Hey guys,

I just bought a 99 audi a4 quatro with the 1.8 engine. It runs pretty good but there are a few problems with it. Mainly it seems to be using a lot of gas, the first time I filled it up it seemed to burn through almost half the tank in 200 kms thats about 15.5 mpg or 15L/100 km. I put some fuel injector cleaner in the tank and changed the air filter which seems to have helped a little, now I think i might be getting about 12L / 100 km or 20 mpg. You would think if I was burning too much fuel that the spark plugs would be dark and I could smell it in the exhaust, but the spark plugs look like they are tan or maybe a touch white (lean). I don't believe its a fuel leak because I think I would see and/or smell gas leaking; I also looked over the fuel lines and there is no where that looks like its leaking. I put a volt meter on the oxygen senor and I think its good. The black wire is reading about 0.4 - 1.1 volts starting at .4 and slowly going up to 1.1 and back down again. Is that good? the manual says it should only go up to 0.9v. The grey wire is reading a constant 0.3v, why is that, is it normal?

I also took the MAF sensor out and cleaned it but I didn't look like it was dirty or that any oil came off of it. I haven't driven it enough to see if that helped the fuel economy or not but I'm a little doubtful. I noticed that a vacuum check valve is broken around part of the casing, and I thought that this may have caused a vacuum leak but the way the direction on the check valve is, its just blocking the line. There is a line that I believe runs from the back of the car to the charcoal canister, and from there it connects to the purge control. Off of the purge control is a Y hose, on one end there is vacuum but on the other end is the broken check valve which stays closed because there is no vacuum from the line on the other side. I have taken and labeled a picture so its a little clearer what Im trying to say. As it is right now that check valve isnt doing anything except blocking 1 end of the Y, so what is the purpose of it. Is it supposed to be the other way around or is there supposed to be vacuum from that line. I couldn't see where the line was going to. Also what is that box that I labeled with a ?

Sorry for the long post and thanks for any help

 

No mention is made of your driving style, but 15mpg is less than I ever got with my B6 S4 Avant. Combined MPG of 20 seems reasonable, but if driven lightly ought to be much more. Our Audi's are heavy and constantly changing speed uses a lot of extra fuel.

In terms of the O2 sensor, a standard DVOM won't have a refresh rate fast enough to properly monitor the switching rate. However, from what you describe it sounds very slow. The OBD2 system will know if there is anything majorly wrong, but may not account for a lazy 02 sensor. I have seen readings over 1 Volt w/o problems. It just means it's very rich at that point. If the 02 sensor looks original, it's probably time to replace it. Not too long ago cars had them replaced every 60K miles, or at least should have.

If the MIL light is not on, then whatever is wrong is likely very minor. Usually any EVAP issues will immediately set a code(s). Again, whether the MIL was on or not wasn't mentioned.

The item with the '?' is the ignition ignitor module, if I remember correctly. They commonly go bad.

It might be a good idea to buy a service manual, probably something more than a Haines, but it might cover what's needed. Replacing the check valve would also be wise, if failed.

My old B5 A4 QMS V6 would consistently get 25MPG hwy at 73mph and high teens around town.

Curious to know what you find out and what all happens.

 

Mostly highway driving but some driving around town too. Maybe my car isn't as bad as I thought, sounds like they just use more fuel than I would have thought for a 1.8l. I'll have to run a full tank through and reset the trip to get a good idea of what it's really using.

As far as the oxygen sensor, it could be original because the wire harness hasn't been cut to splice a new one in. I just didn't want to spend 160 dollars for a new one if its still ok. I was reading it with a digital multimeter and it was going something like this: 0.35, 0.48, 0.7, 1.02, 0.6, 0.38 .... changing about every half a second.

I'm not sure what you mean by the MIL? If its the check engine light then no it is not on, but it does say something to do with service or maintenance when I first start the car (can't remember right now but I will check in the morning). Ive just ordered a VAG COM off ebay so I'll have to hook that up and see what codes show up when I get it.

I bought the Haynes manual but it is basically a waste of money. Its for Volkswagen Passats and the a4 so almost nothing on the car is how they say it is.

 

id go with the Bentley manual for our cars.. its the bible for us.

 

i get 27 in my 1.8T driving with a lead foot and shifting at no less than 3k RPMs so you definitely have an mpg problem. However I am not the man who would know what it is. Sorry

 

i get 22 with a lead foot on the v6 and like 25 on the freeway

 

OK, I definitely have a fuel economy problem. I'll have to wait till I get my VAG COM to see what codes if any come up, and then post them on here.

Anybody know if that check valve is in the right direction or if that line is supposed to have vacuum? There is no check engine light on but when I start the car it says "Service: Insp" Is that just a maintanence thing or is it indicating a problem?