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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!