Changing an injection pump on a GM 6.2L Diesel is not as difficult as one might expect. Getting to the injection pump requires removing the air cleaner assemble and the intake manifold. Before the manifold can be removed, several brackets may need to be loosened and removed from the studs that hold on the intake manifold. This may include the air conditioner condenser bracket and alternator bracket. Be sure and note the location of the studs and the lengths of the bolts so that they can be reassembled in the proper holes. Once the intake manifold is removed it’s a good idea to remove the vacuum pump. This allows enough room for the injection pump to be removed with the injection lines attached. Loosen the injection line brackets and take the injection lines from each injector. Next, remove the oil fill spout from the front of the engine exposing the pump drive gear. Bar the engine over until a bolt is exposed and can be removed. There are 3 bolts that hold the drive gear to the pump but they can only be removed one at a time so after each one is removed the engine should be barred over until the second bolt can be removed and then a third time to expose the last bolt. Once these three bolts are removed the fuel line should be removed. Then the 3 nuts that hold the injection pump on can be removed and the injection pump slid toward the rear of the engine. The pump has to be moved far enough that the button in the center of the drive shaft will clear the engine. Be careful of the glow plug wires and make sure not to hang on one of them. Once the pump is removed note the location of the timing pin in the pump drive (such as 4:00 o’clock position) this will help when reinstalling the pump to the engine.

If a replacement pump is on hand remove 4 injection lines that are attached from the old injection pump and install them on the replacement pump on the corresponding outlets of the replacement pump. Then the other 4 lines can be removed and installed. If a replacement pump is not on hand extreme care should be made that the fuel lines are installed in the proper order. This sets the firing order of the engine the same as the spark plug wires do on a distributor of a gas engine. Other components can then be installed on the replacement pump and the drive of the pump positioned in the proper position that was noted when the pump was being removed. If the location of the pin on the pump drive shaft is not known, the pin aligns with the elliptical hole in the drive gear. There is a round hole in the gear also so make sure that the pin aligns with the elliptical hole and not the round one. When the pump is aligned properly with the drive gear it will mount flush to the engine without being forced and all three drive gear bolts can be installed easily. Be sure to tighten these three bolts to 20 lbs/ft so that they will not back out. The three nuts that hold the pump to engine can be started to hold the pump steady but do not tighten yet. Align the eight injection lines with their respective injector. The line nuts should be hand tightened on the injectors so that the nuts won’t be cross threaded possibly ruining the injector and/or the line. The injection pump should then be positioned with the mark on the pump mounting flange aligned with the mark on the engine. Attach the fuel inlet line and return line to the injection pump. The vacuum pump can now be reinstalled. The intake manifold gaskets should be replaced before reinstalling the intake manifold. Care should be made to reinstall bolts and studs in proper positions so that the brackets can also be installed properly. These bolts and studs should also be torqued to 32 lbs/ft.

Once all the brackets and oil fill spout are reinstalled and everything is retightened the engine can be started. Make sure the batteries are charged up because, it could take a few minutes to get the fuel system reprimed enough to start the engine. Be careful not to crank on the engine long enough to burn up the starter, try to crank the engine for a few minutes and then let the starter cool off. You might want to leave the return hose off and watch for return fuel. Once you have return fuel the vehicle should start. The engine may run rough or even die a few times until all the air is bled out. The injection pump is self bleeding and there is no way to speed up the process so give it time and it will bleed the air out. If the vehicle continues to smoke, have low power, or runs bad in general it may need the pump to engine timing adjusted. This is best done with a timing meter. The timing can be advanced by taking the three nuts loose that hold the pump to the engine and rotating the pump towards the drivers side of the vehicle and retarded by moving it toward the passenger side. DO NOT attempt to move the pump while the engine is running, severe pump damage and even personal injury can result. In some cases when the engine has 75,000 miles or more the injectors may be contributing to the problem and just changing the injection may not solve all of the problems or in some cases new problems will arise due to worn or faulty injectors. Its always a good idea to at least check the injectors to insure that the engine will run properly.

Another important part of changing an injection pump is to keep everything as clean as possible. Any dirt introduced into the system can cause severe problems with injectors sticking, internal parts of the pump sticking or even pump seizure. As long as care is taken the job of replacing an injection pump is not as difficult at one might imagine.