Update time.60K after my last repair the gasket started leaking again. Root cause was the same as all other vehicles, the top LH diagonal bolt loosened. These were things I did different this time around and info that I got talking to a mechanic at the dealer.
1) I bought an OEM lower intake gasket this time around vs. aftermarket. GM has pressed in metal pucks on the top and bottom of the diagonal bolt holes to prevent the plastic from cracking under the new torque specs. My gasket wasn’t cracked but it’s apparently been an issue. All other gaskets were aftermarket.
2) I didn’t use any pipe dope on this repair but soaked them with serviceable (blue) loctite. This was apparently the main contributor to the field failures. GM recommends new bolts because they have a loctite patch on them that the original bolts never had. At $9.00 a bolt, I’ll put it on myself. First time around, I was scared that some of the bolts might run through a water jacket so I put more dope then loctite which was my ultimate mistake. The mechanic told me he only used loctite and never had any issues so that was good enough for me.
3) This time around I completely unbolted the heater line from the engine so this gave me easier access to the fuel line nut that bolts it to the block.
4) When I disconnected the fuel, I disconnected the regulator side first to help relieve the pressure which made catching the O-ring on the pressure side easier. I’m assuming that most people cut corners like me and don’t properly relieve the fuel pressure.
5) Once I torqued the diagonal bolts to 220in/lbs it loosened the horizontal bolts, so I retorqued them back to 115 in/lbs. This didn’t cause the gasket to fail the first time but was something I noticed on this last job and corrected it.
6) I tried leaving the fuel injectors in and it was relatively easy. I disconnected the harnesses that were close to the firewall, loosened the 2 bolts that fastened the rails to the block for a bit of movement then removed the manifold bolts with a ¼” drive socket and extension. An adapter was used to mate it up with my torque wrench. When cleaning the intake gasket surface you have to be careful and not drop any carbon deposits which can fall and clog your injectors that are now pointing straight up at you. I did 2 jobs in which I removed the rail and one which I didn’t. If I had to do it again, I’d leave the rails in. It’s not a real big time saver but it’s just one less thing that may go wrong like tearing an O-ring.
7) Put a foot of 3/8” (3/8 ID, 1/8” thk) rubber fuel line on your shopping list. You have two 2”-3” long hoses that go from the heater line to the plenum that can easily be damaged when removing them. I had to replace one the first time and the other the second time. Both times I had to drop my tools and go get some hose because I didn’t have any. I now have a foot of the stuff in my tool box.