Ok boys and girls, here'* what to do when your intake fails:
What you'll need: New upper intake. Upper intake gasket set. Lower intake gasket set. Plastic coolant elbow. Torque wrench w/adapter to drive 1/4 sockets. 1/4' drive extension. Various other common sockets and adjustable wrenches. Case of oil and 2 filters. New PCV valve. Threadlock.
This was performed on a 1995 H body. All L36'* will vary slightly based on year and platform.
The first thing you have to do is make sure there is no water in the cylinders. If you have a slow leak and are doing this as a preventative repair, it'* not a concern. If you suffered a catastrophic failure, your engine will likely be full of water. (Like mine was) Using a large wrench, turn the engine over by hand several times. If you can do this, you're ok. If you can't, the pull the spark plugs and crank the engine for a few seconds to push the water out of the cylinders.
Now you'll have to relieve pressure on the fuel system. The fuel pump fuse should be in the same place for all 92-99 H bodies. Remove the plastic cover underneath the passenger side of the dashboard. Using the fuse panel diagram located on the plastic cover, locate and remove the 20 amp fuel pump fuse. Crank the engine for 5-10 seconds, wait a few seconds, and do it again. This will run the fuel out of the lines. You MUST do this, or you'll have gas all over the engine.
Disconnect the battery and tape over the terminal. Drain the cooling system. Disconnect the spark plug wires for the rear of the engine. Remove the air box. Remove the belt, alternator, and alternator brace.
Unplug all vacuum lines and wiring from the fuel rail. To uplug the injector wires, push the metal clips toward the body of the injectors until you hear a click. To disconnect the fuel lines, squeeze the quick disconnect fittings and pull up. Wear eye protection when you do this. The fuel in the rail is under high pressure and may spray out when you disconnect the feed line. I very narrowly avoided getting sprayed in the eyes. Remove the 4 nuts that hold the fuel rail in place. Gently rock the fuel rail loose. It may be stuck, so be patient and gentle. These are expensive parts! Place it somewhere safe and out of the way.
Loosen the nuts connecting the spring assembly to the throttle body. Disconnect the ends of the throttle cables. They are tricky, so go slowly and you'll figure out how they disconnect. Remove all wiring and vacuum lines from the intake and throttle body. Remove the bolt from the front bracket on the throttle body. Remove the bolts that hold the upper intake in place. Lift the upper intake out of the way.
The next step is optional, unless your lower intake is showing pitting or other signs of degredation around the EGR pipe. I highly recommend it though, because my lower intake gaskets were showing signs of deteriorating to the point where a leak wasn't far off.
If your lower intake has water sitting on it, you must dry it out. I used a turkey baster to remove most of it, and rags to dry the rest. Now, disconnect the egr tube from lower intake. Remove the upper radiator hose. Remove all bolts holding the lower intake in place. Remember the two located inside the intake, at the upper left and lower right corners. Lift off the intake, keeping in mind that it will still have coolant in it. Place it in a bucket to drain. If the lifter valley has water in it, wipe it dry. Stuff rags in the ports in the heads so you don't drop anything down them.
Clean the gasket surfaces of the lower intake and heads and use throttle body cleaner to clean the carbon out of the ports in the intake. Intall the block to intake seals with gastket sealant. Install the intake gaskets without sealant. Lower the intake into place, being careful not to push the gaskets out of place. Install a new plastic elbow from the intake to the tensioner bracket. Put medium grade threadlock on all intake bolts and install them snugly. Torque all the intake bolts to the proper spec for your year, starting in the center of the intake and working toward the ends. Reattatch the EGR tube. Reattatch the radiator hose.
Remove the throttle body from the old upper intake and clean the backside of it with throttle body cleaner. Install it on the new intake with a new gasket. Install a new PCV valve in the new intake, and remember to transfer the black rubber o-ring from the old pcv valve. You'll probably create a vacuum leak if you forget. Install the new PCV tube into the intake, and install the new gasket. Transfer the large vacuum fitting from the back of the old intake to the back of the new one. Make sure the large bolt that holds the accessory bracket over the rear of the engine is in place. You won't be able to install it once the upper intake is in place. Carefully set the upper intake in place without sealant. Put medium grade threadlock on all intake bolts and install them snugly. Torque the intake bolts to the proper spec for your year, starting from the center of the intake and working toward the ends. Reinstall the throttle cables and spring assembly. Reinstall the bolt in the front throttle body bracket. Pop the fuel rail back into place. Reinstall all wiring and vacuum lines. Reinstall the alternator and brace, and the belt. Reinstall the spark plug wires. Reinstall the airbox.
Now change the oil and filter. Let the pan drain completely to get all the water out. Fill the radiator with water and a bottle of flush product. Reconnect the battery and fire it up! Flush the cooling system as directed on the bottle and fill the cooling system with 50/50 antifreeze and distilled water. Change the oil and filter once more, if you're paranoid like me.