Intermittent Stalling when shifting into reverse

[Lorsar]

I have been having an intermittent problem with stalling in reverse only.  Drive works fine.  I have replaced both pressure switches, checked/cleaned wires, adjusted the css.  I am able to avoid stalling by keeping foot slightly on accelerator while shifting. Once in reverse, I can take my foot off the pedal and it is fine.

About 2 years ago when I replaced the shifter bushings, I saw that the neutral safety switch cable was bent right where it attaches to the trans (reverse light didn't work) and it broke when I tried to straighten it.  Ordered a new one from Bud's Benz.
 
To replace it, I had to remove the plate (circled in the picture)  and when reinstalling it, it was a very tight space and difficult to align.  Afterwards, the shifter was off slightly, I had to push a bit past 4 to get it in gear all the way.  Not too much so I hadn't tried to adjust it. 

Now recently I was thinking: What if that slightly off shift setting is causing my intermittent stall when going into reverse? So, I set about to try and fix it today.  At first I made worse: reverse was in the neutral location on the shift gate BUT it wasn't stalling.  Then I fixed that and in that process I had disconnected the neutral safety switch cable.  And guess what? NO STALLING!  Reattached the cable and the intermittent stalling is back.

I have adjusted the heck out of that cable and no dice.  There is some play in the arm on the neutral safety switch.  I'm wondering if that might be the cause. 

Any suggestions? And why would the safety switch not moving all the way into reverse position cause the car to stall?

[lpeterssen]

Dear Lorsar

Your stalling problem has nothing to do with the neutral/parking reverse light switch.

Let’s start by analyzing what is the function  of the parking/neutral safety switch + reverse light switch.

• First function is to inhibit T50 starter signal whenever you are cranking the engine if the shifter selector is not in parking or neutral position.  In that case if the switch is defective or the linkage not properly adjusted in length, you will not able to crank the engine
• Second function of that switch is to switch on the reverse light whenever the shifter is on the reverse position.  Again if the switch is defective, you will not he able to light up reverse lights when shifter is in that position

As you ca see from above, none of the functions of that switch has anything to do with a stalling engine.

But……. But….

There is a system associated with Mercedes mechanical fuel injected engines that increases iddle when-ever the transmission fluid pressure is low.  Low automatic fluid pressure is an indirect measure of an engine which is about to stall (quit working).  Remember in that time they had no ECU’s so they had no way to set a point electronically to decide on a RPM increase.

So the system works like this:

1. Whenever Intake manifold butterfly is closed (IDDLE SWITCH ON)
2. Whenever automatic transmission low pressure switch is ON

ACTIVATE THE IDDLE INCREASE SELENOID.

If the circuitry for the IDDLE INCREASE system in your car is not in good shape you will not have this RPM compensation needed in circunstancies as described in your post.

So your problem is related to that sub-system.

Best regards
L.Peterssen
Www.wiredoktor.com

[Lorsar]

Yes, that is my understanding of how the neutral safety switch works. 

I disconnected the cable and started the car in Park. Then I moved the switch to reverse by hand. This video shows the stall
 
https://youtube.com/shorts/nPL-9shwEFA?si=0N9FS_H6agMOQe0d

In this video I moved the shifter through p-r-n-4 to show that my css and pressure switches are working (with the nss cable disconnected)

https://youtube.com/shorts/nPL-9shwEFA?si=0N9FS_H6agMOQe0d

[BobH]

Hello, do you have emission control on your car?  The later neutral safety switches have another set of contacts, 6 pin that have some effect on the emission control and or fuel shut off.  I don't know the effect of an out of adjustment or faulty switch on the emission control but it was just a thought
 

[lpeterssen]

Dear Losar

Saw the videos posted in youtube.

Let me study your case once I finish a harness I am
Processing for a customer

Definitely everything is related to the parking/neutral reverse switch.

I see that you have the later style switch with terminals for the emission control system.

I have to re-study the emission control wiring diagrams.

Meanwhile at the fuel injection pump disconnect the terminals for the fuel shutoff solenoid and put some
Tape on those energized terminals.

It seems that your emission control system is not working properly and fuel is being cut.

Best regards
Lp

Best

[lpeterssen]

Dear Lorisa

The emission control sub harness, has two leads that pass through the neutral safety/switch to let the system know whenever the car is in DRIVE.

As far as I remember the emission control harness monitors these conditions in an analogic way to decide whether or not to engage the fuel shutoff selenoid in the back of the mechanical fuel injection pump:

• Iddle switch is closed (intake manifold) - des-aceleration process
• The shifter selector is on DRIVE
• The engine RPM are above a certain threshold, do not know exact figure, but guess is about 1,500 RPM. This RPM measurement is taken at coil negative post, and signal is sent to SPEED RELAY

IF all the above conditions are met at the same time, the fuel shutoff selenoid is activated, and therefore the car emissions are reduced.

The order to the fuel shutoff passes through that neutral / safety / reverse switch if you have the 6 pin version.

Try to momentary take out of the connector the two cables responsible for that function.

1. Pair of violet thick cables are the starter T50 signal
2. Gray/ yellow in combination with black/ red/ yellow are the lines for the reverse light
3. Green wires at the bottom of the connector are the shutoff signal. 

Take those out of connector momentarily to verify that your emission control system is acting weirdly and repeat the test moving the parking neutral, switch among all positions with linkage disconnected with car in PARKING as you did on the video.

If you are full member you can check out this link
https://www.sl113.org/wiki/Electrical/EmissionControlSystem

Best regards
Lp
Www.wiredoktor.com

[lpeterssen]

Dear Lorisa

Found on my stock a refurbished wiring harness for the emission control system on w113-280SL late.

That harness gave me some ideas of what is happening on your car.

In general terms your emission system should be connected incorrectly in many places.

Attached some pictures.

At the parking/neutral reverse switch is an iddle signal lace up.

In my opinion you have the position for pin related with reverse light inverted with the ones that lace up the iddle signal.  That first.

I will post a connector diagram for that 6 pin connector.

Also there should another misconnection somewhere in the emission system since it should activate only if RPM are above 1,500

Best regards
Lp
Www.wiredoktor.com

[lpeterssen]

Here attached the connector wiring order

[lpeterssen]

Another useful drawing

[Lorsar]

Removed the green/black wire from the bottom solenoid and no more stalling.  Also noticed that the wire on the top solenoid was disconnected and I found it taped up nearby (pink/blue).  I reconnected the bottom wire and it goes back to stalling.   
Leo, I attached a picture  of the wiring inside the connector.  For now, I will just leave it disconnected at the solenoid.  Thinking about it now, the NSS cable must have been broken since I owned the car.  I don't recall ever checking to see if the reverse lights came on.  My problem started only after replacing that cable when I replaced the shifter bushings about
a year and a half ago.

[lpeterssen]

Dear Lorisa

I am very glad for you that you found the culprit for the stalling condition on the fuel shutoff selenoid.

The pictures posted by you for the 6 pin parking/neutral & reverse switch + iddle signal switch, show that cables are on the correct position.

Nevertheless now that we know that your emission control system is sending erratic signals to the fuel shutoff selenoid, the next step would be tompost pictures of the components installed on the FRONT LEFT HAND FENDER to see if we appreciate something unusual there.

For time being keep fuel cutoff selenoid disconnected.

Best regards
Eng. Leonardo Peterssen
Www.wiredoktor.com

Ps : will suggest the administrator To move this topic/ thread to the electrical & instruments section, as the root cause was there

[Lorsar]

Left side relays

[lpeterssen]

A better photo of this area is needed, removing the relays from
The brackets to make sure they are the right type of relays for the emission control system

Best regards
Lp
Www.wiredoktor.com

[Lorsar]

Attached are some photos.  It seems like the smaller relay by the coil may have been fiddled with by a previous owner.  The wires fell out when I popped the cover off so I am not sure they are in the right position.

[lpeterssen]

Send the photos in high res to my personal email to help you out.

At first sight it does not appear to be the regular emission control harness I am familiar with

The standard emission control
Harness has much more pins in that area.

The relays shown are standard relays

So this will be a learning case for me

Best regards
L.peterssen
Www.wiredoktor.com

[lpeterssen]

Dear Larisa

Attached a drawing that may explain your early emissions control scheme’s.

This is what I think your system does, which is really basic, and that is why mercedes in later models added more redundancy so that system does not engage accidentally the fuel shutoff selenoid as is your case.

So let’s start.

1. IDDLE SWITCH SIGNAL.  The iddle switch at intake manifold receives on one side a T15 signal coming from main fuse box, which passes through it whenever the throttle intake butterfly is fully closed, letting the system know when the user is not pressing the accelerator pedal.
2. IDDLE SWITCH SIGNAL GOES to PARKING/NEUTRAL/REVERSE SWITCH.  The green cable coming from iddle switch as a positive signal passes through this switch which has continuity on the pins where the green wires are attached whenever the car is in any gear except PARKING or NEUTRAL. 
3. IDDLE SIGNAL, then goes to 4 pin relay in your photos, feeding the 86 port trigger signal.
4. 4PINNRELAY. has 2x black/red cables on port 87.  One of them comes from T15 circuit at main fuse box.  The other is a lace up for the 5 pin relay, which needs a (+) signal on port 86.  This relay has continually ground on pin 85, brown cable.  The port 30 is used as an OUTPUT port which brings main power to the same port at the 5 PIN RELAY.
5. 5PIN RELAY, is used as the last check previous to sending the activation signal to the fuel cutoff selenoid.  The way on which the cables are connected, means that signal will pass to fuel cutoff selenoid allways IF NOT TRIGGERED the relay.  The signal used to trigger this relay is the NEGATIVE SIGNAL PRODUCED BY AUTOMATIC transmission low pressure switch (-).  So, if the transmission low pressure switch which has a GREEN/RED cable coming from it produces the NEGATIVE SIGNAL, this 5pin relay will INHIBIT signal to fuel cutoff selenoid, in the case that previous system conditions are met. (IDDLE SIGNAL ACTIVE+CAR in any gear but PARKING or NEUTRAL)



So check with a multimeter that connection scheme is as I figured it out.

The second thing to check is if your transmission low pressure lead (GREEN/RED) is connected in the appropriate port at transmission.  It should be now be connected to something that is sending a CONTINUOUS NEGATIVE SIGNAL, and that explains the problem you are having.

Best regards
Eng.Leonardo Peterssen
Www.wiredoktor.com

[lpeterssen]

Looking again at this diagram, it matches your case.

What I think is wrong, is that the 4 pin connector should matched to a special device called “drehzahl regler” marked in red on attached photo.

So instead of a standard 4 pin relay you need that device there. Part 0332010001

Best regards
Lp
Www.wiredoktor.com

[Lorsar]

The larger relay is probably that speed switch, it has some wires attached in the back.  I'm away for a few days so I'll post a picture when I get back.

[lpeterssen]

Dear Lorisa

The smaller relay with only 4 pins is the one we should be looking for its part number. 

The larger one for which you already send pictures  is a standard NC / NO relay. That goes on the 6 pin connector and its correct.

So the relay I suspect is the wrong one is the one that connects to the 4 pin plug.

Beat regards
Leo

[Lorsar]

No the previous picture is of the smaller relay.  The 4 pin connector attaches to the bigger one

[Lorsar]

Pic from the other side

[Lorsar]

And I found this thread

https://www.sl113.org/forums/index.php?topic=4257.msg26479#msg26479

[lpeterssen]

Dear Lorisa

Also think that the speed relay is not an essential component as stayed on the link posted above.  If you double check that you have the low pressure signal connected which comes from the automatic transmission, and that the speed relay corresponds to the part number shown on one of my previous post wiring diagram, then we can conclude that your unit is defective.

In that case the best course of action would be to just unplug the 4 pin connector to that relay and place a NOTE “DO NOT RECONNECT” on it.

Having the fuel cut off cable ends disconnected with shrinking tubing on them will be also advisable if someone by mistake re-connects speed relay again.

Best regards
Leonardo Peterssen
Www.wiredoktor.com