Fuel Sender Help

[Jason2tpa]

Installed my new tank yesterday, now working on the console's wiring total makeover. The tank fabricator offered me a WEMA fuel sender at less than half of market price, couldn't pass it up. Hooked up the sender per instructions, very simple. 2 wires, pink wire to common ground and black wire is gauge sender.

When I finished connecting all of my engine/tach/control harnesses I put the engine on flush and started to do an overall check of all electronics. At least 18 gallons of fuel in new tank. Fuel gauge reads "E". Thinking I might have reversed the ground and sender wires tank side, I disconnected both sender ground and gauge and swapped. Still reads "E".

1st pic below just shows you the basic type of analog fuel gauge. 2nd pic is underside with black lines to the 3 terminals indicating Ignition, Ground, Sender. I took the pic after removing the sender wire, that's why you see no connection made on this terminal.






The red wire at top of pic is fuel gauge power wire. The other end is a bullet connector into the tach harness, via the yellow accessory lead (same connections as previous fuel sender). After leaving the boat it occurred to me I should have checked for power from this yellow accessory. However, the tach was receiving power, which is probably why it didn't occur to me to check yellow lead for power.

WEMA's troubleshooting for testing sender operation is as followed:
*Disconnect the sender wires at the sending unit.
*Connect the 2 wires to an ohmmeter or multimeter and set signal to resistance.
*Take measurement of the sender at empty and full positions by removing the sending unit from the tank and then manual operate the float by hand.
*For American Standard, the meter will show 240 ohms at empty and 30 ohms at full.

When I head back to back this evening I'll double check gauge is receiving power from tach harness. If so, I'll perform the test procedure above. If anyone else has a different idea, please let me know.

[DennisG01]

Jason, I only had a minute to read your thread and only read the first paragraph. Forgive me if there's more to the story. But you have your wire colors backwards. The pink is the sender wire - it goes to the gauge.

[fairdeal]

if its not too much trouble to remove the sender from the tank,
that would be my preferred diagnostic:
slide the float up and down and watch how the gauge responds.

other thoughts:

in my experience, even with the sender in the "empty" position,
there is still a discernible movement of the gauge needle from "off" to "empty"
are you seeing that response?

when you "short" the sender terminal on the gauge to ground - does the gauge read full scale?

finally, how big is your tank?
I have a 130 gallon - the Wema is sized to go almost to the bottom -
but <20 gallons isn't enough to budge the float

here's the "calibration curve" for my tank/sender/gauge:

[boscoe99]

I would not use a WEMA sender if it was given to me. Even if the giver was willing to install it.

[DennisG01]

OK, read through the rest and it seems you figure out the color thing. Good. As mentioned above, it could be as simple as the float just isn't "floating" enough to give a reading, yet. Also, where is the sender (front or back of tank) and how is the boat sitting? In other words, is most of the fuel at the opposite end of the tank right now?

As mentioned, do a quick and easy check... Turn key ON to get power to the gauge. Remove sender wire from sender and gauge should read totally empty. Touch sender wire to tank ground and gauge should read totally full. If all turns out well, it's most likely just the amount of fuel you have.

[Jason2tpa]

Jason, I only had a minute to read your thread and only read the first paragraph. Forgive me if there's more to the story. But you have your wire colors backwards. The pink is the sender wire - it goes to the gauge.

WEMA instructions, highlighted in pink:

[Jason2tpa]

if its not too much trouble to remove the sender from the tank,
that would be my preferred diagnostic:
slide the float up and down and watch how the gauge responds.

other thoughts:

in my experience, even with the sender in the "empty" position,
there is still a discernible movement of the gauge needle from "off" to "empty"
are you seeing that response?

when you "short" the sender terminal on the gauge to ground - does the gauge read full scale?

finally, how big is your tank?
I have a 130 gallon - the Wema is sized to go almost to the bottom -
but <20 gallons isn't enough to budge the float

here's the "calibration curve" for my tank/sender/gauge:

27 gallon tank. This sender is custom for the size tank. When you "short" the sender terminal to ground are you just using a jumper wire?

[fairdeal]

27 gallon tank. This sender is custom for the size tank. When you "short" the sender terminal to ground are you just using a jumper wire?

ahh. well then of course you should be seeing somewhere between 1/2 and 3/4

jumper wire, yes - nothing special - just a conductor of some kind

the wire color at the sender doesn't matter, if its a regular WEMA sensor -
there's just a series of reed switches inside that SS tube -
polarity doesn't affect the operation

what IS important that one of the wires is good and securely grounded.

the gauge is "measuring" how much of the electricity leaving the "S" terminal is going to ground -
when the tank is full, little resistance, maximum electricity flow
when the tank is empty, high resistance, little electricity flow
no or bad ground, the gauge reads "empty"

[DennisG01]

Leave it to WEMA to make things more confusing than they have to be! The last sentence then says to maintain coloring. Do it the right way so it's not confusing in the future - use the pink one for the sender wire at the gauge.

But as far "shorting" - yes, either a screwdriver/piece of wire, or do as I mentioned (will show the greatest sweep at the gauge this way).

Don't overthink this one - fuel gauges are about as simple as simple can be.

[Jason2tpa]

Power to gauge is good. Cut out the butt connections to sender. Ohms tested sender with its 2 wires. Per WEMA, float at bottom is 240, top 30. Well it tested 22 at bottom, and 1 at top. Crap.

[DennisG01]

There 'ya go - easy. Do you think your tank guy will make good for it?

FYI's:

- If you do the "short" method, you will come to the same conclusion but also test the wiring between the sender and the gauge, along with the gauge.

- 240/30 is industry standard.

[Jason2tpa]

My previous thread didn't sit well with me, the ohms reading that is. Had the sender unit and meter in my truck so I retested. Got the same readings, using jumper clips. Then just for the heck of it I continuity tested both jumper clips. Well guess what, one of the two had no continuity.

Did away with the clips, used meter probes direct to senders pink and black. Outcome was 240 on empty, 31 on full. So the issue isn't the sender and isn't the ground/sender wires butt connected to the sender. Which leaves the one of two things, power to the fuel gauge and/or the fuel gauge. On my list of things for tomorrow.

By the way, the tach harness when powered should have 12v running through it, correct? There isn't a voltage limiter or anything else that would drop the voltage going to the tach? Thanks.

[DennisG01]

Correct. When you turn the ignition "on" (doesn't have to be to "start") you should get 12V at the fuel gauge. This is ASSUMING the ground at your gauge is good. If you're not getting 12V, put your meter lead to a KNOWN good ground and retest. If still no good, double check with another positive. You can even jump a known good 12V + & - directly to gauge. In other words, just do some analysis.

If you haven't already, do turn the key on and use the existing wiring (at the tank end). Re-ground the sender to the tank and then remove the sender wire and observe gauge, then touch the sender wire to the tank ground and observe the gauge. Be sure the wire you are using for the sender (at the tank) is the same wire connected to S at the gauge. Report back on that.

Another quick test (I may have mentioned this above, so forgive me for repeating myself) is to do the "short" test at the gauge. Report back on that, too.

Doing these things will test all components of the system.

[Jason2tpa]

Update:

Overall, everything is working. Fuel gauge responded with applied power and no sender wire (needle far left) as well as responded when shorting sender terminal to ground (needle far right). Once I discovered this my attention was focused on a bad ground, somewhere.

Found the bad ground, started a new thread for that particular issue. Find that thread here:
http://www.yamahaoutboardparts.com/f...l-th28442.html

[Jason2tpa]

Issues again:


I'm novice at best when it comes to electronics, learning more as more hiccups occur. Like this one. Y'all regulars on the forum can recall that I was able to get the new fuel gauge working. Yes, but I was testing the gauge using one battery, not having setup all the wiring and terminal locations. Be that as it may, let's start from scratch as if I've yet to get the fuel gauge/fuel sender to communicate.

For the record, because I know you'll ask...all 3 batteries are fully charged and verified, 12.7v. The terminal block is receiving 12.7v and its ground is good (the 3 switch rocker panel works). The tach harness is receiving 12.7v.

The schematic I've drawn here shows exactly which battery is powering/grounding what. The only electronic panel I didn't add to the schematic is a 3 rocker switch accessory panel. This panel is solely powered and grounded by the #2 battery (via the terminal block). All accessories tied into this rocker panel work (nav lights, baitwell, etc).

Ok, so once I closed up the fuel tank hatch, sealed it, worked on distributing wires to their proper location, etc. Turn the key ON, fuel gauge is not working. The fuel gauge is powered via the tach harness pigtail (yellow) and it is grounded to the (-) terminal block, which is grounded to the #2 battery.

So I used jumper wires to test a few things:

*With the sender wire attached to the gauge, I removed the sender ground from the (-) terminal block. I grounded the sender ground wire to the #3 negative battery terminal. Results:
Key ON- no fuel needle movement
Key OFF- needle pinned below Empty

*With the sender wire attached to the gauge, I removed the sender ground from the (-) terminal block. I grounded the sender ground wire to the #1 negative battery terminal. Results:
Key ON- needle pinned above Full
Key OFF- no needle movement

*With the sender wire attached to the gauge, I removed the sender ground wire from terminal, bypassing it and directly connecting it to #2 negative battery terminal. Results:
Key ON- no needle movement
Key OFF- no needle movement

I'm not sure if this makes a difference, but I'll mention it just in case. As you'll see in the schematic the fuel gauge receives power from #1 battery (via tach harness) and ground from #2 battery (via terminal block). So the fuel gauge is powered and grounded by two different batteries. Maybe this is the issue?

Too be honest I feel like I've made this into a bird's nest...grounded here, there, try it on this one, sender wire off, on...ugh

It's a fuel gauge/fuel sender...two wires. This shouldn't be so difficult. And yet I've done something wrong here. So any help is greatly appreciated.




Terminal block circled in white