Turbo S80 TCV & Vacuum Line Routing

The pressure from the outlet of the turbo presses on the wastegate diaphragm to keep it closed. When the ECU decides there is enough boost, it stops allowing the air from the turbo outlet from going to the wastegate actuator and allows it to go to the compressor inlet tube. The system is a pulse width modulated system meaning it is never “always on”, but instead cycled on for longer periods of time to increase boost, and shorter to decrease boost. When the TCV is off, air from the compressor is dumped to the compressor inlet, and the spring pressure in the wastegate is what regulates compressor outlet pressure.

Fast Friday #4 — The Boost Variance Problem

Fast Friday Volvo Performance and Tuning

Boost pressure issues seem to be the #2 issue in the Volvo Performance world beaten out only by vacuum leaks. Boost pressure control in the 1994-1998 models is a pretty simple system but for the ECU to manage boost correctly it relies heavily on known base values and settings. If these settings are off or if there are mechanical issues then the boost control system can be out of whack.

How do Volvo turbo control valves (TCV) work?

When they fail, how do they fail? Its a pulse modulated solenoid. So it opens and closes like a fuel injector to get the right boost characteristics throughout the entire rpm range.  No air is lost in these systems. They tend to fail with the red and blue open (no boost) but most are replaced […]

Troubleshooting Low Boost

Underboost is a condition that can be caused by several issues including: Bad TCV Bad Turbocharger Failed boost sensor (for models that have them) ECU seeing overboost and cutting back until reset and condition remedied Failed MAF (for ecu’s that use the MAF to determine boost pressure) Failed atmospheric sensor ( again for those that […]

Turbo Control Valve and its Correct Hosing Routing

TCV Vacuum Hose Routing De-Confusement I have searched for TCV diagram for my 95 Volvo 850 T5 but getting confused with these 2 diagrams. When i look at both of my cars the wastegate actuator has been marked yellow and also the vacumm hose has a yellow sticker on it. That makes sense if i […]