gen 2 mps3 exhaust questions

Hi guys, just bought a second hand gen2 2010 mps 3 and love it. Cat drives good but noticed 1st and 2nd gear seems sluggish. The car seems to have an aftermarket dump pipe, after market front pipe but standard rear muffler and also has a CEL reporting p0421. Car is not missing but thought I would ask you experts for advice, is there a way way to fix the CEL, should I change the rear muffler as it might be causing loss of power or replace the whole exhaust back to stock.. live in Sydney so if there are any kind people that could point me in the right direction it would be appreciated as I'm not sure how the car is suppose to drive as it was the only one I have ever driven...thanks in advance...

Welcome to the forum! No help on the code, sorry. Try searching 'mazdaspeed p0421' on google. I'm sure others will chip in.
The cat-back exhaust (bit including the muffler) isn't very restrictive (until you get to big turbo and big power) and is only really replaced for sound. Removing the whole system including the DP would be a pain and a last resort i think.


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thanks for the response, i think I will leave it as is after your advice and reading up how much trouble they are to change :) after using an obd adapter and torque pro it does no reading for 2nd cat temps so I'm assuming the exhaust has no cat as it is loud at startup, any recommended exhaust shops in Sydney as the CEL is annoying and would like to modify the exhaust to have a sensor or cat installed, thanks

No worries.if you got no Cat that would be the problem (and very illegal). If you want to get dirty under the car you can visibly look for the cats. The second (unmonitored) cat should be just north of the double-exhaust hangers where the exhaust starts to go up into the engine, and the first (monitored with an O2 sensor on both sides of it) should be just above it near the turbo.

If you have a cat and can work out what the CEL means, you might be able to extend the 02 sensor which might be causing the problem (I think @Yeldarb did something like this and it's a common fix for crappy downpipe design) or just get a Cobb AP and turn the CEL off :)


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CEL code most likely due to dump pipe install. Basically means the catalytic converter isn't doing its job. This is measured by the O2 sensors. There are two possible reasons: 1. The O2 sensor is faulty (unlikely)
2. The dump pipe is a cheaper made version, causing it to throw a CEL.

As for power in 1st and 2nd, from factory, these gears are limited, with 3rd gear starting to show the cars potential. Depends on how sluggish it feels, it should still pull relatively hard when you get into 2nd.

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Thanks for the responses and advice, I will get under and have a look, the torque pro app allowed me to clear the CEL but it did come back after 40kms of driving..thanks again

Probably a catless DP, you will need to run O2 anti fouler (spacer)

Welcome to the forum.

A DP was the first major mod I did. I wouldn't probably do that again.

I had a CEL, P2096 for about 6moths.

Depending on your setup, if you have a unmonitored single cat as described above, our solution was to move the second O2 Sensor after that cat. You will need to extend the cable loom, plus install a new bung.

Or, just buy a COBB AP. You're just throwing good money after bad chasing a fix for a CEL. An access port will sort your CEL'S out.

Plus for an extra US$40 you can get some GREAT ACCESS PORT maps for our cars.

That's my recommendation.

Good luck.

so just for the record, i have a gen2 with 2xs dump pipe, and 3" center section to HKS rear muffler. O2 has been extended and moved post cat, no CEL.
pending what track days are on etc, I switch the 200cel highflow cat to a Straight pipe (catless).
have had this on for like 4 weeks now for the event and daily driving (because haven't had a chance to put the cat back in yet). I threw a CEL for 1 day during Motorsport event after throwing some flames out...
but since then I have not had a CEL once, even after the odd flame or two now.

As for that dead feeling throttle, get an AP and go for a custom E-tune mate, will really make that throttle sharp and responsive as you like it to be, i even found the OTS stage2 maps soft and unresponsive feel, so went for RayD eTune.

and FYI stock rear muffler doesn't really affect anything in terms of power and drivability I found. i went fron 2xs dump with 200cel cat. then added rear muffler, then added 3" center section. no difference between current set up and just the dump (maybe extremely minor)in terms of performance.

There you go. I think we've collectively all said the same thing. Go buy an AP! :-D