View Full Version : Poor fuel mileage and four bad plugs

10-28-2012, 07:27 PM
My 16 son just purchased a 2000 a4 recently and we are going through it doing some routine maintenance. We jot some new NGk bkr6e's and when we pulled the old plugs I was surprised to find that all four of them were real black and smelled of fuel. Especially the one in the front cylinder which I believe is the number one cylinder. This one was real wet and had a lot of build up on it. Since the fuel milage has been poor, around 21mpg I am obviously running to rich. The things that I see that are not stock on this vehicle is the air intake and the borola exhaust. As for it being chipped I have no idea. This is the first Audi I have worked on. I just completed a heater core which was quite the project and now I am hoping this issue is not something serious. The things I think I should check are the maf sensor or maybe a fuel pressure regulator? Where should I start to diagnose this problem? The check engine light is off and the vehicle is not throwing any codes. Please help

10-28-2012, 07:45 PM
You are right about checking the MAF. I would buy some MAF cleaner to try and clean the sensor first, as the intake (depending on the filter, how much oil was on it, if it was reoiled properly, etc) may have fouled the sensor element. Not sure if it is running poorly/idling rough, but if it is, and cleaning the sensor doesn't help, you could also try unplugging the MAF, starting the vehicle, and if the car runs better without the MAF plugged in, than this is most likely your culprit.

Another thing to consider that is very common is the primary 02 sensor could be going out. This is the sensor that is closest to the turbo, and doesn't necessarily throw a code in the early stages of failure. Also, Ross Tech's VCDS is your friend here, which allows you to get an insiders view to what is going on with your car (fuel trims, timing advance, pretty much anything, all via the OBDII port), but they aren't cheap, but you can sometimes pick up a Ross-Tech cable on here or ebay for cheaper than retail. You can also get a Chinese copy cable off ebay, and use Ross-Tech's VCDS light software which should work just fine for what you are trying to figure out.

Hope this helps : )

Avant Nate
10-28-2012, 08:27 PM
What is the coolant temp reading? Once the car has warmed up it should be right in the middle, and the the oil temp should be 200-215

10-28-2012, 08:50 PM
I did just notice that idle and low end were a little rough but over about 2500 rims it drives smooth. Also could it be an o2 sensor? Front or rear o2 sensor?

10-28-2012, 08:56 PM
I won,t know the coolant temp untill I install the new coolant over flow tank and g12 coolant that I just ordered from ecs. Hopefully I will get it tomorrow. But from what I remember the oil temp seemed much cooler than usual. I remember driving it and thinking the oil temp is really low. What could this mean?

10-28-2012, 09:29 PM
I did purchase a cheap Chinese vag com from eBay. I was able to plug it in and reset the airbag light that was on due to a bad connector under the passenger seat. And I did turn off the check engine light for a rear o2 sensor code which I believe was on due to the Borola exhaust. I put in one of those spark plug spacers to move out the rear o2 sensor. Since I did that the check engine light has not come back on. My problem with the vag com is that I am completely clueless on how to use this. This came with no instructions and it took me a half of a day just to get it working to clear these two codes? This site has been so helpful already gettin me this far and I have looked for a thread with some insruction on using this vag com but havnt found an idiots guide for the vag com. I know the vag com can do a lot but this is a whole new language to me, and I'm not very tech savvy.

10-29-2012, 04:39 AM
Check for vacuum leaks especially if its the 1.8t

10-29-2012, 05:01 AM
You say the oil temp runs cold? What is the approximate temperature on the gauge? And what about coolant temp, where does that run? If the car isn't warming up properly, that can cause a constant rich air/fuel mixture.

10-29-2012, 08:44 AM
This is your front o2 sensor that is bad.. Any codes?

10-29-2012, 04:33 PM
No codes for the front o2 sensor. I am waiting for my new coolant overflow tank before I put the new g 12 fluid in and run it and as soon as it comes I will get a temp reading for coolant and oil.

10-29-2012, 04:44 PM
My son and I purchased this car from Phoenix and had my brother drive it here to the Midwest. When it got here I noticed that the heater core was bypassed. This seems to be quite common in the desert since they never need heat, so I was hoping the heater core was still good but no luck. It leaked shortly after filling it and turning on the heat. Could bypassing the heater core possibly give a false reading and cause this to run rich? I have not run the vehicle with the new heater core yet since I have a bad overflow tank also. I will be running it as soon as the new tank comes from ecs.

10-31-2012, 04:41 PM
I checked both of my temps oil and coolant. The oil temp barley moved above the 150 mark and the coolant only made it not even a quarter of the way up when parked and then it would drop all the way down to 0 while I was driving. Not good, oil sensor and coolant sensor bad???

Avant Nate
10-31-2012, 07:31 PM
I checked both of my temps oil and coolant. The oil temp barley moved above the 150 mark and the coolant only made it not even a quarter of the way up when parked and then it would drop all the way down to 0 while I was driving. Not good, oil sensor and coolant sensor bad???

Failed open thermostat, super common for Audi. Engine always runs cold to and richens the fuel mix. On the 1.8t, super easy to fix. And less than 20 bucks, if you save your coolant. Oh and don't cheap on the thermostat, no Stant.
for 1.8t

And it should solve your heat issue