Alfa 156 2.5 v6 failing mot on emissions - Alfa Romeo Forum
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(Post Link) post #1 of 25 Old 09-09-16 Thread Starter
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Alfa 156 2.5 v6 failing mot on emissions

Hey,
Any advice would be very much appreciated.
MOT time for my 156, had a load of work to do such as brake pipe, cv boots, front discs, bit of rust etc... Got all that done, then failed on emissions, details below details below for second fast idle:
CO limit 0.2 actual 0.18 pass
HC limit 200 actual 418 fail
Lambda limit 1.030 actual 1.211 fail

At this point they said it was the lambda sensor
Replaced it them went back, details below for second fast idle:
CO limit 0.3 actual 0.57 fail
HC limit 200 actual 50 pass
Lambda limit 1.030 actual 1.026 pass

At this point they said there were holes in the front pipe which gases were escaping from, got it replaced, also found a spilt in the crank case breather that goes from one side of the engine to the other, wrapped gaffa tape around it to tide it over until I could find a new one.
Went back results are below second fast idle:
CO limit 0.3 actual 0.63 fail
HC limit 200 actual 44 pass
Lambda limit 1.030 actual 17 pass

I have done a bit of reading and am now thinking:
Air filter needs replacing
MAF needs replacing
Catalytic converter needs replacing

I have looked at the air filter which has been on the car for less than a year and it looks OK, I will replace it anyway, but apart from the cat I am not seeing anymore that can be done.
The cat is not the original so it could be that, I will get it off the car and give it a shake and look inside it the best I can as I have read they can get blocked or any vibration inside them could indicate they are failing. I have run the engine at idle, then disconnected the maf, the engine revs drop quite a bit, then the engine recovers. Revving the engine with the maf disconnected give very lumpy running, then connecting again and the engine revs and idles fine. I have a 147 as well so I could swap the mafs and see how each engine runs then, but I suspect they will be OK anyway.
So with that I can only see the cat may be in doubt. Apart from that, I can't see a future for it.
Any advice you can give would be good, thanks again.
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I have no direct experience of this but have read several times on here about aftermarket cats failing prematurely and that a good used original cat is the safer option.
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(Post Link) post #3 of 25 Old 10-09-16 Thread Starter
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I'm thinking that as well, I wish I could find an original as my 147 still has all 3 of its cats and they are fine and the thing is 15 years old. I don't know how old my 156 cat is, but I will get it off the car and have a look then update.
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It sounds obvious but can be overlooked but when was the last PROPER full service? Oil, filters, plugs, possibly even HT leads? Changing all this and then an ECU reset might just nudge you under the lines. I know its more expense but apart from the leads, these should be annual parts and usually just before an MOT.
Also, be really thorough when inspecting the rubber pipes for intakes etc as a small leak may cause over fuelling and push up your CO2.
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(Post Link) post #5 of 25 Old 10-09-16 Thread Starter
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Hi,
Oil, filters and plugs a bit more than a year ago. I have only owned the car about 2 years and I like to get that stuff done as soon as I can as I don't really know the car until I have replaced all that kind of stuff myself. All pipes I have checked when I checked the air filter, and apart from the crack in the engine breather, which I have sealed with tape all looks good. I am getting the cat off to look at that in the next few days and swapping the MAF. I haven't heard of the ecu reset though, how is that done, in multiecuscan?
Thanks
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There is no real point in doing an ECU reset unless you change some of the consumables. The ECU learns the performance of the engine based on your driving and the condition of plugs, oil and filters among other things.
Do a search of the forum to see how to reset it, Multiecuscan is not required but as an alfa owner you should have it ready for all eventualities.
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(Post Link) post #7 of 25 Old 10-09-16 Thread Starter
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Already found out how the reset goes so will give it a go when I have a new air filter in and have looked at the cat and MAF. Multiecuscan is always at the ready, I have it in a laptop in a bag with all the leads and that is its only function. I'm always ready for all eventualities, my 147 taught me that, and that is why I bought my 156 so that when one is down for a while I can use the other. Also I purposely went after the 156 with the v6 engine in to get another driving experience.
Damn it why do I keep going with these things? I wouldn't put up with it from any other make, I would have binned anything else by now at the first sign of failure.
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also my 146 failed on CO a long time ago. aftermarket CAT was the reason.
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(Post Link) post #9 of 25 Old 10-09-16 Thread Starter
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Hi,
Thanks for that, how was it running, OK or not? I have read on some other threads that failing cats can cause problems with running like lumpy idle, using more fuel etc...
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CF1 or CF3?

If CF1, take it for a proper spanking, and then drive it onto the ramp. Don't idle, don't pause, don't turn it off. Had this with my 155 V6, which is a very similar system to a CF1 156. The cat wasn't lighting up at idle. The car was fundamentally OK, just failed CO. After a quick thrashing it passed easily.
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(Post Link) post #11 of 25 Old 10-09-16 Thread Starter
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OK, as far as I know it is a CF2? I know a CF3, in a gta for example, has 3 cats. 1 on each manifold and in the exhaust. This car just has 1 in the exhaust and I always thought it was a CF2. If I can do that and it still doesn't pass, doesn't that make a case for it being a cat problem?
Thanks
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Quote:
Originally Posted by leonattpcs View Post
Hi,
Thanks for that, how was it running, OK or not? I have read on some other threads that failing cats can cause problems with running like lumpy idle, using more fuel etc...
was running pretty much OK. but as people are mentioning, make sure CAT is hot enough as you go through the MOT.
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(Post Link) post #13 of 25 Old 10-09-16 Thread Starter
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Quote:
Originally Posted by alfizta View Post
was running pretty much OK. but as people are mentioning, make sure CAT is hot enough as you go through the MOT.
Hi,
I wil try to get them to, but they have been saying they have had it idling and fast idling for 30 mins or so and still failing on CO2.
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The physical amount of gases passing through at idle, without engine load, is possibly not enough for the catalytic reaction to heat up your converter and sustain that threshold heat at which it still works within limits.

If you have to buy one OEM grade cat every ten years, it becomes reasonable value.
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Originally Posted by leonattpcs View Post
Hi,
I wil try to get them to, but they have been saying they have had it idling and fast idling for 30 mins or so and still failing on CO2.
then the CAT should be at fault... (CO, you mean) maybe you'll get away with a 2nd hand one.
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(Post Link) post #16 of 25 Old 10-09-16 Thread Starter
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I haven't got a problem getting a new one as long as it passes. I haven't spent too much money on it yet, the bigger factor for me is time or trying to make it. It's looking more like cat though from what has been said, so I will be getting it off, having a look then maybe buying a new one then going back for MOT number 4.
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just mentioned the 2nd hand option as my previous aftermarket one lasted no more than 40 000 km. a good 2nd hand one could be a better option as they are designed to last a life, but that is just my opinion. there is always the risk of buying a faulty one...
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I know, I would prefer a second hand one, it is finding one though, but genuine alfa would be good.
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Quote:
Originally Posted by leonattpcs View Post
Hi,
I wil try to get them to, but they have been saying they have had it idling and fast idling for 30 mins or so and still failing on CO2.
The 155 I mentioned had been idling for about 20 minutes, the engine was properly hot. The cat wasn't hot enough though. Your HC figures suggest the cat is fine. I've never worked on something that is a CF2, but single cat under the body is the same as a CF1 system. They put the cats in the manifolds of the CF3 cars for this reason, they get properly hot very fast.
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(Post Link) post #20 of 25 Old 11-09-16 Thread Starter
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I will see what I can find out about the cf1 or cf2 thing. The cat is off the car, pictures are below:
Just the cat:
1.jpg
From where the emissions go in:
2.jpg
From where the emissions go out:
3.jpg
I have seen inside cats before and I have never seen the colour to be so dark. My 147 cats still look just about white. I will get a new cat on and show pictures for comparison as at this stage I am just curious and want to find the cause to know for the future. I am not sure the cat needs changing either, hopefully it will cure it, but if not I have already said goodbye to her anyway.
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Looks very small . my cf2 cat is 2 times bigger

that maybe the problem it being so small .(no unclean thoughts please)

Edit. Went outside in the COLD just for you and took a pic
As you can see mine is much longer (sorry had that thought again)
Attached Images
File Type: jpg 20160911_101540.jpg (115.8 KB, 7 views)

Last edited by mirlock; 11-09-16 at 09:20.
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(Post Link) post #22 of 25 Old 11-09-16 Thread Starter
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LOL, no probs thanks for the picture. I kind of thought about the size of the cat when I was first under the car after first buying it and yes it looks nothing like the original and indeed your as well or the one I am buying.
As you say, no funny thoughts, but:
Yours is frigging massive
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That one is a cat, yours is barely a kitten.
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(Post Link) post #24 of 25 Old 11-09-16 Thread Starter
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Ha, nice one very true.
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(Post Link) post #25 of 25 Old 16-09-16 Thread Starter
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OK so a new cat, all fitted and its f@cking passed!!
Finally!!!
I can get back to enjoying the v6 noise again
newcat.jpg
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