Failed emissions test

[BjornV]

Hello everyone.

I would likt to ask if anyone have any good ideas on this.
The car in question is av 1994 6.0L V12 coupé.
Problem Is I can´t get it to pass the emissions test. The CO level is too high at 2500rpm.
It is not the lambda sensors. These were recently changed to try and fix the problem. Did not help.
Other emmission levels are also high, but within limits.

I have had one small test and it does not seem to be a big difference between right and left.

Last year, one ignition coil failed, which of cource made the engine run badly. When two new ones were installed everything seemed fine.

Any ideas?

[XJR-S]

How far out was the CO level? Has the car sat for a while or do you drive it regularly? Depending on how far out it is, I'm a firm believer in the 'italian tune up', with perhaps a bottle of redex, followed by an oil change unless it's been done recently?

Are there any error codes on the ECU?

[greeban]

Definitely try the Italian tune up (I like that!) - if that does not work I would have your new lambda sensors checked out, I have fitted new parts in the past only to find that they are not working properly; if they are OK would have thought the ECU should return a fault as it would not be able to get the trim correct or do these older ECUs not have the logic in them for this; in which case you need to get a look at the output from the lambda sensors before you start looking deeper into the problem - if you are handy, after the Italian tune look at the spark plugs to see that they have the correct colour, you could have a sticking injector in which case the plug may be sooty as it is running rich. Hopefully, if the lambda sensors are Ok and car idles fine I would expect that a fast long run should get everything back in balance and your emissions will return to correct tolerances.

Does your car have lambda sensors after the cats as well - if so, if the lambda sensors are working OK then it could be the cats are end of life. Other possibility is you have a crack in one of the exhaust manifolds putting too much O2 into the system and the lambda sensors are telling the car to over fuel to try and compensate

[dhdove]

Do the cats have a significant effect on CO level or is that down to mixture ignition etc?
If you had a coil down last year you will have filled one of the cats with fuel.......which wouldn't do it any good at all.

TonyS

[davidr]

Tony - you've got a point but there was little difference between the 2 sides.

Another thought to throw into the pot.... Have you looked at the fuel pressure regulators? If they are not working properly (the rubber diaphragms do harden over time) then they will not be keeping the right pressure in the fuel rail. If they're not moving as flexibly as they should then the pressure may be too high, especially at idle. The injectors are designed to open for a controlled amount of time to deliver a set amount of fuel. If the pressure varies from the design (2.5 bar I think) then all that careful calculation by the engine management goes out the window!
Typical signs of this will be poor idling, running rich, fouled plugs and high emissions.
One way to quickly check is to pull the vacuum pipes off the regulators and see if the idle note changes. A better method is to put a pressure gauge on the fuel rail.
As I say, just a thought but may be worth a look.
Regards
David

[steve_m]

Isn't there a trimmer on the ECU that can be used to adjust the mixture? I vaguely remember reading about it on another forum but that may be for a different ECU.

[PaulGover]

As it's producing more CO than the lambda sensors should allow, the ECU should be storing diagnostic codes. I'm not familiar with these late models, but there should be a way to get the ECU to tell you what's up. Possibly you need it plugged into a Jaguar dealer's diagnostic kit.

That said, as I'd expect the system to be putting diagnostics on display somewhere (e.g. my '91 5.3 has a habit of showing FF44 on the trip computer), and you've not mentioned any. Makes me wonder if your ECU is broke, or someone's tampered with the wiring to hide the messages.

[ptjs1]

Bjorn,

As you'll have seen from all the above comments, there are a variety of reasons why the car may be above the CO limit. However, to diagnose fully, i think we need more info. For example:

- Are there any error codes in the system? As your car is not OBDII compliant, you'd need to read those from the trip computer or better, get the systems read by a specialist via the PDU port in the boot.

- What are the overall set of emissions readings - the CO at idle, CO at 2500rpm, HC level and lambda reading? This can help to pinpoint the problem.

- What are the O2 sensors reading? Again, you'll need the car hooked up via the PDU to watch the varying voltage readings. I know you've changed them but are they operating correctly?

- Are the air filters clean and unblocked?

- Is the car fully warm? What the temp readings on the thermostat housings? Do you know that the thermostats are definitely closed when cold and then opening at correct temp?

Perhaps a phone call to David Marks who provides technical advice to members on XJS issues would be a good idea. David'd contact details are in the Forum Contacts page of the XJS Forum web pages.

Good luck

Paul

[BjornV]

Thanks for the input.
You have given me some ideas to start and work with.
I will tell you about the results I get.

Regards

[BjornV]

Because of lack time, not a lot has happened yet.

I started the car yesterday and got the engine up to temperature.

I checked the hose going from the intake manifold to the ECU in the back. No leak detected.

Tried to meassure the temperature at the thermostat housing. The housing itself seemed to be at 98-100 degrees C, but It is bit unsure, because the batteries in my IR thermometer gave up during this.

Someone asked for the overall set of emissions. Here goes:
CO idle: 0,5
CO 2500RPM 0,6
HC 80
Lambda 1,00

I did feel the exhausts, and I could feel that there is a bit unevenness in the flow. Both sides.
Could it be the one cylinder on each bank isn't firing properly?

Will return with more info later. A friend of a friend have equipment for meassuring the emissions. I plan to visit this guy so I can get new data from both right and left. To see if there is any difference now.

[ptjs1]

Bjorn,

What are the CO limits that the car is failing? Those figures don't seem that bad to me, especially the HC and lambda figures.

One of the issues with CO figures on the V12 is that the engine and cats don't get hot enough to burn off the deposits and start functioning properly. That's why many people pour in one of the additives and then give it a high revs run immediately before driving straight to the testing station. Some of these additives used this way are great at bringing the CO level right down.

Paul

[robv12]

my two penneth!!

the car as Paul says is not OBD compliant, you will need a Jaguar PDU to read the car, problem is these are few and far between, David Marks in Nottingham has one of the last functional units in the UK, unless anyone know any different

there is no trimmer on a 6.0 ECU as has been suggested

Now, my personal experience of 6.0 V12 over the last 17 years and 17 mot's is this, V12 is a huge thing to get to operating temperature, which is where the mot emissions should be done, HOT, so book the car in, an hour before go for a good long run, get everything up to temperature, then I lock mine in 2nd and give it a good 10 minutes at higher revs, this gets the cats and lambdas good and hot and will burn some crud out of the little used cats, as has been described, "the Italian tune up" , drove it like you stole it (it's good fun too, if a little expensive on fuel!!)!!, then in for mot and get them to do the emission FIRST, this method has got all of my V12 's through an mot without fail over the years

[BjornV]

Bjorn,

What are the CO limits that the car is failing? Those figures don't seem that bad to me, especially the HC and lambda figures.
Paul

It´s failing at CO 2500RPM. Is 0.6. Should be maximum 0.3. So It was quite a bit off.
I did try to drive it a fair bit before the MOT. Like I usually do.

Now I have checked the history that I have with the car.
In 2013 CO:0.2; CO2500 0.2
In 2012 CO:0.3; CO2500 0.3
2011 CO:0.2; CO2500 0.1
2010 CO: 0.3; CO2500 0.1
2009 CO 0.0; CO2500 0.1

Clearly something has happened. I still suspect that the malfunctioning ignition coil last year ruined things a bit.

[BjornV]

Tony - you've got a point but there was little difference between the 2 sides.

Another thought to throw into the pot.... Have you looked at the fuel pressure regulators? If they are not working properly (the rubber diaphragms do harden over time) then they will not be keeping the right pressure in the fuel rail. If they're not moving as flexibly as they should then the pressure may be too high, especially at idle. The injectors are designed to open for a controlled amount of time to deliver a set amount of fuel. If the pressure varies from the design (2.5 bar I think) then all that careful calculation by the engine management goes out the window!
Typical signs of this will be poor idling, running rich, fouled plugs and high emissions.
One way to quickly check is to pull the vacuum pipes off the regulators and see if the idle note changes. A better method is to put a pressure gauge on the fuel rail.
As I say, just a thought but may be worth a look.
Regards
David

Hi again.

One follow up on this. I just went to the garage and started the car. I had it on idle (a bit high, 1000rpm) and pulled the hose to the fuel pressure regulator. Nothing really changed.
Could that be an indication of a bad regulator?

Does anyone know the best way to actually meassure the fuel pressure on these cars?
The only way to get in ti the fuel-rail seems to be to cut one of the hoses, number 2 in this picture: http://www.jaguarclassicparts.com/uk/ja ... -6-0-litre

[robv12]

you split the fuel fail at the input union front left hand side, connect a wet line pressure gauge and see what it says. Be careful any excess fuel will run onto the No 1 left hand injector connection and possibly ignite, I know from experience!!

that said I do not believe this is your issue, the problem may well relate back to the failed coil and unburnt fuel igniting in the cat, a favourite problem on 6.0 V12, I've had four V12's with this issue, two with disaterous consequences of the cat catching fire, try the Italian Tune up first, the sit down and start pricing cats

keep us posted