Exhaust Leak Causes: Consumption & Tightness

Hello,

I drive a Alhambra, manufactured in 2002, with a 1.9 TDI engine and 115 horsepower.
Recently, I noticed a hole (0.5 cm in diameter) on the exhaust pipe, just before the muffler, which I have now repaired. The noise level has not subjectively changed.

But I believe that the fuel consumption has significantly (approximately 0.7-1.0 liters) decreased since then.

Is such a strong connection conceivable?


Regards,
t.klebi

No.

Turbo diesel exhaust systems can also be properly tuned. I have had corresponding experiences with the 1.4 and 2.0 HDI engines. If this tuning is off, the engine will lose power. We clearly noticed this with the 2.0 HDI, whose leaky muffler caused a significant loss of top speed. Until the replacement part was delivered, it was temporarily patched, and it then ran like new again.

No.

I'm rephrasing }:
What is the general impact of exhaust system leaks on the performance and fuel consumption of a turbocharged diesel engine?

(Once, on a naturally aspirated gasoline engine, the exhaust system completely broke off right after the catalytic converter. The engine's performance was completely gone.)

Regards,
t.klebi

I think that if there were absolutely no back pressure ( ! ), the control behavior/position of the VTG (Variable Turbine Geometry) adjustment would change. However, this would not significantly affect fuel consumption; at most, the turbocharger would spool up more freely, depending on the exhaust gas flow.

In your case, there is no causal relationship between the size of the leakage and the change in consumption. How do you determine the change in consumption?

Hello,

As long as the turbocharger isn't building significant pressure, or if it's a naturally aspirated diesel engine, a 'mismatched' exhaust system can still have an effect. However, at low loads, the excess air is so high that you probably won't notice a real difference. Of course, it also makes a big difference where the hole is located.

If there are already relatively large holes in the mufflers, there is also a slightly higher probability that rust, fatigue fractures, etc., will cause the internal components of the mufflers to become mixed up in an undefined manner. For example, in my G2 1.6D, the pipe in the intermediate silencer came loose and ended up lying across inside the muffler. Of course, this caused a significant increase in flow resistance, and the car then ran very poorly.
Unfortunately, it took me quite a while to notice it, as you couldn't detect anything from the outside except for a slight rattling sound within a specific RPM range.

Best regards, Rainer.

"With the 2.0 HDI engine, the rear silencer was essentially a sieve. It's the only component responsible for noise reduction after the catalytic converter. Despite this, the engine ran very poorly! Acceleration was weak, and the maximum speed was not reached. Overall, the power delivery was very sluggish."

As long as the turbocharger doesn't build up significant pressure, or if it's a naturally aspirated diesel engine, an 'unmatched' exhaust system can still have an effect. However, at these operating points, with low load, the excess air is so large that you won't really notice a difference. Of course, it also makes a big difference where the hole is.

The observed differences in consumption relate to typical everyday use, i.e., the partial load range. The hole was in the pipe just before the ESD (Electrostatic Discharge).

@Hatdriver
I couldn't detect any change in performance. I didn't test the maximum speed.

I'll just continue to observe the situation.


Regards,
t.klebi

I once observed the opposite: sluggish performance and high fuel consumption. Then, the exhaust pipe before the ESD (exhaust system device) broke off. Suddenly, there was a noticeable increase in power, and fuel consumption decreased by almost 1 liter per 100 km. After the exhaust pipe was repaired, the engine reverted to being the same sluggish and fuel-guzzling machine as before.

Reason: Fragments of a defective catalytic converter inside the muffler.


The decrease in consumption achieved by sealing an exhaust leak is not technically explainable based on a TD (technical data) analysis.

The fact that the consumption decreases so much by sealing an exhaust leak is not technically explainable by TD.
If the performance (maximum speed) can decrease significantly (see posting by 'Hutfahrer'), then the fuel consumption might also change, right?

Whatever. Actually, it doesn't really matter why the consumption is lower, as long as it stays that low.

Regards,
t.klebi

According to the owner at the time, the fuel consumption of the 2.0 HDI should (!) not deviate from the normal range.

Quote:

If the performance (Vmax) can decrease significantly (see posting Hutfahrer), then, in my opinion, the fuel consumption might also change, right?

And what should the technical explanation for this look like? Especially in the maximum speed range, all vibrations that affect the filling of the exhaust system are occurring above the turbine.