Exhaust Gas Analyser readings
Turbo Mini Forums

Can anyone make anything of the attached output?

This is from my Mini running the Siamesed Code on the Megasquirt. Its still at the development stage and has AFRs of 15/12 on the outer/inner cylinders respectively.

Interested if anyone can deduce anything from it.

Thanks.

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Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Ok Paul My taughts,

Co to High I would expect to see a reading of 0.5 to 1 max.

Co2 to Low would expect to see this up aroung 13 to 14 I would supect driveability to be down with a figure like that ,

HC 935 to high sugests over fueling or a poor burn.

O2 far to high I would like to see this less then 1 if every thing is rose this shuould be around 0.5 I would nearly go so far as to say you have a mechanical fault with O2 that high

Nearly there Paul keep up the good work.


Edit: was this at idle Paul or what rpm

Edited by PaulH on 2nd Sep, 2008.

I'm guessing that this was at idle.

The engine was very "fluffy" when I picked it up. It took a few stabs of the throttle to clear.

I'm guessing that he had it idling for a while whilst it warmed up. I would not be surprised if one of the outer cylinders had started to misfire at the point the readings were taken.

Would that explain the readings?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

What year car is it being tested as to get a limit on CO of 0.3 ??? presumably CAT equiped.

Has it got a CAT (bearing in mind it's your development engine) ???

High HCs are virtually always due to a misfire (HC being unburnt fuel).

Interesting that the Lambda is OK though.

Need to look up the limits of the others where they aren't on the table.

Oil was cold at 60 degrees (presumably hence their handwritten comment "warm?")

Schrödinger's cat - so which one am I ???

No, there's no CAT fitted at the moment. It was registered on the last day of August 1992, so does not need one ???? This is the 998 Turbo engine without the turbo. Remember I knackered the development engine :$

I would have expected the lambda to be around 0.9 given the 15/12 AFR spread. This makes me think that it may have been chugging a bit. A misfire would increase lambda.

I think that the 60 degree oil temp is the minimum rather than a measured value.

I like to run about 24 degrees advance at idle. Would this affect any of the readings?

Edited by Paul S on 2nd Sep, 2008.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Yes, I essentially agree the HC and lambda don't agree.

High HC is unburnt fuel (usually misfire) but I thought lambda would then read less than one. Need to read up exactly what lambda measures oxygen relative to....

One other thought - it used to be a pain to get some engines through the HC test if they had large overlaps on the cam, unburnt fuel again, but not because of a misfire, just the overlap on the cam letting some straight out. The rules used to say that they could repeat the HC test at 2000 rpm to avoid the overlap.

Igntion timing will always affect CO / CO2 / HC especially at tickover for similar rasons, ie, how much gets properly burnt before it hits the exhaust.

Schrödinger's cat - so which one am I ???

Interesting results and comments. Sorry I can't add anything more constructive - but PaulH and Rod seem to know their beans here... :)

Once we get the Siamesed Code working correctly and I am getting stoich on the inner and outer cylinders, I'll get it tested again.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Ok Nail on head, It sounds to me like you have a clasic case of over fueling at idel, While you drive the car it fuels with in reason close enuf not to cause a major problam, now let the engine idel for a period of time and it begins to over fuel which in turn cools every thing down which causes the plugs to foul which in turns causes a bad burn which leads to more over fueling and so on till you have a bag of spanners or the engine will just cut out and be very stubbron to start. If your test 'er left the car idle for any perioud this is what I would expect when I test Exhaust gas I always bring the car up to 2000rpm for 30 seconds to clear the plugs and combustion chambers.what it looks like is you have a root problam of slight over fueling at idle I have set my own cars to idel on the lean side which combats this problam.
hope this helps you,
regards,
Paul.

CO is partialy burnt fuel, HC is unburnt fuel.

CO is as a result of there not being enough oxygen to convert the HCs into CO2 and H2O.

HC is raw fuel, un burnt. There is normally a small risidual amount in any internal combustion engine due to its inefficiencies, but high HC would be the result of a missfire or bad valve seal for example.

Lambda measured at the tailpipe does not care as to where the oxygen it measures comes from, so if you have even a small leak in your exhaust, it will alter the tailpipe reading. Remember that Lambda sensors are alternatively called Oxygen sensors for a reason, they measure oxygen, not raw fuel.

Excess oxygen and high HCs could indicate a poor valve seal, as compression in the cylinder takes place, some of the charge leaks into the exhaust. Maybe a slight misfire.

CO2 could be low because the engine is running slightly rich, giving the high CO

Lambda could be high as a result of the excess oxygen.

However, the oxygen might not be a result of whet entered the engine, but what entered the exhaust

The oxygen and HCs dont tally and niether does the Lambda

If there is no missfire, check the valve clearancies and unless you know the condition of the valves, get the seats recut

Thanks Sprocket, that's very useful.

This is a newly rebuilt engine thats done about 500 miles at most. The head was fully refurbished, seats cut etc.

I had the exhaust off the car at the weekend and sealed all the leaks up to get it though the MOT.

The engine runs fine, but I've got it set so that the outers cylinders are around stoich and the inners are running at around 12:1. At idle this wanders between 11 and 13:1.

My money is on the overfueling causing a misfire. This would bring about the readings - would it not?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Now there is a thought

Two cylinders lean, giving residual oxygen and the other two cylinders rich, giving the high CO, but doesnt acount for the high HCs

It is by no means the worst I have seen, and would have passed on a BET.

Is the car a Cooper, to justify the 0.3% CO limit?

You may find these useful in the future

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On 2nd Sep, 2008 Sprocket said:
Now there is a thought

Two cylinders lean, giving residual oxygen and the other two cylinders rich, giving the high CO, but doesnt acount for the high HCs

It is by no means the worst I have seen, and would have passed on a BET.

Is the car a Cooper, to justify the 0.3% CO limit?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Edited by Rod S on 3rd Sep, 2008.

Schrödinger's cat - so which one am I ???

Hi Paul,
Just few numbers (don't remember everything) from my 998 with SW5
Idle at 900 RPM, 14 degrees advance, 15% (or perhaps 10%, don't remember, it's lower for idle) inner/outer richness difference.

14.7:1 gives around 0.5%, idle is good but slightly oscillating around target.
12:1 gives 2.5% and idle is very smooth.

I don't remember HC level, at least 500ppm at 14.7:1

Ignition advance have not had a great impact on CO and HC. Tried from 10 to 20 degrees.

std 998 A+, g295, MD266, RHF4, 109hp @0.8bar/5400rpm

Dunno if its any help but when I used to have to get my TR through emissions it always failed on HC >900.

The trick was to retard the timing (10 degrees) and because of that you had to open the butterfly to bring the idle back up. It always worked, I was told because the extra flow of air flushed the unburned fuel that collects in the manifold.

Of course the bloody thing used to overheat so I would advance it again as soon as I got out of the bay!!

Originally the 68 on (1968 was the first year of emissions testing) TR engine had ignition retard as well as advance and the retard module was simply to retard the engine at idle to pass the emission test!! as soon as the thottle went off the idle stop a little valve disconnected it..

website:- http://www.terryhunt.co.uk

It's MOT time again, so I thought I would update this.

The above figures were on a NA 998 running an early version of the siamese code that did not have the functionality of the current version.

Since June 2009 we have been running the engine with the single pulse hybrid mode and results have been good.

At the 2009 MOT, CO was 2.571 %vol and HC 308ppm

This morning, both levels have dropped to CO 2.239 and HC 162.

The only change has been a new set of leads and plugs, oil change and a better fuel pressure regulator.

They are now testing against a CO limit of 3.5, so it passes OK.

However, the CO seems high compared to my high milegae Focus that recorded a CO of 0.009!

Is this due to the lack of a Cat?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I believe the high CO could be because of the lack of CAT. Exes fiesta had a CO reading or about 4% swapped the CAT was around 0.4% after.

If something is worth doing, it's worth doing half of.

Yes, lack of CAT.

Once CATs became mandatory, the allowable CO levels were dropped considerably. 3.5% is for pre-CAT only.

You should be able to achieve better than 2.3 if you want, I can adjust my (pre-CAT) Cossie to 1.2-1.4 for the MOT (small adjuster pot on the ECU case) but I turn it back to a slightly richer mixture as soon as the test is over as it idles better at 2.0-2.5.

The test is irrelevant - it's only at idle and the CO will be completely different at medium or full power (which is where all the environmental damage is done), it's just to force people to maintain their cars.

Schrödinger's cat - so which one am I ???

Thanks.

I'm happy with it. I just wondered why it was so much higher than the Focus.

Interestingly, it is K Reg, registered at the end of August 1992 but they seem happy that it is not currently fitted with a Cat.

Did I read somewhere that one of the letters in the VIN number denotes whether it should have a Cat or not? Irrespective of registration date.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I thought it was a date cut of at the end of 1992??

Yes you did read it somewhere.

http://www.ime.org.uk/ime/c/cat.html

If something is worth doing, it's worth doing half of.

That explains it.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I really should check the vin on my spi shell. It's an early K plate but dunno if I would get away with it.

If something is worth doing, it's worth doing half of.