Violent vibration in P or N at 4000rpm - Drives fine -Help Please!
 

I have a strange problem with my 1993 300CE Cab w/91k miles.

The engine runs as sweet as can be,,, idles perfect, sounds great,,, never overheats,, doesn't burn a drop of oil. Engine harness has been replaced by PO and looks like new.

When I rev the engine in PARK or NEUTRAL (hot or cold, doesn't matter), there is a violent shudder from the engine at EXACTLY 4000rpms. The engine is shaking from side-to-side fairly violently.

The engine does not shake when the car is driving, even at high revs. I just took it out and drove the car to near redline in 1st, 2nd & 3rd gear,,,, it drives just fine. Suspension is fine,,, braking is fine.

Today may have been the first time I've ever revved it so high in Park,, so have no idea how long this issue has been present.

Any ideas?

Thanks in advance.

Probably your rev. limiter cutting out.
M-B does not see the need to rev an engine in N or P above 4000 rpm.

Agreed. Rev limiter. My 93 does the same at 4000 rpms (while in P or N).

Sheez,, thanks, a load off my mind!

Why the violent shaking though? Even way back in 1993 I would have thought the car's brain could be programmed to simply stop the car revving over a certain rpm.

The computer shuts down " random " cylinders, by killing the fuel.
Quit doing that ! :D

ECU drop a couple of cylinders at 4k when in P/N to protect the torque Converter from damage at no load condition.
Normal safety limit cut-out........
If you go down the road faster than 8 MPH and put it in N , you will see that the vehicle speed sensors over-ride the Saftey Limit and you can rev past the 4K.. but don't tell your kids that.

>>Quit doing that ! :D


Hehe. I was just trying to warm the engine up in the garage after fitting a new expansion tank cap.

It was raining outside :)

Thanks again.

<<The computer shuts down " random " cylinders, by killing the fuel.
>>

Indirectly.....the ECU actually kills the ignition , but that in turn kills the gas by default...
Anytime an ignition misfire occures on an HFM/SFI system, the ECU defaults the signal to the injector of the mis-firing cylinder.. raw gas cat emmissions protection mandate.

Thanks for the info. Arthur,,, very interesting.

Seems I was panicking over nothing. I guess my 89 260E doesn't have a limiter,, I just checked and can rev the piss out of it in park & Neutral.

Yes, you 260 does not have HFM/SFI Engine Management, which is full electronic.

Why you would want to rev an engine to 4,000 rpm and beyond in neutral is beyond me!

Steve

Teenage Hole Shots !!!!!!
There was a long hill up the road from my farm and the kids would coast backward down the hill , floor it in N and then drop it into gear....lay rubber for almost a full minute...I would crindge everytime I would hear them..those poor parts.!!!!

'Can I borrow the car tonite , Dad ??? ..Just goin' cruisin'.. "

That really didn't add anything useful to this thread. As I already explained, I was trying to warm the engine up (to test the seal on a new coolant expansion-tank cap).