Failed MOT fast idle CO

[shanra]

It actually took ten minutes to come down to a normal tickover this morning just starting it and letting it warm up at a standstill.

[ColinBarber]

6 hours ago, shanra said:

It actually took ten minutes to come down to a normal tickover this morning just starting it and letting it warm up at a standstill.

Seems a little too long. Might be worth checking/replacing the thermostat.

[shanra]

3 hours ago, ColinBarber said:

Seems a little too long. Might be worth checking/replacing the thermostat.

Thermostat was replaced about 22 months ago when I had cam belt and waterpump etc. done. Coolant flush just after as they hadn't replaced all of the coolant with new. It does take a while to warm up but it always has. Booked a free exhaust check and emissions test at Kwik Fit before taking it back to the MOT garage for a retest on the emissions. It will be interesting what the readings are at Kwik Fit or if there are any exhaust leaks which could throw off the emissions readings. I have added Catalytic and Lambda cleaner to the tank and will give it a good run before.

[Malc1]

31 minutes ago, shanra said:

Thermostat was replaced about 22 months ago when I had cam belt and waterpump etc. done. Coolant flush just after as they hadn't replaced all of the coolant with new. It does take a while to warm up but it always has. Booked a free exhaust check and emissions test at Kwik Fit before taking it back to the MOT garage for a retest on the emissions. It will be interesting what the readings are at Kwik Fit or if there are any exhaust leaks which could throw off the emissions readings. I have added Catalytic and Lambda cleaner to the tank and will give it a good run before.

If there are exhaust leaks causing the issues and those leaks are from the complex mild steel front end …… ( where the Cat is ? ) remember I paid just £360 incl vat a couple of years back for a bespoke quite clever exhaust centre in Maidstone Kent to make afresh the front-end 

The OEM part is simply no longer available and last knockings was @£700 😰

Hope it’s as simple as that ! 

Malc 

[shanra]

Well I had a free exhaust check at Kwik Fit and got told one thing and then another when I went back later, so a waste of time. Went to a specialist exhaust place and they found slight leaks around both upstream oxygen sensor mountings and a leak on the drivers side catalytic converter and will get them welded on the 24th November. Hopefully that is where the problem is! Had another fail on the emissions but it was much closer to a pass.

[John N]

A high CO reading will indicate the engine is running rich. This can easily be caused by a leak in the exhaust near the front O2 sensor. 

This makes the O2 sensor think the car is running lean, so it turns the fuel up and makes the engine run rich.

Don't even think of buying a new catalytic converter until you have checked the exhaust for even small leaks. Find a good exhaust specialist who knows what he is looking for and doesn't want to just sell you a new catalytic converter. 

 

[John N]

12 hours ago, John N said:

A high CO reading will indicate the engine is running rich. This can easily be caused by a leak in the exhaust near the front O2 sensor. 

This makes the O2 sensor think the car is running lean, so it turns the fuel up and makes the engine run rich.

Don't even think of buying a new catalytic converter until you have checked the exhaust for even small leaks. Find a good exhaust specialist who knows what he is looking for and doesn't want to just sell you a new catalytic converter. 

 

The exhaust specialist you are seeing on the 24th sounds your best bet.

I've just had a similar experience. 

The engine warning light came on indicating the bank 2 catalytic converter was failing. An 'Italian Tune Up' and cat cleaner worked for a short time, but the fault kept coming and going. Eventually after a few months the fault came on and stayed on most of the time. Despite the engine running faultlessly.  

Used a scan tool to check the O2 sensors, they were all working OK, but the one after the bank 2 cat was fluctuating more than it should indicating something wrong. 

I then started checking for exhaust leaks, although I couldn't hear anything. There was a small leak on the flange between the catalytic converter and the exhaust right in front of the O2 sensor that was fluctuating. Fitted new gaskets and nuts & bolts to the flanges on both sides and a day later the fault cleared! 

"That's sorted it" I thought. But a week later the fault came back. 

Listening carefully I thought I could still hear an exhaust leak, but I couldn't find it. But after another two months the leak had grown big enough for me to find it. A small crack in the pipe after the O2 sensor.

Finally I had a new Y pipe made and fitted by T G Silencers of Rochdale for £180.

The problem is now solved.

The way your problem has developed slowly makes me think you have a similar issue, as exhaust leaks develop slowly and the problems come on slowly.

This is why I say 'don't buy a new catalytic converter'. Best of luck.

[shanra]

Thanks for your advice John. Unfortunately if it is the Catalytic converter I can't get one as they are discontinued and there are no pattern ones. The problem is I think from around 95-97 The cats were bolted on to the downpipes but at the rear it wasn't bolted on as was the norm, it had the pipe welded on!

 

[Malc1]

John, give the problem to the exhaust guys and they will inevitably ( fingers xd )  sort out all the issues for you

Malc

[shanra]

3 minutes ago, Malc1 said:

John, give the problem to the exhaust guys and they will inevitably ( fingers xd )  sort out all the issues for you

Malc

It's booked in on the 24th with the exhaust specialists.

[shanra]

Passed the MOT today with 0% Carbon monoxide on Natural and Fast idle. Probably helped by Wynns catalytic and lambda cleaner and some of their emissions cleaner also on 3/4 of a tank of Esso Power. I shall still get exhaust welding done as any leaks aren't good!

[Cotswold Pete]

14 minutes ago, shanra said:

Passed the MOT today with 0% Carbon monoxide on Natural and Fast idle. 

I like happy endings, glad to here you are all sorted on the MOT front

[Tinonline]

1 hour ago, shanra said:

Passed the MOT today with 0% Carbon monoxide on Natural and Fast idle. Probably helped by Wynns catalytic and lambda cleaner and some of their emissions cleaner also on 3/4 of a tank of Esso Power. I shall still get exhaust welding done as any leaks aren't good!

I know it’s crazy but clearing out the system really works. Until the last few years I’ve never had to do this but older vehicles have to be on top service. 
 

I believe my Lexus is on point but I don’t take any chances now. I’m not convinced by the MOT equipment or their ensuring the vehicle is up to full operating temp.

I reckon a good clean out and decent fuel will sort things out for a good term. 
 

Time your oil and filter changes close to the MOT, add cat cleaner and ensure you have a good run.  Yup no exhaust leaks. I’ve gone through a few tests with a number of minor blows but depends where they are…

If you don’t have O2 codes and emissions warning codes your motor should not fail. But it doesn’t work like that does it…
 

 

 

 

[John N]

3 hours ago, shanra said:

Passed the MOT today with 0% Carbon monoxide on Natural and Fast idle. Probably helped by Wynns catalytic and lambda cleaner and some of their emissions cleaner also on 3/4 of a tank of Esso Power. I shall still get exhaust welding done as any leaks aren't good!

That's a coincidence!

Mine passed its' MOT today. 

That makes 18 years without a single MOT failure, according to the DVLA Website. It may be more but there records only go back to 2005.

(It is cheating a but though, there is a 5 year gap in its' history when it was off the road before I bought it.)

Check X977HKY

 

[shanra]

Had the welding done on the exhaust and the largest leaks were on the back of the catalytic converters where the heat shields join. Car is back to it's very quiet old self again! All for £72.