Cruise control.. some weird stuff.. serious imput needed! - Mercedes-Benz Forum

 
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post #1 of 4 (permalink) Old 07-15-2004, 08:59 PM Thread Starter
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Date registered: Apr 2004
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Cruise control.. some weird stuff.. serious imput needed!

Hi folks,
here is the deal:
Problem description:
when actuating the accel lever on the cruise control the car accelerates....
but it does nothing with the set/ressume.. does not hold the speed

Thus... I traced the wires and vacuum lines (since my user manual does not cover teh cruise control :-( )

anyhow, there are 2 vaccum lines present on the actuator unit. One connected via a rubber fitting, color of the vacuum hose is solid black with a green pin stripe.
second a solid black hose connected via a M12 compression nut to the unit
an electrial 2 pole plug.

I traced the solid black hose back into the car. and it went INTO THIN AIR!! There was nothing connected to that hose at all!! Am I missing the cruise control amplifier here!!!!!??????
Where is the control unit (amplifier) suppose to sit on my car????
Please anyone kindly give me a hint here .. PLZ :-)

Thanks a lot...
Cheers Mike
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post #2 of 4 (permalink) Old 07-15-2004, 09:02 PM Thread Starter
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RE: Cruise control.. some weird stuff.. serious imput needed!

well... oh darn... of course.. my car
1978 450 SLC US version

Thanks, Mike
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post #3 of 4 (permalink) Old 07-15-2004, 09:47 PM Thread Starter
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RE: Cruise control.. some weird stuff.. serious imput needed!

ok...
I have found the control unit.. took it appart and measured all diodes and transistors, visually inpsected the traces, solder joints, resistors and capacitors. Everything seems to be in order.
Measured the connector pin out on the wire harness.. all switch functions of the cruise control lever do work properly!

Now... the last thing I could imagine is the speed sensor signal not coming through.

Since I can accelerate with the cruise control lever the cruise control actuator must work properly. All switch imput signals are ok.
so either a: the amplifiers IC's are defect (not likely) or something is off on the speed sensor signal....
My speedometer works fine... where do I trace the speedo signal from?
Is the speedo signal generated in the dashboard/instrument cluster? Or is there a seperate black box?

Thanks folks :-)

Mike
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post #4 of 4 (permalink) Old 06-30-2009, 11:59 AM
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Date registered: Jun 2009
Vehicle: 1980 240D
Location: Asheville, NC
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Originally Posted by Guest View Post
ok...
I have found the control unit.. took it appart and measured all diodes and transistors, visually inpsected the traces, solder joints, resistors and capacitors. Everything seems to be in order.
Measured the connector pin out on the wire harness.. all switch functions of the cruise control lever do work properly!

Now... the last thing I could imagine is the speed sensor signal not coming through.

Since I can accelerate with the cruise control lever the cruise control actuator must work properly. All switch imput signals are ok.
so either a: the amplifiers IC's are defect (not likely) or something is off on the speed sensor signal....
My speedometer works fine... where do I trace the speedo signal from?
Is the speedo signal generated in the dashboard/instrument cluster? Or is there a seperate black box?

Thanks folks :-)

Mike
Hi, Mike. I just inherited a low mileage '80 240D and have the same cruise problem problem you described at the Bensworld forum in April, 2004. Did you ever solve the issue?

Bruce2020
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