Turbo noise???

[scottiedog]

Hi all

I seem to have a problem on my 1994,3.0L, which over time is gradually getting worse. When driving normally around town it's non-exsistent - but when the truck is under load (going up-hill or accelerating to join a motorway) it starts to make quite a loud hissing sound from under the front end, which then dissapears when the acclererator pedal pressure is reduced. I'm no mechanic, but would I be correct in assuming that as the turbo spins faster it creates more pressure thus making the hissing sound while the trucks under load?? If so, I have checked the pipes coming from the airbox to the turbo and back to the intake and they all seem to be in reasonable condition.
Is this a known fault or can anyone give me any idea's on avenues of investigation, or procedures to eliminate certain parts from the list.

Cheers
S.

[bullet513]

with out hearing it, its hard to diagnose. but it could be normal turbo whistle. do you have a standard airbox and run standard boost? i could be a slight boost leak? any lack of power? normally with boost loak you get black smoke? could be a slightly blocked exhaust? these are just general things ive come across with turbo cars, not surf specific, my turbo has a bit of a whistle on full boost but no faults with it

[scottiedog]

Hi Bud

The truck is standard (airbox and boost) but now you mention it - yes I have noticed an increase in smoke in the exhaust and it does feel less lively. The best way I can explain the noise is that it's similar to an air crompressor leaking - getting louder the more the trucks under load.

[IanB2]

Sounds like a boost leak to me, the smoke in the exhaust is likely due to less air getting into the combustion mix under boost, so you get unburnt fuel which causes the black smoke.

[scottiedog]

Now I just have to try and locate the leak I just had a look under the bonnet, l have plastic pipework and rubber hoses coming from the airbox to the turbo, and then a short rubber hose coming from the turbo connecting to a cast pipe that mounts to the top of the throttle body. I assume the pipework coming from the airbox to the turbo would not be the cause as its not under any pressure?? if so, I suppose the small hose coming off the turbo would be my first check. I'll remove it to check it properly. If it's not this hose, any ideas on what to check next?

cheers