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[Derek_in_Penzance]

Hi guys, Derek Thomson here from GM6 Spares in Penzance. I need help!

I have rebuilt an Omega 3.0 Elite estate engine very carefully from the block up and put the car through MOT back in November 2022
It passed on emissions but failed on some rust that I had overlooked.
By late February the work was done and the car retested but it failed on emissions. For reasons unknown the C0 was suddenly way too high.
We fitted new downpipes and cats, with new lambda sensors, also a new idle air valve.
The car was retested, but it failed again, with the C0 showing 9.65% at fast idle
Gunsons Colourtune thing shows yellow combustion flame so it is running way too rich
I changed the MAF sensor for one off another car and compared the readings on my Snap-on Ethos scanner. They were the same so I assume that both are in good working order. The Tech 2 shows no fault codes neither does the Ethos scanner.
I am now going to change the temperature sensor as I know that these can cause rich running if faulty or if the incorrect one is fitted.
All the vacuum pipes are correctly fitted and I cannot find any air leaks in the various pipes and ducts.

I have wondered if there is a fuel pressure problem, on other cars I have worked on eg Opel Monzas the return pipe into the fuel tank can get blocked with sludge, resulting in high fuel pressure and very rich running. Or the fuel pressure regulator can go faulty. The engine ECU can get wet and damaged, causing very rich running. 

Are the engine ECUs prone to go faulty on Omegas?

If anyone can suggest anything else I should check it would be appreciated as I am at my wit's end with this car. The annoying thing is that the engine passed with no problem back in November and the car has only done 50 miles since then, mainly to and from the MOT garage multiple times! So something seems to have gone faulty while the car has been sat idle, and I have no idea what it could be.

[JamesV6CDX]

Hi Derek, long time no speak.

From a stone cold engine first thing in the morning - (ignition on but engine off) what is the coolant temp sensor reading? Does it match the ambient temperature outside?

You can watch the temperature of it increase in live data and see if it remains consistent with engine temperature - this will show you if the sensor is working as expected without having to swap it out through guesswork.

On the live data, does it confirm the lambda system is in closed loop once the engine is warm?

Is the engine actually getting up to temperature - thermostat not stuck open?

[Doctor Gollum]

It's possible to swap the plugs for the ecu temp sensor and the purge valve.

The sensor is 5v and the purge valve is 12v.

This kills the temp sensor and usually defaults to - 40°c
Live data will confirm. As will hot starting issues.

Basically it causes the car to flood.

[TheBoy]

And to answer one of the questions, the ECU's on these are near bomb proof.

MAF on a 3.0l with A/C off should be about 13kg/hr once off choke.  Coolant temp sensor readings should be obvious.  B1S1 and B2S1 (the only 2 fitted on the 3.0) should be flicking between rich/lean at about 0.5 to 1Hz.  All the block learns should be approx middle of the scale, around the 120 - 135 mark.

[Derek_in_Penzance]

Thank you for your suggestions. I will check them out tomorrow when I have time to think straight (!) and report back. Much appreciated.

[Derek_in_Penzance]

I have now taken a video of the Tech 2 engine data, please see

 https://youtu.be/dTfEINuwa5A

This was with the engine at operating temperature. Sorry that the video is on its side!

Maybe those that have offered advice would like to look at it and  tell me if they see anything amiss. I noticed that the air intake temperature is showing as 22' C when the ambient air temperature today is actually 11'c. Also there is a lot of lean on 02 sensor 2 rather than constantly switching rich/lean.

I looked at the data earlier when stone cold -the car had not been started at all today -and the coolant temp sensor showed 11'C which seems about right. I noticed that the MID display in the dash showed 22'C or thereabouts, when it isn't, more like 11 degrees -does the display takes its info from the inlet air temp sensor? 

[dave the builder]

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

[Doctor Gollum]

Display takes its temp from the sensor behind the front bumper, and has absolutely nothing to do with the IAT sensor which is either part of the MAF or next to it. 

[TheBoy]

Idle BLMs look high, and MAF slightly low.

Check for air leaks in the intake (post MAF).

[Derek_in_Penzance]

Thanks for all the feedback and help. We have dismantled the front end today down to the black divider at the bottom of the inlet pipes and can find no obvious signs of any air leaks or anything wrong at all.
I will keep you posted. Since we have got this far I will fit a new temp sensor even though it does not appear to be faulty.

[Kevin Wood]

For a CO reading that high it's running very rich or misfiring. I very much doubt it'd be a temperature sensor issue (and the live data shows plausible values).

The odd thing is that the lambda sensors are both cycling, which means it should be OK mixture wise.

As said, the air flow looks a little low, but not much, and I'd say the injector times are a bit high considering, so I'd say it might actually be running rich.

EDIT: What was the HC reading on the emissions test. Is that high too?

[Marks DTM Calib]

Can you check the DIS output using a spark gap tester, they should clear 35-40mm

[Derek_in_Penzance]

Hello again,

This is doing my head in. 

Many weeks have passed and I am still no nearer to solving this emissions problem on the 1998 Omega 3.0 Elite saloon.

Here are the MOT test results (video):   https://youtu.be/2Zhv0ReIUDQ

Here is the summary of what we have done over this period and to date.

Car arrived for repair with engine in poor condition having overheated, head gaskets gone, engine block u/s due to rust in bores having been standing for months with water in the bores.
Good replacement block selected, bores measured etc and honed. Cylinder head mating faces lightly skimmed. Cylinder heads refurbished and skimmed.   Engine rebuilt, using new piston rings on good used standard pistons. New big ends shells and main bearings, on good standard crankshaft.
Engine built up with great care using new parts where needed. Graphogen paste used when assembling pistons, cams etc.
Fuel injectors refurbished by Bosch specialist.
Problem:  passed MOT on 3rd November 2022, including emissions, although tester remarked that engine seemed a bit smoky (possibly due to Graphogen being burned away?)  CO at idle 0.07 pass is 0.50,  at fast idle .03 pass is 0.30
Needed welding so time passed waiting for this to be done, so during December and January the car was parked outside in the wet and cold. After the welding was done we took it for MOT on 7th March 2023. It was all OK except for the emissions, with engine showing 8% CO at idle and fast idle.
After some headscratching, decided to replace both cats and lambda sensors with new. Also a new idle valve. Checked all vacuum pipes and potential air leaks. Nothing found.
Took for MOT again 31st March. Still failed on emissions. (!!!)
CO at idle 0.95, at fast idle 8.87
HC at fast idle 425, pass is 200
Further work carried out:
New temp sensor 1.
Checked air intake temperature and air mass sensor by replacing with known good ones.
Checked compressions. Two cylinders found down a bit possibly due to sticky rings, poured small amount of ATF into bores to free up, this restored compressions to normal
Checked spark plugs and combustion with Gunsons Colortune , appeared good (blue flame)
Took down to MOT tester (PT Autos) for informal check on the gas analyser. Still no change in excessive emissions.
Checked fuel pressure. Gauge still attached to fuel line by fuel tank.
Decided to try a different engine management ECU, so swapped it for another but only had a 2.5 one. No obvious difference in engine running.
Decided to buy a proper MOT spec gas analyser (Tecalamit) so that I could do my own emissions checks. Seems to show readings although it cannot be used  properly as it needs a subscription for calibration and the fully functioning software (calibration ran out in 2021). Checked readings on other vehicles where CO is known from previous MOTs etc. and it seems to be in the right range  For the Omega it shows CO as around 6% at fast idle.
At the moment I am stumped.

Here are videos just done showing engine readings on Snap-on Ethos and Tech 2 (engine warmed up)
I note that the engine air intake temperatures seem a bit high at the end of my testing, eg 30 or 40 degrees, is this normal? Maybe because engine bay is hot? Ambient temperature today is about 17 degrees C.   See https://youtu.be/ujypQ0lDMAM

 https://youtu.be/yt6Bs451xnU

https://youtu.be/LN1AvCNbRtI

Here is a video of the engine bay:
https://youtu.be/Owk_leL0E14


If anybody on here has a lightbulb moment I would really appreciate the advice, as the car cannot be returned to the customer with no MOT!
(Apologies for not acknowledging last couple of posts, I had not logged back on here for a bit)

[Doctor Gollum]

What fuel is in it?

[Derek_in_Penzance]

Hi, unleaded petrol, fresh from the pumps.  But yes, the answer might be something that is completely unexpected! I suppose it is always possible that the fuel tank might have had contaminated or old fuel in it that for some reason is causing the emissions problem.  We haven't put a complete full tank of fuel in because the car hasn't really been anywhere, just a few miles locally and to/from the MOT station four miles away.  The car was standing for almost  a  year because no garage in the customers' home area would touch it (Kent area)... he said that they all said Omegas were too much of a PITA to work on! 

[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 

[Derek_in_Penzance]

Hi guys, update on my emissions problem on the rebuilt 3.0 engine 
The weird thing is that it passed on emissions on Nov 2022 then lay idle for a  couple of months awaiting welding for the MOT. Upon re-testing in Mar h the CO level was way too high, 8%  (see my earlier posts explaining it all).

Here is the engine that was rebuilt. It sounds wrong compared with a 3.2 Elite engine which follows. The strange whooshing noise seems to be coming from the right side of the engine (as you sit in the car). It's as if something is rubbing. 

https://www.youtube.com/shorts/78Ar5M03_ZE

Here is the 3.2 engine:

https://www.youtube.com/watch?v=p7Gmb8ZDU3s
It has only done about 83,000 miles

Anyway I am looking at a worst case scenario in which the 3.0 engine is fundamentally damaged in some way and needs replacing.
Is is possible to use the 3.2 basic engine and fit it into the 3.0 pre-facelift car, ie retain block,cylinder heads, timing belt etc  etc and just change the plenum chamber, injectors?, throttle body and other peripherals.

[Doctor Gollum]

The only things you need to swap over are the loom, dis pack and throttle body. And plenum unless you want to delete the egr.

No need to do anything else except perhaps renew the timing belt.

That said with the audio on those videos is impossible to tell what's making a noise and what isn't  The second engine sounds quieter but the video volume is about half that of the first one.

It could be anything on the driver's side of the engine... Alternator, cambelt tensioner, egr valve, exhaust leak.

A compression test might be a start. And does unplugging the egr valve change anything?

[Kevin Wood]

Going back a step or two... Compression results that differ from one bank to the other speak of one bank that's got the wrong cam timing. An easy thing to check before stripping it down.

[Derek_in_Penzance]

Hi all, thanks for the suggestions, I will check them out.