overboosting

[BUDSY]

I have a 92 16v EVO1 and recently it has started boosting to over 1.2 bar which causes the engine to cough i am fully aware this is damaging the engine. can anyone give me any advice as to what to do. I have been advised that it could be a split in a vacumn pipe.

Paul

[A1.6HPE]

Hello Paul,
I was hoping that someone with more experience would have responded but...
My experience is only with the 8V cars, the 16V boost control is different. However: the boost is monitored by the ECU via a sensor that has a thin plastic pipe connected to it (Manifold Air Pressure sensor). If there is a leak in that pipe or the connections (rubber usually perishes) then the ecu would keep the boost "on" thinking that there wasn't much there. For a 16V engine the boost is controlled by a multi-way valve/solenoid connected to the input and the output sides of the turbocharger and to the wastegate actuator. If there is a leak on the pipe from the output side to the valve that would probably reduce the boost by preventing the overboost action.
I suggest that you locate the MAP sensor and check its pipe. On an 8V car it is fitted adjacent to the coolant header tank and is a black plastic thing with a connector that has 3 contacts. I guess that the sensor itself could be faulty but Ihave never heard of that happening.

Good luck, Leo

[BUDSY]

many thanks Leo for your reply i will check out these pipes right away it is pretty much what i expected was possibly the problem.

Thanks again

Regards
Paul