Mercury smartcraft fuel reading issue

[Jimmy Lee]

Hey guys, I am having an issue with my fuel reading on my smartcraft guage. It worked fine last year and this spring it was stuck on 0% and "low fuel" is on my smartcraft guage. 1 year old phoenix bass boat. I know this isn't really an engine issue but maybe someone can help. The boat has a KUS sendor/sensor. SN is 3B058265

[SilverFox579]

Which Mercury Smartcraft gauge do you have (there are several)?

This topic has pics - SMARTCRAFT Options

Please add engine serial number (required) when convenient.

[EuropeanAM]

Please take a moment to review the Announcements at the top of the Forum, and be sure to provide the Required Info (serial number) when posting. Thanks!

Check to make certain that the Fuel Harness is properly connected at the back of the engine- and verify that there are no small black ground wires laying around the cranking battery (that were accidentally "orphaned" during terminal connections).

[Jimmy Lee]

Thanks for your response. I had phoenix send me a new "sendor" and it is doing the same thing. Where is the fuel harness located on the engine? Thanks again

[EL Skeeter]

Please take a moment to review the Announcements at the top of the Forum, and be sure to provide the Required Info (serial number) when posting. Thanks!

Check to make certain that the Fuel Harness is properly connected at the back of the engine- and verify that there are no small black ground wires laying around the cranking battery (that were accidentally "orphaned" during terminal connections).

If you want help please do as Don asked, post serial number.

[EuropeanAM]

Thanks for your response. I had phoenix send me a new "sendor" and it is doing the same thing. Where is the fuel harness located on the engine? Thanks again

Plugs in at the back of the engine, on the electrical plate, and connects to the sending unit of Tank-1 in the boat (via a pink w/black stripe wire, the sender also has a black ground wire which runs to the battery negative).

Sometimes when battery is disconnected or replaced a lone ground wire gets missed... make sure that's not the case.

[Jimmy Lee]

If you want help please do as Don asked, post serial number.

The SN has been put in the original post before you posting this reply. Congratulations on your BBC Police badge.

[Jimmy Lee]

Thank you Don. I will dig a little deeper to see if I can find where that ground wire goes.

[EL Skeeter]

The SN has been put in the original post before you posting this reply. Congratulations on your BBC Police badge.

Sure it was, that's why Don asked you for it day after you posted.
Just trying to save the man some typing as many posts as he answers.
Good luck with your problem.

[Jimmy Lee]

Still trying to figure out the problem here. Here is what I have tried with no success. Phoenix sent me a new sendor that mounts to tank. I installed it with no luck. I tried running a ground wire directly to my ground block. No luck. When I go to calibrate the guage it allows me to enter the gas tank size. I go to calibrate the levels and when it gets to 1/4 tank I am getting an error that says "calibtation error, default values taken". I have attached a photos if the error it is giving me. I have 2 smartcraft guages and neither are giving me a fuel level reading.

[EuropeanAM]

Still trying to figure out the problem here. Here is what I have tried with no success. Phoenix sent me a new sendor that mounts to tank. I installed it with no luck. I tried running a ground wire directly to my ground block. No luck. When I go to calibrate the guage it allows me to enter the gas tank size. I go to calibrate the levels and when it gets to 1/4 tank I am getting an error that says "calibtation error, default values taken". I have attached a photos if the error it is giving me. I have 2 smartcraft guages and neither are giving me a fuel level reading.

Just to clear up an earlier situation:

The SN has been put in the original post before you posting this reply. Congratulations on your BBC Police badge.

Yes, you indeed added the serial number on June 11th. The second half there... not necessary.

You can't do a manual tank calibration unless you start off with an EMPTY (dry) tank. Specific resistance values must be present for the first step, if you're outside of that, it will not work.

BEST bet is to simply go with the Default setting.

Lets verify the wiring on your new sender:

-ONE ground wire (black) going to the negative battery terminal, and the black wire of the sender (NOWHERE ELSE).

-One Pink w/black stripe "Tank-1" wire going to the sender terminal (and no-where else).

Finally- what TWO Smartcraft Instruments do you have? It's possible that you are not on the Master instrument.

[Jimmy Lee]

I have 2 SC1000 guages. Everything worked as it should last year. This issue started this spring. The wiring is correct as you described. What exactly do you mean by going by the default setting? Is the only way to calibrate the guage is by starting with an empty tank? Thank you for your help.

[Jimmy Lee]

So I have found out that when I turn on my interior boat lighting on the fual.giage goes to 100%. This switch on my boat is like a 3 way switch with off/compartment/both as the options. When I turn the switch to both that turns the fuel guage to 100%. Where should I start?

[Pulsare2020]

So I have found out that when I turn on my interior boat lighting on the fual.giage goes to 100%. This switch on my boat is like a 3 way switch with off/compartment/both as the options. When I turn the switch to both that turns the fuel guage to 100%. Where should I start?

Sounds like you might have to trace where the 12V gauge lights wire to the fuel gauge is connected?
For calibration procedures, you typically start from an empty tank and hit calibrate, then add fuel to the 1/4 tank level, hit calibrate and so on. What I have done that also worked if the tank has fuel in it, was to remove the sending unit from the tank and measure the length if it is the type with a float that rides up the shaft. Move the float to the bottom of the shaft and put it in the calibrate mode and push the button for an empty tank, then move the float to the level that would represent a 1/4 tank, and hit the calibrate button and so on until you calibrate for a full tank. That won't be as accurate as setting the boat to its running angle (up 4 - 6* at the bow) and then adding fuel to an empty tank but you would tie up an gas station for quite a while doing that.

[MichaelJ3]

I have 2 SC1000 guages. Everything worked as it should last year. This issue started this spring. The wiring is correct as you described. What exactly do you mean by going by the default setting? Is the only way to calibrate the guage is by starting with an empty tank? Thank you for your help.

No, there is a "default calibration" where the instrument basically assumes a regularly shaped tank (like a cube or rectangular prism) where the fuel use is linear on the sender resistance (most common for smaller boats). That should be an option on the Calibration, to just accept the default. Maybe Don can remind me if a Calibration Reset is required or not...can't recall.

The fill it by 1/4 tank increments method is better when you have an irregularly shaped tank (maybe goes around stringers, boat structure, is molded to fit boat hull, etc). That really only works when starting w/ a dry tank. It is there to help in this case because the tank volume is not linear w/ float distance from the bottom to top.

But, given you seem to have an issue you describe where guage performance is changing w/ your interior light switch, you seem to have some other sort of electrical issue (weird ground, chafed wire, something connected incorrectly, etc). This seems consistent with your statement of "was working well last year and now isn't." Something has changed, and it doesn't seem to be the fuel sender.

Might try taking the old sender you removed and just manually actuate it across the range, while connected to the gauge and see if that works...use short wires, one direct to ground and one direct to the fuel harness, then slide the float around and see what happens...may also put an ohmmeter on the sender before connecting it to see its range of resistance.

Edit:
Link to Merc SC1000 Instructions see attached for excerpt explaining the Default Tank Size Calibration procedure.

[Pulsare2020]

I thought he wanted to calibrate it using the non linear method but already had gas in the tank, so that was why I suggested removing the sending unit and moving the float before each calibration point, to avoid removing and adding fuel. My tank has a rectangular section with a V section but then a 6" flat bottom. I drew the tank and calculated the fuel volume versus the level. Then I rotated the tank on the drawing program so it simulated the bow 6* up. That of course causes a huge error if the sending unit is at the back of the tank like mine. If the sending unit was in the center of the tank it is barely affected by the angle.

[MichaelJ3]

I thought he wanted to calibrate it using the non linear method but already had gas in the tank, so that was why I suggested removing the sending unit and moving the float before each calibration point, to avoid removing and adding fuel. My tank has a rectangular section with a V section but then a 6" flat bottom. I drew the tank and calculated the fuel volume versus the level. Then I rotated the tank on the drawing program so it simulated the bow 6* up. That of course causes a huge error if the sending unit is at the back of the tank like mine. If the sending unit was in the center of the tank it is barely affected by the angle.

Totally agree that is a better way to do it...but was trying to get him from a TON of errror to a "small error."

My personal advice is Fill your tank, reset the fuel used, then don't run it down more than your tank volume - 5gal.
Fuel used as been spot on for me the entire time I have ever used smartcraft.
I use the "fuel gauge" as a "rough approximation" of fuel remaining. (Usually if it says low, and I hit the throttle, then it looks full again ). Never really trusted a fuel gauge on a boat, too may variables.

[SilverFox579]

My personal advice is Fill your tank, reset the fuel used, then don't run it down more than your tank volume - 5gal.
Fuel used as been spot on for me the entire time I have ever used smartcraft.
I use the "fuel gauge" as a "rough approximation" of fuel remaining.

Exactly how I have done it since adding a Mercmonitor ~10yrs ago. Like you, I left my analog fuel gauge as a visual indicator turns out it was pretty accurate.

[EuropeanAM]

You have something CROSSED in the boat wiring. FIRST THING I RECOMMEND: CHECK BATTERY CONNECTIONS. There may be a GREEN wire back there that belongs on the GROUND (if someone puts it on the Positive Post, a whole array of weird things start happenging, AND it's quite dangerous.