Failed the MOT

[ronnie1995]

Hi all,
Hope you are all well and enjoying the weather.

The cavalier went for it's mot today and failed on the emissions on the carbon: 0.84 where the limit is 0.20.

Does anyone have the knowledge of how to bring the emissions down.

One of the people at the garage said that it's to do with unburnt fuel.

Any words of advice would be greatly appreciated, (silly me-left it to the last day of the mot to get it tested).

Cheers

Ron

[Cavalier342]

First port of call for me, depending on the engine in question would be to check and clean the spark plugs if required, and give it a good clear out down the nearest national speed limit road.

Carbon is basically soot so it might well be that it just needs a good run. It's not a drastic fail though, so won't be anything serious.

[ronnie1995]

First port of call for me, depending on the engine in question would be to check and clean the spark plugs if required, and give it a good clear out down the nearest national speed limit road.

Carbon is basically soot so it might well be that it just needs a good run. It's not a drastic fail though, so won't be anything serious.

Okay, the MOT centre I take it to is an hours drive from where I live, plus was tested straight away. After it failed we changed the spark plugs and the Lambda probe, but still gave the same readings. Even giving it a good revving to try and get the level down didn't work.

I'm not entirely sure on the exact model of engine, but the car is a 1.8 gli prefacelift model, if that helps.

Cheers

Ron

[DiplomaXE]

air filter fairly new?

[iancav6]

We had a Focus that failed on hydrocarbons, eventually traced it to a split breather hose.Of course this was after changing the air filter, plugs and lambda at first to no avail.
We also disconnected the battery overnight to reset the ecu and after replacing the breather hose it passed ok.

Id check all breathers hoses are intact and clear.

[ronnie1995]

Yes, I changed the air filter 2 months ago.

Okay, sounds a good idea to look over the hoses.


One thing that I'm thinking could be linked to it, is that the idle isn't steady and when its being revved up it making a popping sound out of the exhaust. Does anyone know what that could mean?

[Lowrider Dave]

Over fueling/ not all the fuel is being burnt, gets pushed into exhaust where hot gases burnt it off resulting in a popping sound.

[Lowrider Dave]

Could be caused by an air leak, leak in exhaust system, ignition timing. I'd clean the carburetor first off.

[Cavalier342]

Prefacelift 1.8 without an i is the 18SV model. Carburetor. Something can be played about with to get it right, could be the carb itself needs cleaning. Or stripping and cleaning thoroughly.

[ronnie1995]

Prefacelift 1.8 without an i is the 18SV model. Carburetor. Something can be played about with to get it right, could be the carb itself needs cleaning. Or stripping and cleaning thoroughly.

Okay, but mine is the injection model. Do you reckon stripping and cleaning the single point injector could solve the problem?

[Cavalier342]

In that case it's the C18NZ. Cleaning the injector may help but I suspect now the catalytic converter is at fault. I would say the lambda sensor but if it is running ok, then it's likely not that.

[planetc]

Clarify, carbon monoxide (co) or hydrocarbons failed please? Two different things, with different action required. Hydrocarbons are indeed unburnt fuel, and could be caused by anything that prevents a cylinder burning enough of the fuel put into it. CO is reduced by action of the catalytic convertor, if the lambda sensor hasn't helped then a cat would be next.

[planetc]

If the hydrocarbons are high, don't waste your time putting a cat on it until you get them down, unburnt fuel kills cats

[Mikebmth]

I was always told to stick in some Redex and go for a blast to be honest getting her nice and warm before rolling into the test centre, bit like diesels have a DPF filter on newer cars I believe no vehicles burns off its carbon properly until used properly so if you plod around town a lot like I do then a good run up a dual carriageway will do it the world of good..

[Cavalier342]

Redex is shite, STP or Wynns is what you want.

[ronnie1995]

Okay, here is a picture of the readings given for the emissions.

https://www.dropbox.com/s/uvt3znn3q44t9 ... 8.jpg?dl=0

A new exhaust system was put on it before i bought it in 2012, since then I've done just over 20,000 in it. Therefore I wouldn't have thought the cat should be the issue.

However the puffing sound from the exhaust and irregular idling since I've owned the car has been a concern to me, but I just do not know how to rectify it.

Would the fuel additives do the trick though? As if the engine isn't running correctly somehow, then surely it might not make a difference.

Thanks

Ron

[iancav6]

Could the puffing exhaust be a burnt out valve?
Try a compression test or leakdown test.

[iangsi]

Mine 1.8 had rough idle was an air leak in the exhaust recirculation system.

[planetc]

Looking at that print out I would suggest the cat is not much good, but do make sure you don't have an air leak or the egr isn't stuck part open as this would cause the system to over compensate fueling.

[Envoy CDX]

After checking the EGR, check the hose to the MAP sensor on the bulkhead. I had issues with mine and it would not idle right.

[ronnie1995]

Hi there.
Does anyone know if the single point injector unit and map sensor from a 1.6 L reg would be compatible with or the same as on my 1.8 engine?


Cheers

[Cavalier342]

I don't think they are compatible, maybe the C16NZ2, as they are almost identical to the C18NZ, but I'm not 100% certain on that.

[Envoy CDX]

Hi there.
Does anyone know if the single point injector unit and map sensor from a 1.6 L reg would be compatible with or the same as on my 1.8 engine?


Cheers

I've used the injector from a 1.2 corsa in the 1.8 before and the map off a 1.4 no adverse effects that I could tell.

[Envoy CDX]

Hi there.
Does anyone know if the single point injector unit and map sensor from a 1.6 L reg would be compatible with or the same as on my 1.8 engine?


Cheers

I've used the injector from a 1.2 corsa in the 1.8 before and the map off a 1.4 no adverse effects that I could tell.

[ronnie1995]

Hi there,
After swapping the injector unit and map sensor over, it still hasn't made a difference to the running of the engine.

However there is good news, it has now passed the mot and is drivable. just not running as it should.

Has anyone got any other ideas as to what could be the cause of this issue?

Cheers

Ron