O2 sensor test and inverse duty cycle - Page 3 - PeachParts Mercedes-Benz Forum

LeaUK · #31 04-11-2005, 06:15 PM

Uhm, I wasn't quite correct about the UK law in my last post, so for my GB colleagues here's an update:

According to VOSA (Vehicle and Operator Services Agency, our law enforcement body) it appears there's a 'get out' for cars first used between 1 August '92 and 31 July '94, I have no idea why but apparently these cars only need to pass:

CO: <=3.5%
HC: <=2500ppm

GREAT!

A précis:

Cars used before 1 Aug ‘75 – Visual check only
Between 1 Aug ‘75 and 31 July ‘86 – CO <=4.5%, HC <=1200ppm
Between 1 Aug ’86 and 31 July ’92 – CO <=3.5%, HC <=1200ppm
Between 1 Aug ’92 and 31 July ’94 – CO <=3.5%, HC <=1200ppm - strange but it's definitely in the flow diagrams (see below):

Between 1 Aug ’94 and 31 Aug ‘2002 - does exact match exist in the ‘In-service Emission book’?
Yes – Carry out CAT test using vehicle specific data
No – Carry out non-cat test - CO <=3.5%, HC <=1200ppm

On or after 1 Sept 2002 – does exact match exist in the ‘In-service Emission book’?
Yes – Carry out CAT test using vehicle specific data
No - Fast Idle CO<=0.2%, HC <=200ppm, Lambda0.97 to 0.103, Idle CO <=0.3%

So apologies to the MoT garage whom tested my vehicle in '92 - they were indeed testing to the correct limits. Now - this is great news.

For more info and flow diagrams of UK testing procedure see here:
http://www.vosa.gov.uk/vosa/specialnotice04-04inspectionmanualupdates.htm

For the 'In-service emissions data/vehicle specific data - see here:
http://www.dft.gov.uk/stellent/groups/dft_roads/documents/page/dft_roads_028499.hcsp

Duke2.6 · #32 04-11-2005, 07:07 PM

Quote:

Originally Posted by JimF

Checked my wife's smog report (same place) for '01 and '03 and the O2 levels are 0.041 and 0.025 for both. Have a feeling that mine s/b 0.029 and 0.028???

I don't understand those numbers; O2 is measured to the nearest tenth percent, CO to the nearest hundredth percent, and HC and NOx in PPM. One PPM equals .0001 percent, so they chose the measuring units to not have too many zeros before or after the signficant digits.

If those numbers are the HC count they would be 41 PPM and 25 PPM.

Duke

JimF · #33 04-11-2005, 08:04 PM

Quote:

Originally Posted by Duke2.6

O2 is measured to the nearest tenth percent, CO to the nearest hundredth percent, and HC and NOx in PPM.

Duke

Lea's report is 0.03% and O.06% although he is across the 'pond'. My wife's O2 reading from her smog report for '01 and '03 IS as said, so obviously you are not correct. Maybe it changed in '04 or '05 and if I find mine we will see.

So . . . bottom line, mine probably was 2.8% and 2.9% as stated. Maybe it was a 'calibration' problem, maybe it was the actual reading. Either way it's academic since there's no MAX limit on the O2 reading -AND- you can't fail from any reading, high or low.

LeaUK · #34 04-13-2005, 02:09 AM

For the reference of others in the UK there is one slight variation in UK emissions testing that I have recently found: most garages (if not all), for turnover reasons I suspect, perform a Basic Emissions Test (BET) first.

This allows the tester to measure emissions without the need to know the engine code or specific model data of the tested car - no need to follow any flow diagrams to find the exact test limits!

So in the UK this BET limit has changed to match the newer bread of car (September 2002) and is:

CO <=0.2%
HC <=200ppm
0.97-1.03 Lambda

If a car fails this test, it doesn't necessarily mean the car fails, it simply means the tester has to now follow the flow charts to locate the exact emission limits for that exact vehicle and retest to those limits.

Of course this is excellent news for us with elder cars with Cats, as although our cars will be subject to the new BET limits, if the car was first used post July '92 may still only have to pass non-cat limits

Lea

JimF · #35 04-13-2005, 07:18 PM

Quote:

Originally Posted by LeaUK

For the reference of others in the UK there is one slight variation in UK emissions testing that I have recently found: most garages (if not all), for turnover reasons I suspect, perform a Basic Emissions Test (BET) first.

This allows the tester to measure emissions without the need to know the engine code or specific model data of the tested car - no need to follow any flow diagrams to find the exact test limits!

So in the UK this BET limit has changed to match the newer bread of car (September 2002) and is:

CO <=0.2%
HC <=200ppm
0.97-1.03 Lambda

If a car fails this test, it doesn't necessarily mean the car fails, it simply means the tester has to now follow the flow charts to locate the exact emission limits for that exact vehicle and retest to those limits.

Of course this is excellent news for us with elder cars with Cats, as although our cars will be subject to the new BET limits, if the car was first used post July '92 may still only have to pass non-cat limits

Lea

those limits are 'tight'! Strange to do a 'double' test; if it passes, great! If it doesn't, the test to the limits that it SHOULD be tested to.

But the funny thing . . . didn't know cars get to be an 'elder'? Is that like an elder statesman?

LeaUK · #36 04-14-2005, 03:18 PM

LOL...'elder' whoops..

Yes those are rather tight for 'elder' vehicles - seems those of us 'over the pond' need to meet 'real' regulations

although I'm particularly pleased with the loop hole I've discovered

I think the reason for the BET is to keep throughput to a maximum. As you can imagine, if the test station simply uses one set of limits for all cars they only need to gather the required information (VIN, Model etc) and follow the painful flow diagrams upon failure - which I image is probably only 10-15% of cars, if that.

That's the only reason I can see - turnaround. The BET testing had me wondering for a while, why on earth do two tests, but it does make some kind of sense when you think about the 'environment' typical garages work in.

In the UK we don't typically have specific test stations for emission checks but testing is carried out annually at regular garages upon our MoT (annual check for car roadworthyness).

Best thing is that I now have a reasonable if not 'more than average' understanding of UK emissions testing AND that my car scores a perfect 50% Lambda too...

I've saved GBP1500 (not having to purchase a new Cat) so it's off to buy all those 'nice' things I've been waiting for all winter - watch out MB, here I come...

r_p_ryan · #37 04-18-2005, 03:29 AM

Duty cycles all over the place

The duty cycles on one my E's is all across the board. It'll jump from 33% to 65% to 100% to 0%. It's running all over the place with regard to frequency as well. Apparently it's supposed to run at 100 hertz, but it too is all over the place, registering even into the khz. When I unplug the O2 sensor it registers a solid 85% and 100hz., (I believe the appropriate trouble code). My other E is fine (43% +/- 10%), so I'm pretty sure the multi meter works and my setup is correct. The O2 sensor puts out between .1 and .9 volts and responds rapidly.

Thanks,
Robert

raymr · #38 06-15-2005, 07:40 PM

I did my first duty cycle check. At the X11 port, pins 2 and 3 with the ignition on, engine off I get a reading of 70.2%, which drops to 0 after 5 seconds.

With the engine running I see 72-73% regardless of which way I turn the tower screw, both at idle and 2500 rpm. It seems fixed in that range, so what does that mean? I didn't check the O2 sensor yet since I have trouble locating the wire coming into the cabin.

James Redman · #39 08-12-2007, 03:24 PM

"If the duty cycle is 50 percent it means the mechanical mixture is spot on stoichiometric,...

Duke[/quote]

I think Stoichiometric gives a Lambda output voltage of about 0.45 to 0.48 volts (check this) on the black wire of a 4 wire O2 sensor.

I thought a 50% duty cycle meant the injectors are open 50% of the time....I am learning from this Web Site but have I missed something in this thread? At idle I would expect a duty cycle around 5 to 10% and WOT 85%.

In fact may I ask if anyone knows the idle duty cycle for a standard M119 engine?

Jim.

JimF · #40 08-12-2007, 04:06 PM

Menu#4 on my web page shows a 'graphical' Lambda of "1" (when it's at 0.45V) but, as you know, this voltage is sweeping from from top (0.8V) to bottom (0.05V), so it's continually changing.

If you measure Lambda on a 'd/c' meter, it should be 50%. . . at idle and at high rpm. The fact that it isn't could mean a lot of things. Missiing/fouled injector, bad plugs, contaminated O2 sensor, contaminated/failing MAF, and the list goes on.

James Redman · #41 08-21-2007, 03:31 AM

Jin F, Thanks for the steer to your menu 4 dealing with on-off ratio.

This may be silly question time but I am still confused. I think there is an Electronic Engineer Defintion of Duty Cycle and Fuel Injection Engineer Definition of Duty Cycle and both are floating around here.

On Jim's menu 4 I read that the Lambda = 50% is OK (but what is the on-off ratio?). I still cannot relate that to the nice and simple injector opening time definition of Duty Cycle.

Please can some one clarify what is going on for this simple mechanical engineer?

Regards,

JimF · #42 08-21-2007, 10:26 AM

Quote:

Originally Posted by James Redman

Jin F, Thanks for the steer to your menu 4 dealing with on-off ratio.

On Jim's menu 4 I read that the Lambda = 50% is OK (but what is the on-off ratio?). I still cannot relate that to the nice and simple injector opening time definition of Duty Cycle.

Regards,

Lambda is equal to "1". . . scale along the 'X' axis when the D/C = 50%.

megatrack · #43 11-26-2007, 06:36 PM

HI, If anyone can help me with this one:

I checked the duty cycle on my MB 300e 1990 with ignition on it's 10%
if I press on the air plate It goes to 45% if I go full throttle it is 79%
When I start the car it stays to 10% all the time.
Can anyone tell me why am I getting 10%

all the time. it's not fluctuating at all. even idf I turn the mixture adjustment screw.

Thanks
AJ