before the injection pump (IP) is comdemned, we need a fuel pressure reading at the filter.
any 0-10 0-20 psi gauge will do. connect it to one of the ports on the fuel filter head. you should be getting 5-8 psi at idle.
and ok... you never worked on it:
quickie fuel description for mechanical diesel like 7.3idi
fuel from tank goes to a 6port pollack valve near the front of the forward port fuel tank. it is 6port because two are incoming from each tank, two are outgoing return lines to each tank, one line is incoming return line, one line is outgoing to fuel pump.
Lets follow the one to the fuel pump.
It goes up the port framerail, to the engine where it crosses over to the stbd side. there should be a metal line going forward, this connects to a 3/8 hose which runs to the manual lift pump.
These lift pumps are simple, an arm rides on a camshaft eccentric and pushes the fuel up to the filter. There is also a rubber diaghram that keeps the fuel on the fuel side and oil on the oil side. (The previous question of "are you making any oil" could have referred to this, as often the integrity of the seal is broken and fuel oil dilutes the lube oil.
ok than, fuel is incoming at the forward fitting on the filter housing. should be metal lines incoming and outgoing on the filter. On my truck I changed them over to rubber hose.... anyway on the filter head is three ports, on is a return to the #1 injector, one is a schrader valve like on a tire, this is meant for manually bleeding air out of the system. The third port is a vacuum/pressure doohicky which attaches to a wire. This will tell you on the dash lights when your filter is clogged.
On the filter base (bottom side) there is a wheel meant for draining fuel/water out of the filter, there should also be a small stud which has a wire attached to it to inform you of when there is water in the fuel.
ok, outgoing from the filter the metal line goes to the IP or injection pump. It serves a very important role. It controls everything fuel related. Fuel metering, injection start and finish, timing, governing, etc is all controlled by this lil metal box. You can adjust certain things like timing but that is beyond the scope of this manual, and you should consult a fuel injection professional. (sorry, I always wanted to write that).
Anyway, from the IP fuel goes to the injectors, where they (the injectors) are supposedly set at a pressure. At this pressure (controlled by a spring and shims) a seat lifts and injection begins/ends. Excess fuel goes back to the 6port valve previously mentioned.
without the appropriate amount of fuel pressure at the IP it will run very similiar to how yours is running. The IP can pull fuel, but it's not very good at it.... thus why we really need to check fuel pressure.
clear as mud?
drew
