So you have been cranking and cranking your IDI and it never starts? You probably have a fuel problem. It could be a variety of things. The first thing to check is if you are getting fuel to the Schroeder valve [aka Schrader] on the Diesel Filter head.
The IDI fuel system is comprised of one (or two) fuel tanks, fuel pickups, a selector valve, a lift pump, a fuel filter/water separator, injector pump, injector lines, and injectors. The lift pump sucks fuel from the tank, up the pickup, through fuel hose to the selector valve, and through more fuel lines up to the lift pump. Then the lift pump pushes the fuel to the Diesel fuel filter through metal lines on the front of the engine. The fuel is filtered here and then pushed into the Injector Pump inlet, and the IP subsequently pressurizes and fuels the injectors.
If there is a problem, a fuel system repair has occurred, there is a fuel leak, or a part has failed, your fuel system may have drained out. This is how you check to make sure you are getting fuel up to the filter.
On top of the Diesel fuel filter is a Schroeder valve. This valve serves two purposes: purge air in the fuel lines after a repair, and check to see if there is fuel or pressure in the system. The valve is no different than a valvestem on a car or bicycle tire.
Typically, you will need to purge the air out of your fuel lines if the following events had occurred:
- Owner ran the fuel tank dry
- Fuel hose replacement
- Fuel Lift-Pump replacement
- Diesel Fuel Filter replacement
- Engine replacement
- A small screwdriver (Phillips seems to work better)
- A cup
- Safety Glasses
How to purge air or check for fuel:
Using the screwdriver (or any pointy object), depress the center pin on the valve located on the top of the diesel filter housing. In vans, the filter head is located on the top of the engine on the driver’s side, and on the truck, it is located near the passenger side valve cover. Have a friend crank over the engine, in 15-second-START and 2-minute-OFF intervals. Never crank an IDI for longer than 15-seconds at a time. Hold a cup underneath the depressed valve to catch any spraying fuel. I like to wear safety glasses, just in case a drop or two sprays out of control. For the most part, if there is fuel, it will lightly dribble out of the valve.
Once the fuel is flowing without bubbles or spurts, then most or all the air should be vacated from the system. With the fuel lines purged and filter full of fuel, you can move on to purging the air from the Injection System, detailed in this article. At this point, this article is done, if you have fuel flowing.
What if I don’t get any fuel out of the Schroeder Valve after plenty of cranking?
Remember, never crank the engine for longer than 15 seconds at a time.
If you have cranked the engine for a few minutes (not constantly) and you still do not see any fuel at the Schroeder Valve, you have a fuel system problem. Start with the simplest things first, and work your way to the hard stuff.
1.) First off, put fuel in both your diesel tanks. Ford installed all fuel pickups to have these terrible plastic saucers in the tank that fall off. They are commonly referred to as the “cones of failure.” When these break, they don’t reach down into the last quarter of the tank, and even though your fuel gauge shows you have some fuel, anything under 1/4 is effectively “empty.” So put a few gallons of fuel in BOTH tanks, bringing up your fuel level to something the pickups can reach. Why both tanks? Sometimes your fuel selector valve may be stuck on one side, thus only pulling fuel from one tank. If you have one tank full and one tank empty, and the valve is stuck on the empty tank, the gauge will still read as if it is pulling from the full tank. By putting fuel in both, you can at least get your IDI running, and then you can troubleshoot the valve later. Also, some selector valves are water tight, but not always air tight; this means when there is an empty tank, it might suck a little air thru the empty side which creates some air infiltration and weaker running engine. By leaving a gallon of fuel in there, it always keeps the empty side a little lubricated and properly sealed up.
2.) Carefully inspect all your fuel hoses and lines up to the filter head. Look for tears or holes in the lines. You might see seepage or drips from hoses that have a tear or bad seal. A hole in a fuel line before the lift-pump will mean the pump will pull from the path of least resistance, and that usually means air is easier to pull than fuel in a tank.
3.) Replace the Diesel Filter. When replacing the filter, always refill the darn thing with diesel, because it saves a lot of cranking.
4.) Check if you have unclogged fuel lines. Knowing you have a full tank and undamaged hoses, disconnect the inlet hose on your lift-pump (location described in the next sub-section) and put a brake-line bleeder on it.
Try pulling a vacuum.
a.) If it doesn’t build pressure and no fuel arrives in the reservoir, then you have a rupture somewhere. Air is leaking into the system.
b.) If it doesn’t build pressure but fuel quickly enters the bleeder reservoir, then you are good to go; move on to the next sub-section.
c.) If it builds a vacuum and you don’t get any fuel, then you have a pinched or kinked line somewhere, or a clog in the fuel system or fuel pickup, or the selector valve is stuck in the middle. This is the worst of all scenarios because it requires a lot of inspecting and tearing down.
5.) Check the efficacy of your lift-pump. On the passenger side of the IDI block is a small pump that is driven by the camshaft. There is an inlet bib and outlet bib. Stick a meter-long section of hose on the outlet and put the end of the hose in a bucket. Crank over the engine. If you don’t get fuel in the bucket, then your pump is likely busted. Don’t fret. Replacing a bad lift pump is a pretty simple job and you don’t even have to drain the crankcase to accomplish it. Also, this might be a prudent time to replace the mechanical lift pump with a spiffy new Duralift 7-9psi or 9-11.5psi electronic pump (e-pump). The e-pump has many advantages over the lift pump, which I will detail in a future article.
6.) If all these have been tested and you still don’t get fuel to the Schroeder Valve, check the metal fuel line from the lift pump to the filter head. You can easily undo the ends and blow thru it.
7.) This involves a lot more work, but you can try dropping the tank and inspecting the tank and its pickups. I have two articles explaining the drop process for the center and rear tanks. Sometimes the fuel pickup bibs on top of the tank can get weak seals, and those can introduce air into the system, like in the image to the right.
Hopefully these steps have aided you in troubleshooting your fuel system.
Getting fuel to the Schroeder valve but the engine still doesn’t start? Check out this follow-up article:
How to Crack Injector Lines and Purge Air on a 6.9 / 7.3 IDI Diesel Engine
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