MOT failure (emissions) - Alfa Romeo Forum
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Madness MOT failure (emissions)

following an engine rebuild on an 146Ti alloy head (yes, cambelt) I have problems passing MOT due to emissions:

Fast idle test #1:
CO: 0.062% (0.300%)
HC ppm: 381 (200)
λ: 0.978 (0.970-1.030)

Fast idle test #2:
CO: 0.476% (0.300%)
HC ppm: 83 (200)
λ: 0.986 (0.970-1.030)

Natural Idle test:
CO: 0.134 (0.500)

In parentheses are acceptable values

The rebuild included refurbished head, variator, piston rings, big end shells. The car remained for 18 months unused.

Would these numbers indicate that I need a new catalyst? I am perplexed as my λ is low, indicating lean mixture and this should not result in high HC & CO.

Following this test I replaced the λ probe, exhaust downpipe (leak), fixed an intake leak (brake assist vacuum pipe) & 8 spark plugs.

2nd attempt and the tester cancelled the test stating that my emissions are 'off the scale', without more info.

What next? Catalyst?

yiorgos is offline  
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Even if you had no cat at all, if the engine was running fine the emissions would be well within the limits of the test equipment.
So, some background info: was the engine fully up to temperature when tested? (does the thermostat function correctly- normal temperature should be 90) What does it actually drive like? Who did the engine work? How far has it been driven since the rebuild? What year is the car? Does the engine fault light come on at all?
If the emissions were "off the scale", that would imply a serious mixture/combustion problem.
FoxtrotOscar is offline  
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About your first failure,when your engine was rebuilt was tha cam timing set properly?
When you changed lamda ,did you fit a genuine one,or an ebay special??
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emissions , failure , mot

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