Fuel Gauge has funky non linear behavior

[mtngoat]

I swapped clusters a while ago and am just now getting around to whining about the goofy behavior of my fuel gauge. It acts about like it should while I'm doing a long drive and it's usable, but what's annoying is this...right around half a tank it will sit there for a good long while and then suddenly drop to 1/4. From there on out, it drops normally. It's like it was stuck or something while burning the 1/2 to 1/4 tank portion of the range.

 

I'm not sure how close it is in the rest of the range of motion, maybe it runs a little too high all along until then, but I do know that on the long distance drives I do a lot of, this behavior is annoying when I'm trying to plan my next tank up as I go. It blows to always wonder if I should just fill up early again. I'd like to be able to trust the thing a little more.

 

The temp gauge does no such thing. It seems fine and stays nailed where it should, and I have a parallel gauge for it in a panel under the dash so I know this is true.

 

ideas?

[Ratwagon1600]

Corrosion on the pins on the back of the cluster?

 

Have you/can you pull the gauge out of the old cluster and put it in the new one?

 

Bit of arseing around to do this but may solve the problem.

 

Oic of a cluster I rebuilt a while ago.

 

The fuel/temp unit comes out as a complete assembly.

 

[D52E]

The Dime Quarterly did an article in Volume 2 Issue 2 Page 7. The article describes how to clean the temp/fuel gauge unit contact points to potentially resolve erratic gauge issues. https://docs.google.com/folder/d/0ByCvxnHNk90SYzc4N2E1MWEtMzg0MC00YTE4LTkxZGQtM2RjODA5ODA1YjU1/edit?pli=1&docId=0ByCvxnHNk90SYWExMmM2YjMtMDNkMS00MDM0LTljZDQtNDU4ZGFlYjc5YjI2

 

 

Also, more fuel gauge pictures on the510realm: http://the510realm.com/viewtopic.php?f=32&t=25163&start=15

 

[D52E]

one more article that has some info on varnish build-up in sender(halfway down the page): http://desertdatsuns.freeforums.org/fuel-tank-sending-unit-t206.html

[mtngoat]

thanks for the leads on that info! I don't know why it would be in the sender when it showed up with the new cluster, but it could be that slight differences were all it took to make it show up

[datzenmike]

The tank isn't linear either.

 

Generally the coil resistance is

 

FULL....,. 10 ohms

3/4......... 25 ohms... 15 change

1/2......... 37 ohms... 12 change

1/4......... 56 ohms... 19 change

EMPTY... 80 ohms... 24 change

 

So if emptying the tank at a set rate the gauge should speed up very slightly between 3/4 and 1/2 but slow down noticeably between 1/2 and 1/4 and even slower between 1/4 and empty.

[mtngoat]

I had no idea!

 

I'm tempted to design a simple circuit which smooths that out. I'll need to think on it a bit. More likely, I'll figure out where the current glitch is and forget about it, since I lived with it for 20 plus years already. However, this may come back into play if I ever get around to installing that 280z tank back there.

[datzenmike]

By 40-60 miles I'm at 3/4s. The 710 goon tank is 45 L or 9.89/11.9 US gallons (say10 imperial with the filler tube full) I should be able to go well over 300 miles on a tank. The tank appears to be larger on the top half and there's an indent where the spare tire sits.

[mtngoat]

with my stock tank and the many rock dents in it i'm probably nearly a gallon less than the stated capacity. I can't believe it hasn't leaked worse than the one I got last summer! I'm really interested in figuring out how to mount that Z tank under there. Bought a pressure regulator at Canby, even. Five bucks, might as well be prepared!