What's the switch on the valve cover do? (617) - PeachParts Mercedes-Benz Forum

Brewer · #1 03-23-2012, 08:50 PM

I'm tracking down 'slow acceleration' problems... What's this switch do. The arm is broken off, so whatever it's supposed to do as I hit the go pedal, it's not doing...

I also found a connector, not connected to anything. Anyone recognize it? It was wrapped around the cruise control.

Flyin4now · #2 03-24-2012, 12:05 AM

I have been told that the item in your first pic is an A/C shut off under hard acceleration. Not sure if that is correct. I've never noticed the A/C cutting off, though. The black part of that plastic piece of mine has disintegrated. All I have left is the two little pins connected into the grey piece. I wish I knew where to find a replacement. Anyway, hope this helps

sleepstar · #3 03-24-2012, 12:44 AM

did some snooping. your switch is missing a piece

(that wheel that's activated by that black cam that rotates with the throttle)

on a gas motor it's called an "overrun cutoff" switch. on a diesel it's an electric kickdown switch or an injection pump switch. i think it cuts off all fuel if the throttle its completely closed and the RPMs are high?

of course by "all" i don't mean 100% or your motor would stall

i believe that connector to be associated with the switch.

ps i like your clear return lines

mach4 · #4 03-24-2012, 01:59 AM

The switch is the kickdown switch

And I believe that the connector is for the coolant temperature switch as part of the engine overload protection circuitry and plugs into the sensor on the thermostat housing.

Here's the electrical diagram.

Pictures of an '85 Cali OM617.952

If I'm wrong, we'll both find out pretty soon.

JamesDean · #5 03-24-2012, 03:21 AM

That's not a kickdown switch. The kickdown switch is at the end of the accelerator pedal.

This is, as Flyin4Now, indicated, an a/c cut off switch. Seen on the MY 1985 300SD, probably 300D as well:

A similar micro switch is used on the M103 as a throttle/idle micro switch. On the M103, if the switch is bad, the engine will usually idle up pretty high.

mach4 · #6 03-24-2012, 10:23 AM

Quote:

Originally Posted by JamesDean

That's not a kickdown switch. The kickdown switch is at the end of the accelerator pedal.

This is, as Flyin4Now, indicated, an a/c cut off switch.

Thanks for the correction. There is lots of bad info in the forums... The consensus seemed to be kick-down, but obviously it's cut-out.

Again, thanks for the info... with the documentation. I appreciate it.

Where is that control unit shown in the diagram located? Once I get my project signed off I'll be dealing with A/C and I want to make sure I get what I need off the donor car before scrapping (although I can probably use the system on the project car)

JamesDean · #7 03-24-2012, 02:25 PM

I think its located inbetween the two firewalls. If I'm not mistaken it says KICK'D on the box. I think. I might be wrong. I dont remember exactly.

Hit Man X · #8 03-26-2012, 10:39 AM

Just to reaffirm Kris... that cuts off the A/C compressor at WOT.

Brewer · #9 03-26-2012, 09:23 PM

Ah. Thanks for the info on the AC cut out. Don't need to worry about that.

The mystery electrical connector is still a mystery though. There are 3 different electrical connectors on the thermostat housing, all present and accounted for...

I've narrowed my problem down to the turbo... the car accelerates fast enough for me, and shifts really nice. But once it hits 2200rpms, it holds there, and I can't really get over 50mph. I imagine that's where the turbo should be kicking in. I've been going over the throttle linkages, and they seem tight enough...

JamesDean · #10 03-26-2012, 09:33 PM

Look at the back of the engine for a plastic line that goes to a bell looking thing on the firewall. Clean out that line, it should help your boost.

cho · #11 03-27-2012, 03:11 AM

Quote:

Originally Posted by JamesDean

Look at the back of the engine for a plastic line that goes to a bell looking thing on the firewall. Clean out that line, it should help your boost.

x2

(or it goes directly to IP.....)

Hit Man X · #12 03-27-2012, 10:15 AM

Quote:

Originally Posted by Brewer

Ah. Thanks for the info on the AC cut out. Don't need to worry about that.

The mystery electrical connector is still a mystery though. There are 3 different electrical connectors on the thermostat housing, all present and accounted for...

I've narrowed my problem down to the turbo... the car accelerates fast enough for me, and shifts really nice. But once it hits 2200rpms, it holds there, and I can't really get over 50mph. I imagine that's where the turbo should be kicking in. I've been going over the throttle linkages, and they seem tight enough...

Are you sure the fuel rack is fully opening? Check the linkage...

Govert · #13 03-28-2012, 10:02 AM

I think the microswitch also controls the transmission, so that the transmission shifts at higher rpms at kickdown.

Here is another thread about it:

'85 300TD: Throttle Sensor Switch on top of Valve Cover Question - Benzworld.org - Mercedes-Benz Discussion Forum

andrewjtx · #14 08-17-2012, 09:28 AM

The pin bushing housing (ie plug) has disintegrated on my 85 TD. Part number was not obtainable... Since it's an 85 only parts for this model, the parts counter at MB is having a helluva time tracking it down. WE've already been through two bad parts orders.

The part number listed on the Benzwrld thread above is not the correct number for this housing.

Can anyone with an '85 please check the part number on the plug housing for this cutout switch?

Thanks!

JamesDean · #15 08-17-2012, 09:50 AM

Quote:

Originally Posted by andrewjtx

The pin bushing housing (ie plug) has disintegrated on my 85 TD. Part number was not obtainable... Since it's an 85 only parts for this model, the parts counter at MB is having a helluva time tracking it down. WE've already been through two bad parts orders.

The part number listed on the Benzwrld thread above is not the correct number for this housing.

Can anyone with an '85 please check the part number on the plug housing for this cutout switch?

Thanks!

So you're looking for the plastic housing that the wires/pins go into? This same switch is used on the m103 as a throttle microswitch.

Using that information, to find the part number for the connect, then searching the connector number itself reveals

Parts.com has the part (ships from Mercedes-Benz warehouse via Mercedes Benz of Naperville, IL):

for the 300SD, MY 85