[ikarin]

Do any of you perhaps know how the rpm limiter works on Mercedes w140 400 SEL made in 1991?

When the engine reaches its limit (5500 RPM) it gets completely cut off from the accelerator, instead the limit regimen should start working. Probably the injectors get left without electricity, i.e. it shuts them all.

 

[Mercedes Mechanix]

Do any of you perhaps know how the rpm limiter works on Mercedes w140 400 SEL made in 1991?

When the engine reaches its limit (5500 RPM) it gets completely cut off from the accelerator, instead the limit regimen should start working. Probably the injectors get left without electricity, i.e. it shuts them all.

OK, usually the condition you are describing is due to an issue with an air cleaner break down or Mass Air Flow (MAF) issue.... or an issue with the Throttle Actuator (ETA). But as a further simplex overview of an RPM limiter... see the simple drawing below:

Showing the basic ignition including an after market Rev Limiter (Engine Governor Assembly). The Rev Limiter will monitor the "DIST" terminal on the coil. The discrete circuit design within the Limiter picks up the ignition pulses and "calculates" (without a microprocessor!) the engine RPM. When the Rev Limiter determines the RPM is greater than the limit (say 4K or 4.5K on smaller engine) it switches (using solid state technology) a load onto the "DIST" line. The power is shunted away from the "DIST" terminal to ground. This causes a misfire or, actually, a no fire. Grounding this terminal prevents the high voltage build up and release from the secondary coil (HV) to the center distributor cap lead for the spark plugs. Maybe you have seen or heard of the same effect caused by one or both points in the distributor stuck closed or a bad distributor capacitor (condenser) providing a path to ground as well. All of these are extremely basic fundamental methodology for control of an RPM excess and ONLY the above design is/was used in lieu of control of fuel... as when the loss of RPM occurs with the REV Limiter above.... the vacuum will change and of course the fuel rail vacuum fuel control valve will normally control the drop in fuel supply automatically. Therefore.... control of ignition pulses is the more effective method of engineering design! If any desire is wished to withdraw the use of/or by-pass.... the design of this component is of assistance with protection of shift points and power plant needs. If further criteria required... drop a message and will have a Qualified Technician assist with individual requirements.

Robert :thumbsup: