CM870 High Pyro/Low Boost intermittent under load

[Rawze]

it can also be the trubo speed sensor feedback is exceeding the rated turbo speed and derating it too.

That can be for many reasons including blocked up exhaust muffler, intake air filter restriction, after-market charge air cooler that someone has installed, or the turbo itself might have damage to the turbine blades, making it spool faster than normal with less boost.