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 

[madasahatter]

Buy some Cataclean and run that through, does a good job.

[Vintagesixtysix]

And just to confirm….

You don’t loose a lot of engine oil between servicing do you?

[J Henderson]

1 hour ago, Vintagesixtysix said:

And just to confirm….

You don’t loose a lot of engine oil between servicing do you?

Never uses a drop. I bought a 1L bottle years ago to keep in the boot for topping up, and I've never had to use it.

[normski2]

I'm no expert on these things but I'd certainly give the MAF sensor a clean. I do mine every 12 months or so with a spray of electrical cleaner, gentle agitation and leave to dry for about 5-10mins.

Next I'd be looking at the upstream oxygen sensors with a view to replacing both. Think the gods advise changing them after 80 - 100,000mls.

If you need any heads up pointers as to what you may need, have a look through this write up I did on this very subject back in 2017

Good luck, hope you get an easy fix to the problem

[Spock66]

I think from those results the car is running too rich for some reason, I think unlikely to be the spark plugs unless you have misfire symptoms, most likely one of the sensors.

[johnatg]

Yep - it's running mega rich. 

Won't be an exhaust leak - that would give a high lambda reading - too much oxygen in the exhaust. Unlikely to be the lambda sensors - if one or more had failed the car would resort to default values and lambda would be much closer to 1.0 And there'd be fault codes.

Could be a spark plug but not very likely, or a coil but I think there would be fault codes with a coil.

My money's on a leaking injector.

It would be worth checking the spark plugs - 4 are easy and with luck one of them will be sooty. That may indicate where the sticking injector is, (if that's the problem)

Live data on Techstream might help.

In the normal course of events I'd think to put in injector cleaner (I favour Liqui Moly but plenty of others) and / or Cataclean.

But your problem is that you can't legally drive the car on the road (except to a booked Test or repair place)- under the new regime the  unexpired part of your old MoT is cancelled once you've got a failed MoT

But all conjecture from here.

Good luck!

[Vintagesixtysix]

Check the fuel injectors fuse as well.

[Linas.P]

17 hours ago, IS300FSPORT said:

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 

This exactly - either sensors are "lazy" (about to fail) and reports wrong air content and as result car runs rich and obviously pollutes, or there is hole in exhaust which skews the reading of secondary o2 sensors (basically sensor reads air in exhaust and assumes lean condition, therefore ECU tries to adjust for it by pumping more fuel in and making car run rich). MAF also come into this, but usually it causes opposite problem - reads too little air and causes engine to run lean and as result missfire.

In short - ECU get's wrong sensor reading for how much oxygen is entering or leaving the cylinders and as result injects wrong amount of fuel.

Also good shout - unlikely to be sparkplugs, you may get misfires or no-fire on cylinders and you would get very obvious issue with check engine light and rough idling, before the car would fail emissions.

[J Henderson]

I cleaned the MAF sensor. I couldn't really tell if it was any dirtier than usual, but I gave it a good clean anyway. Probably hit it with the most liberal amount of Contact cleaner I've ever done. 

I also put in about 500ml of the stuff my dad gave me to try (Dipetane) when I filled up with petrol, then went for a spirited drive down to the Borders and back. I covered about 100 miles in total, mostly on the Motorway or fast A roads with a heavy foot.

I mostly used S mode and paddle shifters the whole time and the engine was rarely below 3000rpm, with me looking to overtake or go as fast as I could where possible.

Despite the aggressive driving style, I recorded over 36MPG (dashboard reading) for the trip, which seems unbelievable if the engine is performing at a suboptimal level.

The power, response, smoothness and the idle all feel spot-on too with not even a hint of hesitation or a misfire etc. Hard to believe a car that performs like this is "faulty"!

 

[Linas.P]

Well... running rich is not "faulty" from perspective of power delivery, it is just not economical. That said if it is running rich then achieving 36MPG is somewhat surprising, but also not impossible.

Also even if sensor readings are wrong, then they will be most wrong at idle, low RPM and low load condition, like that were the pollution is tested. It will be least affected at high RPM/high load - so perhaps in that regard your headline figures "max power, torque" will not be affected and nor is the consumption. If you were to go maybe for extended drive at steady 50MPH, where RPM is 1500 maybe and load is minimal, then there may be more difference - car that runs correctly may achieve like 50MPG, but one with failing o2/lambda and running a little rich, may only do 40MPG. Basically if the theory of failing/lazy sensor and rich running is correct, then you won't prove it in spirited driving, quite opposite it would be more noticeable in "hypermiling", but then it is questionable if you even have baseline of what car could achieve.

[normski2]

On 10/19/2024 at 9:54 PM, J Henderson said:

I cleaned the MAF sensor. I couldn't really tell if it was any dirtier than usual, but I gave it a good clean anyway. Probably hit it with the most liberal amount of Contact cleaner I've ever done. 

I also put in about 500ml of the stuff my dad gave me to try (Dipetane) when I filled up with petrol, then went for a spirited drive down to the Borders and back. I covered about 100 miles in total, mostly on the Motorway or fast A roads with a heavy foot.

I mostly used S mode and paddle shifters the whole time and the engine was rarely below 3000rpm, with me looking to overtake or go as fast as I could where possible.

Despite the aggressive driving style, I recorded over 36MPG (dashboard reading) for the trip, which seems unbelievable if the engine is performing at a suboptimal level.

The power, response, smoothness and the idle all feel spot-on too with not even a hint of hesitation or a misfire etc. Hard to believe a car that performs like this is "faulty"!

 

Just out of curiosity ... have you managed to rectify the situation?

 

[J Henderson]

Thanks for asking. Yes, the car got a fresh MOT last week.

I didn't do anything else apart from the MAF cleaning, fuel treatment and Italian tune-up mentioned earlier.

What I did do though was take the car somewhere else for the 2nd MOT. The garage I originally went to gave me the impression they were "cowboys" fishing for work.

They failed the car on a couple of other issues besides the high emissions and listed a few questionable advisories. They were also very unprofessional so I wasn't about to give them any more of my time and money.

When it was tested for the 2nd time at the new garage, only one of the previous failures/advisories was repeated - Parking brake needed adjustment. Once that was sorted, happy days.

[normski2]

Nice one .. glad to hear all is good. 
I was prompted to ask as I thought about your issue as I was driving to my MOT centre this morning. 
Pleased to report passed with clean bill of health .. 14 yrs and incredibly little ever advised! 
Tester did a double take when he saw it was 14 yrs old!!

[Linas.P]

On 11/6/2024 at 4:36 PM, J Henderson said:

Thanks for asking. Yes, the car got a fresh MOT last week.

I didn't do anything else apart from the MAF cleaning, fuel treatment and Italian tune-up mentioned earlier.

What I did do though was take the car somewhere else for the 2nd MOT. The garage I originally went to gave me the impression they were "cowboys" fishing for work.

They failed the car on a couple of other issues besides the high emissions and listed a few questionable advisories. They were also very unprofessional so I wasn't about to give them any more of my time and money.

When it was tested for the 2nd time at the new garage, only one of the previous failures/advisories was repeated - Parking brake needed adjustment. Once that was sorted, happy days.

Yeah... sadly that is my experience recently. Don't care as I have purchased car that had many advisories and failures in the past, so there is no "record" to ruin. 

But I remember being really really annoyed when my old IS250 was failed for made-up reason at 172k, despite never having any advisory (apart of covers fitted obscuring engine non-sense), so it really felt like getting criminal record on clean history.

Talking about "unprofessional" - this year I got stupid advisory and also a failure I didn't even know about... And technically I got advisory in re-test which should not be possible, but I really didn't feel like going back and arguing. Basically, the guy tested the car, complained that there is "so much rust, but it will be alright" and how "cars can be deceiving, looks good from outside, but rotten" (side note - just been under the car to did anti-corrosion treatment and apart of some surface rust and bent lifting points, it really isn't that bad, I really expected much worse considering how much MOT centres are in my face about it). After the test, he started the car to move it outside and one headlight didn't turn on, came inside and asked me if I want bulb to be changed... and I said "no, it is Xenon, I doubt you will have that bulb, but it is weird it stopped working just now... what a luck". Then I said "can you just turn it on and off". And that was it, both lights came back on (I suspect it may be ballast on the way out, because bulb isn't even going pink yet). And that was all the discussion about that, he didn't mention anything about fail and I tough, because it was after the test and he already tested headlights and passed it, maybe he just going to ignore it.

So he printed the pass certificate, with like 8 stupid advisories... "wipers not  cleaning effectively" (there was little remnants of dried on a bug on the corner of passenger side), loads of rust advisories, basically all the ones "rust, but not substantially weakened", tyres wearing thin "despite all tyres having ~4-5mm on 75% of the with"... and I was like, whatever - pass is pass. Then I comeback homes and for some reason checked MOT history and it says "failed"... then I realised he first failed MOT, stating the passenger headlight does not work, then right away did a "re-test" adding 1 mile to the mileage and added all advisories and passed it.

Seems like it would have been fair to at least tell me that he will have to fail the car for headlight, even if it was already after the test and sort of say "don't worry, because now it works I just going to record it like you passed retest". He was probably really offended that I said he "won't have the right bulb"... although getting "garage special" Xenon wasn't really my goal. I would rather had accepted the failure and came back another day with set of new decent quality bulbs for re-test. That said I don't even know if it is bulb as it has not happened since... and it was literally one off.