Does seem low.............reasons might be wear between exhaust vanes and housing(,if they can touch),excessive exhaust back pressure ,or turbo too big for motor......the fuel delivery might also have been cut back to stop smoke................the Isuzu manual I have is industrial ,doesnt specify boost,......the green cover Mack book gives boosts from 10psi to 20 psi,with the early Maxidyne at 18psi max........but from memory an early Perkins 354 turbo had 7psi max.......too much boost will blow head gasket.
Just had a chat with a local mechanic and he thinks 5 psi is way too low as well. When I say 5 psi, that's the max too. usually around 3 to 4.5 psi.
He thinks I should check the compressor fins to make sure they haven't been rubbing on the housing, resulting in them wearing away on the edges and now not generating required pressure. He also jokingly asked if both sides are still connected.
I will check for leaks as well. It has an intercooler so will include that obviously.
Has me buggered.
Thanks again folks. Really appreciate your thoughts and suggestions.
If the compressor end breaks up it goes thru the motor and makes a mess.........but an intercooler might stop most of the bits...............anyway ,Id check the intercooler for oiled up passages......they are pretty hard to clean,because you certainly cant use anything caustic in them.
if you wanted oily smoke,the old NSWGR ClydeGM locos couldnt be beat............the whole locos were coated in black goo like tar paint,with the oily goo actually dripping down the sides.....One sat idling at the old Coopers Plains interchange all morning ,and when it took off with a train of empty wagons,it was like a thick putrid fog over the whole yard ,including the houses..........so bad on a calm day,the level crossing had to stay closed till the smoke cleared.
Thanks again guys.
I'll check it out Paul. First thing is check the fins etc on the compressor side.
John, I don't need any more soot. I think the neighbors might get the sh!ts.
I'll post back when I've removed the housing from the intake side.
You don't need to remove the housing. Just remove the air inlet pipe. You can see the impeller and feel for play. When spinning, it should feel slippery. Like rubbing your fingers together with oil on them.
If the piston rings (on the turbo) are leaking, there will be oil on the outlet of the compressor. Not sure about the exhaust side.
I looked up the Isuzu manual; there is no spec for boost pressure (psi/wastegate) for the Garret turbo. 14psi for the IHI.
The one sure indicator is oil usage .......is your oil consumption excessive.?........but if the compressor side is leaking oil ,the rubber hoses will be coated with liquid oil,not just an oily scum......................the exhaust side doesnt normally leak,because backpressure is actually blowing back into the seal......but the compressor side has negative pressure in the centre part,especially behind the wheel at the shaft bearing.
It's not using oil that I can notice on the dipstick. Always remains at/near the mark.
When I had the intake pipe off there was a little bit of black residue but very minimal. Quite dry too.
I will remove it again to check the compressor fins. I didn't look too hard at them last time. The was no play in/out but a little up/down. Will check to see if fins rub or have any wear or touch the housing.
Thanks again for your advice and assistance.