BenzWorld Senior Member
Date registered: Jun 2004
Mentioned: 0 Post(s)
Quoted: 17 Post(s)
Is the smoke blue or black? If it is black, sounds like you could have a problem in the pneumatic governor system, which is totally unrelated to the vacuum pump on the front of the engine. The way this injection pump meters fuel is by using vacuum created at the intake butterfly using a venturi built into the throttle body. When the butterfly is closed, the increased air flow through the venturi creates a vacuum in the hose/pipe at the top of the throttle body. As the butterfly opens, less vacuum is created, until at open throttle, there is little to no vacuum, and the maximum amount of fuel is injected. The vacuum is channeled from the throttle body through a hose or tube to a diaphragm chamber at the rear of the injection pump. This vacuum pulls the diaphragm, which is connected directly to the fuel rack, against a spring to reduce fuel to the injectors. The spring pushes the fuel rack open as vacuum is reduced when the opening butterfly.
I would check and make sure you don't have any cracks or breaks in the line from the throttle body to the injection pump which would suck air. If everything is tight, you might have a bad diaphragm in the governor. This can easily be checked using a hand vacuum pump to see if it holds vacuum. This diaphragm can be replaced by removing the four screws that hold the cover on (that has the line running into it). But it is pretty much necessary to remove the injection pump and do it on the bench as there is a tiny clip that must be removed and reinstalled where the diaphragm connects to the fuel rack.