I purchased an 87 turbo and we can't figure out why it won't build boost. We have rebuilt the turbo, put brand new exhaust in it with no cats,air filter in new, changed the egr valve, checked the wastegate (it's working properly) , checked the ecm, did a compression check and it checked out ok. It won't build over 8 to 9 pds of boost. My next thing to do is change the valve springs. Any other ideas? Thanks.