Why would a decat make my ep3 run rich?

[Paulos]

Been reading up about this,

Everyone's saying that putting a decat pipe on an ep3 will make it
Over fuel, but why? Because surely the 1st lambda sensor is the one that adjust the fueling etc,
And that's obviously before the decat. So the emissions are getting read before it reaches the cat.

And the 2nd lambda does nothing more then read emissions? Correct me if I'm
Wrong.

So why would it make it run rich?

Only been wondering because I have the emissions engine light (p0420) on my ep3 at the minute.
But it does have a cat. So it must be knackered.
So what difference would it make to decat it, if the lights already on if you get me. Other then making my
Magnex louder.

Cheers.
Paul

 

[JamesT]

It won't, it'll run leaner as it's breathing easier.

 

[Paulos]

What's the difference between rich and lean then?
Excuse my retardism

 

[Stoo]

What's the difference between rich and lean then?
Excuse my retardism

Lean = under fuelling
Rich = over fuelling

Both sensors work in tandem to adjust fuelling.

 

[Paulos]

im sure I'VE read somewhere on here that ep3's run slightly rich standard anyway?

 

[stoneyni]

The lambda sensor only works on part throttle to maintain around a stoic mixture at 14.7:1


Once you go to WOT the fuel status switches to open loop with fuelling being set on a mapped grid of MAP versus revs. Now since you have taken a large restriction to the breathing abilities of the engine out at any given rpm their is more oxygen at a specific MAP pressure. The fuel on WOT is not corrected or trimmed hence the same amount of fuel is injected as per the tables.


More air +same fuel =leaner afr