Low Boost Problems?
JDS60R » Underboost is a condition that can be caused by several issues including:
- Bad TCV
- Bad Turbo charger
- 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 use it)
Generally diagnosis starts with the most dangerous test which is disconnecting the wastegate (yellow) line and installing a boost gauge. If the turbo can quickly make the boost pressure the car requires ( don’t go over normal boost level or engine goes boom and wallet gets very thin) then we can assume the turbo is ok. If it was slow to reach the boost level then check the turbo and its hoses for leaks. Also check the wastegate adjustment to be in spec with the info above.
Next is the turbo control valve and its hoses. It is best to replace the TCV with a known good one. You must check the lines and make sure you have no leaks .
Next is a reset. Disconnect power to the ecu and let is reset its adaptations/program. It will take a little driving to let it reset. I take a few short trips and let the computer do its thing.
Next you can check the other sensors. Reset the computer if you replaced any of them.
Finally look for an altered set up. Some owners put unspecified turbos , blow off valves etc on the car and instead of varying the tune to compensate they use all sorts of other measures like bleed off valves , electric/manual boost pressure controllers etc. With a Volvo the idea is to return to stock and build your way up properly.
There are many other things that can happen including failed CBV’s that let the pressure leak out , engine problems etc.
Be patient and methodical and you will find it.
Less boost after wastegate adjustment
Last Updated on August 19, 2020
