Technical Help with emissions mot

[XdKenneth]

Hello,
I’ve had a mot Saturday just gone, failed on handbrake which I’ve fixed and co readings was high.
fast idle : 0.311
2nd fast idle: 0.318.

I’ve change oil filter, flushed the system with oil cleaner, changed air filter, spark plugs, put cat cleaner in fuel, fixed exhaust leak near muffler. I took the car for a hours drive on motorway absolutely ragging it then straight into mot garage for an off the book re-test. But co was reading high again. What’s next? As lambda and hc are passing okay. If the cat was done, surely the others readings would fail?

Lamda
1st idle: 1.012
2nd idle: 1:001

Hc
1st idle: 124
2nd idle: 67

 

[varesecrazy]

Had any exhaust work in the last year..?

 

[GrandePunto PL]

1. Changed sparkplugs...and, what? Any observations/conclusions? You can "read" the sparkplugs and judge the engine condition (Google).

2. Check the OBD2 (FES or MES program), coil charge time ("dwell"): new makes a good sparks at 1,5 ms / average 2,0 / old weak one needs 2,5 ms.
Also there are wires/cables (they get old too). While you there (OBD2), check all sensor readings (if make sense: temperatures, pressures, lambdas).

3. How about oil consumption? Low, normal, high (how much do you add per 1000 km or miles)? It can add a lot to the exhaust gas composition.
Valve stem seals and piston rings are the most common sources of oil. You can try to free-up the rings by pouring some engine oil flush into cylinders (wait few hours, then suck back everything with a syringe etc.). Procedures like that are not 100% safe (may spoil/poison the exhaust system even more).

4. Valve lash/clearance. Never done probably? Exhaust leaks, starting at manifold? Pretty common fault (and will mess up the lambdas - sensors).

5. Your British/English MOT tests are weird, wicked. Ask them for all (5-6) parameters, not 2 or 3.
Lambda, HC, O2, CO, CO2 - five numbers for Euro4 standard (for Euro5-6 + "NOx"). You can get better picture of what your "cat." (and ECU) is trying to do.
It should convert O2 and CO to CO2. And HC to water and CO2.
Maybe it wants to, but other systems or parts are spoiling the performance (including bad, old, dirty oxygen sensors - inspect them visually, there are wear charts too, just like for spark plugs). This is an example of working but too slowly sensor. Fouled, "poisoned" a bit. And brand new one.

Cat. converter (healthy) has some "capacity", there should be a time lag when you force a sudden mixture change (step on the "gas" and release it etc.), it can be viewed using FES/MES, you watch a graph ("waveform") of both oxygen sensors (if the second - after cat. - sensor is oscillating at idle, following the first one, the cat. is probably dead).

Proper emissions test result should look like this... Chemical reactions are there and not much oxygen left and lambda is perfect.

Healthy engine has zero HC and CO. If not, there IS a problem (even if you pass the MOT). Don't trust such data from service manuals/programs.

Catalytic converter works only in a narrow "window" of parameters = initial gas composition must be fairly good already when it enters the "cat." (it is NOT a magic furnace that just burns the bad stuff away, it's a sensitive/fragile device unfortunately).