Dear All,
I have recently acquired a 2004 E55 wagon here in Dubai which was imported from Japan few years back. When I got the car I wanted to test it at higher speed to see if any issues, when I reached 180-200kph the engine seemed to be limited and when I was slowing back down to less than that I could feel that I had no supercharger boost anymore, to get it back I had to slow down the car to 30-40kph and it would re-engage again.
Is this a normal issue linked to some Japanese speed limit within the ECU? OR there is an issue with the supercharger clutch?

Many thanks

You'll need to monitor your intake air temps with a scan tool and see if they are getting too high.

Tiime to upgrade the heat exchanger and get a new pump

Might be going too fast. sd

Thanks all for your feedback, I will check for new pump and heat exchanger, not that I drive at 200kph all day long :-) but just like to know the car is in good working order...

Pump may have gone bad but upgrading your heat exchanger will help your high heat area. Few options below.
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You need to change the boost sensor, clean the damper, change the fuel filter - everything depends on the situation. Also, the Bypass valve can cause insufficient boost and, as a result, cause a loss of power even in a stock car. A similar problem was on my Ford 6.0, but I decided to replace the turbine to add more power, here https://boostyourengine.com/ford-6-0...-turbocharger/ I found the best Ford 6.0 Powerstroke Turbocharger, a new part is always effective.

Which is the best bolt in lower heat exchanger?
I want to do that plus the Bosh 010 ? coolant pump when my Wagon arrives soon touchwood.

I imported my wagon to Dubai from Japan. I had the same issue as mentioned by you. There are two parts to be addressed. First like most mentioned is the coolant pump which I replaced with a Bosch 010 and immediately solved the supercharger cutting off during heavy acceleration.

All cars sold in Japan have a speed limit set to 180 kmph/112 mph. My car wouldn’t go beyond 200kph and felt weird in the top end as it reaches the limit, engine power and torque would cut off like it going out of breath.

I removed the speed limit on the car. You can raise it with a Xentry/Star to 320kph. It’s easy, takes hardly 5 minutes. You will feel a huge difference once the factory limits are removed. I enjoy driving on open roads as I frequent between UAE and Oman where I’m able to push the car and enjoy the beast.

Here is a link to the video I followed

Is the 180kph speed limit mandatory? Both my former C32 from Japan and my current E55 from Japan had the usual speed limit of 255 kph.

For the pump i went with the Pierburg CWA100, which is also used in the W212 E63s. I currently have only one big heat exchanger (for now) and the temps are quite okay.

The speed limit it mandatory for cars sold in Japan however most folks get the limits removed as you know it’s the land of fast and furious