Hi everyone.

Hi have a 99 A6 2.8 v6 quattro Wagon.
I have had it 6 months now. it has around 190000kms on it, in the past few months, the gas mileage has gotten quite bad. I put $30 in which gave me roughly 27 litres. and i only got 160 kms from it. That is very bad. 80 percent of those kms wer highway. I recently changed the purge valve and spark plugs. my check engine light is on but sometime it goes off for a few hours, my central resinator did have to be rewelded because i developed some large cracks in it. i really dont know why the car is so bad on gas now, someone please help me, what is going wrong ?

Thanks Joe

 

You have a check engine light on, have poor gas mileage, and you want us to magically know whats wrong with your very high mileaged car? Are you joking?
Get the fault codes checked, im sure you have a myriad of problems that need to be remedied. Vacuum leaks, bad O2 sensors, bad MAF, fuel pressure regulator, leaking injectors, PCV system, bad CTS sensor, clogged air filter, etc. etc.

 

So your getting 14 MPG after welding your central resinator and you have the check engine light on. Auditech79 is right! Get the codes!

I suspect you don't know much about cars so I sugest you find a good independant shop that understands Audi's otherwise get a ricer.

 

Do you know when the timing belt was last changed? If you don't, then you should have it replaced along with all of the parts which use it, such as water pump. If the timing belt breaks the valves will hit the pistons. You should get a copy of the BentleyPublishers.com Audi shop manual if your car is a USA/Canada Audi.

 

A timing belt won't be the source of his poor fuel economy. Sounds like bad O2 sensors but, without the codes, who knows!

Bob

 

I read the codes and this is what came up :

-16795 Secondary Air Injection Reaction Injection System incorrect flow
-17544 Long term fuel trim adaptive (Bank 1) system too lean
-17546 long term fuel trim adaptive fuel bank 2
-17708 Misfire Low fuel
-18010 Voltage supply terminal 30 voltage too low
-18032 Request for warning lamp on active

 

Well thats a load of yuck.

You want to look at the second and third code, those are the ones that are causing you poor gas mileage. Given the codes i would assume you have a large vacuum leak, which is probably the cause of the misfire as well. Run the engine with the hood open and see if you can hear a sucking noise, pinpoint where that is coming from and fix it.
When was the last time the fuel filter was replaced?