Fuel Sending Unit

[KFunk740]

Ok, here's what is currently in my L320:

IMG_2740 by KFunk740, on Flickr

 

Of course, its a mess for some reason, and it doesn't work right.  It does something, but not much.  When the gas tank is full, it shows half tank.  When it gets to about half full, it shows 1/4 tank, and stays there until you run out of gas.

 

Is this the proper sending unit for this truck?  I presume it's not (judging by all the silicone), and the fact that it doesn't work right.  Any ideas for adjusting it?  I can't find anything without pulling it all the way, and I don't want to hack the silicone apart right now, since it does seem to be holding the gas in there.

 

Will a stock L320 sending unit work with negative ground? Maybe not, and thats why they put something in there half-assed?

 

If a stock L320 unit will work, does anybody have a spare they can sell me?  Or any other sending unit that could work?

 

Hopefully under all that silicone is enough metal to hold/seal a stock one in there.  There's no real rust on this truck, so I suspect the silicone is just there hold in a poorly matched sending unit....

 

Thanks for your help.  I'm getting real tired of having to watch my odometer, and fill up gas every trip I make just to make sure I have enough....

 

 

[wayno]

That is the correct/stock fuel sender unit, this is what they look like out of the tank.

 

 

OK, since you have had the top off of the unit, you can see the little thin arms that run on the coils, when I had mine out, the float travel was limited, meaning I had to force the arm to move it's full travel intended, I squirted PB blaster on it on both sides, and helped it a little at a time.

I suspect that your sender is jammed up somewhat, and if you can, would try to remove it, but clean the shit out if the outside of it before you try removing them screws, you are only going to get one shot at it, and you don't want to screw it up.

I would not try to force the arm from the outside by grabbing them very thin pieces of metal, you need to do it by using the float arm on the inside of the tank.

It works fine either positive or negative ground, as I tested it on my 521 work truck gauge, but the wiring in a 320 is something entirely different, it is wired for positive ground, so some rewiring may be needed if you have converted over to negative ground.

[KFunk740]

Hi Wayno,

 

Thanks very much for the help.  Yep, that does indeed look like I have the stock unit.  Also FYI, its part # 17291-08700, which is listed as $36.65 on  Nissanpartszone.com

 

Hopefully the metal where it mounts is still intact under the silicone, and perhaps they just couldn't get a gasket a seal or couldnt find the right gasket, and gooped on the silicone. 

 

Anyways, it appears mine isn't stuck at all.  Before you responded, I had already pushed the little tabs from end to end on the coil.  It seems to move smoothly back and forth.  I didn't try to see how the gauge responded on the truck while moving it from end to end (cuz I didn't feel like completing an electrical circuit near a full tank of gasoline).

 

It seems that if the tabs are towards the rear, the tank is full.  I can push it forward to the front, but it gently returns to the rear position.

 

Is there any adjustment mechanism on the bottom of the unit?  Or how about the screw hidden underneath the coil in the box?

 

The truck has been converted to negative ground, so perhaps the gauge itself needs modified somehow?  That may be some electrical work thats beyond my paygrade, unless I can find something via google.  Weird that its working in the proper direction, though (just on a very tiny scale).

[wayno]

As I said, I tested mine on the 521 truck, and it worked fine on that negative ground truck using my 521 gauge, it doesn't really care, it just needs the proper wire put on in the proper place.

I just looked at an instrument cluster from a 1965(photo below), so I am not sure, was the 1965 320 a positive ground truck??, but it looks like the fuel gauge is insulated on both feeds of the gauge, so if the wires are routed properly, it should work, but I am guessing at this point.

BTW, I just went out and looked at a 1964 320 gauge, it looks the same as the photo above.

I don't entirely understand the 320 gauge wiring yet, it looks like some wires are shared with other things, like the charge light wire is combined with the temp gauge, I suspect that it will work, but wires are going to have to be re-routed to function properly with negative ground.

[KFunk740]

Hi Wayno,

 

According to the 320 service manual (downloadable in .pdf form at davidcmurphy.com), it says 'terminal grounded....+(positive) side,' and that goes along with what I've always heard as 320s being originally positive ground.  A previous owner switched mine when he put in the J13. 

 

In the 320 service manual, I just found a really informative page and wiring diagram for just the gas gauge.  It explains everything in fairly simple terms, but I'll have to go over it a few more times before I figure out how it can be modified.  It's on Page 41 and 42  There's also a troubleshooting section for testing wire integrity, which I'll try to do. 

[wayno]

It should be real simple, one is a power feed, and one goes to the sender, although it may work backwards, "F" is empty, and "E" is full, I just don't know yet.

I just finished lining a 320 tank, and I tested the sender, which seemed to work properly in my 521.

My NL320 has also been switched to negative ground, so this has come up at a good time for me, as I just need to get motivated enough to switch the tanks out now, and figure out the gauge wiring which seems like would be one way or the other to get the needle to move.

[KFunk740]

Well, it's not quite that simple.  There are 2 different coils on the gauge itself.  One coil for the E, and one for the F.  I got a feeling it matters which way the electrons are flowing through them.  I gotta run right now, but will try to figure it out tomorrow.

[wayno]

OK, the yellow/red line wire supplies the 12V power from the fuse block to the fuel/temp gauges, and the oil/charge lights, I do not see any type of voltage reducer/regulator in the diagrams between the fuse block and gauges.

The yellow wire goes to the fuel sender.

The yellow/white wire goes to the temp sender.

The yellow/black goes to the oil pressure switch.

The white/red goes to the regulator.

 

The yellow/blue wire comes from a yellow/red power wire, and so does the white/red wire.

 

So on the gauges, I am wondering if it is as simple as which wire goes on which post to make the gauge work forwards or backwards, or is there something else involved here, I just don't see how there can be more than one ground.

[KFunk740]

Yeah, I think thats how it should all be according to the diagrams I see.

 

Now for as to how the gauge works, from Datsun's explanation it sounds like a 'balanced coil' type gauge.  There are two coils in the gauge, connected by the variable resistance at the fuel tank's sender.  Depending on high or low resistance at sender, the current flow takes the easiest path between the E and the F coil (or A and B as they're called in manual).  Each coil produces a corresponding magnetic force that push/pull on the needle, which indicated fuel in there.

This provides more of an explanation of this type of gauge: http://www.vernco.com/Sparks/id697.htm

 

 

Now, since mine is actually going in the proper direction from 1/2 full to 1/4 full, I don't think reversing wires will help.  I've got a feeling I just need to clean all connections on grounds, replace weak wires, add grounds, etc. (as described on that site)

[wayno]

I just got threw testing two sets of gauges I have, it is a 3 wire system.

This is what I observed, I connected a ground wire to the black wire which grounds out on the instrument cluster housing, then I connected a wire from the positive side of the battery to the yellow/red wire which also ties into the yellow/green wire, the fuel gauge itself went to full right away, the temp never moved as it already is on full.

Then I grounded out the yellow wire which goes to the fuel sender, the fuel needle went directly to "E".

I then grounded the yellow/white wire, and the needle slowly went to cold.

 

So, what I did next is to ground the cluster housing, connect the positive to the yellow/red wire, the fuel gauge went to full, then I took my fuel tank sender and connected the yellow wire to it, then I grounded the sender housing out and then raised and lowered the float, all the way down was empty, all the way up was full, I did the same thing to the temp gauge, all the way down was cold, all the way up was hot.

 

I then switched the leads to positive ground, I got the same exact results.

[KFunk740]

I just got threw testing two sets of gauges I have, it is a 3 wire system.

This is what I observed, I connected a ground wire to the black wire which grounds out on the instrument cluster housing, then I connected a wire from the positive side of the battery to the yellow/red wire which also ties into the yellow/green wire, the fuel gauge itself went to full right away, the temp never moved as it already is on full.

Then I grounded out the yellow wire which goes to the fuel sender, the fuel needle went directly to "E".

I then grounded the yellow/white wire, and the needle slowly went to cold.

 

So, what I did next is to ground the cluster housing, connect the positive to the yellow/red wire, the fuel gauge went to full, then I took my fuel tank sender and connected the yellow wire to it, then I grounded the sender housing out and then raised and lowered the float, all the way down was empty, all the way up was full, I did the same thing to the temp gauge, all the way down was cold, all the way up was hot.

 

I then switched the leads to positive ground, I got the same exact results.

 

Whoa, thanks for doing all the leg work there Wayno.  Good thing you have stuff sitting around like that.  Like I said, I'm betting I just have some bad connections/wires.  I'll just have to clean all connections, and possibly replace the wires.  I haven't even pulled the gauge cluster in this truck to look at it yet, so new adventures await.

 

Maybe we talked about this before, but have you figured out how the 320 temp gauge works now?  I haven't looked into it too much, but its weird as hell, but its supposed to be that way according to my truck's PO. 

When you turn the key, the temp gauge goes straight to hot (not even possible for the truck to get that hot that fast, so its not real).  Then as it actually warms up, the temp needle drops down to cold.  Then for the rest of my drive, the needle stays in the light gray region down at the bottom of the temp gauge. 

[KFunk740]

Oh, and the link I posted about the balanced coil gauge explanation (focusing on Jeeps I think) helps explain it a bit better, but the Datsun one is backwards from Jeeps apparently.

 

The ignition switch is on the side of the E-coil in the 320.  When you flip the switch on, the current gets the choice of two different grounds it can use (the sender's ground, or the ground on the other sife of the F coil).  If the resistance is really high at the sender, then its gonna choose the ground from the F coil, which gets gets energized and magnetically pulls the needle toward F.  If instead the resistance is really low at the sender (gas tank is empty), the current will choose to come from the tank's ground, and less current will flow thru the F coil, and the needle will get pulled towards the E coil. 

[wayno]

OK, what I have noticed is that when there is no power the fuel gauge needle is controlled by gravity, if it is upside down, then it goes to past full, when the cluster housing has a ground connected, and power feed is connected to the yellow/red wire, the fuel gauge needle goes to past full, when the sender housing is grounded when the float is in the full position, the needle drops about a 1/16", if i remove the sender housing from the ground, it goes back up that 1/16", if I lower the float while the sender housing is grounded, the gauge works correctly, all the way down is empty, half way up is half, and all the way up is full.

 

The temp gauge is different, it is always full hot unless you have the temp sender connected, it needs a cold temp sender to drop to cold, I used the fuel sender to test it, and it does slowly move to cold with the tank sender in the empty position.

 

I really don't understand the technical part of these gauges, I'm just an old guy that connects wires till I figure it out, I smoked 2 datsun 720 intermittent wiper boxes/units figuring out how to make them work with the 521 wiper motor, but I did figure it out.

 

Next weekend I will likely try to get my fuel gauge working on the NL320, but I may have to change the tank out to do it. 

[KFunk740]

Yes, as for the fuel gauge, what you describe is exactly how it should be according to the diagrams and how the gauge works.  When you ground out the gauge cluster, and the easiest path is thru that ground, then all the electrons will flow that way via the 'full' coil, which becomes electromagnetized and pulls the needle toward it.  If instead there's way less resistance at the sender (due to your tank being empty), then all the electrons will take the easiest path from the ground on the other side of the tank sender.  They bypass the full coil, and only go thru the empty coil, which pulls the needle in the empty direction.

 

The reason it went down 1/16" when you connected the sender is because, without the sender connected, all the electrons were forced to go thru that 'full' coil, which became a powerful magnet.  As soon as you connected the fuel sender, the electrons suddenly had a second option of coming thru the fuel sender's ground.  Even though it was a huge resistor since the tank was full, a few still made it thru, bypassing the full coil, and allowing the needle to come down 1/16".

 

 

I think I have a faulty ground connection on my cluster, though.  So, it's not easy to get all the electrons to that full coil, and more are going thru the empty coil.  I started to get my gauge cluster out tonight, but realized once I got so far it would require pulling the steering wheel to get it all out (not sure why I have a big plastic collar on steering shaft that keeps my from getting the gauge cluster out).  Ah well, another day when I have more time. 

[wayno]

The gauge cluster has it's own dedicated ground wire going threw the gauge cluster plug, so basically it is grounded out two ways, the dedicated ground wire, and the cluster housing mount nuts, so you should not have a ground issue.

The ground wire is connected to the housing, not the actual gauges.

 

I am happy that they don't make gauges that work this way anymore, it's just weird.

[KFunk740]

Hmmm, maybe it could be a bad connection on the positive/ignition switch side as well.  Or maybe the needle is just rusty, who knows.  At least I don't have to pull the sender out of its mass of silicone, and/or source another one, as far as I know.

 

I kinda like figuring out how some of this old stuff works.  It's fun thinking about some electrical engineers somewhere (probably getting a real salary), without computers or websites to order digital gauges, just using creativity and Ohm's law.  Just using their textbooks and a slide rule, to try to think of some way of arranging a bunch of wires to move a needle back and forth to do the little things we take for granted. 

Hopefully that guy then patented his design, it got used in every car, he made a ton of money, became semi-famous in his own little town.  Then eventually the digital age came along, and all was forgotten.

 

(Similarly, I was recently in Loudonville, Ohio with my truck, where they had a historical plaque to commemorate Charles Kettering, who invented the electric car starter, which made it far easier for women to drive automobiles)

[KFunk740]

OK, got the gas gauge working again.  I'll try to get some pics of the guts in the next few days.

 

The primary problem was a resistor that controlled current going to the F coil.  It was old/fried, as demonstrated by way more resistance than the 150 ohm spec it said on it.

 

I could only find a 1/2 Watt rated 150 ohm resistor at radio shack, and tried it out, and the gauge works fine now.  By my math, 12V thru 150 ohm should be almost 1W, so this resistor would burn up if I left it there very long.  I've got a 3W one on the way from DigiKey.  Hopefully I can get everything back together fine.

 

The gauge is adjustable, in that you can move the coils inward or outward to affect how much magnetic force they exert on the coil.  I can loosen them and wiggle them around, while playing with sender behind me, and set it at the full scale. 

[KFunk740]

gauge by KFunk740, on Flickr

 

Shown with temp resistor in place, and old fried resistor is sitting behind it.

[KFunk740]

Craaaaap, can't get it right.  Had it working perfect, now whenever I plug in the tank sender wire it drops to half a tank.  Remove tank sender wire, and its essentially infinite resistance, and it grounds thru full coil instead, and shows completely full.  Connect sender, and it drops to half a tank.  I had this happen the other day for a while, and still don't know why.  The sender shows the full scale of resistance from 10 to 90 ohms or so, until you plug it into gauge, then it drops to 35 ohms or so max.