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  #1  
Old 09-14-2018, 05:57 PM
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S124/M104 rev limited at 4K while driving

I tried to search as much as I could so I didn't have to make a post but couldn't pinpoint a solution.

I know the rev limiter kicks in at 4K for park and neutral, however it limits most of the time under heavier acceleration in D/3/2.

I was told it could be the inhibitor switch or NSS, is there a way to bypass it or adjust it?

Is there another solution or the the problem lying elsewhere?

Thanks in advance

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Old 09-14-2018, 05:59 PM
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PS, I should also note that the upper wire harness, ETA, and e-gas computer have all been updated to 1998.
Also I have CEL and ABS lights on that have not been scanned yet.
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Old 09-14-2018, 07:37 PM
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I'd find out what the CEL is lit for, it may be a clue.
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Old 09-14-2018, 08:04 PM
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Not sure what the NSS could have to do with it.

What vehicle?
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Old 09-14-2018, 09:14 PM
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A buddy just had this issue until the other day on his M104 equipped W202. ABS light was on, replaced sensor, and neutered rev limit went away.
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  #6  
Old 09-15-2018, 12:42 PM
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I was told it could be the inhibitor switch or NSS, is there a way to bypass it or adjust it?------------this is completely wrong. the nss in a benz acts just like any other. allows the starter to engage when the shifter is in p or n---nothing else.

only place for a rev limiter is here-

https://www.ebay.com/p/MERCEDES-BENZ-300-SL-MAS-Control-Unit-Module-0125454832/1022976863

it controls spark and fuel with the ecm. not saying it's the problem, just needs more diagnosis. check engine light on? it's tough to tell, we can't see under your hood, the light here sucks. good luck, chuck.
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Old 09-15-2018, 02:52 PM
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Quote:
Originally Posted by 244brick View Post
I know the rev limiter kicks in at 4K for park and neutral, however it limits most of the time under heavier acceleration in D/3/2.


I was told it could be the inhibitor switch or NSS, is there a way to bypass it or adjust it?
There may very well be a problem with the NSS; as you noted, when out of gear (P & N) revs are limited to 4K. If the limiter continues to receive a "Neutral" signal from the NSS even when in gear, the revs will be limited to 4K, the "Neutral" limit.
In some models, Mother Benz has used the NSS to signal the idle speed controller to provide a lower setting when in gear.
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Old 09-15-2018, 06:22 PM
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[QUOTE=porkface;3843465]I was told it could be the inhibitor switch or NSS, is there a way to bypass it or adjust it?------------this is completely wrong. the nss in a benz acts just like any other. allows the starter to engage when the shifter is in p or n---nothing else.

Incorrect.

NSS has a resistor circuit for both gear selection and ASR control.

It is also part of the Rev limit circuit.

PS

An easy test for rev limit circuit is to look for rev limit of 4K in N/P, then drive the car above 18 mph and put the selector in N...rev the rpms and if the circuit is OK, the rev limiter will not be in effect.

That is why a wheel sensor will effect the circuit...the ECU is looking at wheel rpm for rev limit paremeters when in gear.



The main reason for rev limit is to protect the torque converter In N/P, but is also in circuit in lower gear/rpm ranges.
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Old 09-15-2018, 06:27 PM
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Did not know that about the NSS. What a fount of knowledge is this forum.
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Old 09-16-2018, 07:36 AM
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I found what I believe to be a wheel speed sensor unplugged. How do I reset the ABS or ecm? Disconnect battery?
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  #11  
Old 09-17-2018, 11:27 AM
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[QUOTE=Arthur Dalton;3843505]
Quote:
Originally Posted by porkface View Post
I was told it could be the inhibitor switch or NSS, is there a way to bypass it or adjust it?------------this is completely wrong. the nss in a benz acts just like any other. allows the starter to engage when the shifter is in p or n---nothing else.

Incorrect.

NSS has a resistor circuit for both gear selection and ASR control.

It is also part of the Rev limit circuit.

PS

An easy test for rev limit circuit is to look for rev limit of 4K in N/P, then drive the car above 18 mph and put the selector in N...rev the rpms and if the circuit is OK, the rev limiter will not be in effect.

That is why a wheel sensor will effect the circuit...the ECU is looking at wheel rpm for rev limit paremeters when in gear.



The main reason for rev limit is to protect the torque converter In N/P, but is also in circuit in lower gear/rpm ranges.
that's my fault for not consulting alldata before answering. i've not had to deal with a similar issue and shot from the hip, right into my foot. gonna look at the 124 cds and maybe learn something. thanks, chuck.
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  #12  
Old 09-17-2018, 01:57 PM
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nss

<< gonna look at the 124 cds and maybe learn something. thanks, chuck.
>>>

You're Welcome

... and as you suggest, the earlier Benz NSS was N/P starter lockout only, but all later HFM/SFI , full electronic engine management chassis use the NSS on several other modules..specially the EA and wheel sensors ones [ abs/asr]

The tip off is one will note there are several fault codes from EA and Ignition modules [ 8 and 14] that list the NSS as possible fault ..because it is those circuits/
Same goes for the brake lamp switch...EA/CC/ABS/ASR all use the secondary contacts on the brake sw. in their circuits...meaning the brake sw is another one of these dual circuit devices and goes beyond just lighting the brake lamps.

It is all easily seen in the schematics for later 124's..........

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