AndyLyman

iTrader: (1)

Hi all.....

Today I had the new mot done on my 2002 wrx sti (UK) , now done 66000 miles...

When i got the car last year on the mot info it had the following...

fast idle test-

CO <0.20% vol - - Actual 0.01% vol
HC <200 ppm vol - - Actual 2 ppm vol
Lambda 0.970-1.030 - - Actual 1.003

All of the above figures seemed low for my car - however today it struggled to get through on the emissions... it did pass but look at todays figures

Fast idle test -

CO <20% vol - Actual 0.20% vol
HC <200ppm vol - Actual 97ppm vol
Lambda 0.970-1.030 - Actual 0.991

Now since I have had the car the only mods I have had are New Pannel air filter Jr one from Scoobyworld and a Ninja Backbox, at the time of the mot I had a mixture of Tesco 99 ron and Esso Supreme 97 in the tank.

Can someone give me some info as to why the CO emission was 0.01% last year and this year its 0.20%, would this be down to the fuel?, the mot guy thinks it is down to the backbox... pressure or something affecting the output from the cat???

I was slightly worried when I saw the figures but it did pass ok... admittedly I didnt take it for a run before the mot, just home - mot centre 5 mins away then it was ticking over for 30 mins in the mot station...

Anyone help?

thanks

Andy

MazingerZ

Hi there

Have you got a big bore in the exhaust tail pipe? the MOT stations struggle to test emissions with this sort of stuff.

Did you give the car a good run before putting it through the MOT? if you didn't then this would easily explain the high HC levels.

hope this helps

Koji

AndyLyman

iTrader: (1)

Hi mate.

Thanks for the reply......

2 things... one being I onlyrun the car for 5 mins from house to mot centre and the 2nd thing is I have a Ninja 3.5 / 4'' backbox

is this the cause of the high co emissions?

Andy

jaytc2003

iTrader: (1)

Ive neve heard of a big backbox causing problems with emmisions. I have an my92/93 fully decated and it passed a cat test on the mot. That was with a jap cut 4 inch tailpipe.

[Davey]

The classic was off the scale with the De-cat! Luckilly technically it doesnt need the emissions testing for the MOT lol!

MazingerZ

Ask your mot tester what would be easier to test a 2" tail pipe or a 4" tail pipe....

MazingerZ

Did you have the OEM backbox on the car last year?

Give the car a good run before heading to the MOT centre, that will burn off any HC that may be in the exhaust system due to the engine temp (ie: cold - ecu sends more petrol)

Hope this helps

Koji

AndyLyman

iTrader: (1)

Yeah the mot guy did say to me that it was the backbox that was causing the co2 to be higher???


Yes I did have the standard Sti backbox on last year..

Andy

jaytc2003

iTrader: (1)

Why? the question wasnt about how hard it is to test, but the difference in emissions. The fact that the engine is older with more mileage will partly contribute to it, as well as things like a dirty air filter etc.

AndyLyman

iTrader: (1)

I guess that the fuel mixture - 99 Tesco & 97 Esso in the tank didnt help matters...

Around MK at the moment the Shell garages seem to have a shortage of Optimax ..


Andy

MazingerZ

I wouldn't know the reason behind it mate, I am not a mechanic, but I would imagine it would be harder to get a more accurate reading with a bigger bore...

As I said, ask your mot tester.

Koji

360ste

iTrader: (1)

Know the feeling. I normally run a GEMS ecu. Didn't realise i needed to fit the OE ecu for the MOT CO= 3.0% on GEMS (OOPS). The one point that everybody seems to have missed, (or I am doing selective reading), is that the car was sat for 30 minutes at idle. Working on mainly HGV electrics it is easy to see the results of leaving a engine idling whilst working on it. I try top get the garage to do the emissions test as soon as I arrive for the MOT as there is no build up of partially burnt fuel sitting in the exhaust system. What difference the OE back box might make unsure, the logical thought is that as it is not as free flowing as a Ninja BB the gases pas through the CAT slower thus a better reaction occurs. This is my opinion any other comments appreciated, thanks Steve

ALi-B

iTrader: (1)

At a guess fron those results, I would say the engine wasn't fully warmed up before doing the test. As this would create an increase in emission of both HC (unburnt fuel) and CO. The AFR being lower confirms this.

You can get quite different emissions test results from taking the car for an extremely hard blast, as opposed to just tottering round the block. A car that has had a hard blast beforehand and so, is nice and hot will always give the lower emissions reading.

HC is very slightly up for a car with a cat fitted (unburnt fuel), but that wouldn't worry me. When was the spark plugs last changed??

AndyLyman

iTrader: (1)

Spark plugs were last changed 6k miles ago... it was a major service 60k @ Spratton Subaru

car is running fine, no error logs, plenty of power... New JR pannel filter and Ninja backbox from scoobyworld are the only items changed since the last mot...

I cant work it out why such a big difference in 6k miles?

Andy