'Adjusted' lamda tower screw...car won't start. - PeachParts Mercedes-Benz Forum

socaleuro · #1 03-04-2009, 02:58 PM

Quote:

Originally Posted by professor

Absolutely! The CIS computer will generate a nice steady square wave if you just turn the ignition on without the engine on. That signal will stay steady as it is a reference signal. Once you turn the engine on, you will have to wait for operating temperature so that your reading is reflective of what the O2 sensor is detecting. At this time you will see the signal drift a little, the top of the signal gets wider when there is a rich mixture being called for and the bottom gets fatter when a leaner mixture is called for ( you can see these on the scope of course, otherwise use a voltmeter and watch the voltage increase for a richer mixture and decrease for a leaner one). The ratio between the upper side and lower side of the signal is your duty cycle. Basically how much of the whole cycle was dedicated to the upper side. If the signal is exactly the same at the top and bottom then you have a 50% duty cycle for example. With a voltmeter you should get half of what your battery is generating if you are at 50% duty cycle.
Does that help?

Great explanation, really Helps to understand how things work in these cars!

Now,As SLK was saying, doesn't the car have to be in some sort of 'diagnostic mode?'

slk230red · #2 03-04-2009, 03:06 PM

Quote:

Originally Posted by socaleuro

Great explanation, really Helps to understand how things work in these cars!

Now,As SLK was saying, doesn't the car have to be in some sort of 'diagnostic mode?'

I see you are in California, doesn't your car have the built-in LED and button on the Diagnostic Block in front of the battery?

@1988 California and
@1991 with diagnostic trouble code
storage:
The CFI control module must be switched over
to output of on/off ratio because the signal for
the diagnostic trouble code (DTC) display is
output as priority.
The output of the on/off ratio is performed once
all the DTCs have been read out and the start
button of the impulse counter scan tool or the
non-locking switch on the diagnostic connector
(California version only) is then once again
pressed (see section m).
The % readout now fluctuates when the engine
is running at normal operating temperature and
there are no DTCs.

On/off ratio
in %
Possible causes of fault
- No voltage or ground at diagnostic connector (Xl 1)
- Cable from diagnostic connector (Xl 1) to CFI control module (N3) has open
circuit
- Lambda control tester defective
- Mixture setting too “rich”
(on/off ratio 0 - 8 % also possible)
- @ California model year 1988 and @ 1991: CFI control module not
switched over to on/off ratio output.

socaleuro · #3 03-04-2009, 03:25 PM

Quote:

Originally Posted by slk230red

I see you are in California, doesn't your car have the built-in LED and button on the Diagnostic Block in front of the battery?

@1988 California and
@1991 with diagnostic trouble code
storage:
The CFI control module must be switched over
to output of on/off ratio because the signal for
the diagnostic trouble code (DTC) display is
output as priority.
The output of the on/off ratio is performed once
all the DTCs have been read out and the start
button of the impulse counter scan tool or the
non-locking switch on the diagnostic connector
(California version only) is then once again
pressed (see section m).
The % readout now fluctuates when the engine
is running at normal operating temperature and
there are no DTCs.

On/off ratio
in %
Possible causes of fault
- No voltage or ground at diagnostic connector (Xl 1)
- Cable from diagnostic connector (Xl 1) to CFI control module (N3) has open
circuit
- Lambda control tester defective
- Mixture setting too “rich”
(on/off ratio 0 - 8 % also possible)
- @ California model year 1988 and @ 1991: CFI control module not
switched over to on/off ratio output.

Never even tired looking for that LED and button by the battery. When I do find it, all that is reguired is to turn the key to the 'on' position and then press the button for 2-4 seconds and record the pulses, correct? After that I should be able to read the lambda @ pins 3&2 of the X11 connector if everything is all good?

slk230red · #4 03-04-2009, 03:44 PM

Quote:

Originally Posted by socaleuro

Never even tired looking for that LED and button by the battery. When I do find it, all that is reguired is to turn the key to the 'on' position and then press the button for 2-4 seconds and record the pulses, correct? After that I should be able to read the lambda @ pins 3&2 of the X11 connector if everything is all good?

If it doesn't switch over, you might have to press it again for 2-4 sec.

professor · #5 03-04-2009, 03:08 PM

Quote:

Originally Posted by socaleuro

Great explanation, really Helps to understand how things work in these cars!

Now,As SLK was saying, doesn't the car have to be in some sort of 'diagnostic mode?'

I have done these adjustments on my 1988 190E last week and my 1989 560SEL a couple of years ago without the knowledge of a "diagnostics mode". Such a mode might be true on newer cars but I never had to deal with that on my old clunkers.
The 560 has passed emissions and has been the most reliable car ever at over 300K miles.
What is your car model and year (maybe I should read the first thread

)

slk230red · #6 03-04-2009, 03:13 PM

Quote:

Originally Posted by professor

I have done these adjustments on my 1988 190E last week and my 1989 560SEL a couple of years ago without the knowledge of a "diagnostics mode". Such a mode might be true on newer cars but I never had to deal with that on my old clunkers.
The 560 has passed emissions and has been the most reliable car ever at over 300K miles.
What is your car model and year (maybe I should read the first thread

)

I'm pretty sure it pertains to California models '88 and up, and all others '91 and up. My '93 requires it and Steve Brotherton said so!