GM 5.7L intake manifold gasket
The GM 5.7L(and 5.0L which is virtually the same engine) intake manifold gasket is an extremely high failure item. Of the millions of cars and trucks sold with this engine, 99.9% will have an intake gasket leak at least once, and if the vehicle lasts more than 100,000 miles, it may leak two or three times. This means that every 5.0 or 5.7 liter GM car or truck that comes into your shop should be inspected for a leak.
Inspection
The most common area of failure is at the front of the engine, behind the alternator bracket or air conditioning bracket. Behind the alternator is not easily visible, so a small mirror and a flashlight will be needed to verify the leak unless it is very bad. You should be looking for oil, coolant, or a combination of both. If coolant is seen, a disclaimer must be attached to the ticket waiving the shop of any responsibility in the event that coolant also leaked into the crankcase and damaged the bearings, possibly resulting in future engine failure. Also check for a leak at the rear of the engine. It can be seen with a mirror on top of the transmission bell housing, or in extreme cases, leaking down into the bell housing and out of the drain at the bottom of the torque converter shield. Although leaks at the front or more common, the rear of the intake will sometimes leak as well.
Disassembly
Begin the procedure by draining the coolant. Remove the air filter box lid and air intake boot with filter attached. Leave the bottom of the air filter box, as it makes an excellent tray for brackets and other larger pieces that will be removed from the engine. Next, remove the upper fan shroud (one of GM's best ideas), the fan clutch assembly, drive belt, and idler pulley. The water pump pulley doesn't have to be removed, but it does give a little more room to work later. Now remove the electrical connectors at the front of the engine and from the AC compressor. Release both of the cables at the throttle body and the throttle cable bracket. Unbolt the compressor and fold it over to the passenger side of the engine compartment and fold the throttle cable bracket over to the driver's side.
The alternator does not have to be removed, but again, it makes the job easier later (don't forget to disconnect the negative cable at the battery). Once the alternator is out of the way, inspect the coolant hose quick disconnect fitting behind it. If it does not appear to have been replaced in the last 6 months, you need to do it now. These fittings are made from an extremely cheap metal and break very easily. It is likely that it will break off in the intake when you try to remove it. A tool can be purchased on most tool trucks that can be hammered down into the broken fitting and twisted out (buy this tool before the fitting breaks). Now remove the other coolant hose from the water pump and fold it over to the side along with the hose from the quick disconnect and the AC compressor. Remove the upper radiator hose and the EGR fitting.
Getting into your work
At this point, the easiest way to proceed with the job is to climb up into the engine compartment and sit on the radiator support (careful not to catch the seat of your pants on the hood latch). Watch the placement of your feet so that you don't damage any of the components on either side of the engine. Many techs have found that the best position is the left foot on the alternator bracket and the right on the sector shaft. This places you in a position easily accessible to the engine and all components. Make sure to have your tool cart close by as well.
Now release the evap. hose from the valve on the passenger side of the intake. With a small screwdriver, press the white clip into the fitting(seen above), releasing the catch, and pull the hose off of the valve. Fold this hose over to the driver's side of the engine compartment. Now release all of the electrical connectors from the top of the engine and all of the clips that hold the wiring harness. Be extremely careful when removing and installing the large fuel injector connector in the center of the intake. If one of the pins is bent, that injector will not activate, causing a hard to diagnose misfire.