😒 Inspection Fail

TL;DR: Their failure, not mine

In Belgium, the first periodic technical inspection (MOT-equivalent) takes place when a vehicle reaches 4 years of age. Then you're left alone for 2 years, and have to pass it yearly after that.

The car was made ready just in time for me to schedule the visit. With a dead lithium battery, I had a standard "government-issued" Banner on loan for the week.

Overall that inspection made for a rather enjoyable experience. Everyone was friendly and interested or curious about my pocket rocket.

They didn't even try getting on board, and let me do the brake test myself instead. On the column lift, they were afraid of breaking anything and didn't dare lift one axle at a time for the regular checks.

Quick and easy then.

Except that it failed the emission test with a measured lambda value of 1.12. Far off from the 1.00 +/- 0.03 allowed margin.

With all the CO2 and NOx well within tolerances and the ECU reporting the expected slow oscillation between 0.98 and 1.02 (necessary to manage the three-way catalytic converter), the agent thought there might have been an air leak somewhere. He was nice enough to let me retry; this time in "sport" mode (full-fat ECU map), where I was only able to keep a stable-ish engine speed of 4000 RPM. It did zilch.

I sent a message to my engine tuning expert, who wasn't surprised. He sees that about 15 times a year. The explanation is that the exhaust system on a Caterham is rather short, and rather girthy, resulting in a pulsating gas flow that lets air come back in.

NOx are the best indication that the mixture is perfectly where it should be, as they would be through the roof and the engine barely able to run at 1.12 anyway.

So the guy with the sensor on a stick was right that there was air in the flow; but he was at fault for not pushing the rod far enough into the exhaust or using their flexible pipe extension - I've been told.

I'll have to go back with the car, untouched... to demonstrate that it's ticking like a clock at 1.00 and have them redo their homework.

Yay.