P38A V8 De-Catting advice

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PastyMuncher83

PastyMuncher83

Active Member
Posts
249
Location
South Somerset
How do all, can anyone help me source a de-cat exhaust pipe for my 4.0 ‘01 P38?

I’m having to replace the exhaust system due to it failing the mot for the centre box and rear boxes being heavily corroded and leaking.

Speaking with the MOT tester as it was presented for the test on LPG it doesn’t get emission tested so I can loose the Cats and hopefully free a few more ponies.

I’ve recently bought a second hand stainless custom system but it seems to be missing the de-cat pipe, will a Classic de-cat pipe work?
 
PastyMuncher83 said:
How do all, can anyone help me source a de-cat exhaust pipe for my 4.0 ‘01 P38?

I’m having to replace the exhaust system due to it failing the mot for the centre box and rear boxes being heavily corroded and leaking.

Speaking with the MOT tester as it was presented for the test on LPG it doesn’t get emission tested so I can loose the Cats and hopefully free a few more ponies.

I’ve recently bought a second hand stainless custom system but it seems to be missing the de-cat pipe, will a Classic de-cat pipe work?
Click to expand...

As it's all hitting the news about emmissions regs being tightened, you may want to hold fire on that idea ... for a while at least ...
 
Not to be a downer but that won't make more than a horse difference unless there seriously blocked. This mod is overrated and a waste of effort.
 
If your tester is going to pass it, crack on. You could hacksaw the cat out and buy a piece off eBay to replace it in 304 stainless.
I don't think you've been given correct info though. Post 1993 it needs to have a cat (visual inspection, they can't tell if it has any innards). It has to pass emissions on whichever fuel it is presented running on. You get to choose whether you want it emissions tested on petrol or propane
 
Your vehicles log book designated fuel will be petrol, therefore is MUST be given a full cat test no matter what it is running on at the time of test. On this class of vehicle if a cat is missing that was fitted as standard it is an automatic fail.
 
wammers said:
Your vehicles log book designated fuel will be petrol, therefore is MUST be given a full cat test no matter what it is running on at the time of test. On this class of vehicle if a cat is missing that was fitted as standard it is an automatic fail.
Click to expand...

You sure about that? Last time I took an LPG one down he said it runs on the fuel it was brought in running on?
 
Mine's always been tested on the fuel it's been presented on, LPG in my case.

Though my V5 does have it registered as Gas Bi-Fuel in the fuel type section.
 
All I know is the MOT tester has said he will pass it without Cats. Mine also says dual fuel on the V5.

Either way no going back now I’ve had to cut the Cats to get them out as didn’t fancy removing the cross member. Will let you know how it goes once I’ve got the decats made up!
 
In the MOT manual, straight away in the exhaust chapter 3rd paragraph it's stated that if it's a vehicle that qualifies for a full CAT emissions test and a catalytic converter is missing... that is a reason for rejection, and we haven't got to the emissions yet..

So does yours qualify for the full test or not? Simples
IMG_4106.PNG
 
PastyMuncher83 said:
All I know is the MOT tester has said he will pass it without Cats. Mine also says dual fuel on the V5.

Either way no going back now I’ve had to cut the Cats to get them out as didn’t fancy removing the cross member. Will let you know how it goes once I’ve got the decats made up!
Click to expand...

If it can be run on petrol and has a cat fitted as standard the cat MUST be present no matter what fuel it is running on for test.
 
The vehicle doesn’t qualify for an emissions test if presented on LPG, not at all.
As looking for a Cat is part of the emissions test this doesn’t get done.
I understand it’s a bit of a grey area and open to interpretation but at the end of the day is down to the individual tester.
 
It's not a grey area. It has to pass cat test on LPG by way of an emissions test and it has to pass visual inspection on the cat.
If you have a tester willing to turn a blind eye then fine. Don't expect it to pass elsewhere.
My only issue is that others may read this thread, go away misinformed and fail the mot after removing an expensive to replace cat.

The most current edition of the mot inspection manual copied below. There are also flow charts in section 7.3c which direct to test type. Maybe @discool can screenshot it, it's a bit beyond me.

The M.O.T. Inspection ManualIssue Date 01 January 20127.Multi fuel vehiclesVehicles which run on more thanone fuel(e.g. petrol and LPG)should be tested on the fuel theyare running on when presented.There is a slight difficulty with LPGvehicles: the hydrocarbons emittedare propane rather than hexane. Sothe HC reading obtained must bedivided by the “propane/hexaneequivalency factor” (PEF) markedon the gas analyser. For example:An LPG vehicle gives a reading of700 ppm. The PEF marked on the machine is0.48.So the actual MOT value is:7000.48= 1458 i.e. failSome exhaust gas analysers havean automatic facility for doing this
 
Last edited:
Im just repeating what the MOT tester told me.

If the vehicle is presented running on LPG it requires no emissions testing, no reading with the gas analyser.

The fact is that even with the cats removed it will still pass an emissions test on LPG.
 
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