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Full Version Catalyst Removal Problemos?

Club XM Forum > Petrol Specific Issues
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Hi guys,

as you guys know i will be getting a 24v V6 soon, and i will put a lpg kit on it, like 'citroemxm', now running on lpg, you lose some bhp, big deal i say, but running on lpg i heard it's ok to take the catalyitic converter off. Here is where it gets complicated.

I've been reading the technical bulletin on the v6 engine in question, and there are actually 3 catalytic converters (WTF), one is a small priming catalytic converter to warm the exhaust for the ones further down, and THEN it splits into two pipes and off the pipes go to two other catalytic converters (one for each cylinder bank, how that works after the exhausts have mixed in the fat pipe where the small catalytic converter is i don't know, i would think you lose the harmony of the exhaust flows from each cyllinder in order).

I'm thinking if you take 3 catalytic converters out you get a lot of BHP back (not forgetting letting the engine sing nicer)!! So my question is, if i take out the three converters out, the later two having an Oxygen Sensor each, what do I do with the sensors then, just put them directly into the pipes? The sensors have a lot of say on the runnning of the engine so I think they must be kept.

Seems like a lot of power can be extracted out of this V6 unit, there are a lot of systems which could be tweaked here. I'll see how I get on with 200bhp first wink.gif
I think eventually I will run the car on a Megasquirt custom ecu too.

Thanks guys!
Nope - the two manifolds don't meet up again, possibly that's the 12v; can't say I've looked
closely at a 12v one for a good while so my brain's a bit rusty. On the 24v the forward cylinder
head drops it's manifold down onto the primary cat and flexible that then joins onto one of the
siameased cats; the rear cylinder bank feeds the second from it's manifold downpipe - there's
actually a whole load of extra space here compared to the 12V arrangement as there's a weird
collection intermediate manifold that then drops into the downpipe here on the 12v.

Incidentally, did you get my 24v Technical bulletin off XM-L Yahoo, as it's a pdf download there?

The lambda sensors sit in the plain pipe upwind of the cat and there shouldn't really be any
change without the cats.

If you don't want your cats I'll have 'em - mine don't look very clever.

yes andrew, thats where i saw the technical bulletin. so it's only the front banks that have the pre-cat? so where are the lambda sensors, between the first bank's manifold and first cat, and one after it before the second cat?

i've not got the car yet, fingers crossed mine sells quick, when i get it you are free to have mine when i take them of, so you have an xm too, 12v?

great technical bulletin there andrew, thanks for that, do u have loads of other technical bulletins? where do you get hold of them?

Ok, just for completeness for register purposes if anyone's doing that kinda thing;
Xm's I've currently got:

G406 YHT. 3.0SEi MAN - VF7Y3AG0000AG9239 - grey saloon 120k miles.
G823 BBL. 2.0SEi MAN - VF73AC0002AC8133 - blue saloon. 120k m.
G397 SKE. 2.0i MAN (another i!!) - VF7Y3AC0002AC7629 - maroon saloon. 150k m.
G plate. 2.1SD - Can't find the documentation - maroon saloon
H179 GKX now CAZ1820. 2.0i MAN (yes, just an "i") - VF7Y3AC0006AC3726 - blue saloon. 140k m.
H138 GLP. 2.0i MAN (gawd another wun) - VF7Y3AC0005AC6154 - blue saloon. 130k m.
H43 YYM. 2.0SEi MAN. VF7Y3AH0002AH5036 - blue (again!!) saloon. 130k m.
H564 TEP. 3.0Si MAN. VF7Y3AG0003AG5527 - blue (yawn!!) saloon. 130k m.
H882 YHT. 3.0SEi 12V AUT. VF73AG0002AG8524 - green saloon. 120k m.
J648 YDT. 2.0Si MAN. Can't find the documentation... - maroon saloon
EBZ6961. 3.0Si 12V MAN. No documentation! Oh dear - keep forgetting to sort these... gold. saloon.
K766 CJH. 3.0SEi 24V MAN! VF7Y3AL0001AL3015 - blue/grey saloon. 180k m.
K391 ETW. 2.0i Prestige MAN. VF7Y3AH0004AH9089 - green saloon. 110k m.
K371 WFD. 2.0Si CT Turbo MAN. VF7Y3AX0000AX1602 - grey saloon. 130k m.
K246 YAC. 2.0Si CT Turbo MAN. VF7YAX0000AX0895 - grey saloon. 130k m.
K430 WOF. 2.1SD MAN - grey estate. 130k m.
L394 ULM. 2.0Si MAN. VF7Y3AH0006AH0652 - maroon saloon. 120k m.

BTW, these are what I've still got, there's been 4-5 others I've scrapped and there are
probably a couple of cars I cannot find paperwork for and/or have forgotten about. Didn't know
I had as many, and haven't counted them - I really don't want to know the number...

Three are on the road at the moment all legal and being used. Think I'm mad, well, then there's
the Cx's, Gs's, 2CV's and Xantiae...

...and I REALLY like Cx's... smile.gif

I've got the full set of S1/S2 XM factory workshop manuals that were saved from a closing down
Cit workshop - were dumped in the skip and saved by one of the mechanics - I paid him 50quid
for them from an ad in the local Freeads. Felt like a lot of cash back then but worth every penny now!


hope your not bragging!!!

How about letting some other people having XM's!!!!!

Surely you aint got ALL those cars sitting around???

What are you? An XM loan company? dry.gif

Seriously though, youre right, the 24v has TWO indipendant exhaust manifolds that DO NOT join together, they are both 6 to one manifolds, that go down two seperate pipes then join at the back box!!

Straight throughs I think is another name for it for better gas flow and more power.

WHAT? 17 XM's all road legal??
Are you crazy man? Do you live on a farm or something?
you are joking right?

why isn't it called 6 to 2? wouldn't that make more sense?

Dead serious - it's not really anything to brag about - more a big liability/millstone around my neck
- may have to have a clearout sometime - when their scarcity increases & demand improves... biggrin.gif rolleyes.gif

All are running cars. I only said 3 were fully legal and on the road though
> 24V V6, 2.0i & 2.0Si CT Turbo...

The rest are in a barn on an ex Dairy farm - I only had them as nobody else wanted them.
Good pal gave me 6...

Just remembered another 3.0Si V6 auto in maroon on a cherished plate too... huh.gif

The carry on with all the V6 exhausts I guess is down to the pressure off the engine
- must be for sound insulation more than emissions.


As an other post on here, if you EVER come across a 1993 K/l Reg V6 SEi 12valve IN BLACK then let me know, thats the only car that will replace my Superb V6 Auto 12v K reg, in green!!!


I've got a fabulous looking H plate 2.0SEi saloon in black (that I haven't mentioned earlier)
that's worth mentioning if you're not afraid of messing about swapping engines!!

Lovely car with totally immaculate leather/wood interior and FCSH...only thing, the 3-4th
gears on the autobox have gone awol and IIRC the mileage isn't too high either cool.gif

It's a real looker mind... wink.gif


Does she have cruise????!!!!

I have a 2 litre auto box to fit it however, so not worried about that..

Aye, I know, that's why I asked the other day when there was a mention about autoboxes. Would make a nice car if I made the effort - It drives, "just" the lock-up of the banding in the box doesn't bring in the higher ratios - at least it does still go forwards as well as back unlike many auto Xm's I've seen. I don't think it's got cruise mind. Has full towbar electrics and the damned thing has a working sunroof!! When was the last time you saw that... rolleyes.gif biggrin.gif

Guess I could get piccies IF you're keen - one less in the way. Won't be too photogenic at this very moment as it probably needs a damned good clean as dust has settled on it - the panelwork is straight and when clean it's a real head turner - that's why I've kept hold of it and not done anything with it - have "borrowed" a front indicator off it, that's all!


Thanks for your reply. I would need to have cruise to make a worthy replacement for my K reg V6!!

There WILL be nothing wrong with my 1993 V6 auto,when I change the box over!! Hence as I said, only a BLACK V6 SEi will replace it!

EVERYTHING except Air con works on the car including Sunroof!! And an ambiguious ABS fault were it works perfectly but the ABS light is on

While the front end is off and the auto box is getting changed, I shall also finish converting her to R134a Air con system and get that going too!

When I'm done it will be perfect.

Even the glove box works, and the Immobilser Keypad Cover works too!

I thought cruise control was the green Nissan Micra stuck in front
of you doing 25mph with no gaps in the oncoming traffic... dry.gif

is it true the engine won't last long w/out the cats?
Very much doubt it - no substantiated evidence to back this up mind!

Plenty of performance mod cat bypass pipes on the market though,
and if that were to kill the engine the 'word' would certainly get around
and they just wouldn't sell.

What also backs this view is my first hand experience of seeing a 12v V6
working extremely well with a hollowed out cat; the innards were spiked
out effectively leaving a 'straight through' middle box aka cat - the
exhaust did run louder and was 'boomier' than it should.

The car was noticeably "sprightlier" to drive!!

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