Customer regrets their exhaust mods ⬇ 𝗥𝗘𝗔𝗗 𝗗𝗢𝗪𝗡 ⬇

We’re often asked to fit customer-supplied parts downpipes, exhaust systems, various bolt-ons and that’s absolutely fine. We’re happy to help. But whether we’re fitting, removing, or replacing something, our technicians’ time is billable. No one works for free, and that includes us.

Now and then, we see situations where someone buys performance parts without fully thinking through the implications especially when it’s not just them driving the car. It might seem like a great idea at the time, but then comes motorway drone, MOT issues, or family members complaining. I still remember fitting a system to a brand-new A45. A few days later, the customer was back — not because of a fault, but because his wife had had enough of the noise on the school run.

More recently, we had a customer bring in a downpipe for us to fit. Straightforward job but the post-cat O2 sensor was faulty (heater circuit) it was infact bent in shape.
We offered to supply a new sensor, but he opted to buy one himself, likely due to budget concerns. Its also worth noting that even removing the O2 sensor can destroy it. Sometimes when you twist them the internals get damaged, or they just don’t come out at all. It’s luck of the draw.
O2 sensors are actually service items. If you've got a performance car consider why replacing the sensors is part of regular maintenance on the like of many Ferrari, Maserati and other supercar models. Ideally you'd be supplying a CAT off downpipe and some new sensors.

We continued with the job and tuned the car with a CAT-off setup. It made reasonable power on the dyno, but of course the O2 heater circuit fault remained. Whilst I tried to explain this to the chap, it seemed to go over his head to some degree.

A few days later, he returned. I assumed with an O2 sensor for us to fit, but whilst we had a new O2 sensor he also said the car was too loud for long journeys, and he wanted the cat refitted. No issue, since we hadn’t done anything permanent. However all the talk about it being a track car seemed to vanish as now it was a daily driver again…

The O2 sensor he’d sourced. Unfortunately, it was the wrong sensor.

He seemed to be in utter shock that we’d be billing him the time it took to refit the cat. We didn’t really know what to say. He seemed to be expecting “its ok mate, you spent some money here and we’ll do some mechanical work for free”

What would you do? It isn’t even like we recommended the downpipe.

In fairness if it were just the O2 sensor maybe we'd have done it for free. But if we'd lifted it up in the air and found the O2 sensor was the wrong one, would we then do it free on a third trip to us?

At this point, it’s worth clearing something up: does removing the cat mean you don’t need a functioning post-cat O2 sensor? Sometimes, yes but it depends entirely on the ECU.
Some ECUs will let you disable cat monitoring completely, others won’t. His downpipe had bungs for both pre- and post-cat sensors, which is a clue: the manufacturer expected both sensors to be used, and so did the car’s ECU. In many cases, a missing or inactive sensor causes readiness faults or keeps the MIL/CEL light on, even with no actual DTCs.

If this had been a Bosch MED9 setup (as seen on EA113 TFSI engines), it would’ve been easy to sort. But this wasn’t a Bosch ECU, it was French. And no matter what we did, the MIL light stayed on. A working post-cat O2 sensor was still required, plain and simple.

Let’s not forget, this was supposed to be a track car. And that’s fine, but in reality it wasn’t a dedicated track build. It was still used on the road. That’s where things get tricky, because what works on a track doesn’t always work for daily use. There’s always a compromise.

Some golden rules for track builds:

• Be honest with yourself if it’s not a dedicated track car, build it for real-world use.

• Always have a budget for things going wrong because they will.

• Whatever budget you think you need, add 50%.

• Build a relationship with whomever you want to help you with the car. Unless you're an automotive engineer you're going to need help and you'd best find someone you trust and can work with. If you're going to second guess people then ask yourself if its really for you!

The moral of the story? We’re happy to fit your parts. We’re also happy to remove them if you change your mind. But none of that is free and based on experience, we’ve learned not to assume that’s obvious to everyone. To be honest with this customer there were a number of signs that we missed lol