It’s a no-brainer to realize that a diesel engine doesn’t care how the fuel gets to the tip of the nozzle. The engine responds to air and fuel delivery – period. With no throttle plate, diesels get all the air they want, so unless the filter is clogged or the turbocharger on the blink, air isn’t an issue. The wrinkle is that fuel has to be delivered at the proper time, with the proper pressure, and in the proper amount, and the operator has to be able to control fuel delivery in such a way that the engine responds the way a power plant should, regardless of what the power is being used for.
At two degrees Fahrenheit per pound of compression, cylinder temperatures can reach 1000º before the fuel is injected, and when a spray of anything combustible from engine oil to gasoline does hit that superheated air, no matter how it gets there, combustion is bound to follow.
Power Stroke Direct Injection
Ford and International teamed up with Caterpillar more than a decade ago to produce the engine now known as the Power Stroke. Where the old fuel system shot the fuel into small chambers with small openings into the cylinder, the new design injects diesel directly into the combustion chamber
Indirect Injection Direct Injection
With the advent of the Power Stroke, the mechanical injector pump that “popped” the old kind of injector was replaced by a low-volume high pressure oil pump and an electric-over-hydraulic way to control the pressure, which is delivered to an oil rail cast into the cylinder heads. The oil rails feed pressure to the HEUI (Hydraulic Electronic Unit Injectors) injectors (hidden away under the valve covers) along with the six-inch long self-current-limiting glow plugs.
The Hydraulic Electronic Unit Injectors ingeniously designed by Caterpillar are electrically operated and driven by the high oil pressure supplied to the rails in the cylinder heads. The PCM monitors inputs, including Engine Oil Temperature, Injector Control Pressure, Throttle Position, Manifold Pressure, and Cam Position, then sends commands to the Injector Driver Module, which provides the 115 DC volt electrical muscle (7-15 amps) required to operate the 2.0 ohm injector solenoids at the necessary speeds, allowing the high pressure oil to act on the head of an intensifier piston. The intensifier piston uses Pascal’s Law to multiply the incoming oil pressure by a factor of seven, effectively injecting and atomizing the fuel in the precise quantity and at the precise time the engine needs it.
The injector fuel fill cycle allows the chamber below the intensifier piston to fill with fuel (pink). Notice the two check balls, the upper one allowing fuel in under pressure from the fuel supply system (about 50 psi) and the lower one trapping it there until injection pressure forces it open and allows fuel to spray out the nozzle. When the solenoid (yellow) is energized, the poppet valve (green) closes the atmospheric vent, then opens the path for oil to enter the injector pressure chamber, allowing high pressure oil (dark gray) to drive the intensifier pistion (orange) down, and the resulting fuel pressure opens the bottom check ball, filling the nozzle chamber with enough pressure (>2700 psi) to pop the injector pintle up against its spring and off its seat. The fuel sprays out of the nozzle through holes too small to see with the naked eye.
Fuel Delivery
On the earliest Power Strokes, Fuel is pulled from the supply tank by a two-stage fuel pump that sits directly behind the fuel filter in the center of the valley behind the filter housing. The low pressure part of the pump creates vacuum and draws fuel from the tank. The fuel is pumped into the filter housing, rises to the top of the stand pipe, then is fed back to the pump (lower fitting) through the high pressure, positive displacement part of the fuel pump to the cylinder head fuel rails, where the fuel fills the lower cavity in each injector. Shop manuals call for a Cetane rating of about 50 for Power Stroke engines.
Trivia: Cetane is a clear, colorless liquid with near- perfect combustion qualities, and is rated at 100. Diesel fuels are rated compared to Cetane.
The in addition to the filter element itself, and the stand pipe, the filter housing contains a heater designed to keep the fuel at 70 degrees Fahrenheit. If the heater shorts out, the EEC fuse will blow and kill the engine. The housing also contains a Water In Fuel (WIF) sensor. The silhouette of the fuel Shrader valve can be seen at the top right of the illustration below.
1994-1997 Return Fuel System
The small return head on the side of the filter housing has a filter in it that catches solid material (like o-ring particles) coming from the cylinder heads. The small black reservoir was deleted after 1995, but the return filter head (with a built-in non-changeable filter) remained until the birth of the Second Generation Power Stroke, which had a different fuel filter assembly and a simpler fuel delivery system. (below) The fuel pressure is regulated on the return side of the heads by the spring and plunger assembly you see me holding here. If the spring is bent or weak, the fuel pressure will be low, but in most cases, the pump is the culprit.
Returnless Fuel System
In spite of the fact that this fuel system is called “Returnless,” the Second Generation Power Stroke fuel system actually does return excess fuel to the tank, but the pressure is regulated before the fuel ever gets to the cylinder heads instead of after it leaves as on the First Generation system. Notice that there is no return from the heads on this diagram. The fuel returns from the filter housing rather than the heads. The fuel pump is controlled by a PCM-controlled relay through an old-fashioned Ford inertial switch and runs for 20 seconds at key on. If no rpm signal is evident after 20 seconds, the PCM shuts the fuel pump down.
Thermal Recirc Module Filters.JPGThe filters you see here are in the tank and are part of the Thermal Recirculation Module, which is a temperature-sensitive mechanical apparatus that mixes return fuel with incoming supply to keep fuel temperature between 50 and 150 degrees Fahrenheit. The filters you see here can cause fuel starvation if they trap enough foreign material. It may happen after a hundred or so miles of highway driving, and the problem may go away after the vehicle sits for awhile, only to return a hundred miles later. The black item in the picture is the “nib” assembly, which sits on the bottom of the tank vacuuming up small particles and globules of water while they’re still at a manageable level.
Oil Systems
Low Pressure Oil System
Power Stroke’s low pressure oil system is similar to other V8 engines. The oil pump is a gerotor style unit driven by two flats on the nose of the crankshaft, and it draws oil in through the large pickup tube from the sump, then sends it through the oil cooler to the filter head, where it is filtered and regulated before being delivered to the oil gallery. The filter head also contains an oil filter bypass valve in case the oil filter becomes too clogged to allow oil flow. An air leak in the pickup tube can cause driveability problems, since it introduces aeration into the oil system, and the high pressure oil system is negatively affected by that in a big way.
Notice that one short gallery bypasses the rest of the system on startup to quickly deliver oil to the reservoir for cold or initial starts. This is necessary because the reservoir must supply oil to the high pressure pump, where the oil pressure is boosted and controlled before being sent to the injector oil rails. Without this short circuit oil passage, the high pressure oil pump reservoir’s oil supply would be exhausted before the gallery. If the short circuit check valve (short circuit device) malfunctions and lets the reservoir drain, a hard or no-start condition can result. If the oil filter bypass valve malfunctions and lets the oil gallery drain, the engine will start and run for about fifteen to twenty seconds before reservoir runs out of oil, then the engine will spin awhile to burp the air out of the gallery and refill the reservoir, then the engine will restart.
Power Stroke’s high oil pressure is controlled by the PCM by way of the ICP regulator, using a 0-65% duty cycle. The higher the duty cycle, the higher the pressure, but the high pressure pump contains a relief valve that limits the pressure so that it goes no higher than 3,750 psi.
Feedback information on high oil pressure is provided by the ICP sensor, mounted in the front of the driver side cylinder head. The high pressure pump doesn’t produce much volume, so any leakage in the system will either cause poor performance or, more commonly, a no-start.
When starting, the ICP regulator duty cycle is usually pretty low, but the PCM will ratchet that signal in degrees if the engine doesn’t start right away. If IPR pressure remains below 500 psi, the PCM won’t operate the injectors at all. A high IPR duty cycle with low pressure, (whether spinning or running) indicates a low oil pressure concern that may be caused by a system leak (invisible if it’s under the valve cover), a bad IPR, or a faulty ICP sensor signal. Unplugging the ICP sensor causes the PCM to default to a 725 psi ICP sensor reading, which will cause the PCM to operate the injectors and start the truck, provided sufficient oil pressure is available. Unplugging the IPR with the engine running should kill the engine. If it doesn’t, then the IPR is sticking and should be replaced.
Turbocharger and Related Systems
The early Power Stroke turbochargers had no wastegate, but they did have a built-in exhaust backpressure control valve. Interestingly, this butterfly, which is PCM controlled, only operates in ambients of less than 40 degrees Fahrenheit and only at low idle, no-load conditions. Raising the exhaust backpressure on an idling engine warms the coolant faster for better heater and defroster operation. If this system is rendered inoperative in the open position, it isn’t much of a problem, but in some cases, the oil piston that drives it (by way of a PCM controlled solenoid) can receive oil through a bad solenoid and close the butterfly when it isn’t supposed to. This causes a low power concern. Second Generation Power Strokes with Charge Air Coolers (Intercoolers) will have a wastegate, which is also regulated by the PCM through Wastegate Control Solenoid (pictured at left).
Glow Plugs
The glow plugs are PCM controlled through a relay that looks like an old Ford starter relay. With an oil temperature warmer than 131 degrees Fahrenheit (Power Stroke ignores Engine Coolant Temperature), the glow plug relay will not be energized, but the glow plug lamp may come on anyway, since the PCM is programmed to check the bulb. If charging voltage is higher than normal, the PCM will also limit glow plug operation.
Because of the strategy used on pre-Power Stroke glow plug systems, a Ford truck or van wouldn’t start on a cold day if a single glow plug was burned out. The controller will determine that a glow plug is out of the loop and click the glow plugs at about one short cycle per second. Power Stroke doesn’t operate that way. Even if a glow plug is burned out, the rest of the glow plugs continue to operate.
The glow plugs, like the injectors, are under the valve covers, and get their feed through the same connector shell and wire harness that carries the 115 volts to the injectors. With that in mind, always check the connectors for melting when a running problem is present. Sometimes a glow plug will short out instead of failing open, and when it does, the connector at the valve cover and the small harness for the two injectors and glow plugs in that quadrant will have to be replaced.
Relays like to burn out; the glow plugs pull about 25 amps each on initial burn, dropping back to about 15 amps as they heat up. On Second Generation units without a catalyst, a manifold heater is used to reduce white smoke, but it only operates for a short period of time right after startup.
The Power Stroke engine controller is a 104 pin PCM that sells for about $250. The Injector Driver Module, which is just as important as the PCM to the operation of the engine, runs about $850, and sometimes they have to be replaced to repair a no-start or rough running concern. Cruise control is built into the PSD PCM, getting its information from the steering wheel switches, vehicle speed sensor, brake switch, park brake pedal switch, clutch switch (where applicable), and a normally closed brake pressure switch that opens a 12 volt circuit when the brakes are applied. Since the Power Stroke has no throttle linkage, no speed control servo is used. The speed control strategy is programmed into the PCM.
The throttle position sensor (called an Accelerator Pedal Sensor on the Power Stroke) is a part of the Accelerator Pedal Assembly inside the truck, along with a separate idle tracking switch built as a part of the same assembly. If the Idle Tracking Switch and the APP sensor don’t agree, the vehicle won’t do anything but idle, and if a sensor is faulty, the entire Accelerator Pedal Assembly has to be replaced.
The Injector Control Pressure Regulator is a PCM-controlled solenoid and spool valve assembly that is mounted on the high pressure pump. Electromagnetic force applied as the solenoid is energized and it moves its internal spool valve to control high oil pressure feed to the heads. The high oil pressure runs from 500 to as high as 3500 lbs. Feedback from the ICP sensor closes the feedback loop to the PCM in the high oil pressure system. Adaptive learning is applied to this feedback loop - if the engine has low fuel pressure, the PCM has no way of knowing that, and so it may ramp the control oil pressure up to very high numbers just to get the engine started. And if somebody replaces the fuel pump and normalizes the fuel pressure, that learned high cranking ICP might cause a lot of white smoke and a no-start - I've seen it happen.
Backpressure Sensor.JPG from the rear of the passenger side exhaust manifold to a solidly mounted plate near the high pressure oil reservoir. The EBP sensor can short out internally, taking the reference voltage signal to ground, a condition that will disable the engine and kill scan tool communication. Also, the steel tube can stop up with carbon, a condition that will generate Diagnostic Trouble Codes. An old piece of speedometer cable on a drill will usually unclog the tube if that happens. The illustration shows a new EBP sensor plugged into the harness connector and the old sensor still mounted in its hole. The cam sensor is a major player; the PCM does nothing to start the engine if that signal is absent. The cam sensor signal is read and interpreted by the PCM to determine engine position and speed, particularly marking the positions of cylinders 1 and 4 (first and fifth in the firing order) for sequential injector operation, which means a lot whole lot more on a diesel than it does on a gas burner!
The PCM controls the relay that fires up the Injector Driver Module and communicates with the IDM on three different wires.
The IDM receives two digital control signals from the PCM, namely, the Cylinder ID signal and the Fuel Delivery Control signal. The IDM sends an Electronic Feedback Signal to the PCM, reporting injector circuit problems and other bits of pertinent information the PCM isn’t personally privy to without the IDM’s cooperation.
Finding a weak Power Stroke Nozzle
Isolating a malfunctioning injector on an ailing Power Stroke can be challenging, to be sure. When I was at the Ford dealer, before the $1000 Rotunda cylinder-killing tool became available, I used a Radio Shack project box and built a tool that could be plugged in between the valve cover connectors and the wire harness, and by operating eight toggle switches, we could kill injectors and listen for a change in sound with the idea that we could isolate the weak cylinder by sound like killing cylinders on a gas burner.
The biggest problem with that approach is the fact that a faulty Power Stroke injector might be delivering at least some of the fuel it is supposed to inject, and even when the guilty injector is electrically neutralized with the tool (whether it be my tool or somebody else’s), the PCM’s propensity to instantaneously alter the fuel delivery to the other cylinders usually renders the listening ear ineffective.
Ford’s approach to this problem was to access the Mass Fuel Desired (MFDES) PID on a tool that can record minimum, current, and maximum numbers and watch for the injector that changes the MFDES PID the least. For example, if killing injectors 1-7 each cause the MFDES to increase but killing injector 8 doesn’t raise the MFDES value, then 8 is the guilty nozzle. The injectors that are completely dead are fairly easy to find, but locating the partially dead ones can be disgustingly time consuming and uncertain.
My friend Tim Hogan, who was at one time the training director of AASP Houston, armed with an Interro Systems PDA and a low amp probe, has come up with a better way to isolate faulty injectors.
Setting the scope’s timeframe to 500 microseconds and the range to at least a 70 amp scale with the low amp probe clamped around the injector trigger wire in question, the pattern in the screen shot tells the tale. The jagged sawtooth part of the pattern represents the jittering signal that machine-guns the oil control poppet off its seat, creating what Tim Hogan calls a “Bart Simpson Head” (we’ll call it a BSH for short).
First generation Power Strokes only have one BSH, as seen in the ‘94 injector waveform illustration.
Second generation Power Strokes apply an initial amount of amperage to the injector coil to unseat the poppet, then a lesser amount of current to hold it open for a short period of time, thus the two BSH areas on second generation engines. Interestingly enough, the second generation PSD waveform looks almost exactly like the Duramax injector waveform, BSH included! The point is that the down slope right after the BSH should be a straight line. The ragged bump (see the area indicated by the yellow arrows on the bad waveforms) indicates an injector that needs replacing. If you don’t replace every injector with this bad bump pattern, the engine still won’t run right.
The exact reason why a bad injector waveform exhibits this scratchy bump (some look considerably nastier than this) is something of a mystery at this point.
Tim says he has used this method on a lot of different trucks with excellent results.
Above is a good 1999 Waveform:
Notice the nice straight downslope. Below is a bad waveform on the same truck. (All Screen shots courtesy of Tim Hogan)
Bad 99 Injector Waveform.JPG
While the first generation Power Stroke has a different waveform, bad injectors can be isolated using the same criteria.
Basic Knowledge 
Feedback information on high oil pressure is provided by the ICP sensor, mounted in the front of the driver side cylinder head. The high pressure pump doesn’t produce much volume, so any leakage in the system will either cause poor performance or, more commonly, a no-start.
from the rear of the passenger side exhaust manifold to a solidly mounted plate near the high pressure oil reservoir. The EBP sensor can short out internally, taking the reference voltage signal to ground, a condition that will disable the engine and kill scan tool communication. Also, the steel tube can stop up with carbon, a condition that will generate Diagnostic Trouble Codes. An old piece of speedometer cable on a drill will usually unclog the tube if that happens. The illustration shows a new EBP sensor plugged into the harness connector and the old sensor still mounted in its hole.
The cam sensor is a major player; the PCM does nothing to start the engine if that signal is absent. The cam sensor signal is read and interpreted by the PCM to determine engine position and speed, particularly marking the positions of cylinders 1 and 4 (first and fifth in the firing order) for sequential injector operation, which means a lot whole lot more on a diesel than it does on a gas burner!
