AFB High Fuel Consumption: Common Causes

"Hey guys, a friend of mine has an A6 V6 TDI (AFB) and he's been experiencing increased fuel consumption for about 2 months, roughly 2 liters more than usual, so averaging around 10 liters."

We have already examined all the known potential sources of error, but we haven't found anything.

LMM (mass airflow sensor) is new, all filters are new, camshafts are also in excellent condition, with no signs of wear, the ignition coil is also clean, and the catalytic converter doesn't appear to be clogged. The timing belt was also replaced 2 weeks ago, and the fuel injection timing is correctly adjusted.

The car is running fine overall; the acceleration and top speed are normal, although it starts a bit poorly when it's cold.

As I said, the consumption is really high. I used to drive an A6 V6 TDI myself, and I never used more than 8 liters.

It would be great if someone had a tip as to what might be causing this.

Regards,
Al.

Hi,

Have you also checked whether the intercooler piping (pipes/connections) and the intercooler itself are airtight?

Best regards, Rainer.

Have you checked the temperature sensor, or perhaps tried replacing it temporarily?

So, we haven't checked the straight-line distance, but if that wasn't accurate, wouldn't the result be significantly worse?

@Mullemaus:

Which temperature sensor are you referring to?


What else he noticed is that the engine isn't reaching its operating temperature. Even on longer drives, the temperature gauge doesn't go above 70° (Celsius/Fahrenheit - specify if known).

Regards,
Al.

Hi,

Quote:

So, we haven't checked the direct distance, but if that wasn't airtight, wouldn't it perform significantly worse?

It depends on the size of the hole. Having a constant leaf blower in the engine compartment will, of course, consume fuel.

The suggestion about the temperature sensor is also good; many engine control units regulate the fuel injection timing differently when the engine is cold, which can lead to increased fuel consumption.
First, check if the coolant temperature sensor on the engine is faulty. If not, replace the thermostat. 70°C is too low.

Best regards, Rainer.

Okay, cheers. Did you have the belt replaced two weeks ago (or did you do it yourself), and did you also replace the thermostat at the same time?
If you do it yourself, you have to disassemble everything and replace the part. If a workshop did it, then the discussions will likely begin.
The water pump and thermostat should always be replaced along with the belt when servicing this engine. While this doesn't explain the increased fuel consumption, it's a good starting point.
Did it also consume too much fuel before the belt replacement?

It could still be the injectors. Try running a fuel cleaner through the system or doing a 2-stroke oil treatment. With a quarter tank of fuel, add 1/2 liter of 2-stroke oil (mix it with diesel first) and then drive, preferably on the highway.

Get back to me.

Oh yeah, how many miles has the car been driven?