Glazedham42

iTrader: (4)

Hey guys,

I am in a desperate attempt here to save myself the $100 cost of a new fuel sending unit from Mazdatrix. For those of you who don't know, I am in the process of restoring this car, and am very close to being done. As part of the restoration several months ago, I dropped the tank on the seven, cleaned out all the rust, coated the outside, changed the hoses, lined the inside of the tank, basically the whole nine yards. The fuel sender was functioning properly before I removed the tank. Well I hooked everything back up, and the sender is messed up now for some reason. I'm getting the same resistance in every position, which obviously means "bad sender." I have tried moving the sender around by hand, and the gauge never moves. When I ground out the connectors, however, the gague pegs nicely like I believe it should. So I have basically concluded that the problem is coming from the sender, not the gauge.

After doing some research I have come to the realization that my sender may be missing some wiring. You will see in the comparision pictures the difference between a known functioning sender, and my own broken one. The first picture is one that I found in a former post. You can see the wire on the end of the sender that I am obviously lacking. I am not sure if I am coomparing different styles of senders, or if mine should really have this extra wire at the end. I faintly remember this wire being on there when I removed mine, and for some reason I almost remember breaking it off. Not really sure though.

So anyway... You can also see the pictures of my sender. The wire that wraps around the rod ends nicely at the top of the little silver bulb. (Which I'm guessing is a resistor???) Everything appears to be just fine, however upon closer inspection of my sender I have been able to locate some mysterious solder markings. One place that has been soldered is where the rod hooks to the side of the metal bulb. The other is at the bottom of the bulb, where there is absolutely nothing attached. Is there supposed to be a wire hooked in there? If anyone can shed any light on this, in any aspect please do so! I see two possible scenarios at hand:

1) My sender is not the same as the one in the picture I found. Mine is fully intact with all required pieces, and after years of use it just coincidentally went bad at the same time I removed it. (Probably because I wasn't gentle enough). Replace the sender.

2) My sender IS supposed to look like the one in the picture below. I broke a wire off of that silver bulb thing while removing the sender. If I solder a new one back in correctly, the sender should function again. Get out the soldering iron and save myself $100 by being resourceful.

Please let me know what you think guys! I know there are some knowledgeable people out there! Please don't be too lazy to answer even if you know and don't feel like it!

Thanks fellas.
Jamie

Siraniko

iTrader: (13)

I have an extra 84-85 non-SE gas tank. If you still need to confirm it, PM me so I can pull out the sending unit on Sunday.

RX7Rox

I shouldn't reply since I'm taking a guess. But with the sender working before, is it possible the coating you applied to the outside of the tank is insulating the sender and not getting a good ground?
The wire you say maybe missing, isn't that part of the sender for the "Low Fuel" light? If the wire broke off that soldered part, sometimes there are strands of wire still there. If you have a jumper wire with alligator clips, try that after you verify the ground.

vipernicus42

iTrader: (4)

When I got mine from Mazdatrix (I bought a new one) it DID NOT have that extra wire.

What I would do is check that you're getting proper grounding on the ground wire. If you are... well I have no idea why it wouldn't be working. I just wanted to let you know that you don't necessarily have to have the wire, because my new one didn't have it and it works fine.

Have you tried it in a tank of gas? I don't know if the wiring up the side relays any different information when gassed up.... I dunno.

BTW: I have an '84 GS

Jon

Glazedham42

iTrader: (4)

Jon,

Thanks for the good info. I guess that rules out the possibility of me knocking off that small wire. So I either have some kind of a wiring issue, or else the sender is just plain worn out.

As far as the wiring I was also wondering about the sender not getting a good ground. I checked all three of the wires in the plastic connector that hooks to the sender. I'm guessing that this would be the appropriate way to check the grounds? Apparently two of them are ground wires and the third is the hot wire. My two grounds appeared to be functioning just fine.

I also wondered about what would happen if the sender was immersed in fuel. But I came to the conlcusion that it shouldn't really matter either way. The Haynes tells you to check the sender with it completely out of the tank. No fuel in that situation. And as a second thought, the only time the sender would really be immersed in fuel is when the tank is near full. So I've pretty much ruled out the fuel thing. It was worth considering though.

Looks like I may end up breaking down and getting a new fuel sending unit.

darkfrost

iTrader: (1)

Post a picture of the terminals and cover of the sender, I managed to solder mine back together, and you may have the same problem as me.

vipernicus42

iTrader: (4)

Another thing that the local tank shop did to mine was attach a wire to one of the sender's mounting screws and ground it to the frame. That might do it.

I don't think two of the three are grounds, but I could be wrong. Check the wiring in chapter 13.

Jon

darkfrost

iTrader: (1)

One of the three terminals is a ground, and it connects to the circular thing on the tank. But, if its all rusted, that connection is bad. I sanded down an area on it, and soldered a wire from there to the ground terminal. After being hooked back up to the harness, it all worked fine.

darkfrost

iTrader: (1)

I found the picture, I basically fixed the ground on it and everything worked again. What Vipernicus said will also help, but only if the link between the hub and the terminal havent corroded away.

[img src="http://www.imagestation.com/picture/sraid167/pc1805988dbada81ac2d1254095fa0af7/f4401ff9.jpg"]

I covered the solder and wire with hi-temp silicone. Its been this way for over a year now, and not a problem.

gsl-se addict

iTrader: (3)

There are three terminals. One is to the gauge. One is ground and the thrid is for the low fuel light. That part hanging down with the wire wraped around it is part of the low fuel light and not part of the actual level measuring. The part that does the actual measurement is in the silver box at the top. It is just a variable resistor setup that changes with float position. I would suspect that either one of the terminals on the top of the sender (where the plug goes) is broken, the contact on the variable resistor is broken, or one of the wires that goes between the variavle resistor and the output terminals is broken.

I am not sure how to open up that box as I haven't tried. I do have a spare sender that I can look at to see how to do it. I replaced mine a few months ago because my low fuel light never worked and the gauge would stop reading when the tank was below about half full.

I will see how to take it a part and let you know. It may be just a simple soldering job to fix the sender in your case.

Kent

Glazedham42

iTrader: (4)

Thanks for the great help so far guys. I'm hoping this thing may be fixable, and if it is I may be able to put together some kind of a writeup when I'm done, so future people can do a more thorough diagnosis than the Haynes manual allows. Anway, back to business...

Kent, if you would go ahead and do your thing it would be MOST appreciated. I've had a little bit of experience with this type of stuff before, but I still am pretty clueless here and would love some help.

I took several more snaphshots of the sender and you'll see them below. The face of the sender caught A LOT of overspray when I was coating the outside of the tank. I'm not sure if this would really affect its performance or not. Also, at this point my sender is only held in by 3 of the original 6 fasteners. Three of them ended up breaking off when I was removing it. You can see the red arrows of the face of the sender plate. These help me to remember which holes to insert the screws in when I'm re-assembling. I've got a gas-resistant sealant that I put all over the gasket, and then just tighten down the remaining three screws. Probably not the best idea, and something that I should have fixed along the way, but I didn't wanna spend the extra cash at the time. I don't know what this would affect but I want you guys to have all the information that I do.

I don't really understand how the grounding of the sender works. Basically, it looks to me like the tab on the connector is riveted to the plate on the sender. Then on the other side of the plate they soldered that brass arrow looking thing on the "full side" of the sender. I don't really see what paint, and some rubber undercoating could harm here, but I guess anything is possible at this point. In any case here are the pictures of the sender.

I was able to pop the cover off the inside of it so we can see the guts. I'm guessing this thing is just a potentiometer, and then whatever voltage isn't dropped across the sender, goes on to move the needle of the gauge. Thus, when the tank is full there is almost no resistance (3 ohms) and the gauge gets plenty of voltage and pegs out. When tank is near empty (110 ohms) most of the voltage is dropped across the sending unit and you get the empty reading since the gauge isn't getting much voltage.

Hopefully these new pics will provide you guys with some more accurate info as to what I have screwed up. Thanks.

Jamie

Glazedham42

iTrader: (4)

Here is one more picture....

darkfrost

iTrader: (1)

Try adding your own ground like I mentioned above. Here's the pic again since I screwed up posting it the first time: