Gas Needle Dropping

11,495

Asked by Nov 01, 2014 at 02:26 PM about the 1998 Audi A4 2.8 quattro Sedan AWD

Question type: Maintenance & Repair

I am pretty sure i have some sorta vacuum or vapor issue but i am just fishing for other opinions. Basically i noticed my gas meter has been going down faster then usually. So since i had a spare fuel filter and it has not been changed in a while i changed it. Before this tho my gas needle would bottom out saying my tank was empty then bounce back to where it was. Now idling it will just slowly drop till it says empty and when i hit the gas it bounces back to full. So what you guys think vapor, vacuum or short issue ?

8 Answers

118,925

The fuel sender in the fuel tank is possibly going bad. Or either loose wire harness connector going the the sender in the fuel tank.

Best Answer Mark helpful
118,925

I would Check the wire harness connections first before digging into replacing the sender.

11,495

i checked the harness there was no corrosion and it all had the proper voltage all the way to the pump. I opened the tank to take a look at my fuel sender and reader and it all looked alright no rust no dmg not bad wiring. So if it is the sender it is probably going bad. I just came back from a drive If in neutral and i am throttling up and down the gas needle stays on empty. In drive when the car is moving my needle depending on the rpms Will go to say 1/4 - 1/2 fuel tank and drop back to empty and periodically jump between 1/4 tank and empty And it only does this If the car is moving or rolling. Find it does not do this in neutral no matter the speed or idle .

118,925

Pull sender assembly out of tank and manually move it while some one watchs the fuel guage. Does needle move as you move sender. Oh and check for a good ground (negative) in harness. A bad or loose ground can also cause this to happen.

11,495

I read a few articles and most fuel gauge issues were related to the bad speed sensor in the trany. And considering i don't get a gas read out unless my trany is engaged and moving speraticly and my car is running fine i am guessing a bad speed sensor in the trany. oh and yes both my negatives were fine i tested both both were equally putting out a charge at the proper voltage.

118,925

With car idling open drivers door stand outside grab roof and give car a good shake. Watch your gauge. Does it move sporadically? If so possibly bad sender. That's what I have to do to check fuel level in one of my company trucks.

11,495

zero activaty the only time it goes up is when my trany is engaged

11,495

well after i had to swap my fuel filter back out for my old one last night (had a bad leak in the new one) i put a bit of gas in and it is reading the regular amount of gas its just the thing only wants to pickup when it feels like it so my best guess is the sending unit is most defiantly bad and ill have to replace it.I think i may change the fuel pump while im at it while im in there mostly due to the age of it not sure if the previous owner had replaced it but if not it has over 370k on it and i been riding on empty a bit more then i should the last couple years. Thanks for the input you been helpful

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