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Catalyst Woes. Mk2

359 Views 5 Replies 3 Participants Last post by  GaryR
bit cheeky of me as I have only just signed up on here, but I was wondering if there is any MK2 1.8 owners about in the East of England that could very kindly lend me a catalitic convertor ?

to cut a long story short my local garage replaced my CAT last year due to the MOT failing on CO2 emissions, its just failled again this year on the same thing. As it stands my MOT on my beloved MX5 is due to run out tomorrow, I have it booked in for a re-test on tuesday afternoon. however my local garage that are supposed to be getting a warranty replacement cat for me havent come up trumps yet and I know that chap I was dealing with is on holiday next week. so I am going to be a minimum another week without my car.

my CO2 emissions were only .2 over the max, but as much as we tried warming it up and revving it we couldnt get it down.

if there is anyone out there that could very kindly lend me or sell me a mk2 cat for a 1.8s I would be very grateful, obviously it has to work !


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Was the cat a pattern replacement, was it checked after it was installed...? It's doubtfull the cat could have failed within a year unless you were running pig rich as a result of overfuelling and hence faulty O2 as previously stated. You'd have noticed really bad fuel consumption if you were running rich enough to take your cat out in a year.

Other causes............

High CO= Rich condition, CO is partially burned fuel
-High fuel pressure
-Leaky injectors
-faulty temp sensor
-thermostat stuck open
-clogged air filter
-charcoal canister full, faulty purge solinoid
-Fuel in the crankcase
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What steps can I take to make these checks ?

1. the car is completely standard, so I am guessing the fuel pressure shouldnt have changed.
2. its just been serviced so the filter was changed
3. it had a brand new thermostat last summer, so I doubt its that

* I can check the charcoal canister

however is there any easy way for me to check the Lambda, temp sensor and injectors ?

The MOT centre told me the Lambda reading was spot on so I expect the Lambda is working 100%

I must admit the gasses from the exhaust do smell a little unburnt.

thanks for your replies and suggestions.


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okay so far I have checked:

the Lambda sensor is clean, completely sootless and appears to be fluctuating .2 - .8v on a multimeter on the signal wire which suggest its working and burning clean.

charcoal canister is dry,
thermostat is opening an closing as it should
air filter is brand new and fine.

sadly it looks like its gotta be the CAT ?
Sounds like you have done the ground work there.

Does your car start up and idle behave the same regardless cold or hot.? A faulty IAT (intake air temperature sensor) could cause permanent enrichment.
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