Increase in exhaust emissions .

[texaxile]

Hi,
Car is an 04 WRX Impreza, 112k, prodrive performance pack (fitted by Subaru). Sports CAT in the front down pipe.

According to mot history on the fast idle test, the CO2 was .06 last year, this year it’s up to .18 which is pretty close to the limit allowed I think. Low idle test it’s down to 0.04% (same as last year). Everything else is well within range.

No fault codes showing, exhaust is in good order with no leaks , air filter is new and genuine part, and nothing has been changed on the car apart from oil and filters in the last 12 months (I get the service done along with the MOT test). It was serviced prior to the MOT (same day).

I will get the exhaust re checked in case there’s a hole or leak, but surely that would be audible ?. Then I’ll check for split air hoses anywhere, but again, unlikely as idle is smooth and perfect regardless of conditions. Next might be to get an ASNU injector clean (at 112k they may be a bit grotty).

Any ideas as to what might lead to a higher fast idle CO2 reading like that, especially as the low idle is unchanged?. MAF maybe?. Any suggestions about what I might be missing here and also suggestions on how to fix it would be appreciated.

TIA and virtual single malt to you all

Edited by texaxile on Saturday 30th September 14:07

Edited by texaxile on Saturday 30th September 14:53

[stevieturbo]

CO2 is not a testable item.

Post your actual results in full

[Chris32345]

Co2?
I assume you mean CO
Which is carbon monoxide

[E-bmw]

How long has the "sports cat" been fitted and what make/type is it?

I ask as the cheaper ones are renowned for only lasting a couple of years.

[texaxile]

Hi Gents

Yes, apologies for my utter stupidity , I meant CO (Monoxide) emissions.

As Stevieturbo requiested, here's my results in full:

Fast Idle Test:
Engine speed = 2875RPM
CO = 0.18 %vol (Limits 0.20)
HC = 15 PPM
Lambda = 1.005

Natural Idle Test
Engine Speed = 690 RPM
CO =0.05 % vol

Temperature guage showed a warm engine.

In answer, The downpipe is a Genuine Prodrive downpipe, fitted to the car on purchase 19 years ago.

I've had the car since 2016 and replaced the pre O2 sensor for a genuine item back then, Nothing else has been changed sensor - wise, and CO emissions have always been low up until this year.

I run it on Momentum fuel, the car is used everyday for a 20 minute A road drive to work and back and also other reasonably long journeys most weeks.

thanks again guys.

Edited by texaxile on Saturday 30th September 19:07

[stevieturbo]

It could simply be down to temperature on the day, maybe a slightly different rpm used, variances in the test equipment or how it is used

I wouldn't be going round chasing a problem, until there is an actual problem

[texaxile]

Ok Thanks for the reply Stevie.

I guess I'm overthinking it just now. As you say, I'll just keep the old thing serviced regularly with decent oil and fix the issues as they come along. Part of the joy of owning an old car I reckon.

[Belle427]

I normally stick an additive in my cars once a month or so in the hope it helps keep everything as good as it can be.
Premium fuel can help too.
Currently using Millers products.