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I'm not sure those are the right plugs. Which ones came out? I think VVC will be wasted spark so you need BCPR7ES or NLP100290 or I'm currently using Denso K16PR-U11 which also seem fine.

This image is stolen from Umicore. It shows that a common three-way catalytic converter needs to be very close to lambda 1 for best efficiency of all 3 conversions. Below lambda 1 (running rich) the ability to reduce HC and CO drops off rapidly. It may still be reducing NOx levels but those aren't checked on the MOT.

The only important thing to take from those results is the lambda values - it's running very rich for some reason. Until the lambda is within range the cat won't be functioning anyway so you can ignore that for now. Sorry I don't know the sigma engine very well but I would start with checking the lambda sensor, coolant temp sensor and throttle position sensor.

I recently had a problem with the alternator warning lamp started flashing on and off regularly when the engine was running regardless of rpm. It still seemed to be keeping the battery charged at just over 13V. I have replaced the alternator, and I now get the warning light staying on constantly when the engine is running - although not as brightly as when the engine is stopped. The new alternator is still charging the battery (now closer to 14V) and I have no other electrical problems. Do you think this issue is related to the above? EU3 K series with standard tacho. Thanks.

Just to update this.. I must say I had fantastic service from QED and Jenvey. I sent the throttle bodies back to Jenvey and within a week they had sent back what appears to be a brand new pair. I have fitted them and the noise seems to be slightly reduced but still present. By lowering the idle speed I could get rid of the noise completely at idle but it's still present at very light throttle just above 1000rpm so not a complete solution. I think I have to put it down to a characteristic of the engine unless I can find another solution.

Great photos. Thanks Dave!

That's really good to know, thanks. Out of interest what sort of mileage did yours do before you rebuilt them?

Thanks, that's what I'm thinking too. It's very good to know it's not something inside the engine going wrong but still a bit annoying that I can't easily stop it. If it's not normal, I wonder if the throttle bodies are serviceable.

That's interesting Revilla. I did wonder if it could be some sort of combustion still happening when the intake valve opened. But in my case it's very regular and I couldn't see any flashes around the butterfly. I took a quick video showing what happens when I press on the end of the butterfly shaft

For a while I thought it was the injectors but using a screwdriver to my ear on them I couldn't pick up the same noise. Also I swapped the injectors around and the noise still seems to be coming from the front cylinder. I'll do some more investigating today.

I've been chasing an annoying ticking noise coming from the engine at idle and on overrun below around 2000rpm for a while now. It's most noticeable when the engine is up to temperature and everything else has quietened down I suppose but it's very noticeable from inside the car and really quite loud when standing near the front of the car. It's a k series with forged pistons and Jenvey (QED) DTH ITBs and the engine runs fine but I keep expecting this noise to turn into something much worse! Anyway I've finally narrowed it down to the front cylinder on the intake side. And after more playing around I found that the noise would stop if I pushed on either the centre of the butterfly shaft (pushing towards the engine) or pushing on the end of the shaft (pushing towards the back of the car). It seems like such a small amount of movement of the shaft when I do this that I'm amazed this is causing so much noise. I wondered if anyone else has seen/heard this and if anyone knew a solution to permanently stop the loud rattle/ticking noise? The throttle bodies were fitted new about a year ago and I think the noise has been there from the start it's just taken me this long to work it out.

Hi Rich, Yes the pistons are still available. I've updated the first post to show which bits have now sold. Thanks

David that's the best explanation of the workings of the ATB that I've seen - thanks!

Hi Jack. Sorry, I don't know on that one. It was supplied with Jenvey DTH throttle bodies so I suspect not but can't say for sure.

Yes you can PM sent