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[Doctor Gollum]

First up, given the ambient air temperatures recently, seeing 30°C at the intake shouldn't be unusual or unexpected.

That said, the residual heat on these engines is something to behold.

Is it a separate IAT sensor on the 2.5/3.0, or is it combined in the MAF?

What difference does unplugging the IAT make to the emissions? If any.

If the IAT is a concern, then you need to remove it from the equation.

Some suggestions for bringing it down: duct air from a colder supply/additional fan cooling/*remove the air filter, half fill the lower chamber with ice, then refit the air filter and cover.

Using additional forced air may impact the coolant temp, so try to focus on the air intake ducting. If the ice idea doesn't make a noticeable difference to the IAT then I would suggest that the IAT sensor is either the wrong one or not working.

*It goes without saying that the ice needs to stay on the intake side of the air filter and not be allowed into the engine side.

Another point... is the water pump pushing water through the TB... It has an integral coolant line to prevent icing in winter and regulate temperature in the summer as well as assist initial engine temps for emissions purposes (not dissimilar to the way the oil cooler is arranged).

Is the cold start enrichment working correctly?

[omega2018]

I've had similar issues ,head scratchers with stuck open EGR valves and leaking injector (albeit on a vauxhall 4 banger ,NOT V6 ) 

Second the 'stuck open EGR valve' thought -  lower temp resulting in unburnt fuel/high emissions.  Most of all though this is a very easy thing to test - undo 2 bolts and just blank it off. My 2.5 V6 ran very happily for 1/4 of its life with a blanked off EGR.  If the EG is stuck open you would expect some rough idle when cold, not so obvious on a V6 perhaps.

[Derek_in_Penzance]

Thanks for the suggestions guys, I will check them out and report back asap.

[Marks DTM Calib]

More importantly, what was the lambda value for the emissions?

[omega2018]

More importantly, what was the lambda value for the emissions?

0.763

[Derek_in_Penzance]

Update 2.30pm Thursday 13th July

Checked intake air temp, started off at 19 degrees when engine running after five mins or so. Fitted another one to compare, same reading.
Waited for 20 mins for engine to get hot, at 95 degrees checked again. IAT showing about 22 to 24 degrees. Checked with Snap-on Ethos and Tech 2, both  show same readings.

Removed EGR valve, seemed OK, gave it a light clean, but fitted another one. Tested emissions again, no change. Still showing 8% CO at fast idle 2,500 rpm, about 3 to 4% at natural idle.

Water temp to throttle body seems fine.

[Doctor Gollum]

Cambelt set correctly?

[dave the builder]

Have you pressurised the fuel rail and left it under pressure for a decent time to check the injectors don't leak ?
(return clamped , ideally spark plugs out ,to check for fuel in the bores )

If's very strange and worrying that you have had stuck piston rings  on an engine that's been "rebuilt"
I've had stuck rings on am astra  (I took over the repairs AFTER a garage did engine flushes to "cure" high CO  made things worse )

HCs where high 400+ and CO off scale high   

I stripped the block, cleaned everything (lots of sludge "released" by flushing by the garage) , new standard rings (correctly gapped) ,light hone of the bores  . I also cleaned the EGR and injectors while apart .

once rebuilt , it had a Mexican tune up to clear the exhaust of contamination with cataclean .

dropped it down for MOT test  and watched the emissions

virtually NO CO and the HCs where low (32 IIRC )

subsequent  MOTs the emissions where low for a further 5 tests and i retired it from the fleet /scrapped it due to rust .

I gave a corsa engine the same going over (purchased car "spares or repairs" with high HCs and CO and smoke, that was gunked up oil control rings, engine full of sludge , that passed emissions well for 2 MOTs and was sold from the fleet ,replaced with a Zafira B .

I'm not saying any of the things i have mentioned is your issue .just giving you pointers based on my personal experience.

[Derek_in_Penzance]

Thanks Dave, I will look into all your suggestions. Dr Gollum, the cambelt was set up very carefully and engine runs fine so I will never say never, and will do what I can to check. Thank you. 

[JamesV6CDX]

What is the coolant temperature sensor (on live data, not the gauge) saying from cold (before start)  and then when up to temperature?

I wouldn’t expect to see two cylinders low on compression after a job that thorough. What actually were the readings?

When you poured ATF into those bores, did the compression permanently increase or was it a one off (eg - what are the compressions now?)

You say you fitted new cats - were these pattern / type approved?

You also said the engine appeared Smokey, but thought it might be residual - is it still Smokey now? That will obviously help us know if there’s a longer term mechanical problem.

If the cat converters and engine management sensors were all ok before the engine change then I don’t think one of them has coincidently failed.

I think the problem is more likely to be contained to the areas where work was completed (in this case, the engine internals).

[Derek_in_Penzance]

@ James V6CDX   Thank you for your suggestions. We checked the compressions on Friday and they are all good, although the right bank is slightly down compared with the left. I will post the exact readings tomorrow.  I have roped in the assistance of an experienced MOT tester/mechanic who works next to us and sometimes worls on our cars. He agrees with you that the problem might lie in a mechanical aspect of the engine and is checking valve timings etc tomorrow. More news as it happens. Thank you again for your suggestions. 

[Derek_in_Penzance]

Hello friends, just an update on my X30XE emissions problem. Having tried absolutely everything I can only conclude that there is something wrong with one or more of the piston rings, so I am resigned to stripping it down and starting again.  Thank you to all those that contributed with suggestions.

[Andy B]

....
 so I am resigned to stripping it down and starting again.   ...

  bugger 

[Derek_in_Penzance]

You can say  that again. I will keep you updated on how things go.

[dave the builder]

Hopefully something will be obvious when you strip it down 

some piston rings (not sure about X30XE ,Y32SE etc ) need to go a specific way up .one edge is sharp, another rounded  etc

also,  LIGHT hone of the cylinders to hold the oil ,new rings need to "bed in"


you may be already aware of this 

best of luck