Cabin fumes

[cumblechook22]

I possess a first edition Proceed GT 12/500, which I thoroughly enjoy modifying and driving; nonetheless, I have encountered this issue since the day of purchase. The stock exhaust of the GT includes a primary catted downpipe positioned post-turbo and an additional one located immediately thereafter (which I purchased without). During a test drive, I detected an odour during heavy acceleration with the windows down, but I dismissed it. Fast forward one to two years of ownership, I resolved to enhance power and sound by constructing a custom catless downpipe. Following the installation of the downpipe and subsequent tuning, the exhaust fumes are incessant and overwhelming when the windows are lowered. Even with the windows closed, I perceive that they still infiltrate the cabin. Nonetheless, I am uncertain about the issue, given the odour was present prior to my removal of the catalytic converter. I attempted to extend the tailpipes, but there was no alteration.
Do you have any recommendations?

[Rashman4u]

To be honest. Reinstall the previous system, as there appears to be an issue with your custom-built system. 🤷‍♂️ Subsequently, verify that all connections are secure and free from leaks.

[cumblechook22]

In all honesty, I likely ought to. However, in actuality, the odour was present since the inception of the stock system. To clarify, the "homebuilt system" is constructed by my friend, a skilled exhaust fabricator. I believe I should commence with a smoke test.

[DSM10000]

Only a corrupt MOT examiner would permit a vehicle, originally fitted with a catalytic converter by the manufacturer, to pass the inspection without the converter installed.

[cumblechook22]

Fortunately, for automotive aficionados, the regulations in my locality are merely theoretical.

[guyskin]

The sole distinction between MOT tests in Cyprus and the UK is that in Cyprus, the initial test occurs at 4 years, followed by further tests every 2 years. All examinations are comparable to those conducted in the UK.

Operating a vehicle without a catalytic converter in Cyprus is equally unlawful as it is in the UK. Furthermore, one of the key principles of this forum is our disapproval of illegal vehicle modifications.…someone may rectify my error if I am incorrect 🤷‍♂️!

[cumblechook22]

I apologise if this is the situation. I need guidance regarding the presence of odour in the cabin despite the exhaust system being in its original condition.

[SkippyTom]

Have you inspected beneath the vehicle with the engine operational to identify any leaks?
My earlier Ceed is entirely standard but may exhibit some similarities. A flex joint at the front may visually seem to be in excellent condition, yet it can possess a leak that is detectable by sound or tactile sensation when the entire flex section is examined with fingertips.
If the exhaust has undergone a comprehensive inspection for leaks while elevated on a lift with the engine operational and no issues were detected, may there be a problem with the crankcase ventilation? or any other loose connection within the engine compartment related to the turbo? Pay close attention to any hoses connected to or from the intercooler.