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This W126 has a problem that we cannot solve. These cars it appears are limited to 4000rpm when revved in neutral. This limit however is permanently in place and the motor is limited to 4000rpm at all times. Any suggestions of the cause will be appreciated.
 

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Hi Richard. Where are you based please? I'm thinking not in the US, too narrow out down. Since that model and year would be rare there.

If you have a European 500SE from 92, that is one lovely motor you have there. High compression and all.

The rev limiter is in the fuel pump relay. I don't recall either of mine being limited to that in neutral. I would check you have the correct part number in there and then try a different one.
 

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Hi Richard. Where are you based please? I'm thinking not in the US, too narrow out down. Since that model and year would be rare there.

If you have a European 500SE from 92, that is one lovely motor you have there. High compression and all.

The rev limiter is in the fuel pump relay. I don't recall either of mine being limited to that in neutral. I would check you have the correct part number in there and then try a different one.
Thank you.
Makes sense, we will try it.
I am in South Africa, in a little town called St Francis Bay, not far (+/- 68 miles) from Port Elizabeth.
 

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Thanks. good luck, and welcome by the way.

The FPR is no longer available from MB. So sometimes I think the wrong one gets fitted and so on. Do beware of cheap aftermarket ones as they can go as far as to catch fire. Although some people get lucky and they work OK.

The kickdown function of the transmission is also controlled via this little box.
 

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why are u revving to 4000 anyways
 

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Discussion Starter #7
Thanks. good luck, and welcome by the way.

The FPR is no longer available from MB. So sometimes I think the wrong one gets fitted and so on. Do beware of cheap aftermarket ones as they can go as far as to catch fire. Although some people get lucky and they work OK.

The kickdown function of the transmission is also controlled via this little box.
Hi Ianrandom,
Mechanic called last evening. You were spot on and the problem is the FPR. Replacements are available from a dealer in Johannesburg.
Many thanks for your input.
 
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