For you guys that want to swap your fuel gauge in your v8 Z's

[RedZ85]

I have been working on a way to conver the 240Z Fuel sending unit to work with a NORMAL autometer 0-90 ohm gauge. After pulling my sender out, anylizing the POT used and taking careful measurments, I have managed to find that the senders resistance output is BOTH linear and exponential. Go figure. So Im writting software in C++ that i plan to program to a PIC micro controller that will interprtate the datsun resistance to a resistance understood by a 0-90 ohm gauge. This will allow the gauge to be accurate from empty to full and everywhere in between. I created a calculator that shows the relationship of resistance for a given fuel level and vise versa.

 

Calculator download:

http://www.magshooterz.com/images/Downloads/Datsun%20240Z%20Fuel%20Sender%20Calculator.exe

 

 

Tell me what you guys think!

[RedZ85]

I forgot about the compiler that i use.

[Jolane]

I am a little confused with this. How can it be both linear and exponential? Does it just have a linear region, then an exponential region? Are you talking about just the sending unit as it travels through its motion, or are you talking about the output of the sensor versus actual tank level?

If talking about the sensor only, it seems like it should be linear throughout the range. If talking about actual output versus tank level, I could see that considering the tank is not uniform in vertical cross section. It should show full and then drop rapidly until the tank is more uniform (the region under the spare tire well).

In the end, what are you after? I guess I just want to know that the gauge is accurate when the tank if half full and below. The upper part is not so important for me.

Just curious is all. I plan on using a 0-90 ohm sending unit with an aftermarket gauge.

 

Joshua

[mark]

You guys are too smart. Makes my head hurt. I took my stock gauge apart and made the E and F and the F and E. That's how cave men do it!!

[Sparky]

You guys are too smart. Makes my head hurt. I took my stock gauge apart and made the E and F and the F and E. That's how cave men do it!!

 

 

lol, now thats the way to do it!

[pparaska]

Pretty cool. If your game for showing us how you build the electronics and program it, I'd like to play with that too.

 

I took the data in your calculator and tried various linear trends to see how bad the data would be, and it's not possible to have E and F read correctly and have the middle be at all close - 3/4 would read like 3/8!

 

I look forward to seeing progress on this.

[SpeedRacer]

I think the rheostat is not linear because:

 

A) It has to compensate for the swing of the arm and

 

More importantly, it also has to compensate for the differing volume in the tank because it is not just a perfect rectangle, (as Jolane mentioned).

 

I adapted an aftermarket generic sender to mine and just made sure that full read “full†and when it read “empty†there was about two gallons left in the tank - which is the only thing I was really worried about. Yes, the gage seems to drop faster for the first half then the second half. I think it has to do with the shape of the tank because there is a lot less volume in the top “half†then in the bottom “half.†In the end it really doesn’t make any difference.

 

However, the nerd in me thinks it sounds like an interesting project – good luck.

[getZ]

I want to put an autometer fuel guage as well using the stock 240z sending unit. It's not important to me to be exact. Just tell me when it's getting near empty.

 

What did you measure for the resistance range of the stock sending unit?

 

If it goes from 0 ohms to greater than 90 ohms it should be easy enough to just add a resistor in parallel or another option is just use an autometer guage that can be calibrated.

 

From the autometer website:

 

Another option is if you are using the Cobalt, C2, Ultra Lite, Phantom, or Sport Comp series full sweep programable fuel level guages. (not the standard short sweep version). The full sweep programmable unit may be custom calibrated to operate with nearly any variable resistance to ground sender that has a range between 0 and 270 ohms.

[pparaska]

getZ: I used the stock 240Z sender and an Autometer Pro Comp Fuel Level gage for the older Fords:

http://store.summitracing.com/default.asp?target=partdetail.asp&autofilter=1&part=ATM%2D5416&N=115&autoview=sku

 

I then used a resistor in parallel with the sending unit (at the gage, from the sender terminal to ground) to get it to read near the correct range (E when empty, F when full). Here's how I figured out what resistor to use:

http://alteredz.com/gagecalibration.htm

I did the same thing to get the electric temp gage to read correctly at 180 and 210. But I'm installing a mechanical gage now - they are much more accurate than the electric ones.

 

Ultimately, I'll probably have a custom fuel cell built and not use the stock sender, but a 0-90 one instead.

[getZ]

pparaska,

 

Thanks for the info. I assumed 0 ohms or the lowest resistance was empty. I didn't realize gm and ford were the opposite direction. Good thing! I would have mounted the sending unit back in upside down.