Hellfire
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| posted on 21/1/04 at 12:27 AM |
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How does a Catalytic Convertor work?
Pardon my ignorance - but I have NO idea how one of these work - does it require a seperate electrical feed or is it independant? Is the Lamda Sensor
required for a BEC and is this independant or not?
Any answer will do as we have to put one on our's for SVA and there is not any sort of provision for a CAT on the loom diagram...
Thanks in anticptn
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simonH
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| posted on 21/1/04 at 07:26 AM |
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How a CAT works
Basicly the cat is a honeycomb of a catalyst (to give lagre surface area) normaly platinum based or in some a ceramic . the catalyst when hot (is
heated by the exhaust gasses) make the gasses react with them selfs and the air they are in and produce less harmfull chemicals. the cat needs no
power input other than the heat from the engine. i have no idea on how the sensors work, just the chemistry !
Also remember if you need it for SVA you need it for MOT as well !
[Edited on 21/1/04 by simonH]
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progers
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| posted on 21/1/04 at 09:27 AM |
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Hi,
The explanation of the cat is good, but for a cat to work properly the exhaust gases from the engine need to be kept at a level where the engine is
not running too rich to get the emissions down to the required level. This is why there is normally a Lamda sensor in front of the Cat. This gives a
reading of the unburnt oxygen in the exhaust gases and this reading is used by an ECU (usually found on fuel injected engines) to adjust the fuel into
the engine to maintain a correct air/fuel ratio (i.e. engine running not to rich or lean).
Now, when it comes to the SVA, you are unlikely to pass the emissions test with a CAT alone if you have a carb'd engine. What you need is some
kind of feedback system that controls the air/fuel mixture and keeps it lean enough to pass the emissions. Typically the "rent a cat"
systems from the kit car manufacturers include an end can with CAT + a lambda sensor and a control box. The control box will typically pulse air
valves which inject additional air into the intake manifolds of the engine to maintain the correct balance. (The air is injected into the holes you
would normally use to connect a vacuum gauge to when setting up the carbs)
I used one of these systems and *just* managed to scrape through the test.
There is a strong debate as to whether kit cars once passed the SVA then have to meet the strict emission tests again. Currently all Q plate and age
registered cars face only the normal no visible smoke test. There is no way that the MOT station can tell that the engine neds to meet the new
standards. This may change when MOT stations go Online to get test requirements (It'll be time before some of the back street MOT places go
online and use it!!) I managed to get a new reg so no MOT for 3 years :-)
Hope that helps
Paul
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Wadders
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| posted on 21/1/04 at 04:28 PM |
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Just to add further confusion to the issue.
I have the full caboodle on my car, Cat & closed loop lambda system, it's a carbed 98' ZX9 engine. To pass SVA emmisions i had to
disconnect the air bleeds, so effectively passed with cat only. Furthermore by the time i got home (100 mile round trip) the cat had 60% melted, this
despite being fitted exactly as per manufacturers instructions. Its a lottery. an expensive one at that, my system was over 300 quid.
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progers
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| posted on 21/1/04 at 05:07 PM |
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I must admit the setup of the systems can be tricky and the instructions that came with mine were shite..... In your case it sounds as though the
engine was running very lean. Couldn't have been good for your engine either!
I rented mine for £100. Can't be arsed having a cat for normal use saps too much power!
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Wadders
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| posted on 21/1/04 at 11:27 PM |
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The only reason i bought one was because from what i can gather, once MOT stations are all computerised you will need to meet emmisions at every MOT,
not just visible smoke.
I rented mine for £100. Can't be arsed having a cat for normal use saps too much power!
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