I am thinking of fitting a de-cat up pipe on my 01 WRX. Already have PPP with a de-cat centre section and are planning on sticking with the existing catted downpipe for now.
Wondering if I will get the CEL light if I run with just the one cat in the DP and will I have a problem passing emissions at MOT time.

I know the STi7 PPP runs this set up, but maybe there is a fix in the ECU to counter the increase in emissions and cure the CEL?

Or would I just be better forgetting about the up-pipe and fitting the sports cat downpipe from a STi7?

 

Anyone?

 

Can't comment about the standard down-pipe. However, with a sports cat down-pipe and a de-cat up-pipe, it's a bit of a lottery as to whether the CEL will come on or not. I have APS sports cat downpipe and de-cat up-pipe on my 02WRX, the CEL did come on. Allegedly, about 3/4s of cars with the APS system it doesn't.

An ECU re-map can cure the CEL, or so can a cheap resistor/capacitor tweak to the sensor (I posted the details over a year back - do a search for DIY CEL fix). I don't believe that prodrive do anything fancy with the map specifically targetted at emmissions on the PPP, but I may be wrong

As to emmissions: I can't believe the sports cat PPP downpipe fitted to the STi will fail the MOT, as it's a dealer fit option on the STi! (and note the STI doesn't have a cat in the up-pipe). I know my APS sports cat is also meant to be MOT compliant, I believe MRT guarantee their's will pass the MOT, so general gist, you should be alright with a sports cat. Probably worth making sure the car is well warmed up to be on the safe side. As I'm not due my first MOT for a few months yet, I can't comment for certain.

 

You shouldn't have any problem as Prodrive already changed the thresholds in your ECU before it throws PO420 code.
Of course there is always a small possibility but is negligible.
JIM

 

My light did not come on for about 3 weeks ,mostly driving in town,the car was 03 WRX with all 3 cats removed.It came on on A roads after driving flat out for a prolonged period of time.Bought cel fix from H&S for £10.00 wired it in and the light never returned.It comes with instuctions and is a half hour job JASON

 

It won't come on in town. The code is thrown by comparing closed loop values of the sensor with the eqeuivalent value measured from the headers. The most likely thing to set it off will be cruising for a while at a steady 70-80, e.g. normal motorway use!

Jim - did Prodrive change the thresholds on the WRX PPP too? I accept they did with the STi PPP to suit the downpipe change. However, the earlier (non ECUTEK) WRX PPPs won't touch the CEL issue - IIRC they add boost and maybe a little fuel - didn't think that the more recent ones did either (why would they when you keep the up&downpipe cats?)

 

My bug passed emissions with flying colours with only the centre cat on!--And that was a legitimate test before you ask

 

Hades I say mostly driving round town,I went on around trip of about 130 miles with the family mostly on motorways at sensible speeds no light came on,and i dont think it would have done.when it did come on i was abusing it revving to the limiter in high gears,and before you moan about that i have no mechanical sympathy,and it had a warrenty,just my experiance JASON

 

Cheers for that, is anyone running a decat up-pipe and centre with the standard cat-downpipe still in place? would that mean the turbo spooling up boost quicker and then having a bit of a problem trying to dump it through the standard downpipe cat?

 

Hi BrynO,

You've got to take the down pipe off to do the up pipe, so you may as well decat'em both at the same time ;-) You know you want to!

Regards,

Ian

 

Hi Ian, yeah, I know it will happen! looks like do both and just stick the centre cat back in at MOT time, or go for a de-cat up pipe and sports cat downpipe as STi...

 

You wont gain much power from just removing the uppipe cat apart from a slightly better flow at high revs,but you will get the "reliability" due to not having the possability of the uppipe cat breaking up and trashing the turbo(it has been known to do this with higher boost than std) -its the downpipe that gives you the better spoolup/better held boost.
I decatted both the up and downpipes and left the centre cat in for emissions-and i must say,it made the car feel more like my classic used to by giving you more of a punch when the turbo came on song-also revs a hell of a lot better

Gary

 

Jason - I've never met you or seen you driving, so I have no grounds to comment on your mechanical sympathy.

I do know that the "normal" Cat inefficiency CEL code (0420 IIRC, I may have the number wrong) comes on when the engine compares the two O2 sensors output when running in closed loop mode (i.e. steady throttle), and doesn't see a suitable difference between them. This normally takes some time - when I had the light, it came on after a few minutes at steady speed, usually at least a week after the last ECU reset or whatever. There is another "fault" which comes up relating to the response time of the O2 sensor (0189??), another relating to high measured EGT in the up-pipe, both of which could be effected by a decat, I'm sure there are others. However, the way the 0420 (?) cat inefficiency code works, if the ECU is working correctly, it shouldn't trigger when you're thrashing the car. At a steady speed immediately after, perhaps. Do you know which code yours triggered on?

 

AFAIK last remaped WRX PPP ECU's have increased thresholds "just in case" as every aftermarket cat can't be as efficient as the three factory cats, may be I am wrong though!
If you want a permanent simple solution have a look HERE preferably the mechanical CEL fix!
JIM

 

just fitted a full 3" decat turbo back system the engine warning light has come on . i know i need a remap to solve this long term. with an engine remap will this pass the emissions test at m.o.t time? or do i need a cat in there?

also in the kit a purchased there was a small decat up pipe. how and where does this go? does it bolt on the standard downpipe after the first cat? really appricate help lads cheers john ..p.s does anyone know in the midlands where i can get a remap done for a reasonable price.

 

my 05 wrx has no cats on it at all and passed emissions test and is well within the limits. but nthe light is on the dash though.