InDirect Injected Diesel Page

Injection pump solenoids
The only other electrical check is to make sure that there is power reaching the injection pump fuel solenoid and the cold timing advance/high idle solenoids. If the engine is cold and the high idle solenoid activates with the key on, it's good. If you have no high idle, check for voltage at both terminals of the cold start switch just behind the thermostat housing.
The cold advance solenoid also aids in purging air from the injection pump.

Fuel system
Next check for fuel delivery through the fuel filter. On 6.9 engines this is checked at the 3/16" hose barb on the fuel filter outlet elbow, and on 7.3 at the fuel filter orifice/return line fitting or restricted filter sensor port. If checking either at the filter return line fitting, plug the return hose. Fuel pressure here should be 1 psi minimum at idle. Lift pump pressure is taken at the fuel filter bleed schrader port and should be 2 psi minimum at idle. Fuel volume is taken at the same point and should be at least one pint in 30 seconds at idle. Inspect the fuel taken during the volume test for signs of water or contamination.
If the engine won't start, these specs may be lower as idle speed is 675 RPM and cranking speed will be less.

Fuel supply and return line restriction is normally tested with the engine at 3300 RPM. For supply restriction a vacuum gauge is tee'd into the lift pump inlet hose and should read less than 6 in/Hg at 3300 RPM. For a return line restriction a pressure gauge is tee'd into the hose running from the rear of the engine. This should read less than 2 psi at 3300 RPM. But a return line restriction can also be detected by installing a clear hose in place of the return line hose at the fuel filter. Watch the flow of fuel while cranking and if it flows towards the filter, inspect the fuel return circuit.

Installing a clear line at the filter return can also be used to detect air intrusion into the fuel supply system if this is suspected, although at this point the symptom would most likely be a stall after starting followed by a hard start, in which case by changing the location of the clear line you can pin point the area of the air leak. If air is getting into the injection pump, this would cause hard start concern. A clear line can be installed at the injection pump outlet to detect this.
If the concern were a rough idle, the clear lines can be used to detect aeration of the fuel. Install the lines and start the engine. Run the engine at 3000 RMP for 2 minutes, then watch the clear lines for signs of air. Some bubbles less than 1/16" is normal, but if the bubbles are larger, constant, or if the fuel appears to foam, there is air being pulled into the supply system.

To check the transfer pump pressure inside the injection pump, a special adapter which replaces the transfer pump cover lock screw and attaches to a 160 psi gauge (the cover lock block has to be in place). Transfer pump pressure is taken at 3300 RPM and should be 90-110 psi for 6.9; 90-120 psi for 7.3.
If the engine won't start, all other checks are normal, and there is no air inside the injection pump, chances are the transfer pump is not producing enough pressure to start the engine. This can be checked by opening one or more injector lines while cranking. If no fuel is reaching the injectors, suspect an internal injection pump problem.

Compression test
To perform a compression test on this engine, you need to have a diesel compression gauge and a glow plug adapter. Remove all the glow plugs to check any cylinder. Crank the engine at least five revolutions and the same number of revolutions for each cylinder. It would probably be a good idea to have a battery charger hooked up during the test. Ford lists no compression specs for these engine, only stating the lowest cylinder should be no more than 25% lower than the highest cylinder, with a low to high comparison chart showing a range of 195 to 440 PSI. In reality the compression should be at least 350 psi.

Timing these engines depends on what equipment you have. Luminosity probe timing gauges depend on fuel cetane level, engine and ambient temperature and can read as much as 10 degrees retarded from the actual injection time.

Cylinder missfire
To detect a missfire, you could slowly loosen each injector line to see if the way the engine is running changes, but an easier method is to disconnect the glow plugs and measure their resistance with the engine running (the glow plugs have to be in good condition). As the engine gets hot, glow plug resistance increases. A cylinder that isn't firing will be colder than one that is. After starting, glow plug resistance usually rises to 15-20 ohms on a operating cylinder, but stays below 10 ohms on a weak one--even lower if the cylinder is dead. If you own an infrared temperature gun, you can detect the missfiring cylinder by measuring exhaust port temp. If the miss cannot be isolated to any cylinder(s), then there may be an injection pump or fuel quality problem.