replaced egr cooler and now getting a p0090 code...

[southerntp]

07 LMM...Someone installed a egr blockoff plate and damaged the gasket...this is where i came in. I removed the egr cooler to replace the gasket and install a new egr blockoff plate. Had to unplug multiple connections, unhook the positive side off of both batteries, and take the hot wire off of the alternator as well as take a wire off of a little junction box on top of the egr valve elbow. Installation went fairly easy without any major complications. Started the truck and now it has a check engine light with a p0090 code saying something about fuel pressure regulator. I unplugged the regulator with the truck running and the sound of the engine didnt change at all. I checked both of the wires running into the fpr and neither one of them had any power going to them. The check engine light was not on prior to removal of the egr cooler. Any ideas as to what would of caused the fpr code? Surely unhooking the batteries wouldnt have set this code. I tried clearing the code with a scanner but it doesnt seem to clear at all. Any suggestions cause they think I have messed it up somehow even though i never even touched anything in that area. Thanks in advance guys.

[southerntp]

forgot to mention that i check all the fuses with the key on, engine off and they were all good.

[JD4440]

Check all your electrical connections, especially at the main and ECM harness.

From DieselPlace:
I told him about the threads I found here where it seemed to be an electrical problem, so I had him start the truck and watch the Tech 2 while I started moving things around in the engine bay. When I got to the grey bale connector for the ECM to Engine connection, I singled out the wires for the FRP Regulator circuit and moved them. Nothing. Then, I noticed that the connector had snapped off of the mounting bracket it goes on. With the engine running, I pulled the connector and started to slip it back onto its tab and the truck went haywire. It immediately started stumbling and blowing the white smoke, and threw 8 DTC's.

I immediately moved it back and it stopped. Then moved it around some more and got it to run erratic again. He jumped out to see what I was doing, and kinda shook his head. He knew what I was thinking (bad ecm my a$$) and I just said well, there is the gremlin.

I left him to work on it, I had to go back to work, he pulled the connector apart and found terminals with the wires broken under where the terminal was crimped on from the factory. He also founds signs of arcing where the connection was broken. He re-pinned all the connections in the harness and greased it up really well, and I picked it up about an hour ago.