No CEL light after 100 cell cat was installed

[JUST VTEC]

Does this mean that the " suppose high flow " cat i got put on today is not as high flow as said, becuase its still not flowing enough to set off the sensors??

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[Karl]

Does the dc5 have a senor after or before or both.
As the dc2 only has before the cat. Meaning u can hollow out the cat and the engine light still wont go on!

[JUST VTEC]

Mine has before and after .
Iv gotta go bak tomorro as soon as i drove away i was getting bangs n shatters from the exhaust but i couldnt go bak as i was late from wrk
Not impressed
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[Karl]

Correct me if im wrong. The 1st sensor is used for air to fuel ratio. The second is to check the gasses to see if the cats doing its job.
So the light shouldnt come up

[JUST VTEC]

I couldnt say if your right or wrong
Even so, shouldnt the gasses contain alot more emisions now as its not being filtered as well ?

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[Karl]

Why do u want the light on?

[JUST VTEC]

.lol.. i dont.
After doing some researching pretty much all aftermarket cat upgrades iv read up on give this cel light on dc5s
Im questioning the supposed " high flow " effectivness of the cat

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[Stephen_AUS]

Just for reference, I had the 70RR on before an 200 cat modification. Neither decat or cat poped up any CEL's. And it still ran fine both ways and I still have stock ECU.

[FRDK20]

im running a 100 cel high flow cat and no CEL light on stock ECU

[Oz Striker]

My CEL didn't come up for a couple of days, was pissed off when it did though! I wouldn't be stressed either way, if your light doesn't come on then good for you! if it does it's a good excuse to get kpro lol


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[fatboyz39]

^ I like that idea

[Master_Scythe]

what determins this is how well your engine is running from the time you get the change done.

Lets use simple numbers\examples to make it really clear

Say the 'im poluting too much' (cat failure) light comes on when it senses 50% of your exhaust fumes are 'bad gasses' (the type the cat normally burns away)

Say your engine makes 60% 'bad gasses'
Normal CAT cleans up 40% of these (sensor sees 20%)
Drop your CAT's effectiveness (hiflow), and it may only remove 15%
Your sensor will be seeing 45% 'bad gasses' still not enough to trip the sensor.

HOWEVER, if your engine is less tuned, worn, or you have a VERY bad batch of gas, it may START at 75% 'bad gasses'
Meaning after a hiflow droping only 15%
Sensor is seeing 60%; enough to cause a CEL.


Thats not how a sensor works by any means, but its simply a nice clean logical way to look at it.

The reason some people get away with no CEL for a while, and it eventually appears, is one of 2 things.
1. sensor SLOWLY getting dirty from less cleaned exhaust, and eventually being 'wrong' about how much of these nasty fumes are actually new.
or
2. the ECU notices better flow from the exhaust, compensates with more fuel, and the subtle but new tuning is now 'dirty' enough to trip the sensor.


TL;DR?
Your engine runs clean already, so making the CAT less efficient, isnt tripping the sensor like it would on a bad engine.

[JUST VTEC]

I see , makes alot of sence dude and clears it up for me abit.
Iv now done a fair bit if driving on the new 100 cel cat nd still no light .sp i guess its a good thing

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