Ford Powerstroke Diesel Engines.
Today’s diagnostic tools and advanced engine electronics have made it easier to pinpoint drivability problems in diesel engines, but it doesn’t mean that all problems are solved so easily.
One thing that is common on the powerstroke 6.0L DIT engines is what is known as injector stiction.
First of all, you need to understand how the injector functions. In the top of the injector is what is known as a spool valve. The spool valve is controlled by two 48-volt, 20-amp coils that direct oil flow in and out of the injector. One coil is used to open the oil circuit and the other is used to close the oil circuit. Basically, you have the spool valve in the middle with a coil on each end. When the open coil energizes, the spool moves one way and when the closed coil energizes the spool moves the other way. This movement of the spool valve is only 0.017˝. When the open coil is energized, the spool valve moves to allow high-pressure oil in from the rail to flow into the injector. When the closed coil is energized, oil is allowed to drain from the injector into the crankcase.
The coil is energized by the FICM (fuel injection control module) for 800 millionths of a second. So when the spool opens, high-pressure oil enters the injector. This, in turn, pushes the intensifier piston and plunger downward inside the injector body. Fuel enters the injector through an opening on the side of the injector body, which is delivered by the fuel pump and surrounds the injector through passages in the cylinder head.
At idle, the high-pressure oil is around 600 psi. When the engine is at WOT, the high-pressure oil can reach 3,000 psi. So, as the piston and plunger move downward inside the injector, fuel in the bottom chamber of the injector is being squeezed. The intensifier piston is seven times greater than the surface area of the plunger. This means that the injection force will be seven times greater than the high- pressure oil. Put it this way:
let’s say the engine is at idle and the high-pressure oil is at 600 psi. When the open coil is energized, the high-pressure oil comes into the injector and the piston and plunger move downward. The pressure of the fuel in the delivery chamber being forced through the tip of the injector nozzle will be 4,200 psi.
Now realize that if the engine is at WOT, this would be 21,000 psi!
Loss of Power on PowerStroke:
Injector stiction has to do with the injector spool valve. When the FICM commands the injector to open, there can be a delay in the spool valve movement, usually from the spool valve sticking in the bore.
There are several things that can cause stiction of the spool valve.
One of the biggest culprits is the type of oil being used along with the viscosity.
Powerstroke engines can be very picky about oil. It is not that there are bad oils on the market, but some are better for this engine than others. As you can see, these engines use hydraulic pressure to operate high injection pressures. One thing that tends to influence hydraulics is the amount of air that can be entrapped in the oil. Hydraulics do not like air. Air in the oil causes foam.
When foam enters the injector, it will cause misfires and rough running due to the “fake” injection pressures the foam is producing.
One thing that you have to remember is that all of the oil is going to foam after being churned by the pump and slung around in the engine. But, there is only one way to release the foam: manufacturers use silicone as a release agent. So use the engine oil that the manufacturer recommends. Manufacturers of vehicles know what the engines need and have to stand behind their products.
If you are using the oil that is recommended by the manufacturer, then hopefully you are also changing it by the manufacturer’s recommendations. Sometimes injector stiction is caused by negligent servicing of a vehicle. Deposits and scum tend to build and leave behind debris that can cause the spool valve to stick. Of course, over a period of time, the coils in the spool valve can also fail, resulting in a dead injector. So in order to give the best service life for your engine, follow the recommendations of the manufacturer.
Start Your Scanning Going back to diagnosing, you have to have the proper tools. There are scan tools on the market that will show a lot of data along with the trouble codes. But in order to find out what is happening with the 6.0L injector, you need a tool that can actually see the injector spool times. While there are many diagnostic tool options available out there, one tool in the aftermarket for independent garage is from Hickok Inc. It’s called the G2 Diesel Injector Tester and is for diagnostics used on-board while the engine is running.
This tool is helpful in diagnosing 6.0L injector issues, as well as saving the customer some money. The reason for this is that a lot of times when you have a couple of injectors that may have issues, some shops feel they have to replace them all. As you know, diesel injectors are expensive and this can be very costly. With a tool like the G2, you can see which injectors are causing the problem and replace only the ones that are bad. With the use of a laptop computer along with the G2 tester, injector spool times are identified quickly. While a laptop is not necessarily needed, it will give some data capabilities along with some graph displays on what the injectors are doing.
Sometimes the oil branch from the HPOP can leaking. This will also cause a loss of high-pressure oil that the injectors will not actuate when they were pulsed by the FICM.