Good thoughts on the wiring. One question though - I have shorted across the terminals on both sending units, and the gauge will then read full. Could there still be a problem with the wiring if this is the case?

 

[sparkroost]

Re: Fuel Gauge problem?

DEfinatly! you are bypassing the wiring when you do that. Where is your ground connected?

 

[bderks]

Re: Fuel Gauge problem?

The ground from the sending unit is grounded to the tank, and then from there it looks like it goes back up the gauge cluster. So should I try grounding it directly to where the battery is grounded instead?

 

[sparkroost]

Re: Fuel Gauge problem?

No.. <br /><br />If you are testing with the sending unit out of the tank, the sending unit needs to be grounded. If it's out of tank it's not grounded. hold the metal on the sending unit on the tank when you test, or tie a wire from the sending unit directly to the ground on the gauge. The current loop is from the gauge through the sending unit and back to the gauge.

 

[bderks]

Re: Fuel Gauge problem?

Alright, I'll give it a try and let you know what I find out. Thanks for all your help Sparkroost!!!