skinut365

I've been trying to find all of the visible problems with my recently purchased 86 5ktqs and one of them is the fuel guage. The odometer is frozen or i wouldnt care too much since i could calculate fuel based on that. Anyways, all of the instruments in the cluster work, speedo, tach, temp, and the fuel guage moves from empty when the car is off and just goes right to full when the car is switched on. I don't know if the problem is in the tank with the sensor or what since the guage does "work" in the regard that it actually gets some kind of electric signal.

I have also noticed that the "miles until empty" function on the trip computer must calculate from the fuel guage since i have been driving the car for 5 hours total now and it is still telling me that i have 400 miles til empty.

The wiring in the front of the car is a little buggy i think because i have been having trouble with the guage cluster illumination fuse lately. It blows fuses as soon as they are plugged in so i am assuming there is a short somewhere in there. I am thinking about going to a junk yard sometime in the near future and just pulling a complete wiring harness for the front and re-doing it all. Until then if anyone has an idea of what might be wrong i would appreciate it. Thanks in advance.

AndrewsQuattros

Most likely you need to replace the fuel tank sending unit, which I believe can be accessed through the trunk (top of the fuel tank) where the fuel pump can be accessed too. More people who have done it will probably have some input... I wouldnt think it's too complicated. Not sure how much a new one costs though.I would think thats the reason your trip computer isnt working correctly too. My 90 does the same thing at times. All Audis suffer the same symtoms
GOod luck!

audiqv8

Could be that the float used by the fuel sender is hung up on the wires to the pump. Sometime when the fuel pump is replace and the person is not careful the float will hang up on the wire.

Or your car is getting really good gas mileage. OPEC would really hate to see that.

rooster 2

if you haven't done so already. Look for broken wires, and most importantly loose or corroded ground wires all over the car. It helps to use a multimeter, or test lamp to check for power.

Track the wiring from the fuse to the instrument cluster lights to see why its shorting out.

Will Ng

regarding the fuse blowing, check the trunk hinge wiring harness for fraying and breaks. I heard the 5k's instrument cluster illumination can be affected by it.

As for the fuel gauge, I would do as audiqv8 suggested, and do a quick inspection of the fuel sender to see if it's hung up by a poor fuel pump replacement job.

In the 100/200 cars, the fuel gauge accuracy can be calibrated. There is actually two calibrations...one being mechanical for the gauge needle position, and one being electrical for the trip computer calculation.
Right below the gauge, there is a plastic hex opening. It can be turned with an appropriate sized hex key. It is geared to the needle shaft and meant to dial in the correct position for a given amount of gas in the tank.

The hex is hollow, and nestled behind it is a small potentiometer. It can be reached with a 4 inch long flat-bladed precision screwdriver.
You turn this pot to electrically 'match' the needle, so that the trip computer and autocheck knows when you've reached your last 3 gallons.
Once properly set, the miles til empty should be more meaningful.

audiqv8

Good point Will. I also heard that the license plate light and the glove compartment light will cause no dash light if either bulb is blown.

Urban Legend???<ul><li><a href="https://forums.audiworld.com/v8/msgs/35746.phtml">No dash lights from previous post</a></li></ul>

moving violation

Agree. checking this is easy, and it happened to me once.

skinut365

That might make sense, my warning lights on the dash are telling me that i have lights out and i know one of them is the license plate light and my glove box is broken. Maybe not an urban legend, i will check it out tomorrow

tonyj

Chech the trunk hinge wiring like Will said 1st