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  #1  
Old 12-03-2003, 04:07 PM
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Join Date: May 2003
Location: Dallas, TX
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300CE- Idle & cruising RPM? and ASR?

Hello you all good people out there.

Have a 92 300CE. The idle and cruising rpm are as follows:

idle = 600-700 rpm
40mph = 1,800-1,900 rpm
50mph = 2,250-2300 rpm
60mph = 2,900-2950 rpm

They seemed to be high compared with my other Japanese cars. Is this normal? Secondly, what is an ASR and what does it do. Does the ASR affect rpms or transmission gear changes?

Thanks a bunch.
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  #2  
Old 12-03-2003, 09:46 PM
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Join Date: Jul 2000
Location: Seattle WA USA
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The coupe has a fairly low final gear ratio (high numerical) (3.06:1) compared to most MBs and I suspect many other cars.

ASR (automatic slip regulation) is a form of traction control, but it is not what we generally think of as Limited Slip Differential.

I'll briefly relate what the Owner's Manual says. More info is contained in Brake System job 42-0800.

The acceleration slip control (ASR) will engage at all vehicle speeds, if one or both drive wheels begin to lose traction and spin due to excessive acceleration. While engaged, the yellow function indicator in the speedo lights up.

With the ASR engaged, the brake is applied to the spinning drive wheel until it regains sufficient traction. If both drive wheels lose traction and spin, the brake is applied to both wheels and simultaneously, engine torque is limited.

As traction on the road surface increases, the allowable engine torque also increases again and the brake is no longer applied to the drive wheels.

As I mentioned, there is a brake moment control circuit and a drive moment control circuit. The three control ranges of the ASR are:

A. Control mode with one skidding drive wheel and at wheel speeds < 40 km/h. The allowable slip threshold is higher for the Drive moment control than the Brake moment control, so the brake is applied to the slipping wheel. If it still slips too much, the Drive control comes in and retards the electronic accelerator control.

B: Control mode when both drive wheels skid or at a speed < 40km/h. Drive control has priority and retards accelerator. If wheels still skid, brake control is added.

C. Control mode when cornering at speeds between 20 km/h and 120 km/h. Depending on lateral acceleration, Drive moment control comes in sooner than for mode "B".

In addition, there is a console mounted switch, "snow chain" switch, that, when activated, increases the speed threshold of when each mode will start to engage. This "buffers" the ASR a bit and lets some slippage occur when first starting out from a stop.

There is no traditional locking differential; the asymmetrical braking independently applied to the rear wheels provides this function, sort of.

...probably more than you want to know.
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Steve
1992 300CE Sportline Sophie
1990 300E Emma - in the family
1979 240D Josephine - sold, but not forgotten
2004 Pacifica AWD
http://web.mac.com/dakota/Mercedes/Home.html
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  #3  
Old 12-04-2003, 03:49 PM
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thanks dakota,

you must be a univeristy professor. since you also own a 92 CE , are the rpms on my car appear normal? if not, what is needed to correct. thanks,
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  #4  
Old 12-04-2003, 07:07 PM
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Those numbers are consistent with my car.

glenmore
1991 300CE
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  #5  
Old 12-04-2003, 10:27 PM
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they are consistent with my 300SE. also note that Mercedes tachs tend to err 100-200 rpm above actual values
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  #6  
Old 12-04-2003, 11:08 PM
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Not a professor, I don't even play one on TV. I just summarized stuff out of the manuals. I didn't check my exact RPMs but as glenmore says, those rpm numbers seem consistant with my car also.
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Steve
1992 300CE Sportline Sophie
1990 300E Emma - in the family
1979 240D Josephine - sold, but not forgotten
2004 Pacifica AWD
http://web.mac.com/dakota/Mercedes/Home.html
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  #7  
Old 12-04-2003, 11:11 PM
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Dakota, can you explain an ASR mode when the engine seems to run normally i.e. no loss of power, just the accelerator pedal drops back?? l have experienced this often. In earlier episodes l noticed a drastic drop off in engine poer, i.e. engine timing seemed way off.
thanks.
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  #8  
Old 12-04-2003, 11:48 PM
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Join Date: Jul 2000
Location: Seattle WA USA
Posts: 469
That sounds like the "limp home mode". The ASR system is very complicated (read: I don't really know how it works). I've gone into limp home mode once, and that was for about 30 secs. I shut off the motor and restarted...never have had the problem again (~25K miles ago).

I guess if i had problems with ASR, the first few things I would do is the easy stuff:
1) disconnect the battery for a couple minutes and reconnect...I've heard of one person who did this and it worked; apparently it resets the system.
2) Another 'no-cost' thing I'd do is make sure that the entire linkage (ie, all the little ball/socket connectors, etc) are absolutely clean and lubed with ATF.
3) Then I would make sure that all the axle sensors and various relays and connectors are clean and not damaged.

There are then several tests that the manuals go thru to check the system, including adjustments. The ASR system has at least 15 electronic/electrical components, 5 hydraulic components and one mechanical component. It's tied into the ABS system and the Tempomat cruise control system.

I believe you would be wise to get the manuals and understand the system more before you dove into it. Or you may want to take it to someone who understands it and has worked on them before. There are expensive parts in there.
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Steve
1992 300CE Sportline Sophie
1990 300E Emma - in the family
1979 240D Josephine - sold, but not forgotten
2004 Pacifica AWD
http://web.mac.com/dakota/Mercedes/Home.html
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