Can an exhaust leak cause bad MPG?

Question

One of the connections between the exhaust downpipe and DPF filter is leaking (I guess the gasket may be the problem).

Recently the leak got a little bit more obvious, I can hear it when reving the engine after around 1700RPM (I guess that's the point where turbos are kicking in).

I also noticed that the fuel consumption got worse, from around 7l/100km to 9l/100km (33.6MPG to 26.1MPG)

• Could the exhaust leak be causing this rise in fuel consumption?
• Can I damage other system while running with this leak?

Answer 1

In a gasoline vehicle, the answer is yes. If the leak is far enough upstream to affect the reading of an oxygen sensor. If the oxygen sensor reads too lean of a mixture the vehicle will erroneously add more fuel. Eventually, this will be flagged by the computer with a check engine light.

The OP does not state the make, model, or year of the vehicle but the leak is before the diesel particulate filter and so I assume this is a diesel. Diesel vehicles don't have oxygen sensors. Hense there is no way for an exhaust leak to affect fuel economy of a diesel. There may be a subtle effect on the regenerative properties of the DPF but they are difficult to predict.

Answer 2

could there be a clog downstream? This would explain both the louder exhaust leak (it has no where else to go) and the worse mileage. It's possible also that there's something wrong with one of your turbos doing all of this also.