I finally decided to buy one of those much balyhooed Sears DMMs and check the duty-cycle on my '91 190e 2.3 California model only to be surprised to see that the KOEO reading at pin 3 of the X11 connector was at 69.6%, which would be inline with a 49 state car.

I'm quite certain this is a CA car as it has the yellow emmisions decal under the hood and the VIN shows it is a CA car as well, along with the X92 connector.

I'm running about 60% duty cycle at the moment in closed-loop, but I have to wonder; Is there something wrong here??

Anyone? Everything I've seen in these forums suggests that California models should be at 85% duty cycle with the key on, engine off..

"I'm running about 60% duty cycle at the moment in closed-loop, but I have to wonder; Is there something wrong here??"

Do the numbers oscillate around 60%, as they should, or does it stay fixed on one number?

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'90 300SE 298k
-300K and it gets put into retirement.
'80 300D 255k Purchased new by family in 1980.

Had a:
1973 220 (gas)
1980 300SD
1992 400E

Yes they do oscillate around 60% From about 58%-62% I understand this is on the lean side, but so far it's as good as I could get it on the first try.

Ok, I think I figured some stuff out. As I mentioned before, my car is a California car and here's what I found out today: When I first switch KOEO, my fixed-duty cycle is at 85%. At that point, I cannot perform any static tests on the air flow sensor or throttle position sensor. However, when I press the button on the X92 test connector a couple of times, it then shows 70% fixed-duty cycle and all tests can be performed. I assume this is normal.

Now, the reason for my interest in the duty cycle is that I failed Arizona emissions. My HC readings were 347 Loaded and 439 Idle, with both at a max allowable of 220. CO was 1.46 Loaded and 0.95 Idle with both at a max allowable of 1.20.

It seems that the car has always had a slightly audible misfire, so I was suspecting that was the cause. I bought the car two years ago and since then I've changed all the usual suspects like plug wires, cap and rotor, spark plugs, air filter, fuel filter along with regular oil changes. I even went so far as to change out the ignition coil, fuel injectors and seals. Everything as a whole helped the cars performance, but it still has that miss.. Finally, I just threw on a cheap cut and weld cat to get it to pass for the last couple years.

Anyway, I just did some lambda adjustments and here's what I came up with:
With the black/wht striped purge hose disconnected, I can get it to run at ~50% duty cycle (all readings fluctuating) at idle and ~44% @ 2500RPM. With the black/wht striped purge hose reconnected, I get ~45% duty cycle at idle and ~33% @ 2500RPM.

My understanding from these readings is that it's trying to compensate for the rich condition at 2500RPM (due to the misfire). I also now realize that I should have adjusted the idle duty cycle to +/- 10% of the reading at 2500 RPM. Instead, I adjusted the idle close to 50% and then took a reading at 2500 RPM. Still, that equates to +/- 10% of the reading at that the point where I had the purge hose disconnected.

Therefore, my question is, are my Lambda settings as good as I'll get right now until I fix the miss? Or is it possible, that the miss might have something to do with my lambda adjustments?

I'd also like to know the answers to his questions.

Haasman

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'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)

I think your readings are okay. As you stated, on CA cars you have to place the system into "test mode" with the button on the X92 connector. This is explained at:

www.landiss.com/mixture.htm

The mixture adjustment screw establishes the open loop mixture idle mixture, which is important for good cold start and idle, so I recommend setting the idle duty cycle a little less than 50 percent, which is slightly rich. I measured my car at 40-45 percent at idle and 50-55 at 2500. It colds starts and warms up very well and is with the +/- ten percent range (barely) so I did not adjust it.

I don't think your misfire is due to a lamda system fault, but I can't give you any specific direction on where to look. I would suggest a compression or leakdown test to establish the basic health status of the engine and inspect all the secondary igntion system componets. I've not seen a spec for wire resisistance, but they should be in the same general range per foot.

Even with an inoperative catalyst, the idle CO should not be more than about one percent, and less than 0.5 percent with a good catalyst.

The reason the evap cannister purge valve should be disabled during the test is to not "contaminate" the readings with fuel vapor that may be drawn in from the evap cannister. I'm a little surprised it made as much difference as it did in your case. You should check the evap system to make sure all lines are intact and there are no leaks. The signal line to open the valve goes though a 70C temperature switch and then to the valve. This is the line you disconnect and plug to disable the valve. If you don't plug it, there will be an air leak, which will affect the duty cycle (make it lower to correct the lean mixture back to stoich.). This will be most noticeable at 2500, because the vacuum port for the purge valve signal line is usually above the throttle blade at idle, so purging only occurs when the throttle is opened some amount above idle.

There is a second line, which is the actual purge line - when the purge valve is open air is drawn through the cannister, which pulls the stored HC into the inlet manifold. There should be only a very limited draw through this line. An evap system schematic is on the emission/tuneup decal on the upper radiator support member.

Duke

I'd like to make the same adjustments, but can't get my 1992 300CE (CA) car to go into "test mode" when I press the button on the X92 connector. I have an 1988 300E (CA) that does go into test mode when I press the button, so I know what to do with this. Is there another way to enter the TEST MODE on the 92 model?