Log #16 - Front Exhaust Pipe Repair and Inspection Retest

Exhaust leak repair, comparison of two emissions tests and a passed inspection

September 2026 — Inspection retest: 12 September 2026

Documented by: Ali Çınar Aslan

The removed twin-branch front exhaust pipe, showing its two flex joints and surface rust.
The removed twin-branch front exhaust pipe, showing its two flex joints and surface rust.
Flange-side view of the old front pipe; the exact leak point has not yet been confirmed.
Flange-side view of the old front pipe; the exact leak point has not yet been confirmed.
Rear view of the car during the repeat emissions test on 12 September.
Rear view of the car during the repeat emissions test on 12 September.
The car and test platform during the second emissions test.
The car and test platform during the second emissions test.
Emissions report dated 12 September: CO 0.01% at both test speeds, lambda 1.000; test passed.
Emissions report dated 12 September: CO 0.01% at both test speeds, lambda 1.000; test passed.
Front view of the car during the inspection retest on 12 September.
Front view of the car during the inspection retest on 12 September.
Inspection retest report at 288,480 km, listing six minor defects.
Inspection retest report at 288,480 km, listing six minor defects.

Finding the Leak at the Exhaust Workshop

Following the failed emissions test in Log #15, we took the car to an exhaust specialist. The car was positioned over the inspection pit. With the technician's guidance, I went into the pit to examine the exhaust system.

A substantial amount of exhaust gas was escaping from the connection area of the twin-branch front exhaust pipe. The technician showed me the affected area. We thought this leak could have influenced the emissions readings.

Repairing the Front Exhaust Pipe

The exhaust technician carried out the repair. The damaged front-pipe section was removed, a new connecting section was fitted, and the pipe joints were joined by gas-shielded arc welding. The engine was then started to check for leaks. No obvious gas leak was found in the repaired area.

I took the removed twin-branch front exhaust pipe home. It has two flex joints, surface rust and areas where the coating has deteriorated. I have not yet confirmed the exact physical leak point on the removed part; I am keeping it for a separate examination later.

Change in Engine Response

After the repair, the engine felt freer to rev and the throttle response seemed more lively. This was a driving impression; no increase in engine power or cylinder compression pressure was measured.

Second Emissions Test — 12 September 2026

We had the emissions test repeated after the repair. The two reports showed the following results:

Comparison of the emissions tests on 8 and 12 September 2026
Parameter8 Sept.12 Sept.
CO, idle0.46%0.01%
CO, fast idle0.55%0.01%
CO₂, idle14.43%15.27%
CO₂, fast idle14.61%15.29%
O₂, idle0.88%0.24%
O₂, fast idle0.64%0.11%
HC, idle100 ppm15 ppm
HC, fast idle77 ppm19 ppm
Lambda1.0101.000

In the second test, CO fell to 0.01% at both idle and fast idle. The vehicle passed the emissions test, and the report was approved with validity until 12 September 2028.

Vehicle Inspection Retest

We returned to TÜVTÜRK for the inspection retest at 08:59 on 12 September 2026. The odometer reading was recorded as 288,480 km. The vehicle passed, with six minor defects listed on the retest report:

  • Aftermarket tinted film on the front windows.
  • Aftermarket tinted film on the rear windows.
  • Missing protective cover on the positive battery terminal.
  • Inadequate battery fastening.
  • Weak dipped-beam headlamp intensity.
  • Incorrect main-beam headlamp alignment.

The report stated that these defects needed to be rectified. The vehicle was approved for the next two-year inspection period.

Outcome

CO readings dropped substantially after the front exhaust pipe leak was repaired, and the vehicle passed the emissions test. I also felt an improvement in the way the engine revved. The emissions-test failure was resolved without replacing the catalytic converter.

However, catalyst efficiency was not measured separately. The initial high CO readings therefore cannot be attributed entirely to the exhaust leak, nor does this establish a definitive diagnosis of the converter's condition.