Fuel sending unit signal question? Need help asap

[marley4us]

Ok so I am converting a guage cluster and I need some help. What type of signal does the stock 1985 4ac Fuel sending unit send? How does it work, I need to convert it to my new dash... and its not reading any signal? I am using a Nissan NX1600 digital dash. Everything else seems to work, but the fuel gauge. details on how this sensor works would greatly help.

[Red]

A stock fuel tank "sender" isn't a sender and isn't sending any active signal at all. It is just a potentiometer, a variable resistor, and your fuel gauge is actually an ammeter measuring the current through the potentiometer as the float moves a wiper arm over the coils. This is the standard way that "all" cars have always used for oil pressure, engine temperature, fuel tank level. Nothing digital, nothing active, no real senders generating anything. Typically a potentiometer used this way has a 0-250 ohm range. The shop manuals will tell you the exact range in order to test them.

No idea what a Nissan digital system expects to see.

[marley4us]

I have not been able to find out what the range is, so I can convert it to the right ohm range for the toyota tank... any idea what the range is?

[Red]

Take an ohmmeter, read the pot. Offhand, no idea although if you have access to an FSM the spec should be listed somewhere in the fuel gauge R&R, which should be in there.

[Rue]

I'll pull my digi sending unit and measure the resistance and let you know what I get... give you another option/opportunity

[Red]

Looked through the FSM a couple of times and it LOOKS like the 1985 FSM doesn't mention the fuel tank sender at all, except for one page that shows "this is what's back there, replace it if it is broken." So to speak.

Honestly, if you can't use an ohmeter to measure the range of the tank sender, you're not going to be able to "adapt" it to a digital gauge set at all, unless the digital cluster happily was designed to use the same range analog sender.

[marley4us]

red- kinda hard to test it when i dont have one to test.... the OEM 4ac is analog... so I dont think I can do anyting about it to get it to work. I can possible retro fit a ka (which i beleive are all digital) but how to get it to level right... might be very difficult.

thanks Rue ya if your digital sending units range is the same or close enough to work and modify to work I will pick one up.

I am trying to find out what the range is for the KA, to see if it will match with the range of the digital AE

[Red]

I'm not understanding. If you don't have an AE8x sender, why are you trying to adapt one to some other kind of digital cluster? Why not try to get the sender that works with your cluster, and see if it fits in the 50 liter tank from an AE8x? I know you said 4AC sender, but the sender will be matched to the fuel tank, which is matched to the body line, not the engine.

You could always test the gauge the other way though. Run a zero ohm circuit, or a 20 pohm circuit, see if it shows full or empty. Add some cheap 20-ohm resistors and see what values bring it tlo the other end of the scale. Shouldn't cost more than five bucks even at Radio Shack's prices for resistors. Remember it is probably a true 12-volt regulated voltage to the tank sender, never just battery voltage.

[marley4us]

red- I have the analog sending unit, in my ae86, not the digital.. The Stock US cars pretty much all ran Analog sending units and gauges clusters. So since my new cluster is digital, I need a digital sending unit. The Ae86 had an option for a digital unit, but I wanted to measure out the range so I could figure out if I could use it with my Nissan cluster, before buying it, as it is kinda expensive. I believe the AE86 digital sending unit reads the same as the digital supra and cresida if anyone knows what the range is on those? That way I can compare it to the Nissan dash and use the drop in digital AE86 sending unit. But if the range it reads is different and I can not change the resistance enough, then I will have to use a nissan digital sending unit, and that will be a bit harder since I need to figure out how to mount the nissan sending unit in the toyota gas tank.... Hope this helps explain what and why I am asking for help.

[allencr]

Looked through the FSM a couple of times and it LOOKS like the 1985 FSM doesn't mention the fuel tank sender at all

That's nothing at all like my manual, it is VERY complete, 1985 Toyota Corolla FR #36241A
Page BE-24,
full = 3ohms +-2.1
1/2 = 32,5 ohms +-4.8
empty = 110ohms +- 7.7

[Red]

No fair, you've obviously memorized yours!

I missed it on the way through the BE section, and of course, there's no index or TOC entry for it.

For extra credit, can you find any diagram that actually shows the 1157 tail lights and how they are wired up? <G> The only one I found shows single-filament bulbs. Coupla oddities like that still limit my faith in what is, generally, a very well done manual.

[marley4us]

omg thank you so much!!! now I just need to test my dash!!