Last weekend I took the the car out on the interstate and opened it up. the acceleration was good and was running 80 mph at 3000 rpm. I noticed that the turbo boost stopped when the gauge went about 1/3 into the yellow indicator. I pulled he hoses this weekend and replace the small hose from the AMM to the turbo. The others looked pretty good. I was wondering if anyone has an idea of why the turbo boost would stop at where it does? I had previously gotten it significantly higher into the yellow area. Thanks Ed

My 740 turbo wagon was loosing air from the intercooler outlet hose ( approx. 3 in diameter, 2" lenght hose, feel along the lower side for rupture. If you have an oil film on the oil cooler ( below) then that hose is leaking. $ 10.00 or so on the relacement aftermarket version.

Thanks I will recheck that and the other hoses. Ed

Yes, check all the hoses past the AMM. Mine was a blown hose from the Idle Control Valve up to the large port on the intake manifold. It has a 4-inch split on its underside -- hidden vrom view.

Try disconnecting the turbo hose at the trbo outlet. Drill a 1/4" hole in the plastic top from a can of spray paint and shove the cap into the hose there. Then pressurise the turbo system with 10-15 psi shop air, or similar.

Look, listen and feel for escaping air from somplace between the turbo and the intake manifld, including the intercooler, turbo hose connections/pipes/hoses, idle control hoses, and vacuum lines.

Is your exhaust blowing black smoke? Sure sign of turbo'ed air leaking.
--
'Can't understand why people abort Volvos, either' '89 740 Turbo, 122,000 miles