From experience with my old Peugeot V6 you don’t ‘need’ to get a car remapped to lose the cat...
Allow me to expand, my old V6 and any car generally, the upstream oxygen sensor will fluctuate and vary as the Ecu adjusts mixture when it’s idling and just off, the first sensor will generally vary from 150-900mv and constantly look like a saw tooth pattern, the second sensor on a decent nicely working cat is the one that causes issues, generally the cat takes the varied mixture and stabilises the oxygen levels (that is oddly what an O2 sensor measures) so generally the second sensor will read around 400-600 depending on where the revs are, so effectively the second sensor will read a midline level of o2 and then it knows the cat is fine
now when the cat isn’t working correctly the o2 levels will start to fluctuate and vary like the top sensor, and guess what happens when the decat is put into place, the cat is in effective because it’s not there anymore
So you have a sensor that wants to read a constant level of oxygen and be warm, well what did I do on the van... it ran two precats after the second sensor (Peugeot call them pre cats but they are pre atmosphere, French call all sorts of things bizarre stuff!) and two proper cats which are on the manifolds like a lot of modern cars (the cats need to be warm to be effective so the closer you can get them to the exhaust port the warmer they get!)
So I swapped the late V6 mani cats for the earlier under floor cats and forgot to put the underfloor one back on... I had to weld two bosses into the downpipes so the two upper o2 sensors could still read as these need to vary and control mixture depending on whether it’s open loop or closed loop running, that’s them sorted
The second sensors needed to be warm to work and read a constant source of steady oxygen...
You’ll not believe what worked...
Two jubilee clips to the manifold, air is as constant as you can get, effectively it thought the engine was putting out fresh air and it loved it, they sat at 525mv and all was good, ran it for a few years like that, the manifold kept them warm and zero engine management issues
So in essence a remap may or may not be required to improve power as gas may well flow better, but gains from stock will be single figures I’d think, but don’t assume you ‘need’ a remap immediately, I don’t see why it can’t just be clamped to a tube of the manifold for starters and a blank put in, it may help a cash strapped person to fund a manifold and then get it mapped later to get rid of any flat spots etc
Allow me to expand, my old V6 and any car generally, the upstream oxygen sensor will fluctuate and vary as the Ecu adjusts mixture when it’s idling and just off, the first sensor will generally vary from 150-900mv and constantly look like a saw tooth pattern, the second sensor on a decent nicely working cat is the one that causes issues, generally the cat takes the varied mixture and stabilises the oxygen levels (that is oddly what an O2 sensor measures) so generally the second sensor will read around 400-600 depending on where the revs are, so effectively the second sensor will read a midline level of o2 and then it knows the cat is fine
now when the cat isn’t working correctly the o2 levels will start to fluctuate and vary like the top sensor, and guess what happens when the decat is put into place, the cat is in effective because it’s not there anymore
So you have a sensor that wants to read a constant level of oxygen and be warm, well what did I do on the van... it ran two precats after the second sensor (Peugeot call them pre cats but they are pre atmosphere, French call all sorts of things bizarre stuff!) and two proper cats which are on the manifolds like a lot of modern cars (the cats need to be warm to be effective so the closer you can get them to the exhaust port the warmer they get!)
So I swapped the late V6 mani cats for the earlier under floor cats and forgot to put the underfloor one back on... I had to weld two bosses into the downpipes so the two upper o2 sensors could still read as these need to vary and control mixture depending on whether it’s open loop or closed loop running, that’s them sorted
The second sensors needed to be warm to work and read a constant source of steady oxygen...
You’ll not believe what worked...
Two jubilee clips to the manifold, air is as constant as you can get, effectively it thought the engine was putting out fresh air and it loved it, they sat at 525mv and all was good, ran it for a few years like that, the manifold kept them warm and zero engine management issues
So in essence a remap may or may not be required to improve power as gas may well flow better, but gains from stock will be single figures I’d think, but don’t assume you ‘need’ a remap immediately, I don’t see why it can’t just be clamped to a tube of the manifold for starters and a blank put in, it may help a cash strapped person to fund a manifold and then get it mapped later to get rid of any flat spots etc
