The engine revs fine to 4.5K then i can hear a strange but not loud sound from the engine.
I can hardly get it to rev more than 5K.
It sound like a leaking sound Fuzzz.
I have changed a lot of things which have helped me on other problems.(OVP,COIL)
I also do regular service air filter,plugs and the others.
The fuel filter is not changed.
The lambda works fine.
My first thought was some kind of fuel delivery problem.
But i have kind of ruled that out because my engine starts perfectly in cold wheather.
Could it be the valve guides or the timing chain.
Have anybody had this type of problem ?

Pelle 300E 4M -89

I'd guess a clogged catalytic converter.

I would definitly change the fuel filter since it hasn't been changed. I had a similar problem, my car started fine, but everything went back to normal after a new fuel filter and spark plugs. Fuel filter might not be your problem, but it's definitly worth a cheap try, and it's good maintenance!

Well, Pelle, if you are reaching 5000 rpm, then it's unlikey that it's fuel delivery. You are near the top of the safe rpm range for the M103 motor. You didn't mention whether or not the engine seemed to be breaking up, ie. go stop go stop or perhaps a high speed surge. The sound you are hearing could be a high pressure exhaust leak, associated with high engine speed, which might just point to an obstructed cat. Has the car burned a lot of oil,has it had valve guides,seals done. What is the mileage on the engine? Another thought is the distributor cap and rotor. Have those pieces been replaced or checked?

it is a high speed surge,the car has 150K.
I haven´t changed cap/rotor.
The guides and the seals have not been done any work on.
I have however checked the rotor/cap and they look okay but i think i will change them anyway.
I had some trouble with the coil and the wire from it to the cap but i have changed them.(misfired)
There are some tapping sound from a bad lifter that comes and goes.
I recently have done an emmission test that was okay.
The high rpm range is not used frequently.
The oil change is done every 6K and i have to fill from low to high after about 3-4K.

Pelle 300E 4M -89

I have finally replaced the cap and rotor.
No difference in the high rpms.
Since i have changed and inspected every electrical component in the ignition system i have to rule it out.

Is it possible that the guides/seals can begin to vibrate or something on high rpms ?

What happens if a/the fuel injector(s) wears/clogges up.

If i have a clogged up cat and it is the leaking that i can hear - where is the leak ?

The sound is coming more from the driver side of the engine.

Well , i have to fix this problem because my wife is complaining about it.

Pelle

wow! your wife really drives fast. i cruise at about 4000 rpm
max which is equivalent to 140-150 kms/ hrs. oh, i see you
are from sweden, obviously different driving speed standard.

i' ll stay tuned to what may be your problem, since i suspect
i may have a clogged cat, too!