Can't or won't develop full boost

[Gabrielm]

Guys,

I'm hoping you can help me here.....

My 86' 951 has a problem with the boost. Sometimes it is fine and I can accelerate with the boost guage all the way over to the right (just under the 2.0 mark), more often than not though the car can only develop 1.2 under full accelaration.

I have no idea what could be causing the problem, where do I start? I always let the car warm up thouroughly before getting on the gas. it has been pretty cold recently so maybe something is frozen (left out over night in sub zero temp).

The car is totally stock with no modifications with 120K on the odometer

Any advice would be gratefully received.

[Lawrence Coppari]

There is a recycle valve near the coolant reservoir. It is controlled by a vacuum line. Remove the vacuum line. Attach another line to it and see if it holds a vacuum. The valve is a diaphragm type so there should be no leakage.

Follow the line I'm talking about back to the T near the fuel damper. If these vacuum lines leak, everything gets messed up.

While you're at it, check all the little vacuum lines. See if your cycling valve has broken nipples. It has 3 nipples. It's between intake runner 3 and 4. Check line to waste gate.

Check vacuum line under throttle body.

[robm-951]

more often than not though the car can only develop 1.2 under full accelaration.

Your car might me going into its safe mode. At that point it will only allow 1.2 bar absolute pressure. To check this, go to Dan Nguyenphuc web page here and follow the procedure. When you go out for the procedures test drive, you'll want to be sure you are only getting to 1.2 bar before testing.

Good Luck,
Rob