Bleeding a GM 6.2 diesel fuel system purges air from the fuel lines between the fuel tank and the injection pump. Air sometimes enters the fuel system following replacement of fuel filters or when fuel lines and connections are broken or leaking. GM modified this fuel system several times during the period of manufacture--from 1982 to 1993--so be sure you can identify all of the components in your own engine's fuel system before beginning.
Check what year your engine was manufactured. You can do this by checking your insurance papers, or look on the post on the driver's side door where you will find a metal printed tag that states the year of manufacture and other information like engine size and type.
If your engine was manufactured in 1982 or 1983, it will have a spin-on primary fuel filter mounted on the firewall. The secondary filter is either a spin-on type mounted on the back of the intake manifold or a box-type filter on the intake manifold.
If your diesel engine was manufactured in 1984 or later, it has only one fuel filter mounted on the firewall. This box-type filter has fuel inlet and outlet ports, an air bleed valve to allow release of air and retaining clips to hold the filter in place. This filter assembly heats fuel, separates water and dirt from the fuel and has a filter change signal device built in as well.
Fill the primary filter up with clean diesel fuel and screw it into place, giving it three-quarters of a turn after the gasket touches the metal ring. If there are no other leaks or changes in your fuel system, you can start the motor at this point and let it run to purge any last air from the top filter.
To bleed the rest of the fuel system, you must now bleed the secondary filter as well. Remove the air filter assembly and locate the secondary filter on the intake manifold.
Disconnect the pink wire from the fuel injection pump to prevent the engine from starting when you crank it.
Put a rag under the fuel outlet on the secondary filter and crank the engine for 10 seconds or less until fuel flows from the outlet. If no fuel comes out, let the engine sit for 15 seconds and crank it again. When fuel flows out, connect the fuel line to the outlet and tighten it.
Connect the pink wire back to the fuel injector, start the engine and let it idle. This will purge any remaining air in the fuel system.
Be sure to check all the fuel lines, filters and connections for leaks.
Early model box-type filters do not have an air bleed valve. Fasten the top clip on the filter but unfasten the lower one with a flathead screwdriver to release fuel pressure. Air will be purged from the opening this creates. Put a rag under the filter to soak up any fuel that drips down before unfastening the lower clip.
Later model box-type filters have an air bleed valve on top and a water drain valve on the bottom. The air bleed valve is a large cross shape indented like an oversized Philips screw head. Use either a large coin or large flat head screwdriver to open it. If you opened the water drain to purge water from the filter, close it now.
The short tube on the side of the filter just below the air valve is where fuel will come out during the bleeding process, so be prepared to collect this fuel so it does not spray all over the firewall and onto the ground. You can connect a piece of rubber tubing to it and run fuel into a container, or place a rag below it to absorb the fuel.
Disconnect the pink wire from the fuel injection pump so you will be able to crank the engine without it starting.
Crank the engine for 10 seconds or less until fuel flows from the outlet. If no fuel comes out, let the engine sit for 30 seconds to cool and then crank it again. Repeat this until clear fuel comes out. Collect the fuel with either the rag under the filter or in a small bottle from the tube under the bleed valve. Never just let fuel spray the engine or drip onto the ground.
Close the bleed valve, fasten the lower clip, reconnect the pink wire and crank the engine to start it. Let it idle for a few minutes to purge whatever air might remain in the system.
As a final check in bleeding your 6.2 diesel engine, look over all of the fuel lines, connections, filters and other components for leaks while it is idling. Fix any leaks that exist, then repeat the air bleed procedure. Take your vehicle out for a short drive and test it under acceleration and various speeds to ensure it is running smoothly.
Make sure you identify all of the components of the 6.2 diesel fuel system before you begin this repair, including the primary and secondary filters, the injection pump, and the pink wire lead connected to the injector pump. Collect any fuel you bleed out rather than letting it run onto the ground and into storm sewers, streams or groundwater. Put the fuel into your waste oil container and take it to your local waste oil collector for disposal. Some mechanics prefer to pressurise the fuel tank with air to 4 psi to push fuel through and purge air, rather than cranking the engine. This method requires an air pump and some way to seal the air line around the filler cap. Keep in mind that diesel enthusiasts commonly upgrade and modify these engines, and yours might not have the original fuel system. The earlier two-filter systems are often changed to the later single, box-type filter, or the whole system may have been swapped out for an after-market system. After-market upgrades are common when owners have added a turbocharger.
Diesel is not explosive like gasoline, but it is flammable. Keep a Class B fire extinguisher close by in case of fire. If the engine has been running, the fuel may be hot enough to burn your skin, as may some of the fuel lines. Be careful when you are cranking the engine to bleed the lines since fuel is meant to come out of the lines to remove air. Wash diesel fuel off your skin with soap as soon after exposure as possible.