Twin Turbo Problem

is it possible that the wastegate is partially open on the secondary turbo or perhaps the boost controller solenoid isn't bleeding off boost like it should so it is running strictly off of wastegate spring pressure?

Hi Thanks for the suggestion. This model dosn't have a wastegate on the secondary turbo (unlike pre'96) it uses the primary turbo wastegate to contol boost during the primary & secondray phases. The primary wastegate could be a little stuck open preventing boot build up at higher loads, the primary turbo seems a little sluggish as well. I'll take a look Thanks Mike

It doesn't *change* to the secondary, it uses the secondary as well.

There is a valve between the output of the secondary turbo and the intercooler with a differential pressure sensor across it.

It is supposed to open when the pressure from the secondary turbo matches (exceeds) the pressure in the intercooler.

If that valve (or pressure sensor) isn't opening you share exhaust gasses between turbos but only get boost from the primary. No idea about common problems but the effect matches your symptoms.

Thanks for the clarification.

I measured using my boost guage the secondary turbo pressure by tapping into the airline that goes to this sensor and measured low pressure - it never exceeded 10 psi. In a seperate experiment disabled the pressure relief valve (AKA BOV) on the seconday turbo to see if this was leaking resulting in pressure loss but it had no effect.

The only things I can come up with is faulty exhaust valve - either primary wastegate or changeover control valve or the secondary turbo bearing have died. But there are no audio indication of the latter. BTW Here is a good website for twinturbos if you are interested