Re: 7.3 IDI slight update..

Posted by LJD on December 04, 2011 at 15:53:46 from (72.171.0.143):

In Reply to: 7.3 IDI slight update.. posted by Brad Gyde on December 04, 2011 at 09:11:28:

If you haven't read the article posted at the bottom of this message already, read through it carefully (it's not written by me).
Ford and GM diesels with mechanical fuel pumps were known for fuel drain-back problems and the fixes were pretty much the same for both. They both used the same Stanadyne fuel injection systems. Ford's fuel filter system is a little different because of the many Schrader valves that can get air leaks.

Here's the guy's article covering problems similar to what you've described:

Stall after starting (especially after hot-soak/cool-down) then hard start
Air intrusion into the fuel supply system. Usually, the source of the fuel leak can be determined by the time from when the engine starts to when it stalls. On 6.9 engines with a firewall-mounted water separator, the engine will start and run for upto a couple of minutes before any air which may be in the separator reaches the injection pump. The 6.9 water separator is prone to leaks, both fuel and air. The best cure for this is to replace the OEM seperator with an aftermarket one (much cheaper--$30-$60 vs. $180), or remove it and its hoses and connect the line from the tank to the one running to the lift pump. Since it's not recommended to operate a diesel engine without a water separator, replace the fuel filter with the 7.3 type filter/water separator assembly. You can either purchase the header and sedimate bowl from Ford or a wrecking yard and install a new 7.3 filter. Another option is the Racor fuel filter/water separator kit. This kit contains a filter which fits on the original header and has a water sedimate bowl which screws onto the bottom (@ $35). The filter can also be purchased separately (@ $20), and you would want to keep a spare on hand as the replacement filter would not be available at your local parts store.
The 7.3 filter/water separator can develop fuel/air leaks at the fuel heater and restriced filter sensor or the filter drain (all three are servicable) and water in fuel sensor o-ring. The air bleed Schrader valve can leak on either filter.
The next common area for air leaks on both the 6.9 and 7.3 engines is at the injector return cap o-rings and hoses. This will cause the engine to stall after about 30 seconds of running if the air is able to travel into the fuel filter. On 6.9 engines the return line from the filter should be long enough to loop about four inches above the filter.
The 6.9 can be modified to have a check valve at the fuel filter return to prevent air from entering the filter. A 7.3 Econoline filter outlet fitting (E8TZ-9C402-A) can be installed in place of the original outlet fitting. An early 3/16" 7.3 filter return orifice with a "flapper" valve can be installed into the port ment for the E-van's restricted filter sensor.
On 7.3 engine the filter return orifice contains a check valve. This check valve is usually a rubber flap inside the fitting, and if this fails air is drawn into the filter as the fuel cools and contracts. This can be detected by removing the fitting and trying to blow through it from the hose barb end. If you are able to blow through it from this direction, it needs to be replaced. Seal the threads on the orifice with Loctite 515 Gasket Eliminator or PST. There are two different flapper valve orifices--3/16" and 1/4"--and the correct one needs to be used with the coresponding hose size or leaks may occur. Starting in 92 a 1/4" filter orifice was introduced without a flapper valve using a spring and plastic check ball. The spring-and-ball and flapper orifices are not interchangable; they have different headers. Also, the correct size return lines hose needs to be matched to the injector caps and the proper clamps used--not worm-gear, this will distort the hose; either OEM spring clamps or fuel injection system screw-and-band type. When replacing injector return o-rings on one injector, you should replace all on that cylinder head as they tend to leak after they have been disturbed. Use silicone dielectric grease to aid in reassembly and some times it helps to install a third o-ring between the return cap and injector line nut to keep the cap in place.
On the fuel supply lines at the filter inlet, filter outlet and injection pump inlet, there are seals which can allow air to enter the fuel system if they become deteriorated or dried out, even if there are no visible signs of fuel leakage. If there is a leak on the line between the filter and injection pump, the engine will seem to try to start, then become hard to start. Note that there are seals of the same type on the injection pump return line at the injection pump and at the return line collector fitting on the rear of the engine (some applications).
Less common areas for air leaks are the injection pump outlet check valve and the fuel lift pump, but both have been know to happen. Using clear hose on various sections of the fuel suppy and return systems can usually pinpoint the area of the air leak. Install the clear hose at the suspect areas, start the engine to purge any air, then allow to cool. Watch these hoses for large air bubbles or pockets when starting the engine to determine the origin of the air leak. Also allow the engine to come up to operating temperature to look for air leaks which may occur when the system is hot. These may migrate into the filter and cause a hard start concern.

Engine stalls at stops or when deprsessing clutch
Stalls returning to idle after snapping throttle open. Injection pump problem caused by poor quality or contaminated fuel. Check for presence of water in the fuel--removal of the injection pump governer cover may be necessary to find contamination, but is not advisable unless you have experience. Check idle speed setting and injection pump timing, as well as cold timing advance--timing should advance at least 2 degrees with 12 volts applied to the rear solenoid terminal. Adding Stanadyne's All Season Diesel Fuel Conditioner may cure this problem, but if it persists, or if there is no cold advance, replace the injection pump. Recommend that the Stanadyne All Season Fuel Conditioner be used periodically to prolong injection pump life.

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