Sunil Hari wrote:
On my 92 300D, the cruise control has stopped working. One day, perfect -
next, nothing. Where do I start troubleshooting? First, fuses have all
just been replaced. Second, the rear overhead light and the small square
reading light don't work.
Cruise control failures are often intermittent - works fine one day -
not the next - works for 5 minutes - then not for an hour - then back
on. Those failures are almost always because of poor solder connections.
Maybe half (or more) of the cruise control amplifier failures are due to
the solder joint problems and perhaps somewhat fewer from capacitor
problems. The actuator CAN fail and few DIYers have repaired them so
they work reliably. A few failures result from the Hall effect sensor on
the speedometer failing. You can test most everything except the amplifier.
The Mercedes test rig tested everything (power, switches, sensor, etc.)
except the amp and if everything else was okay, the amp was presumed to
be bad.
Start by cleaning the contacts of the pins on the actuator plug (in the
engine compartment) and the pins on the amplifier connector. If that
doesn't cure the problem, then you can try resoldering the amp. There is
a test for the actuator by Doug Quance that appeared on another list.
Here is my test procedure for the speed sensor and actuator.
I tested the hall effect sensor by placing an analog voltmeter across
its input to
the cruise amp and slowly moving the car. As I recall I saw a voltage
fluctuation
of about 2 to 8 volts. THis gave me some confidence it was working.
On someone else's test procedure a resistance value for the sensor was
given.
I found this to be inaccurate, and I dont recall what mine read.
You could also put the one wheel up on blocks and slowly "drive" the car
to move
the speedo cable and check out the sensor.
The actuator I tested as follows:
The resistance of the release clutch solenoid between pins 6 and 7
I measured to be:
1.3K forward biased, and infinity reverse biased. Your measurements may
vary, it should read about 35 ohms forward biased. The discrepancy is
due to my meter not having enough power to forward bias the diode. If
you were to apply 12v and insert a current meter it should read about
320 - 325 milli amps.
The feed back pot was measured at 3K ohms, thats from pin 1 to 3.
The resistance between 1 & 3 should be = 1 & 2 plus 2 & 3.
The motor measured about .25 ohms.
These were static measurements that may or may not identify a problem.
I felt a dynamic test would be more accurate.
I tested the actuator by simulating the power thats applied to it by the
CCamp. THis must be done very carefully!!! I have some spare MB female
pin connectors with about 6 " leads. These I placed on the plug from
the actuator.
I placed an ohm meter across the feedback pot contacts(alternating
between the 3 connections). Before powering the clutch move the
connecting rod to the accelerator to a mid point. Then connect the
proper polarity of voltage from the battery to the clutch(you should
hear an audible clunk).
Give the servo motor a few momentary connections of power(12v).
Reverse the polarity of the motor connections and again supply momentary
power.
I did leave the power on too long when the servo was moving to
full throttle and the clutch released, I believe there are some internal
limit switchs.
You should see the accelerator linkage move and the resistance
on the feedback pot change. After several movements this way I felt
confident the actuator was functioning properly.
Good luck and let me know how you make out.
-- SANTÉ Doug Quance
Marshall
--
Marshall Booth (who doesn't respond to unsigned questions)
"der Dieseling Doktor" [EMAIL PROTECTED]
'87 300TD 182Kmi, '85 190D 2.0 161Kmi, '87 190D 2.5 turbo 237kmi, '84
190D 2.2 229Kmi (retired)
