MOT Failed Emissions
 

Hi all,

Forged / mapped 2007 STi.
Just failed on emissions on Thursday.
I did fit a recent brand new Subaru MAF a few months ago as my old one was giving low voltage, it helped but only to a degree.

I've been getting what I see as low bottom end performance for a while.
Would a faulty front 02 sensor cause laggy bottom end performance and bad emission readings?....even though I've never had a CEL?

The 02 sensor has done 100k miles....

laggy performance would more point to an exhaust leak, possibly pre-turbo which would certainly cause emissions issues.........

what level did it fail on , co etc , may point in the right direction , was it fully warmed up before being tested ? 👍

From DVLA website :

• Exhaust Lambda reading after 2nd fast idle outside specified limits (8.2.1.2 (c))
• Exhaust carbon monoxide content after 2nd fast idle exceeds manufacturer's specified limits (8.2.1.2 (a))

just wondering on the levels if it failed by a mile or a bit , was it hot enough first ? , if they ask for a fast idle , mine passes more easily at 3 k rather than 2.5k , one car i have has to be on hot cats or it’s a no go , the others i keep warm outside the mot place , some one said remove the air filter for the test , im not sure if that works as i’ve never done it , would mot place be able to tell you what exactly it failed on

I'll have to find out on Monday, I don't have the car back yet and I can't see the emissions actual readings sheet online...

It’s a great shame that you don’t know a proper mot tester 😎

our gas guzzling Subarus are a rare breed on the road now

And now £630 road tax for mine! WTAF! :banana:

The reason i bought jdm , 280 £ tax and ulez exempt , i bought for the long term so have three fairly fresh new shape jdm Fsti and a collection of spare parts including diff gearbox and a forged 2.5 lump 👍 i was lucky i bought before prices went silly ☹️

Apparently a new AFR 02 sensor hasn't changed any readings....

as above was it fully warmed and cats hot before the mot ? 👍

You need a proper Italian tune up before the test, the night before will do, but its got to be a proper one, on a private road 160 mph did it for mine.

😂 yes thank you Jdm stig , on a more chilled driving note , take it for a sensible blast before an mot get it fully up to temp and boost , get them to do the emissions straight away on your arrival , keep the car running , keep the revs up a bit before the test , if they have to do a fast idle , on my car 3000 rpm worked better then 2500 , good luck with your test 👍😁

unless the original was faulty then a new Lambda will simply replicate the situation...........
have they checked for leaks or done any other kind of basic diagnosis?? has it actually got a functioning cat fitted??

I will put a fiver on that not working, tried it in years gone by.

All of this, plus make sure the fuel in it isn't ancient if it isn't driven much.

my monaro is the hardest car to pass mot time , if cats are not hot it won’t pass , it’s a well known issue with them , i do the same with my Fsti that have 200 cell sports cats and they are passing no issues , it’s the cheapest option he has at the moment , as before we need to know what it actually failed on and work back from there 😁👍

I don't have the car back yet, it's still with the garage waiting to finish off another car so the mapper can plug it in etc. I also don't know the actual emission results as I can't see them online....
I suspect it's running pretty rich as for ages now it's been drinking fuel more than usual....but whatever, never a CEL which is annoying.

Is that no CEL light on the dash or no codes shown on a code reader ??

Certainly nothing on the dash, and I would've thought the garage I use would scan for codes. He has a laptop with pretty good software.....not sure what it's called though.
Would a failing coil pack throw up a CEL on the dash / store a code?

Yea i have a 100 cell one and its a pain to pass, needs to be roasting hot before it will go though, might try some cat cleaner this year.

Ok car back and running very well.
Bob Rawle was called in in the end, turns out the ECU had "locked" itself on a rich setting / scale....or something like that.
Bob adjusted the AFR scaling to suit.
No idea what would've caused the ECU to do that? Any ideas? Could head gaskets cause the AFR / CO readings on the fail?

Here are the readings :

Fail :
https://cimg5.ibsrv.net/gimg/www.sco...a68a51d72b.jpg


Pass :
https://cimg2.ibsrv.net/gimg/www.sco...d609d21eb5.jpg

good to hear it’s now passed 👍, Bob is going to know way more then me , what did he say ? is car not driven much , flat battery at some point , that’s me guessing

Thanks dude.
Not sure exactly what he said as I wasn't there. It gets driven enough, decent Yuasa very healthy battery.
Perhaps if Bob reads this he'll tell us exactly what he found - Newbury, reg number ending EPA.

Funny you say about flat battery....about a year or so ago, I changed my A/C belt. I wanted to check it was tight enough by running the car at idle and switching the A/C on and off to check for noises.
I did this without the alternator / power steering belt on and it put up an EML.

The EML went out the next day, not sure what the stored code was but I think it said something about the lambda not pre heating or similar? I wonder if it was that incident that the ECU never recovered from...it has been running sh1te for about a year....

from my understanding , if there is a fault ,and the the fault is sorted , the ecu will normally re learn and go back to what it was before the fault , the code (eml ) may come off the dash display but i would expect it to be stored in the ecu till it’s cleared 👍