Originally Posted by radomirthegreat
It could be that your dash is wrong. The boost gauge is vacuum driven, so you could have some loss in that respect.
You are half right. The MAP sensor actually controls the boost gauge, and nothing else. But the MAP does feed off of the fuel pressure regulator vac/boost line, so it would behoove you to check it just to make sure the lines are good.
Another thing to check is the BCA, both the actuator itself and the butterfly valve it is attached to.
Those are the two most common things to check for this problem, but there could be other, less common things as well. Huge amounts of KR, low fuel pressure (which would cause the huge amounts of KR), clogged cat, even a clogged air filter can cause lower than normal boost readings. Oh, forgot to mention...check ALL of you vac lines for loose-fitting or cracked shells. You might also want to check the vac canister that is attached to the firewall. That connection there is a common failure point.
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