We'll I'm resorting to forums to help me resolve an issue. I've recently become the owner of a 2001 B5 audi A4 1.8t Quattro. The car was recently my brothers but he was incarcerated 2 months ago and now, it's up to me to try and resolve this issue with help. Before I begin I do not know much knowledge on Audis as I own a Benz. Alright so back in June the car was in a flood with a water level up to the bottom of the gauge cluster. We both replaced fuses, relays and checked the computer which was unharmed. I cleaned the wiring harness connections inside the car and under the hood. The car runs good except with the other issue of the cam chain tensioner which, ticks on startup and when the car has been ran for about an hour but, I will deal with that issue later. My main problem is at 1/2 or full or no matter how much gas is in the tank, the car reads 5mpg and varies 5-30miles left. I have replaced the float in the tank but before I did I tested a theory. I ziptied the float so it would read Full and show maximum miles which was 355miles. Shortly after, I put the float back in the tank, started the car and began to drive around my house to see if the miles would drop. Certainly enough, the mileage began dropping from 355 all the way to 150 and lower as the mpg reads 5.0. If I disconnect the terminals and reconnect, get back in the car and start it up, it will read 23.5mpg and however many miles will be left as to what I have in the tank, which is over 100 as you will see in the picture. If I move the car over 5mph my 23.5mpg and 100miles left or however many I have left, will drop to 30miles and 5.0mpg. So I ask. Can anyone help or provide what to check?

Also if it is asked, the gauge cluster is from another Audi. The car has 170k.

 

You're working under the assumption the inst cluster is taking its fuel consumption data from the float. I don't think that's the case. I believe the ECU is calculating fuel consumption based on fuel injection time, and that's what the mpg in the dash is based on. I don't know how to solve your problem, except to say that I think you've been going down the wrong path with the float in the tank.

EDIT: Couldn't find that in Bentley before I posted, now I see it. That is the case.

 

The ECU sends fuel consumption information to the cluster, and the cluster compares that against speed/distance to determine instantaneous/average MPG.

The instrument also uses the the tank float and compares the fuel level against the average MPG to come up with a distance-to-empty mileage estimation.

Does your fuel level vary during this process?

 

Fuel level doesn't vary at all. Only thing iv'e found is once you move the car while running, it reads 5MPG everytime. Possible the ECU is faulty?

 

Does the speedometer work properly?

Can you scan for codes?

 

Speedometer isn't off but, the only codes that iv'e retrieved were an 02 sensor and Camshaft Position Sensor which, has been replaced.

 

The fuel consumption signal should look like a square wave, if you have access to an oscilloscope. I would try cleaning the connections at the ecu and instrument cluster... other than that the fix could be expensive.