Please!!Need tech advice on strange problem
 

I have seen alot of great advice shared on this forum and I hope someone might have be able to help me on this one. Thanks in advance for any suggestions!

I have a strange problem with my '88 560SL that I need some advice on.

During normal driving (below 4,000 RPM) the engine runs strong and accelerates smoothly. But on occasion (like most of the time) if I really get on it say from 60 mph it will downshift to 2nd and the tac will jump to about 4000 rpm's and it's almost like the timing gets retarded or the fuel flow is reduced and there is a slight vibration coming from the engine. When this happens it will continue to accelerate to redline but at a reduced pace. When it shifts to the next gear and the rev's drop below 4000 rpm's it begins to feel strong again. It's almost like a governor or rev limiter kicks in slightly. I can also cause this to happen if I put it in a lower gear and gradually accellerate past 4000 rpm.

I bought the car about 6 months ago and have already replaced the following:

Sub frame mounts and motor mounts
rear flex disk
both fuel pumps and filter
idle air valve and hoses
new copper spark plugs, rotor, disributer cap, plug wires and air filter
air distributor hoses that connect to the fuel injector's.
timing chain and tensioner

I have also checked for a vaccume leak and ther doesn't seem to be any.

Is it possible that a coil or EHA could cause this????
Any help or suggestions would be greatly appreciated. Thanks in advance...

any ideas???

four suggestions
1) is air filter clean?
2) have you changed the fuel filter?
3) run some injector cleaner in the fuel
4) check the OVP relay - I believe it also is a rev limiter (doubt if problem - but maybe)
I take for granted that your spark plugs and distributor cap and rotor are good. If all the above does not help - check the output of your coil. - sorry I lied - FIVE suggestions:D ;)

Thanks Moedip for the suggestions, but the air filter nad fuel filter are new and I have run injector cleaner through several times. The fuese on the OVP is new also. I have considered the OVP, but it doesn't exibit any of the common symptoms of a bad OVP. It idles smooth and no ABS light. Is there a way to check the OVP. I don't want to just start swapping parts. The strange thing is that it run great around town and only has this problem above 4000 RPM. I may have been mis-leading when I said there was a slight vibration coming from the engine when this happens. It is more like change in the harmonic frequency of the engine.
weird huh....

Have you checked the dist. cap and rotor, plugs and coil - at high rpm they have to perform flawlessly. Check for a crack inside your dist. cap - stranger things have happened on new product. Have you metered your spark plug wires - they should read- I believe - 700-1200 ohms. They should all be about the same in resistance. Like I said - could be a bad new wire - just cause they are new - doesn't mean cannot be bad. - Is you idle nice and smooth?

As stated in my original post all those items are new. thanks

???

Mine does something d¿similar to that, i was thinking O2 sensor

How about a partially plugged catalytic converter.

Thanks for the suggestions.

A blocked Cat or O2 sensor are both on my list of suspects. Any idea on the best/quickest way to test to be sure?? I guess I could disconnect the O2 sensor and see if there is a change...I was also thinking that the coil may be breaking down. Does that sound possible?? It almost feels like the timeing doesnt advance..
What is really strange is that it runs so strong right up to 4000 RPM, and sometimes will go all the way to redline and seem OK. Thanks ...

a partially plugged catalytic converter, not in my case I don't have one, I would say the O2 sensor, don't you have to replace it after so many milles any ways?