[mikelotus]

Hi there my car constantly fails the mot on 2nd emission test and the lambda sensor readings keep going in and out on the test screen.
I've taken the centre section out of the exhaust and the cat looks good don't know about the front two in the down pipes.
The car is slightly hesitant when running from cold but seems to run okay aprt from that can't say what the consumption is as i can't use it on the road.
The mot man says change the cat and the lambda and it should be okay.
Any advice as i don't want to spend too much more money on it as i've done loads and to be honest have got to sell it.
Whats the best way to do this ?

Cheers

Mike

 

[Zoo]

V6?

 

[mikelotus]

Hi there it is a 2.0 twin spark on an 02 reg.
The previous engine suffered a head gasket failure due to lack of coolant ie a hole in the radiator.
I just need to get it done so that i can sell it, ive spent loads on it and don't realy want to spend another £200 for just the one cat.

Mike

 

[Guest]

I would firstly try replacing just the lamda (with a Bosch one) not a cheap dodgy one off Ebay... Out of curiosity... how many miles has it done?
Do you have fiatscan or other OBD2 software? Is the engine management light on?

 

[mikelotus]

Hi there the engine management light hasn't come on since i turned it off with an OBD code reader.

Which sensor should i change as there are three two on each of the pre cats and one after the small cat under the car ?.

Thanks

Mike

 

[Guest]

If you have an OBD reader, are you able to view the outputs of each lambda sensor? do this and you should see if the Lambda are switching from open to closed circuit after a short time of running (5 minutes at most)

 

[alexGS]

...and if they aren't, check the simple things before replacing sensors - intake air leaks, spark plugs and coils (might be a misfire that explains the lack of smoothness too), perhaps even the MAF faulty - could all lead to wrong lambda sensor readings (rather than the sensor being faulty). It would be unlikely for all three sensors to fail, so if they are all 'stuck' then I think that really suggests a problem elsewhere. The lambda sensor is the last stage in a long chain of cause and effect, so (as you probably know) it's important to look for causes. Unless physically damaged I think it's unlikely that the catalyst requires replacement, though a new one might mask the true problem for a while (or might not - after all, you have three of them).

-Alex

 

[stagbeetle]

My 52 plate GTV TS (109k miles) is also borderline/fail on emissions at the moment. HC and CO are high on the fast idle test (higher revs = higher values).

I've found a series of videos here Kanal von TennecoInc - YouTube which go through various diagnostic tests, some of which you may be able to do, some are more involved. Could be useful, especially the simple temperature test to check if the cat is actually doing anything at all. Also, in looking for cats, this is the cheapest I've found Cats Direct | BM91292H (from the picture it looks like it should fit - no idea if it's much good, but hopefully will at least get me through MOT next month).

I have read (whether it's true or not) that the two pre-cats aren't really necessary overall for the MOT. Apparently they heat up quicker (being small and right by the engine) so get to work on the emissions before the main underfloor cat is up to temperature. Since the MOT emissions check should be done with it all warmed up, the underfloor cat should be enough (assuming everything's running well, I suppose). Certainly Alfaholics sell a full stainless system without pre-cats which they say is MOT compliant...

Mine was in today for service and the chaps reckon the little silencer behind the cat may be partially blocked (highly technical "see what sound it makes when you hit it" test), which could affect things.

The two lambdas on the front pipe are responsible for letting the ECU know what's going on, so they're the important ones if you've got running issues (aside from other potential causes anyway). The single rear one after the cat is only as a check on the cat function/emissions itself, so won't affect running, but will turn on the warning light. I called Alfashop last week and they're doing the proper Bosch ones for £60-66+VAT.

I might do some further tests on mine over the coming week or so; I'll update if anything shows up that might be of some use...