Doesn't the CFI Module have to be in the 'Diagnostic Mode' from '88 up to read duty cycle? On my '93, I use the homemade LED Tester to check for DTC codes and also to put it into diagnostic mode to check my duty cycle. Otherwise, all you'll read is battery voltage across pins 2 & 3.

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.

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:D )

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!;)

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.

Ok, I found the led and button thing by the battery, whats the proper name for it by the way? #2 is the push button and #4 is the led. When I discovered this diagnostic connector the led was on solid. What should I do form here?

Observation: When the car is at operating temp and I try to increase engine speed via throttle cable the engine wants to die. Assuming since mixture isn't properly set, it's either too rich or too lean to keep up?


Here are the measurements @ 80C

Battery: 13.84v

Green connector of O2 sensor wire: .495v

Pin 3 of X11 connector: 2.093v (non-fluctuating)

EHA:0mA (non-fluctuating, almost as if I wasn't getting a reading at all!)

if the car is not running those values will not fluctuate.

The car is running.

Congratulations! What did you do to get it to run?

Actually got it running on Saturday, but didn't want to start up reliably and it ran not so well. Today I got to to run generally smooth (not as near as it did before though) and fire up rather easily each time.

So, does anyone know what to do when the led light is solid red?

If you are not getting any current fluctuation at the EHA while the car is running then you may have not connected the Ammeter correctly or your car's computer is fubar

or bad harness

Will have some time tomorrow to look at the car in the morning, I'll try to take a reading at the EHA again.

The led was sold it the diagnostic connector when I pulled the little cover off, should I do anything special, or just go ahead and hold the button down for a couple of seconds to get the codes?