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Discussion Starter · #1 ·
Can anyone help with my MOT failure?
Fast Idle Test
Engine Speed 2440 pass
CO 0.23 Max 0.20 fail
HC 318 Max 200 fail
Lambda Pass

Second Fast Idle Test
Engine Speed 2595 pass
CO 0.73 Max 0.20 fail
HC 240 Max 200 fail
Lambda Pass

Natural Idle Test Pass
 

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13,570 Posts
Can anyone help with my MOT failure?
Fast Idle Test
Engine Speed 2440 pass
CO 0.23 Max 0.20 fail
HC 318 Max 200 fail
Lambda Pass

Second Fast Idle Test
Engine Speed 2595 pass
CO 0.73 Max 0.20 fail
HC 240 Max 200 fail
Lambda Pass

Natural Idle Test Pass
There are even different regulations within the UK – let’s take Northern Ireland as an example. Their emissions pass regulations are CO less than 3.5% and HC less than 1,200PPM. In England, Scotland and Wales the pass values are CO less than 0.2% and HC less than 200PPM.

The silly thing about this is that if you fail the MoT on emissions in these three countries, you could catch a ferry to Northern Ireland and pass. You can see with their limits, it is virtually impossible to fail!

Also, their MoT certificate is valid all over the UK. In theory there should be a sliding scale of emission values within the MoT, for example, 3 to 5 year old cars, 5 to 10 year old, and over 10 years – with the toughest values for the newer vehicles. In my opinion, this should be a standard test throughout the EU.

False consciousness

Unfortunately, the general public look upon the MoT as a health check and if their car passes the MoT they believe it is in excellent working order. As we know this is not always correct.
If a vehicle only just fails its MoT on emissions, it is possible to replace the catalytic converter which could result in a pass.

This would appear to be the correct diagnosis, yet nine times out of ten it is not! There could be an overriding problem which needs rectifying immediately, otherwise the problem will reappear.

Fitting a new cat which is working at 100% efficiency, will just mask the problem. In time, the new cat will also fail and the chances are it would be detected in another twelve months at the following MoT. The easiest way to pinpoint the fault is to carry out a 4 gas test.

If the values exceed CO <0.2, CO2 >13.5, HC <15PPM, O2 <0.2, and a Lambda of 0.99 to 1.01, there will be a problem. Depending how the values exceed these parameters, will depend on how large the problem is, and by evaluating the 4 gases you can locate and rectify the fault, e.g. CO @ 9.48, CO2 @ 9.10, O2 @ 0.58, HC @ 533PPM, and a Lambda reading of 0.76.

This was a report given to me by a customer of R&J Doncaster. The aforementioned diagnosis points to a failure located at the intake manifold area, due to a lack of air accessing the combustion chamber, thus increasing the HC, which in turn has damaged the cat.

Know your enemy

Hydro Carbons are the greatest enemy of a catalytic converter. If they are greater than 40PPM, they will be damaging the cat, which will result in a deterioration of the coating and, in extreme cases, a meltdown of the monolith.

EEC is committed to an education and training programme within the industry to help technicians understand, evaluate and diagnose emission problems.

The introduction of type approval for catalytic converters has been a great leap forward and has created a more level playing field. We have invested heavily in our own wash coating facility in Denmead, thus ensuring we produce a top quality product for our home and export markets.
 

· Registered
Joined
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33 Posts
Can anyone help with my MOT failure?
Fast Idle Test
Engine Speed 2440 pass
CO 0.23 Max 0.20 fail
HC 318 Max 200 fail
Lambda Pass

Second Fast Idle Test
Engine Speed 2595 pass
CO 0.73 Max 0.20 fail
HC 240 Max 200 fail
Lambda Pass

Natural Idle Test Pass
Exactly the same numbers that mine had (when warm). Engine emissions were fine when engine was cold. Turned out to be warn valve guide seals. Run the engine on tickover for five mins or so then open up the throttle to 2500 rpm. If smoke belches out, valve seals are likely to be the problem.
 

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13,570 Posts
Exactly the same numbers that mine had (when warm). Engine emissions were fine when engine was cold. Turned out to be warn valve guide seals. Run the engine on tickover for five mins or so then open up the throttle to 2500 rpm. If smoke belches out, valve seals are likely to be the problem.
HC content pointed to oil burning its whether the raised co levels are due to oil being used as fuel or a under lining issue with running hot as timing retarded form the normal issue with prince engines the 60-80k life span of a timing chain maybe,
if car was pre gen 2 then prob just stem seals,
 
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