I have rebuilt a 3126 again and I have a check engine light on but didn't before the OH. There are three active codes. One is Inj. Act. Pressure System Fault, Second is Inj, Act. Pressure Sig. Erratic, & lastly Inj. Act. Pressure Output Fault. I have checked connections and can't see anything wrong. Any ideas?
Normally that group of problems leads to either an IAP sensor, or the valve. Do you have an old sensor laying around or one to swap? I wonder if something is hung up in the shuttle part of the valve...they are pretty sensitive to old engine oil viscosity, but I'm guessing this has brand new oil.