De-cattting a P38

I am looking for advice,

I am looking into removing the cats of my 2002 p38 as I'm on LPG so they are not neccessarily needed, speaking with my local garage they have advised against this as the reckon it may affect the set up (with regards the electronics) apologies for the terminology but i'm no mechanic.

Has anyone successfully decated and if so what did you do with the sensors remove them or put them back?

Thanks in advance

MSX150 said:

I am looking for advice,

I am looking into removing the cats of my 2002 p38 as I'm on LPG so they are not neccessarily needed, speaking with my local garage they have advised against this as the reckon it may affect the set up (with regards the electronics) apologies for the terminology but i'm no mechanic.

Has anyone successfully decated and if so what did you do with the sensors remove them or put them back?

Thanks in advance

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They may not be needed by the LPG but they are needed by the law.

Had no cats on my p38 with stainless exhaust, lpg passed emmissions no problem.

as for legalities i have no idea but it didnt attract attention was never commented on when in the garage (quite often being a p38) and sounded nice too

I am not getting into the legalities - I was told the lambour sensors (or name to that effect) may play havock with the set up - does anyone know if this is the case?

Ignoreing the legalities, I have decatted mine with a set of the RPI decat pipes which also have some silencers that look a bit like cats.

Since fitting them it is deffinatley running better and seem to be getting better performance and fuel economy.

Mine is a 2001 Vogue, only has one set of probes before the cats and not after them.

You will need to re-fit the lambda sensor (or O2 sensors as they are often called ) these are essential for the engine ecu to read how the engine is running. That said I believe Australian spec P38s didnt have them at all.

i have taken the elements out of both cats, i believe the car should have cats present for the mot. but they dont check inside!!!!

present it on lpg and they have to test it on lpg so they will be none the wiser!!!

its a fiddly job knocking the elements out but it saves a few quid!!!

MSX150 said:

I am looking for advice,

I am looking into removing the cats of my 2002 p38 as I'm on LPG so they are not neccessarily needed, speaking with my local garage they have advised against this as the reckon it may affect the set up (with regards the electronics) apologies for the terminology but i'm no mechanic.

Has anyone successfully decated and if so what did you do with the sensors remove them or put them back?

Thanks in advance

Click to expand...

both my p38s are decated and run perfect on lpg and petrol, if you by a decat pipe they will have the holes in to screw the sensors back in which is a must
after decating i noticed more mpg more power and better sound ,allthough some of the sound improvement is down to the janspeed stainless exhaust system
never had a problem with mot test as soon as i tell them its lpg they dont even check the emissions

rewmer said:

You will need to re-fit the lambda sensor (or O2 sensors as they are often called ) these are essential for the engine ecu to read how the engine is running. That said I believe Australian spec P38s didnt have them at all.

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weld a nut either side of the cat to screw in thje lamda sensors

Does it have 2 or 4 02 sensors? If it only has 2 (1 each side before the cat) all good, but if there is also a sensor after the cat you may have a problem.

The cats are worth a bomb if you sell em to scrappies lol, might even get more on ebay I know they give £40 for a tiny cat of a small car, Range cats are huge.

Cheers for the advice, i think im going to go with the "decatting the cats" so to speak, may be a fidly job but sounds a sensible approach, I already have janspeed exhausts but sadly i purchased the "cat back" system as that was the advice i took at the time

you are going to need the cats as stated if you have the post cat ox sensors fitted which were on most 2001 v8 petrols some slipped through though
another option is sport cats which will let more through but keep the post sensors happy

Apparently cats work by oxidising harmful pollutants to form less harmful ones. this means they reduce the level of free oxygen in the exhaust gasses. post cat lambdas are therefore to compare the oxygen in with the oxygen out to get an indication of how well the cat is doing its job. bottom line, if you have 4 lambdas you can't simply decat unless you are willing to mess with ECU programming.

I think it's unlikely he has the 4, my research leads me to believe that they were never fitted on the uk Market. Rasheed is spot on with his comments.

MSX150 said:

Cheers for the advice, i think im going to go with the "decatting the cats" so to speak, may be a fidly job but sounds a sensible approach, I already have janspeed exhausts but sadly i purchased the "cat back" system as that was the advice i took at the time

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janspeed cat back system is no problem this is what i have , go to a breakers yard buy the front y section which contains the cats , cut the cats out and weld a straight pipe in their place you will have the holes to put your sensors back into bolt in place job done ,if yours is a thor engine make sure you get the same y section as the sensor threads are different on pre thor engines,both mine have pre-cat sensors so no problems here i have yet to see a p38 with post cat sensors and keep your old y section in case you ever need to put it back on , sell the cats you cut out to get some of your money back, only drawback it will be loud !!it will make people on the roadside look round with the cats out of the system and through the janspeed system you will notice it 50-60% louder which isnt a problem if you like the v8 sound
0-45mph is ok 50-70 can be rather noisy 70+ seems to most quiet maybe the speed takes the sound away with extra wind noise etc
but you will also get better mpg more power and the engine will run cooler
this is what i have done on both my 4.6 p38s
i do remember some company selling decat pipes on ebay in s/steel about £150 may save time and trouble buying and welding a y section
the choice is yours

Sounds like a lot of aggro for little reward.

klf400 said:

i do remember some company selling decat pipes on ebay in s/steel about £150 may save time and trouble buying and welding a y section
the choice is yours

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Looked for that during months and couldn't find anything

Just got an Email from my mate. It reads.


"Will anyone considering removing the catalytic convertor from a vehicle made after 1993, regardless of the fuel it uses, please publish their registration number on Landy Zone. It makes prosicuting you so much easier".
Regards VOSA.

Nice joke ah ah