Manually into limp mode...?

[Rud]

Is it possible to invoke the “Limp Mode” manually?

The reason: I distribute a satellite tracking system, where I can track e.g. stolen or hijacked cars. This device can be told to set a couple of switches/relays just sending a SMS to the unit, to lock or unlock. Since its not legal to stop the car completely I wonder if I can set the car to limp mode through one of theses switches, so the person can only drive it with 40km/h or so.

Today the system works, so when you get an alarm, you get a call on your phone, and you can follow the cars movement on a web map. The unit transmit the coordinates via GPRS, and when this is not available via SMS messages. You get a position every 200m or every 2nd minute. But I guess it would be an additional feature if you can reduce the speed of the car so its hard for the person to get away with it or end up in a accident crashing the car, because of high speed driving.

I guess this is something many Mercedes cars can benefit from, if possible.

[ctaylor738]

A very interesting idea.

The trouble is that limp mode is different depending on the model. In the mid-80's cars (380/560SL), limp mode just means that lamba mixture control and maybe electronic idle are shut off, along with ABS, but I am not aware of a restriction on speed.

On the newer cars, you might be able to trigger an OBD fault that would accomplish your objective.

Suggest posting this on the main tech forum.

[David Langsam]

My 560sl has a limp home mode? How does it work?

David

[dkveuro]

Would be possible in f'ly by wire' control. Command the throttle to stay at idle.

Even in a carb'd engine you could slow down the fuel flow to a point where it starts bucking.

How about an exhaust retriction flap choking down the engine over a few minutes?

[Roncallo]

Originally Posted by David Langsam

My 560sl has a limp home mode? How does it work?

David

It does not have a limp home mode as you know it. It just has a feature any computer controled car had back in the early days. When a computer fault is detected, the check engine light comes on and the computer reverts to open loop mode (no lambda or feedback control) engine just runs on predetermined settings just like it does before being fully warmed up and essentially the same way your early fully mechanical CIS injection systems worked.

John Roncallo

[smallblock450sl]

I'm going to make this short. Don't go into "Limp mode" "Stop the car!" Shut off the fuel or the ignition systems! Do you realize how much damage can be caused at 35/45 mph ? Car damage/personal property damage/ or worse "loss of a life". You have a great start. Listen to other suggetions and go from there. My last "soapbox reply"... I would reather have my cars put into a "Rock Crusher" than used as a deadly weapon ! Just my opinion.

[Rud]

Originally Posted by smallblock450sl

I'm going to make this short. Don't go into "Limp mode" "Stop the car!" Shut off the fuel or the ignition systems! Do you realize how much damage can be caused at 35/45 mph ? Car damage/personal property damage/ or worse "loss of a life". You have a great start. Listen to other suggetions and go from there. My last "soapbox reply"... I would reather have my cars put into a "Rock Crusher" than used as a deadly weapon ! Just my opinion.

I’m not sure I understand you correctly. Do you mean it’s better to stop the car, then having it running at 25mph, which I understand, is the maximum in limp mode on a R129?

First of all, it’s illegal in Europe to force a complete stop unless it’s necessary due to an accident or malfunction. I would also imagine that it’s safer to slower the speed on the highway, so that the driver can get off the road, as soon he discover that he can’t force the car to run faster. The speed limit in this country is 80mph on highways, 50mph on open roads and 30mph within the city boarders. This means that a car thief will probably take a run instead, knowing, if he continues driving at this low speed, he would probably get caught, either because some police car would find his slow driving suspicious or the satellite tracking will lead them to him.

Yes of cause in desperation, he might crash the car. But I guess this is better then killing people because he tries to escape at a much higher speed. We have seen too many of these hazardous driving with innocent people getting killed. 25mph can kill, but 80mph and more will defiantly kill!

Thank you for feedback. I will investigate the OBD option and ‘fly by wire’ option. I wasn’t aware that the R129 had ‘fly by wire’.

[dkveuro]

Originally Posted by Rud

................................

Thank you for feedback. I will investigate the OBD option and ‘fly by wire’ option. I wasn’t aware that the R129 had ‘fly by wire’.

The throttle has an auxillary throttle control system over ride, callled the ASR.
This system shuts off power to the engine when the managment system detects rear wheel acceleration slip.
These systems malfunction sometimes...the wires crack/burn or the potentiometer track goes bad, in which case the engine will only idle and the ASR light will illuminate.

Satellite tracking can activate this system with the correct software and hardware as I am told.

[JimF]

Originally Posted by Rud

I’m not sure I understand you correctly. Do you mean it’s better to stop the car, then having it running at 25mph, which I understand, is the maximum in limp mode on a R129?

First of all, it’s illegal in Europe to force a complete stop unless it’s necessary due to an accident or malfunction. I would also imagine that it’s safer to slower the speed on the highway, so that the driver can get off the road,

If you know how to 'manipulate' the accelerator pedal and have limp-home (L/H) experience, you can go 50-60 mph very easily.

I'd vote for the smallblock's idea since driving with a L/H mode is dangerous if you don't know what you're doing.

[Rud]

Originally Posted by JimF

If you know how to 'manipulate' the accelerator pedal and have limp-home (L/H) experience, you can go 50-60 mph very easily.

I'd vote for the smallblock's idea since driving with a L/H mode is dangerous if you don't know what you're doing.

From all the feedback I agree, shutting off the ignition or the fuel pump, is probably the best way. No one will ever find out if the car thief has done something that makes the car stop, or it’s a relay controlled by the satellite tracking/alarm system that stops the car. Anyway, the ticket I guess is cheap compare to loosing or having you car crashed.

Still if someone can tell me a way to lower the speed to less than 25mph not invoking the L/H mode, it would be great.

Regards,

Rud

[Mike Miller]

Rud,
Continue with your L/H idea. Our USA forum friends (I am one) are correct. I too would rather have the car disabled via the system than allow it to limp around town. Having said that, I have also lived off and on in Europe for many years. You can not commercially market a product that is going to break the law. Is the law good or bad? Who knows? You wouldn't want the guy doing 240 k/hour on the Autobahn and have the engine quit!