Smoke Opacity Analysis - what does it mean?
Discussion
Hi,
So the e39 touring has made it through another MOT
and now I have a piece of paper with the smoke opacity analysis results.
Uhhhh owkay...
What does these numbers mean and is there anything that can be derived about the general health of the lump at the front?
Opacity Values [m-1]
Acceleration 1: 2.01
Acceleration 2: 0.53
Acceleration 3: 2.63
Acceleration 4: 1.31
Acceleration 5: 0.59
Acceleration 6: 2.85
Zero Drift: 0.02
Opacity Mean Value: 2.06
Obviously the key thing is the PASS but would be interested in understanding what these numbers mean from those with the knowledge and if it's a scrape through!
Many thanks,
So the e39 touring has made it through another MOT
and now I have a piece of paper with the smoke opacity analysis results.Uhhhh owkay...
What does these numbers mean and is there anything that can be derived about the general health of the lump at the front?
Opacity Values [m-1]
Acceleration 1: 2.01
Acceleration 2: 0.53
Acceleration 3: 2.63
Acceleration 4: 1.31
Acceleration 5: 0.59
Acceleration 6: 2.85
Zero Drift: 0.02
Opacity Mean Value: 2.06
Obviously the key thing is the PASS but would be interested in understanding what these numbers mean from those with the knowledge and if it's a scrape through!
Many thanks,
Thanks!
So as far as I can see the main blurb is:
3. After 6 free accelerations, the mean of the last 3 smoke levels is:
a. for vehicles first used on or after 1 July 2008, more than 1.5m-1 for both turbocharged and non-turbocharged engines
b.for vehicles first used before 1 July 2008:
. for a non-turbocharged engine, more than 2.50m-1
. for turbocharged engines more than 3.00m-1.[/b]
Given that this is a 2001 turbo diesel with 140,000 miles on it a result of 2.06 (and for a pass need < 3.00) seems not too shabby!
Thanks again,
So as far as I can see the main blurb is:
3. After 6 free accelerations, the mean of the last 3 smoke levels is:
a. for vehicles first used on or after 1 July 2008, more than 1.5m-1 for both turbocharged and non-turbocharged engines
b.for vehicles first used before 1 July 2008:
. for a non-turbocharged engine, more than 2.50m-1
. for turbocharged engines more than 3.00m-1.[/b]
Given that this is a 2001 turbo diesel with 140,000 miles on it a result of 2.06 (and for a pass need < 3.00) seems not too shabby!
Thanks again,
Unfortunately, for any common rail diesel the smoke test is really rather pointless!
Back in the day, when diesels were mechanically controlled, you could get an idea of the basic fuelling parameters (ie the health of the mech injection pump system) by reving the engine in neutral.
However, on a modern CR diesel, the engine management system only puts in enough fuel to meet the current torque demand. Hence, if you floor it in neutral, the car knows that it only has to put in enough fuel to negate engine friction and so during that test will still be running at between 60 and 120 to 1 AFR! In effect, due to the torque control mapping, just because the accelerator is flat to the floor doesn't mean the engine will be adding a lot of fuel.
As such, unless you engine is catastrophically knackered, it will easily pass the smoke test!
Back in the day, when diesels were mechanically controlled, you could get an idea of the basic fuelling parameters (ie the health of the mech injection pump system) by reving the engine in neutral.
However, on a modern CR diesel, the engine management system only puts in enough fuel to meet the current torque demand. Hence, if you floor it in neutral, the car knows that it only has to put in enough fuel to negate engine friction and so during that test will still be running at between 60 and 120 to 1 AFR! In effect, due to the torque control mapping, just because the accelerator is flat to the floor doesn't mean the engine will be adding a lot of fuel.
As such, unless you engine is catastrophically knackered, it will easily pass the smoke test!
ETA: Just looking at your test results that vary by a factor of 4 (0.5 for some tests, 2 for others!) shows that the test is broadly pointless. Actually tailpipe smoke opacity is heavily influenced by a large number of factors, and the precise entry conditions, and how the acc pedal is depressed will make huge differences to the results (and also exactly when the machine samples the sensor compared to the inital tip in event etc)
I would add that the readings you got make very little sense and the test appears to have been conducted improperly. Since you say your engine is a turbo with a mean limit over any three consecutive tests of 3.0 then it had already passed after the first three tests and any more tests were unnecessary. Moreover the mean of 2.06 reported does not appear to be the mean of any three of the actual tests, consecutive or otherwise.
As Max states, the fact that the readings go up and down by such large margins from test to test indicates they are essentially worthless in the first place.
As Max states, the fact that the readings go up and down by such large margins from test to test indicates they are essentially worthless in the first place.
Aye, random number generator is what that appears to be.
Had a look at two old MOT test result - single acceleration each with 0.75 and 1.34 for the results.
No idea what happened with that one - up there with bigfoot and Rongorongo.
Had a look at two old MOT test result - single acceleration each with 0.75 and 1.34 for the results.
No idea what happened with that one - up there with bigfoot and Rongorongo.
Edited by pistonheadforum on Wednesday 29th July 21:17
Hi, could someone help please. I can't seem to start a new thread. My car failed emmisions test on zero drift. Infact the result was error, not fail. I'm wondering if zero drift is referring to the test of the test equipment and not the car? The car doesn't smoke. Any help appreciated, thanks
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