240Z/240K Fuel Guage reading incorrectly

[Alfadog]

Hi guys,

I wasn't exactly too sure WHERE to ask this, so I put it in Electrical under 240Z, since I know if I put it under 240K I won't get any responses! I am assuming the petrol guage in the Z is the same as the K. Sorry for any inconveniences if this isn't true...

My problem is that when empty, the guage will read just under a quarter full. When full, it will go maybe half way between 3/4 and Full. The latter is not so much of a problem... I'd just like it to be able to tell me when I'm nearing empty a bit more accurately.

So the problem has to be in the guage, or the sender unit in the tank, right? I'm putting on my new dash fascia at the moment so now's the time to check the guage.

I've attached some pictures in the hope that one of you has knowledge on how these things work, and if in fact my problem lies here. Can anyone help me?

[Alfadog]

No one knows??

[Inf]

I glanced through my manuals trying to see how the sending unit works, but they were pretty void of any real information about that.

I'm guessing it has a different resistance value depending on where a float is located in a tank, maybe by some arm moving on a rheostat? Thats my guess anyway. You could maybe find out the resistances (from some obscure electrical manual or another member maybe? my FSM said nothing) that the sender SHOULD put out at full and empty respectively and get some resistors to suit those values and just power the gauge up on the bench and see if the gauge is the faulty part or the sender.

It would make sense if the lower of the resistances is the 'full' value, and the higher is the 'empty' one. I suspect the gauge is simply a galvanometer with a resistor built into it within the case and that the current passing when 12V is applied changes the deflection of the needle (since the powered-off position is on the empty side, then full would be more current)

I wonder if the part number for the sender is the same for the 240Z and 240K? Do you have access to microfiche for your 240K? That would certainly make things simpler to some degree

[Alfadog]

Thankyou for your help Andrew! I'm no Electrician, so a few of those words I didn't get. But I understand (kinda) the concept. I won't be testing out the guage... I wouldnt really know where to start.

My guess is the sender's are probably more likely to fail over time, yeah? Is it an easily replaceable item do you know?

[Daniel]

Im having to answer based on 240z. There really is no adjustment on the gauge. To test when the switch is off it should go to E or more left. Add 12v and it should go to max full. The sending unit in the tank has a small screw that allows you to adjust the output to the gauge. It looks like a metal finger that is pulled across a file. That area usually get gunked/rust etc. and that is the first thing to check/clean. Make note of the adj. screw as if you replace the unit you'll need to adj it to function with the gauge. Make sure the connections at the ouside of the tank are fresh also.that may save you from removing the unit.

[Alfadog]

Thanks Daniel, I'll try that!

[Razor]

I'm HAVING THE SAME PROBLEM!!!!

would really be interested on how to fix this issue.

is there a float in the tank? maybe the float needs adjustment?

is the fuel tank sender unit available in auto parts stores like repco or something cos it would be a waste of time getting the ones from the wreckers as they've been sitting there for a while.

[Luke240z]

I have had the same problem with both of my Z's. Mine now reads just over half on the guage when it is full to the brim. If I run it to empty or very close to, when I refill the tank, it takes about 25 liters. So I must be not even going through half a tank. Giving that the 240z tank is 60 liters.

Any solutions to this would be greatly appreciated.

Thanks

[28Zero]

Same here, my gauge reads 3/4 full when it's full, and on reaching E it still has at least 6 gallons left (as I found out when I dropped the gas tank to install my rear bumper this past summer - had a 5 gallon, and ran to get another 2 gallon. :-)

In december I'll try seeing if there's an adjustment on the gauge itself, if not, I'll try taking apart the stuff in the tank (and replace those hoses while I'm at it).

Hope you find something that works!

-Cheers-

[Daniel]

Trust me there is no adjustment that can be done to the gauge. It's all in the tank float. If you ground the wires that attach to the tank sending unit and you do not show full then it's time to find a gauge.

[bpilati]

Let me add something here. I ran out of gas a 1/4 full once. I talked to the Z shop near me and they told me that the float on the sending unit rides along a set of windings similar to a rheostat. If one of the wires breaks, it can cause the float to get hung up on it, not allowing it move the full range. Consequently, as the gas level changes the fuel gage reading does not. This seems plausible, so I hope this helps you guys. A new sender is $45 according to the Z shop.

[Daniel]

The sending unit is more like a straight cut file. As the float goes up and down it moves a contact. Things that could happen are 1) rust sediment has made more resistance as this contact patch IS in the tank. No kind of cover. The other that I would start with is nice clean connection AT the unit. All that involves is removing the right rear and inside wheel well cover door. Put a jumper across the two connections on the unit ( you haven't removed any wires yet )and your guage better go full and HOLD full/ passed full with the key on.That an easy rough test of the guage. Dead/poor contact spots can also happen because you only keep a small amout of fuel ,don't want it to go bad thing, Now the open air area in your tank is subject to moisture/rust. Thats why you never hanger an aircraft with less than a full load of fuel.