need solid advice on high flow cat issue.

[TopherSho]

So My ford is weird.  It has the right part numbers stamped on oem cats... but the pipes are not the right length. Both my private mechanic and Ford themselves advised the new PPE high flow cats do not fit as is.  So the PPE cats I bought do not fit without some ''work''.


Since I assume the PPE's will either need cut down or lengthened I need to understand what triggers a CAT code?  If we take a few inches off the PPE's I assume its not a big deal .. but if they lengthen the pipe leading too the cats I assume we could see temps that are lower then normal... 

What triggers the P0420?

[TopherSho]

From Brad who is still the best damned dude ever :


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I would not add lenght before the cats....You could shorten the pipe though. The Upstream 02 sensors should be no more than 4" from the turbos and oriented as to not allow condensation to collect on the sensor. That goes for any sensor. And the Rear sensors should be pretty close to the cat like how PPE designed.


The P0420/30 is triggered when the cats do not catalize the hydro carbons as well as the stock pipes...Honestly it's hard to have your cake and eat it too. If you get more flow then that usually comes at the cost of how well the cats do their thing...If they catalize well then they must have a large substrate which will affect flow.


The ECU uses logic that compares air fuel ratio relationships between the up and downstream sensors.


If there isn't enough of a difference between them the ECU determines that the cats must be bad...The trick is to use enough substrate to catalize well enough but offer more flow...PPE typically rides the line well.
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[ThePresidential]

Can you widen the pipe up to the cat without setting off any codes?

[Macgyver]

Yes but its wont do anything for performance. Sound yes. Perf no.

[ThePresidential]

Would it spool up a little quicker?