3.8L throttle cutoff speed actuator - The Unofficial BMW M5 Messageboard (m5board.com)

SteveC · 10th August 2000, 00:32

Hoping a knowledgeable 3.8L owner in Europe can shed some insight on the "cutoff speed" actuator.

My, I believe, is on the blink. Periodically while driving, I get a clinking noise which seems to emanate from under the dash, yet can be felt in the steering column. Then, shortly after the noises stop, the accelerator pedal resistance seems to disappear momentarily, with the sensation that unless you further depress the pedal about half an inch or more, there is no throttle control at all - like there is a complete dead spot in the linkage. Then all of a sudden, I think the actuator re-engages and because the accelerator is depressed slightly to compensate for the momentary dead spot, the engine revs up and the car zooms forward. Very spooky feeling.

So, exactly what is the purpose of the cutoff speed actuator? I assume it's part of the over-rev protection.

Is there any harm any disconnecting the actuator from the control box?

Any insights would be greatly appreciated.

BIMMER NUT · 10th August 2000, 08:15

HEY STEVE:
HOW YA DOING?? I HAPPEN TO DISCONNECT MINE AS WELL AND HAVE NO PROBLEMS THAT ARISED FROM IT. I'VE HAD MINE DISCONNECTED NOW FOR A COUPLE OF 1,000 MILES. FROM WHAT I'VE HEARD IS, THAT ONLY THE EURO SPEC M5'S HAVE THIS KICK DOWN ACTUATOR. I KNOW THIS ISN'T EXACTLY WHAT YOU WANTED TO HEAR BUT IT'S A LITTLE INPUT ANYWAY.

PAUL

Alan Archer · 26th August 2000, 12:03

Quote:

Originally posted by SteveC:
Hoping a knowledgeable 3.8L owner in Europe can shed some insight on the "cutoff speed" actuator.

My, I believe, is on the blink. Periodically while driving, I get a clinking noise which seems to emanate from under the dash, yet can be felt in the steering column. Then, shortly after the noises stop, the accelerator pedal resistance seems to disappear momentarily, with the sensation that unless you further depress the pedal about half an inch or more, there is no throttle control at all - like there is a complete dead spot in the linkage. Then all of a sudden, I think the actuator re-engages and because the accelerator is depressed slightly to compensate for the momentary dead spot, the engine revs up and the car zooms forward. Very spooky feeling.

So, exactly what is the purpose of the cutoff speed actuator? I assume it's part of the over-rev protection.

Is there any harm any disconnecting the actuator from the control box?

Any insights would be greatly appreciated.

Hi my friend !!
I am the man from europe with the 3.8 !!
Sounds like your limiter is playing up,
Look under the bonnet(hood) and locate the extra cable next to the main accelerator cable...it is held on by a puny white clip.

Take the ***** off !!
I bet the car will run normally now.. however if the noise gets to you, you'll have to get it checked out in the garage.

ps...this also removes the top speed limiter and lets you hit the rev limiter in top...enjoy!.

SteveC · 4th December 2000, 15:56

I solved the problem this weekend.

The system in question is officially called "Top Speed Regulation" for the S38 B38, and has an internal BMW designiation of "VMX". This system consists of two components. The first one is the electro-mechanical throttle actuator which controls the throttle linkage. This part is visible on the left side (driver side) engine compartment, and has a connecting plug fitting immediately forward of the diagnostic plug. The second part is the VMX control module, which is located in the E-box.

I hooked up my Modic and did a diagnosis on the control module. The module returned gibberish characters and wouldn't return proper identification to the Modic, making is highly suspect as being defective. I installed the new control module and redid the diagnostic test. This time, the read-out was perfect, and I was able to activate the actuator and cycle it with the Modic. All operations were within specification, and contrary to my initial guess that the problem would be with the actuator, it turned out to be a defective control unit.