Hi, first post here but I've been reading the forum for some time for advice, go easy on me

My 2004 Subaru Impreza WRX has recently failed the MOT on emissions with very high CO levels. The figures were:

First fast idle test CO = 1.12%, lambda = 1.001
Second fast idle test CO = 0.67%, lambda = 1.046

I've had similar 2 years ago and went to a "friendly" MOT station to pass. Some months on I got an engine warning light relating to the front lambda, swapping the front lambda (with original Denson part but sourced from somewhere other than Subaru) actually also cured emissions to allow it to pass MOT the following year (last Feb).

Now a year on and I'm getting similar emission problems meaning I am failing the MOT and I want to be certain that I need a new cat before I shell out £££ on a new one! As it was the lambda last time I'm wondering if it is the same issue (a lot cheaper than a cat).

My car has an Xtreme Scoobies "01" exhaust and remap in July 2009 (my mate who owned the car previously had it done). Reading up it is possible this is a Hayward & Scott exhaust but not sure. It comprised of the following (price without VAT):

Back Box Longer @ £250
Cat pipe small @ £90
Centre pipe @ £90
Downpipe with Hi Flow Cat @ £510
Up pipe without EGT Hole @ £115
Cel Fix @ £28.50

So I've done away with standard rear cat as well as the pre-cat in the uppipe leaving just a hi-flow cat in the downpipe (correct me if I'm wrong).

I'm not sure of the lifespan of such a cat but it is now about 30k miles old and 4.5 years old.

I've used the likes of FreeSSM and romraider to log values from the lambda sensors and to me they look fine, but I'm no expert! There are no errors logged at all that are read using the tools.

Here is a log I created which I thought would help show if the lambda sensors were working.



I've tried to understand from the garage about what this shows but they weren't interested. I don't even know if I'm reading the right info here. I can't seem to log the voltage from the front lambda which was what I was originally trying to check.

The garage has said after some diagnostics that my front lambda isn't switching correctly but they believe this is due to my cat not doing what it should be and i should replace the cat before then seeing if the lambda is still "not switching". I find this odd as the front lambda is before the cat?

I've cleaned the MAF, reset the ECU, had the car serviced (minor service as had new plugs and air filter 10k miles ago), run some fuel additive through the system, given it a good old run, the garage have said they have got the cat nice and hot before testing, so I think I've done most advised things there.

If it is the cat anyone recommend a new downpipe with cat to replace my current exhaust? I assume I have a 3" pipe which isn't standard but is standard for aftermarket exhausts? I'm making some assumptions here based on my research and being quite new to Scoobies!

Any advice would be gratefully received!

Thanks

 

Def something wrong there as I have no cats whatsoever and have no problems making the required threshold (NI mot centre testing too, which is fairly strict).
Does the car run 100% or is it a little lumpy?

 

I've seen people say they pass MOT tests with no cats but I assumed that these were "friendly" MOT stations which don't mind passing a car on emissions only, as long as it is safe.

I don't think the car is lumpy but it may have gradually got worse without me noticing. The only issue I've noticed which may not be an issue is when I lift off suddenly after heavily accelerating I get a judder (more so than you'd expect).

 

My favorite subject is "let's start looking for vacuum leaks".
Have you had the bonnet open a. Listening for hissing and b. Rechecking all rubber lines for cracks and tight fits?

 

I've not checked every hose no, I'll do that. No obvious hissing with my head in the bonnet, not pulled the throttle cable while listening though.

Only sounds from the drivers seat while driving are what I would consider normal turbo whooshing.

Anything scientific I could read from the ECU to indicate vacuum leaks?

I would have hoped the garage pick up on something like vacuum leaks. Saying that though they put a new jubilee clip on my bottom radiator hose today after I asked them to check a suspected leak around the bottom of the rad. Charged me to drain the system etc. and fit a new clip and then when I get home tonight notice it is still leaking as much as it was before. Probably a new rad needed as mine is bowed out pretty bad and has parts of the core falling out, but this is what I wanted them to confirm, not charge me £60 for nothing other than saying they fixed the leak with a jubilee clip and my rad is in poor condition. Urgh..

 

Same here, I live in Belfast. Put my classic through twice with a Blitz Nur Spec R system and a 3" decat downpipe with no issues yet.

 

another norn iron lad here - straight through MOT with a straight through pipe

Yes btw - you can use the SHOW LTV button in Romraider Logger instead of freeSSM to see the long term fuel corrections. If you have big values in there (say higher than plus or minus 5) then you could well have a leak that the ECU is correcting.

Also - could be map related, depending on what idle timing has been set to this can impact on the burn efficiency which will have a knock on effect to what the cat is doing.

Rear o2 should be disabled if you have the second cat delete done - no point logging it though as it can only read on/off.

 

sorry - also mean to ask I take it the cat is well up to temps before testing? If the car has been sitting in a corner and had 5 minute warm up that's not enough. Needs a good hoofing to clear out the bugs!

 

I hope that it is hot enough, when it first failed they asked if they could put some additive in it and take it for a run to get it hot. It is possible they just aren't getting it hot enough though, it did drop from 1.2% to 0.6% CO from one run to another which might be temp related, got to get it down to 0.2% or less though. The second run did show a lambda setting which was a fail though.

 

I'm not sure how they would disable the rear o2 sensor, is it done with an ECU mod? My graph I've linked to shows the rear o2 sensor voltage so I assume it is still sending values back. I have the CEL fix, so maybe that is for the rear o2 sensor or is that for the EGT sensor? I'm new to this so still trying to piece this together as I bought the car modified.

 

you said the car had been remapped - the map should have taken care of the rear o2 and the EGT (uppipe temp probe) without the need for "cel fix" or any other tricksies.

Do you have romraider logger - are you able to grab the LTV screenshot to see if there are big corrections going on?

If the CO value dropped from 1.2 to 0.6 after a run - maybe you have a leak somewhere that is closing/sealing better when things heat up?

 

I guess the remap did do this, I just have the vague receipts to go by from Xtreme Scoobies (who don't exist any more I believe?) which don't give much detail. Maybe when this was carried out in 2009 the fixes were more electronic than in software? They receipt has this on it:

remap @ £500
Cel Fix @ £28.50
Labour fitting cel fixes @ £50
cel fix egt @ £5
mapping time (driving) @ £50
heat shield modification @ £15

This was all done with the exhaust costs I put in my original post. About £3k in total with VAT added.

I do have romraider logger and will certainly check out the LTV screen tomorrow. I think I had a look at this at the weekend but can't recall the values.

The car has been passing the MOT fine since 2009 it is just on one occasion it failed due to emissions which was the front lambda and this time which is possibly the cat being no longer effective!? This is what I am trying to determine. I've been offered to run some diagnostics on the car with SSM3 (a Subaru ECU diagnostic tool?) to see what might be going on, might give something more concrete to pinpoint the problem? Although I guess I could get the same info from romraider logger if I knew what I was looking at?

Thanks!

 

how can they charge for mapping then mapping time then cel fixes (which should be done in the map anyway?!) CHANCERS!

Aye mr - SSM = Subaru Select Monitor. Anything you can get there you can get from romraider logger.

Grab the LTV shot - save as image - post the image here

 

£3k for in essence fitting an exhaust and a map...Im in the wrong business.

 

Here is the Romraider logger LTV data:



I am quite surprised at the cost and work done looking at the invoice for the exhaust and remap, but as I say I didn't get it done myself so I've not looked into what is normal for remap and exhaust. The cost of the exhaust seems similar to the current Hayward & Scott exhaust prices and visually it looks very similar.

 

OK so - IAM 16 is good and airflow corrections look grand - this suggests it's not an airleak mr. Do you have some kind of induction kit fitted?

That leaves you with sensor failure (either MAF or o2 most likely) or even an exhaust leak after the turbo.

It's unlikely to be a failed cat unless your just not heating it up enough. This depends on what the cat itself is made of - some of them need to be super hot to get the job done. Is the car off the road at the moment or can you take it for a good 30 minute horsing to get it hot as a hot thing?

 

I don't have an induction kit fitted, standard air-box as far as I can tell with a standard air filter.

I have given it a good blast since it first failed, I've just not done that prior to going for MOT test (just a 10 mile drive to the station). I'm not sure how long they left it after dropping it off with them and how long they spent heating the cat up on the tests, they did say they had taken it for a blast to heat it up though.

 

how much are they charging for a retest - maybe you could call in advance and they could test the emissions as soon as you roll up to the door? At least that way you'd know it's hothothot.

Is there anyone you could borrow a MAF sensor from to see if it helps?

 

Hi Mate,

Not sure where in Cambridge you are, but Im down the A14 at NN10 9**

I have a spare MAF sat in the garage you could try

 

Thanks guys and thanks for the offer of a spare MAF. I was hoping that reading the MAF stats using romraider would indicate if it was functioning correctly or not but I don't know what a healthy MAF should read.

I have now managed to get it booked in at a more knowledgeable garage so all being well they will be able to pin point the issues. Unfortunately I need the car and without an MOT I am a bit stuck.

 

hopefully they can get to the bottom of it for you mr - don't forget to post back what the issue was in the end.

 

Sorry it has taken a while to report back.

A garage took a look at the car with a SSM3 diagnostic tool and also gave it a once over, confirmed that everything looked pretty healthy, no issues they could see with the lambdas. Said it was spot on. The only issue they believed was present was the cat being a little "lazy"

Good to confirm that the car is running well! I have an MOT now as well which is nice.

Now to get a new rad as mine doesn't have long left by the looks of it! It is bowing out massively at either end and the cooling fins are pretty much falling out. It is also leaking from time to time around the bottom right (when looking into the engine bay from the front of the car).

 

And thanks for all of your suggestions, advice and kind offers for borrowing spares, very much appreciated!