Dwayne

I've searched the list and looked at the WSM and can't find any information on what the voltage range for "Empty" and "Full" fuel levels.

Our Fuel Guage always max's out at 3/4 tank ever since we bough the car 12 years ago. So I replaced the sending unit since I had the fuel tank out any way and replaced both filters and fuel pump.

I measured voltage at the CEB and the sending unit and the voltages match. I got a reading of about 2.5V when the guage registered approximately 1/2 tank. Then I went to the station and left my digital voltmeter connected while I observed the fuel guage movement while filling up. As the needle slowly rose, the voltage slowly dropped off until the guage reached 3/4 tank and the gas pump shut off (full). The voltmeter showed approximately 0.5V (0.45V) for 3/4 tank of gas on the fuel guage.

So, before I take the pod apart and inspect/clean connections, I want to understand how the voltage/fuel level is SUPPOSED to work. Does anyone know what the voltage going to the fuel guage is supposed to be at FULL?? Is 0.5V correct?? THANKS!

Garth S

For what it's worth, I had a similar issue with my 993 - the fuel gauge was locked on full. A sadly optimistic full tank had me driving using the trip odo as a guide ..
Swapping the panel gauge had no effect, so I pulled the sender and disassembled: it is a looped high resistance wire with a float/scraper contact, such that when full it read 0 ohms .... and empty read 70 ohms. I carried a DMM, and pulled the sender plug to verify a linear response.
This variable resistance acts as a bridge for the 'central informer' module - which conditions a signal for the pod gauge .... so replacing the module cured the problem. I think that the early 928s are direct wired ( except for the low fuel alarm) such that you are likely looking at contact cleaning; also, I have some dim recollection of the fuel gauge having a trim pot for full scale deflection/calibration. I did say 'dim' ... for it may have been on another car.

jpitman2

On my 928 sender I made the range 0 - 80 ohms. Its very common for the wire to get coated with crap if the car stands for long periods. See write up by Sharkskin for very good details on dismantling and cleaning sender. The float has little wipers on each side shaped like > to rub the wire line >| - on mine, one had got behind the wire - |> so contact was intermittent. Just be careful cleaning the fine wire, lube the rubber part that seals the sender cap, and find a way to loosen/tighten the big cap properly. You may need somebody to hold the sender from turning while you tighten the cap, to keep the return line inlet in alignment with hose - you'll know what I mean when you see it.
jp 83 Euro S AT 51k

Dwayne

I did replace the sending unit this fall with a brand new one so I'm guessing the sending unit is working fine but I'll check the resistance between the G and W terminals anyway. I"ve also read Sharkskin's write up - EXCELLENT resource and I planned to use it if I needed to take the pod apart. Just wanted to know if anyone actually measured voltage going to the fuel guage when tank is full (and fuel guage working properly). Is it 0.5V??

ZEUS+

Mine read 3/4 when full also. Pulled the gauge and adjusted needle.
http://www.nichols.nu/tip325.htm

Dwayne

OK....I'll assume 0.5V is normal for "full" tank and look in the pod for the problem (after motor mounts and transmission leaks). THANKS for the tips.