My 2003 Jeep Cherokee 2.8 turbo diesel has whistling sound above 2 000 RPM, what can this be?

cute no year, no country stated then posts to usa forum.
we dont have this car. here. i think.
so are you asking how to diagnose turbo issues, on fixya
that be like asking how to do brain surgery on , Mr, PHIL
the PCM may see the boost too low for load and RPM.
so, that can be lots of things, besides a bad turbo cant spool.
even a stuck open waste gate.
or controls issues,
best is to get a complex car serviced, by someone that can work complex turbo diesels,

if serious on DIY, why not buy the book on the car
the FSM
then see the turbo section and do the tests stated there.
if that sounds hard, it is,

turbo whistle is common as it comes from the tips of the compressor wheel passing through the sound barrier and the turbulence occurs. IN the older trucks you would the turbo whistle as the engine reached full RPM just before a gear change. In smaller engine it is not do noticeable as there is an excess of air pressure that keeps the compressor wheel at a lower rpm and the pressure is dumped out. Turbo compressors reach revolutions in excess of 120.000 rpm under full load If it has just started to make the noise then check the intercooler system for leaks--loose clamps--- splits - Have the turbo compressor checked for damaged fins from the ingress of fine dirt from a bad air filter---check the air filter is not blocked as the turbo speed may result from running in a partial vacuum ( no load on the compressor wheel)

check your breather for a restriction or the filter may be plugged

Possible air leak on one of the air intake pipes or worst case scenario it could be the turbo at fault

1985 Jeep Cherokee came with either a 4 cylinder 2.5L with a 1 barrel carb or a 6 cylinder 2.8L with a 2 barrel carb. The 4WD only had the option of a 4 cylinder 2.1L turbo Diesel.

Remember, what is heard as turbocharger noise may not be caused by a noisy turbocharger. Before replacing a turbocharger perform the following diagnosis.
A. If a loud whine or whistle is heard during acceleration and increases or decreases with rpm and load. This condition is most often the result of a loose clamp/hose at the turbocharger compressor outlet, charge air cooler inlet, outlet or at the intake manifold.

1. With the engine running at idle and the transmission in Park or Neutral with the parking brake set, feel for boost air escaping at each connection between the turbocharger compressor outlet and intake manifold. For limited access areas, spray soapy water on those connectors and look for bubbles.

2. Check the exhaust manifold and exhaust system for leaks.

I hope this helped.

Thank you,
Norse

check fuel filtres and clean lines

I would first check that there is not a split in one of the turbo hoses or one of the hose clips has come loose, as you description sounds like a loss of turbo boost. Does it blow a lot of black smoke?

hi i have bean told it is the number 1 injector with the wire attached you might need it replaced thanks