So, I took my new Sears DMM with Duty Cycle into the garage and made my first attempts at diagnosing my symptoms of low pwr, rich mixture, hard cold starting. Here is what I found so far:

Pin #3 Test

1) key off = 0%

2) key on, engine off
Initially = 94.6%, then I heard a noise near the valve cover (like a relay moving to a new position) and the duty cycle immediately dropped to 14.9%

3) engine on
This is where things got strange. Duty cycle was all over the place, but no matter how big the swings, it quickly tended to 0%. I kept moving the ground connection of the DMM to other points on the car, and then I'd get another reading for a few seconds and then it would tend to 0% again. I was unable to get readings for more than a few seconds without playing with the ground lead for the DMM.

I tried adjusting the lamba tower, but I didn't take much of a turn before the car died, and the DMM duty cycle still tended to 0%.

I unplugged the connector from the eha to see if this made a difference. The engine check light did come on, but I was still unable to get any duty cycle readings. Unfortunately, I do not yet have an EHA harness, so I was unable to test the EHA.

Can anyone shed any light on why my duty cycle is quickly moving to 0%?

Thank you in advance.

__________________
Steven
1989 260E (276K miles)
1995 E320 (50K miles)

That is strange, Key On Engine Off should read either 70% or 30% (depending on the meter).
I wouldn't pay much attention to readings with engine running until the 30 or 70% reading is achieved. That is the first step to know whether the computer is OK (I think).
May be an expert like stevebfl will provide his always "on the money" advice.

__________________
1999 Porsche 996 Carrera Convertible
1994 420E - SOLD
1986 300E - SOLD, what a car
609 Certified

I'm just reading throgh the thread at: My LAST ovp/eha question, I promise!!!! as this thread seems to address my issue. Not sure I understand it all yet, but I'm working through it.

Please feel free to add any more comments if you think that they would be helpful.

Thanks again

__________________
Steven
1989 260E (276K miles)
1995 E320 (50K miles)

I definitely never got 30% or 70% with the Key On Engine Off. I'm using the Sears DMM that everyone on the board has been referring to in their post

__________________
Steven
1989 260E (276K miles)
1995 E320 (50K miles)

By the way, this is a California vehicle. Just looking at some older posts, and it appears this makes a difference in how I should go about testing lambda. Can someone help me through this?

Thanks.

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Steven
1989 260E (276K miles)
1995 E320 (50K miles)

Go to: www.landiss.com/mixture.htm

Print it out!

Read it carefully paying particular attention to testing CA models under "static tests".

As a brief summary, when you turn the ignition on the duty cycle should indicate 85% for CA models.

Manipulate the X92 connector button (at the front of the battery compartment) as described to place the system in "test mode".

Start the engine and observe the duty cycle.

Duke

Thanks Duke, I did not know about the X92 connector button

__________________
Steven
1989 260E (276K miles)
1995 E320 (50K miles)

Well, I's just finished another round Pin #3 Testing, this time I was armed with instructions for depressing button #2 (California Vehicle)

1) key off = 0%

2) key on, engine off = 14.9%

3) engine on

Well, initially it was roaming between 30 & 38% and I was unable to gain control. I tested the voltage across the O2 connection and found that it was exactly 0.5V. So, recalling Stevebfl's instructions, I disconnected the O2 sensor and ran the car at 2-3K RPMs for a while, in order to see if the O2 sensor was foul. After doing this a few times, I was able to adjust lambda. It is now 48 - 52% at idle and less than 5% off of this at 2K RPM's.

My remaining question is what is the correct lambda setting for my California 1989 260e? Again, it is currently set at 48-52%, but I've seen other discussions saying that it should be at 45%. Does anyone have the recommended setting information?

Thanks again.

__________________
Steven
1989 260E (276K miles)
1995 E320 (50K miles)

First, since you have a Ca car you should have 85% KOEO (key on, engine off). This corresponds to the inverse of your 15% reading and is thus probably correct except for convention.

Since your convention is off, the desire to set 45% will in effect give you 55%. If you set it to 50% it won't matter. Using your convention setting 55% will get 45% true to convention.

To understand convention one must understand duty cycle. If you look at the signal with a scope you will see in one period a high signal and a low signal. The relative amount of each is the duty cycle of the period. So the statement is either: they duty cycle was high 85% of the time or it is low 15% of the time depending on your point of view. Since the proper convention is to state that the condition that exists at KOEO is 85 on CA cars you must change the reference on the meter or do the inverse calculation.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

As Steve said, you want to see 85% key on engine off on CA models. If you read 15% and can't reverse the polarity of your meter, just swap the leads.

As the Landiss write-up says, there is no actual spec for duty cycle, but if it's in the range of say 40-60 percent at both idle and 2000 RPM, no load, it's okay.

If the duty cycle was at exactly 50% it would mean that the basic mechanical mixture adjustement is right on stoichiometric, but it's imprecise, relative to the O2 sensor, electronics, and EHA correction, so the actual duty cycle will usually vary in a range of 5 - 10 percent. If it's near 50 percent then the system is operating near the center of it's operating band. You should only have to adjust the mechanical mixture adjustment if it's operating near the edge of the band, which would be indicated by a very low, say less than 25 percent, or very high, say over 75 percent duty cycle.

When I tested my 190E 2.6 last spring I had a duty cycle in the range of 40-45 percent at idle and 50-55 percent at 2000 no load, readings which I deemed acceptable. Since I also had a scope I pulled the O2 sensor signal lead out far enough to connect a test probe so I could eavesdrop on the O2 sensor voltage signal and the waveform was nominal.

Duke

Thanks Stevebfl and Duke.

Will setting to 55%, using my reversed convention, result in a more lean mixture?

Also, one other point of note. When I monitored lambda with the O2 sensor disconnected, I saw a result of 49.9%, and it did not change.

Overall, the engine is running much better. I am still experiencing some roughness at idle. Also, low power and poor mileage was the primary reason I started down this path. I'm not sure if I am still experiencing low power, as I have only tested the car around the city. Acceleration from a start seems fine, but still not sure about hill climbing around the streets of San Francisco. I'll have to watch is for a few days and see what I experience.

Thanks again.

__________________
Steven
1989 260E (276K miles)
1995 E320 (50K miles)

In normal convention a 45% duty cycle represents a system that has used up 5% of its correcting ability to lean out a 5% too rich calculation.

What you have to realize is that any percentage exhibited in closed loop creats the same mixture. Try very slight pressure on the airflow plate. You are richening the mixture. Watch the duty cycle. It will go lower and lower until the resulting mixture is back to closed loop control. It will do that within its capability or about from the range 10% to 90%.

So, if you turn the allen adjustment the system compensates... always keeping the actual mixture going into the engine the same.

The point to setting the car a little rich (45%) is that although closed loop mixture is the same, open loop mixture is richer. Open loop is all cold running, full throttle and non steady state operation (sudden acceleration).

Now that you are adjusted, you need to see if the problem still exists. It probably does. The next step would be to watch the duty cycle during the event and preceeding. You are more likely to need a fuel pressure gauge. If you are running out of fuel due to say a weak fuel pump or restricted filter, you could see the condition as it unfolds using the above technique. As the pressure dropped and the mixture dropped the duty cycle would go off range way before any actual symptom was felt. Actually the system doesn't react as fast as problems can appear, but within seconds of a fuel pressure related mixture change the system will correct or run out of room trying.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Thanks again, Steve.

When I first noticed the problem I thought I had purchased a lousey tank of gas. So I changed my fuel filter and realized that I had a fuel leak in the hoses around my two fuel pumps. So I also replaced all of my rear hoses. But I have yet to touch the two fuel pumps, which are both almost 3 years old (60,000 miles).

I've also noticed that I have been loosing pwr on the freeway when I attempt to accelerate throught 3,000 RPM. I'll have to test the car again on the fwy this week, now that I've adjusted lambda.

Lastly, I just changed my plugs, which were black, and I'm now running Techron to clean the injectors.

__________________
Steven
1989 260E (276K miles)
1995 E320 (50K miles)