Fuel Sending Unit Repair

[Skipper]

Late in the season, the fuel sending unit went out on my '95 Prostar. Somebody suggested that it could be fixed. Instead of fixing it, I purchased a new one for $160.00 plus shipping. I left the old one on my work bench....until today.

If you have this type of fuel sending unit, and it is inoperative, it is likely that the magnets have come dislodged from the foam float. It is a simple repair to get you back on the water.


There are three main components: The tube assembly, the circuit board, and the float. To disassemble the unit, remove the two screws at the bottom of the tube and remove the plastic cap. Then unscrew the two nuts at the top of the unit to allow the circuit board to slide out of the tube.

The culprit in my unit were the two magnets that are supposed to be lodged in the foam float. They came out of the float and were resting on the tab at the bottom of the circuit board. I just used some 5 minute epoxy to connect the magnets back into the float. Then I used a fine file to smooth out the repair.


I tested the unit by attaching an ohm meter to the circuit board, then moving the float. You can see in the next pictures that the reading on the guage changes as the float goes from the top (full) toward the bottom (empty).



Reassembly is just the reverse of disassembly. I cleaned everything up with WD-40 first. Just be sure to insert the foam float into the tube before pushing the circuit board all the way to the top or the tab at the bottom of the circuit board will prevent you from inserting the float. Once assembled, I tested the unit again, this time by holding it right side up and upside down. This just verified that the unit is back in action. You can also connect it to the fuel guage wires and (with the key on) turn it up and down to view the fuel guage changing.



Hope this helps somebody else in the future. I sure could have used that $160 some place else. This repair took only about 20 minutes and cost nothing.

[FrankSchwab]

Thanks, Skipper, that's the best write-up I've seen on this.

I had to do the same to my boat 4 or 5 years ago; at that time, there were a few active threads on here about re-attaching the magnets. Haven't seen another mention since then.

/frank

[wtrskr]

When I first purchased my 1994 prostar 190 this summer I attempted fixing mine. I reattached a magnet that was loose without any improvements. I think my problem is that the foam float gets stuck.

I may give mine another try next year after seeing that you were able to successfully fix yours.

[Skipper]

Originally Posted by wtrskr

When I first purchased my 1994 prostar 190 this summer I attempted fixing mine. I reattached a magnet that was loose without any improvements. I think my problem is that the foam float gets stuck.

I may give mine another try next year after seeing that you were able to successfully fix yours.

The tube in my unit had some old fuel residue built up inside. I cleaned the tube and the circuit board with WD40. You can test the system by connecting to an ohm meter and moving the foam float across the back of the circuit board. The reading should change with the position of the float. If this works, then after you reassemble the unit turn it up and down and the foam float should fall freely. If it is cleaned up inside there should be nothing for it to hang up on in the tube. Also, be sure to file or sand down the front of the float where the magnets are closest to the circuit board. This will keep that surface smooth and will give the best interaction between the magnets and the circuit board.

[WTRSK1R]

Originally Posted by wtrskr

When I first purchased my 1994 prostar 190 this summer I attempted fixing mine. I reattached a magnet that was loose without any improvements. I think my problem is that the foam float gets stuck.

I may give mine another try next year after seeing that you were able to successfully fix yours.

I used to have a 92 ProSport 205 and when reformulated fuel came to our area in the mid 90's I had the same issue with the foam getting stuck. I think it swelled slightly with whatever they add to the gas. Anyway, I was able to sand it down slightly all the way around the edges of the float and did not have any further issues with the float for the remainder of the time I had the boat.

Steve

[FrankSchwab]

I found the same as Skipper - I had to do some shaving of the float to get it to move smoothly without sticking.

[Skipper]

There are two magnets. One goes on each end of the foam in the slot. If you have only one magnet, then it will not trigger the sensors in the circuit board. Using a fine file, I removed all of the epoxy covering the magnets on the foam and made the overall surface smoother.

[formosa]

Great write up - thank you. I would only add that I only had one magnet on my float. I confirmed this by only finding one magnet when disassembling, as well as there was only one visible area on the float that anything was attached to. Not having another magnet handy, I tested successfully with one magnet (both ohm meter and fuel gauge). I do not want to confuse anyone off your instructions, just relaying my situation.

Also, how did you manage to get the round/slotted nuts off to remove the circuit board? I ended up using vice grips to loosen although based on the amount of work I put into it --- I'm certain there must be the right/better tool given the slots on each side of the bolt.

Thanks again - this is an awesome write-up!

[east tx skier]

Excellent walkthrough. I added it to the FAQ.

[JMann]

I bought a new sending unit on skidim for $60. Seems a lot easier to replace than repair.

Either way thanks for the write up very informative.