I have a 1994 Mu with a 4JG2 - the 3.1L turbo diesel. It has developed a whistle under load, I'm pretty sure it's turbo related as it only happens at certain boost pressures.
Here's what I've tried:
-Briefly ran the engine with all accessory belts removed to confirm it's not belt noise. It's not belt noise.
-Connected my compressor to the air intake just after the air filter to confirm it's not a boost leak. I gradually increased the pressure until it blew the intake hoses off at about 25PSI. No boost leaks.
-Connected my compressor to the exhaust pipe and repeated the same test. I found a few minor exhaust leaks, but they only occur when I pressurise it to beyond what you would expect exhaust pressure to reach. I couldn't make any of them whistle at any pressure.
-Tried to replicate the issue while stationary - it's very difficult to do. I can make it produce a very short whistle if I open the throttle suddenly. It seems to be coming from the side with the turbo, alternator, and aircon pump. It might be the turbo, but I don't want to buy a turbo unless I know for sure.
-I've removed the intake tubing and inspected the intake side of the turbo. It looks fine to me, but I'm not an expert. No significant play in any direction.
What do you think it could be? What else can I try?
My best guess is to pull the turbo off completely and inspect the exhaust side. What am I looking for? What do I need to know about removing and reinstalling the turbo? How much should a replacement turbo cost? Thanks guys.