Early '71 240. I am trying to find out the ohms reading for the fuel sending unit to fuel gauge. We have installed a AutoMeter Ultra Lite gauge that reads 0-73 ohms. Part of the problem is the person at Auto Meter states that 0 is empty and 73 is full. Then, I spoke with some one else at Auto Meter (for a different matter) and they say they own a 240, and the sending unit is 0-90 ohms but the gauge we installed is a 90-0 ohms.

What is the ohm's on the 240 fuel sending unit? Which is the empty reading (should be 0 I believe).

Thanks Ed

I'm not sure if the 240 is the same as the 280, but if it is...

Bunch of other related discussion in this thread:
https://www.classiczcars.com/forums/topic/55746-fuel-gauge-accuracy-1975-280z/?

 

10-90 ohm (F - E) is the spec I’ve always worked with. I can test a few senders....

Thanks, I reread my post and discovered a typo. When I was saying empty was 0, I missed the 9. (should have written 90 not 0).  Opps.

Thanks for the refresher.  Nice drawing however. Where did you find that picture?

Ed

I'm not sure if the 240 is the same as the 280, but if it is...

Bunch of other related discussion in this thread:

https://www.classiczcars.com/forums/topic/55746-fuel-gauge-accuracy-1975-280z/?

 

 

 

Utter genius captain!!!! I have saved it for future ref. [emoji106][emoji106][emoji106]

 

 

It also shows me that I have some additional impedence as mine never quite gets to F even with the breather hoses in tact and the fuel all the way up the filler neck. Then again, the PO wasn’t into cleaning contacts when he did things. One to look at for me on my next Z play date.

I have never had consistent, repeatable, long term stability fuel gauges in any Datsun regardless of how clean the wiring, how new the sender or how stable the voltage. You just learn how much you use for how far you travel and how much is left when you fill up. The gauge just means “yep you just filled up” or “got some still”, but that’s about it.

Pretty much gave up and went to modern senders and aftermarket gauges that you program. 

6 hours ago, Ed Brock said:

Nice drawing however. Where did you find that picture?

I made that picture. I hooked the gauge up on the bench and tested it and that's what I got.

5 hours ago, AK260 said:

It also shows me that I have some additional impedence as mine never quite gets to F even with the breather hoses in tact and the fuel all the way up the filler neck.

I have the same situation. Never gets to F, and I still have about three gallons in the tank* when the needle is on "E". I need to clean some contacts as well, but it's just further down the priority list.

*estimated knowing the claimed FEM tank volume versus how much I can put in at fill-up.

Oh, and remember... That's just one gauge that I had laying around. I have no idea how much variability there would be if I were to test a bunch of them and average the results. I suspect the gauges themselves are relatively consistent, but without testing, that's speculation.

@AK260, I had a few spare minutes yesterday, so I took a quick preliminary look at my fuel gauge system.

Not sure if all the years have this, but my 77 has a convenient access port in the rear deck to get to the tank sender unit:

Take the screws out and pop the cover:

I pulled the wiring up a little and found the connector between the body harness and the sender unit. Looks a little crusty, but it's not green. Disconnected it and then took turns grounding the gauge connection and the "FUEL" warning lamp connection:

Here's what my fuel gauge does when the sender wire is grounded. Clearly my gauge itself and all the connections leading back to the sender are fine:

And just since I was working back there, I verified that my fuel lamp works when I ground the other wire:

So I cleaned up that connector and put it back together. I don't know if doing just that will have much effect on the needle position on my gauge. I'm assuming that most of my issue is within the sender unit inside the tank and I'm not going to pull that to mess with it until I'm really ready.

I won't know if simply cleaning that one connector up did anything until I fill up next time. I'll keep you posted.

Not all the fuel senders are as easy to get to as yours. This car an early 71 series has the sending unit assess at the front of the tank (towards the front of the car). It is easy to get at, just not as easy as yours. 

Thanks Ed

[mention=32052]AK260[/mention], I had a few spare minutes yesterday, so I took a quick preliminary look at my fuel gauge system.
Not sure if all the years have this, but my 77 has a convenient access port in the rear deck to get to the tank sender unit:
Take the screws out and pop the cover:

I pulled the wiring up a little and found the connector between the body harness and the sender unit. Looks a little crusty, but it's not green. Disconnected it and then took turns grounding the gauge connection and the "FUEL" warning lamp connection:

Here's what my fuel gauge does when the sender wire is grounded. Clearly my gauge itself and all the connections leading back to the sender are fine:

And just since I was working back there, I verified that my fuel lamp works when I ground the other wire:

So I cleaned up that connector and put it back together. I don't know if doing just that will have much effect on the needle position on my gauge. I'm assuming that most of my issue is within the sender unit inside the tank and I'm not going to pull that to mess with it until I'm really ready.
I won't know if simply cleaning that one connector up did anything until I fill up next time. I'll keep you posted.

Thanks for sharing CO!! I envy that hatch - my ‘77 260z doesn’t have that!

I’ll take a photo of mine tomorrow and share - the connectors are different to yours and awfully crusty!!! The are positioned perfectly for being splashed with road crud. Also we didn’t get fuel warning lights in Europe so my connector is just like spade connectors.

I will have to pull the tank or some tubing as the small fill up today resulted in a lot of smell inside. Also going hard on the anchors did the same so I suspect something has come lose or given up the ghost.