Emissions Failure

[J Henderson]

My car just failed the MOT emissions test, and the result wasn't even close to say the least.

Does anyone have any suggestions on where I should start troubleshooting? Anything really obvious to glean from these results?

No check engine lights and has never ever displayed one. The car is also fed a strict diet of E5 Super unleaded and runs perfectly.

[McShmoopy]

1 hour ago, J Henderson said:

My car just failed the MOT emissions test, and the result wasn't even close to say the least.

Does anyone have any suggestions on where I should start troubleshooting? Anything really obvious to glean from these results?

No check engine lights and has never ever displayed one. The car is also fed a strict diet of E5 Super unleaded and runs perfectly.

I had a similar issue with my IS250, could be that the spark plugs needed changing that was my issue. Thought it was more likely a minor exhaust leak but even after addressing that it failed on the emissions til the spark plugs were changed, turns out cheapo ones were used instead of OEM dense 40k miles ago 

[IS300FSPORT]

Usually it's just the exhaust Lambda sensor or possibly a bad MAF sensor.

Bank 1 (Pre-catalytic converter) <-- usually the faulty one

Bank 2 (Post-catalytic converter) rare to go faulty

MAF Sensor found on the airbox remove it & see if its full of dust a clean may work but it's a fragile part have to be very careful.

Spark plugs also a possibility as well as air filter (unlikely)

Do you have an ODB2 diagnostic machine plug it in to read if there are any codes stored? A check engine light won't always light up right away.

If there's no exhaust leak try bank 1 oxygen sensor if I was a betting man that would be the 1st part I'd replace followed by the MAF but they are not cheap unless you can source genuine from an eBay breaker.

In the early 2000s owned a Honda Accord with a similar issue failed on emissions. A mechanic told me years ago to run a tank of Shell V Power & bring it in after a good hard drive to burn off any soot & as the exhaust is hot it will fly through emissions & surprisingly it worked. Although I acknowledge tech has improved since then so may not be as easy to get away with a good old Italian tune up 

[J Henderson]

Good stuff guys. The exhaust is only 2 months old, but was custom made so it's possible that it could have a small leak somewhere. Maybe where it bolts up to the manifold since that's where old meets new.

If the spark plugs really are faulty I'd be disappointed since they've done less than 30K. They were also Denso ones bought from Lexuspartsdirect so I'd be even more disappointed if they were fakes.

Its been at least a couple of years since I last cleaned the MAF sensor, so I'll definitely try that first. My dad has also given me a fuel treatment that he swears by, so I'll give that a go as well, but because the CO figures are so far off, I'm thinking that a faulty sensor is most likely.

[McShmoopy]

21 minutes ago, J Henderson said:

Good stuff guys. The exhaust is only 2 months old, but was custom made so it's possible that it could have a small leak somewhere. Maybe where it bolts up to the manifold since that's where old meets new.

If the spark plugs really are faulty I'd be disappointed since they've done less than 30K. They were also Denso ones bought from Lexuspartsdirect so I'd be even more disappointed if they were fakes.

Its been at least a couple of years since I last cleaned the MAF sensor, so I'll definitely try that first. My dad has also given me a fuel treatment that he swears by, so I'll give that a go as well, but because the CO figures are so far off, I'm thinking that a faulty sensor is most likely.

MAF Sensor and Throttle body is a pretty easy to do job, just get the relevant cleaner and do it all in one go. Come to mention it I could do with cleaning mine... new filters also are worth doing