If the duty cycle reading is as I described, then all should be well with the lambda system. I like to look at the O2 sensor output to make sure it has a nice, crisp jump between the high and low voltage readings within the specifed frequency range, however this test is not prescribed by the Mercedes diagnostic procedure, and it not actually necessary if the duty cycle behavior is within accepatable limits.

Given your CO readings, I don't see anything wrong with your catalyst. These KE-equipped engines are usually higher on HC than other fuel system designs for possible reasons that I've outlined in other posts and is probably one reason why it was eventually abandoned for a pure electronic system with solenoid injectors.

In California and other state emission tests, many KE-equipped engines are just squeaking by due to high HC and many have marginal failures. Further details at:

http://www.peachparts.com/shopforum/tech-help/117048-successful-ca-asm-emission-test-ke-fuel-system-post833484.html#post833484

Duke

Duke

An interesting and well written post, thanks for the link. However I still have three questions:

1. Is the purpose of the diag signal to allow visibility of the adjustment (whether richening or leaning) the system is making compared to the 50% base?

2. How to read duty cycle for this diag output?

3. Does residual O2 in the exhaust lead to increased CO too?

I think this thread answers 1+2 (thanks guys) but can someone confirm.


Much appreciated.
Lea

__________________
'93 R129 500SL-32
'89 190E 2.6 - sold in 2002

http://antron.pwp.blueyonder.co.uk/i...nature/Sig.jpg

1. I think thats a fair description... (- the 50%) 50% (fluctuating) would be a reading of the adjustments being made and the plain old base mix is whats being adjusted.

How about: Is the purpose of the diag signal to allow visibility of the adjustment (whether richening or leaning) the system is making to the base?

2. I am unfamiliar with X11/4 and your specific engine (M119 UK?) but you might find that info. in your factory manual or here: http://mb.braingears.com/default.htm The manuals are incomplete but There should be a section for your engine under a similar model Look under engine, combustion,... in an appropriate manual for the specific diagnostic technique.

3. If there is O2 in the exaust and the cat is heated up that means more combustion could have taken place but did not. Without O2 no further combustion would be possible.

__________________
-Marty

1986 300E 220,000 miles+ transmission impossible
(Now waiting under a bridge in order to become one)

Reading your M103 duty cycle:
http://www.peachparts.com/shopforum/831799-post13.html
http://www.peachparts.com/shopforum/831807-post14.html

I don't know what you mean by "diag signal".

A stoichiometric mixture should result in "engine out exhaust" that contains a small concentration of HC, CO, and O2 plus some NOx. A three way catalyst requires this exhaust constituency to provide both oxidation and reduction reactions. The amount of 02 in the after converter exhaust is a good diagnostic tool. If it is zero, the catalyst is operating at maximum efficiency by using all the available O2 to oxidize HC and CO. A tenth of a percent or more indicates that full catalytic oxidation reaction is not being achieved. This is often due to the converter being too cool, and these KE-equipped engines seem to be particularly suspectible to catalyst cool down by improper conditioning prior to testing such as shutting the down before the test or excess idling prior to the test.

Duke

Hi Guys

Thanks for the comments.

Just to be clear, my engine is a LH not KE and therefore has much more control all round.

When previously posted, my referral to the 'diag signal' is the signal that is present in the X11. The R129 (from around '92 upto around '95) was fitted with both x11/4 (38pin diag conn) and the traditional x11 (9 pin) connector for fault diagnostics.

I'm specifically interested by the o2 emissions as these are good clues to whether the Cat is hot enough - thanks for letting me know.

Lea

__________________
'93 R129 500SL-32
'89 190E 2.6 - sold in 2002

http://antron.pwp.blueyonder.co.uk/i...nature/Sig.jpg

I got chance to make a few measurements this weekend and my observations were as follows:

1. My Cat just needed a real good heat up. 20 minutes in second gear up and down our local 60MPH motorway resolved that and produced these results:

At idle:

CO 0.062% (0.3% limit)
CO2 15.13%
HC 14ppm
O2 0.06%
Lambda 1.000
NO 8ppm

2500-300RPM (as required by UK Law)

CO 0.141% (0.3% limit)
CO2 15.10%
HC 23ppm
O2 0.03%
Lambda 0.996
NO 11ppm

For comparison, what's the 'normal' level of CO would one expect from a 12 year old LH V8 engine with Cat?

2. The 9 pin X11 diag connector (pin 3 and 6 for my car) outputs a nice signal (which as Duke2.6 previously mentioned) representing the amount of adjustment the engine is having to make to ensure that the Lambda sensor reads the 14.7:1 ie a Lambda of 1.

So this signal is ideal to determine if the car has any minor air leaks. Mine was perfect, at a fluctuating duty of 48-52%.

To prove that unmetered air would be compensated for I pulled one of the vac hoses of the intake manifold - and watched the duty change down to 10%, or of course up to 90% depending how you've connected your DVM/Scope and also if your reading negative or positive going duty cycles.

For me it was irrelevant, as to see the change right in front of my eyes was great.

BUT - from pulling a hose (only a 2mm diameter hose) it took nearly 10 seconds to complete adjustment and settle, or at least display the adjustment. So why so slow? Closed loop systems are usually capable of reacting much quicker.

Is this dependent on O2 sensor reaction time? Thinking about it I was at idle, but still 10 seconds!?

Any thoughts welcomed.

Lea

__________________
'93 R129 500SL-32
'89 190E 2.6 - sold in 2002

http://antron.pwp.blueyonder.co.uk/i...nature/Sig.jpg

'blue-baby' passed with flying colors!

Just came across this thread re comments about X11 pins. As far as I know, using my car as a reference, pin 2 is 'ground' (chassis) and pin 3 is the output signal. Pin 6 is the battery voltage, so reading of DC should be made with the stated convention.

There's a picture in MENU#4 on my page showing 'directions'; lean or rich and if you click on the "M0039" link, you see a pin out of X11 connector. In '95 the O2 signals were moved to the 38 pin connector (pin 14 O2, pin 2 ground, pin 3 battery).

Bosch rates their O2 sensors for about 60k miles, so if it's not been replaced you will be surprised at the better performance. I'd imagine that the response time could be used as an indicator of how well the O2 sensor is performing. 10 secs tells me it's may well need to be replaced.

I believe that it (O2 sensor) should 'switch' in a second or so from rich to lean given the right stimulus. In servo design, the 'electronics' behind the sensor is always made to be slower than the sensor otherwise the system would "HUNT" (oscillate). I would think that it should correct in 2-3 seconds at most.

__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page

Hi Jim

I did take a quick review of your page before testing and again some good info - ta.

Unfortunately I used the pins rather blindly as these were the two my documentation points too, I guessed one would be 0 or 12V but as I don't understand if I'm measuring negative or positive duty cycle, I decided it didn't really matter at first. I've read MB invert their DC reading and maybe this is why they connect between the Lambda signal and 12V as opposed to 0V? Of course, had I found that she was biased above or below 50% I would need to find out more .

I also note that in documentation (and on your site) the 'purge' valve should be disconnected before testing - do you know of it's function? and what effect on the test this has. I never removed mine, if my car has one of course!

With regards to the O2 sensor I've placed the order already but unfortunately my local dealer has no stock, so next week should see further testing and comparison

10 seconds seems slow but I certainly agree it's response has to be much slower than a sensors output with the characteristics of a typical O2 sensor. The control system has further interesting factors, such as, although the engine prefers to run at 14.7:1 infact cats actually need O2 to operate correctly so I guess that's one reason why we see high swings on the O2 sensor o/p - and of course this sensor also has a very high transfer ratio around the 14.7:1 mark too.

Can't wait to get a little more time to carry out further testing now...

Cheers

__________________
'93 R129 500SL-32
'89 190E 2.6 - sold in 2002

http://antron.pwp.blueyonder.co.uk/i...nature/Sig.jpg

I doubt if there's anything wrong with your system including the 02 sensor. Measured emissions are commendably low, but your standards seem unusually tight. For example, in California the CO limit for cars from the late eighties to early nineties is near 0.75 percent.

MB specified a replacement interval for O2 sensors because in their first decade of use degradation was not well characterized, and no one knew how long they would last, but they turned out to be more durable than originally thought. My recommendation is to not change them unless testing shows that they have definitely failed or their response time has become sluggish. The addition of on board diagnostics has eliminated the need for specified O2 sensor replacement since modern OBD systems monitor their performance.

I don't know how quickly the system should respond to a signficant lean condition, such a pulling a vacuum hose, since there is no MB published spec, but all feedback control systems are designed with "damping" that limits the rate of correction. The lambda system is actually designed to "hunt" back and forth centered on lambda = 1.0, but the nominal deviation its designed to correct is very small. Also, your "test" pushed the lambda system to near, if not beyond, the limit of its control authority, and the conditions are not something that the system would have to deal with in normal operation. Only an engineer with indepth knowledge of the lambda system design could answer questions about system response time to various deviations in lambda.

Given your test results, I would say leave it alone, but your experience is another illustration of the importance of "conditioning" i.e. making sure the catalyst is a hot as possible before the start of the test. The LH system may be inherently cleaner than the KE system. I've never seen a KE system that was this clean! Many KE systems in the US just scrape by the limits, especially HC.

Duke

rates their O2 sensors for 60k miles; MB doesn't make them. Sure, to be positive that you need to replace it, it should be tested. If I remember correctly, Art Dalton described a test that he has done to see if its response time is ok.

The term "hunt" is probably a bad term because "hunt" means that the system will never lock. I'd offer "correct" as a more appropriate term since when it's 'locked', it corrects. When it's OPEN, it 'hunts'. As an engineer with expertise in servo systems, that would be a better use of the more correct terms.

As I said, the overall system should correct a few seconds slower than the O2 sensor. If I recall correctly, a good O2 sensor will correct in within a second from the extremes; if it takes 10 secs as an example, I would say that it needs to be replaced. So would Bosch.

On my car, that test 'corrects' within a few seconds. I have a new O2 sensor with 5k miles on it.

__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page