How the Oil System Works on Ford's Power Stroke DieselPosted 12/13/2003
By Jeff Boskowitz
Do you believe in magic? What else could account for the operation of the high-pressure oil system on Ford's Power Stroke Diesel? This much I can assure you - it was not designed by Harry Houdini. But hey, maybe a distant cousin?
What I do believe is that the oil system used on this engine is an engineering marvel! While space limitations won't allow me to babble on endlessly, I hope this article will give you a better understanding of how this system works.
When the engine is cranked over, crankcase oil pressure builds. In addition to lubricating all of the engine's internal moving parts, the oil has one more path to follow. It travels through the timing cover to a high-pressure injection reservoir mounted on top of it, used to supply oil to the high-pressure oil pump. This pump then increases the pressure to the high levels needed to pop open the injectors, and to increase the pressure of the diesel fuel entering the cylinders for complete combustion.
The oil pressure increase is accomplished by a solenoid similar in function to an idle air control valve. This solenoid, the injection pressure regulator (IPR), is duty cycle controlled by the powertrain control module (PCM) to boost the oil pressure to the levels needed for good performance.
The oil then flows from the pump through braided steel lines to the center of each cylinder head where it runs through a central galley next to the injectors. When the PCM determines which cylinder needs to fire, it electrically energizes a solenoid in the injector to allow the high-pressure oil to enter, intensifying the pressure of the diesel fuel and injecting it into the cylinder. The PCM uses an injection control pressure sensor (ICP) to determine the oil pressure. The sensor is mounted in the inside face on the driver's side head. The more ground time applied to the IPR, the higher the pressure rises. The minimum amount of pressure needed to open the injectors is 400 psi. With a pump designed to put out well over 3,000 psi, the PCM should be able to achieve that pressure with no more than a 12 percent duty cycle on the IPR. If the ICP indicates pressure fails to reach the minimum value, the PCM continues to increase the duty cycle on the IPR until it reaches the maximum of around 60 percent. Somewhere around 50 percent, even if adequate pressure is achieved and the engine runs, the PCM sets a code for ICP above/below normal.
The first step in diagnosing a fault in this system simply requires checking the oil level in the crankcase. If the oil level drops three quarts or more, it lowers the level in the high-pressure reservoir, reducing pressure in the injection oil system. Once oil level is verified, watch the engine oil pressure gauge on the dashboard while cranking to verify that it jumps to the middle in a short amount of time. In real life, this "gauge" is an idiot light with a needle. It uses a normally open switch instead of a true sender. When engine oil pressure exceeds 5 psi, the switch closes, completing a path to ground for a voltage applied through a dropping resistor in the gauge, causing the needle to jump up. This switch is located in the top of the high-pressure reservoir. If engine oil pressure for any reason is low, it will need to be addressed first, as insufficient high pressure will result. If it is OK, monitor the rpm, ICP and rpm PIDS in the datastream with a scanner. Upon cranking, at least 150 rpm should be noted. The PCM then activates the IPR to build pressure. If the IPR reaches the max and under 400 psi is showing on ICP, or you see a reading of 2,000 to 2,500 psi (a default reading generated by the PCM when it believes the sensor is in error) and the engine doesn't start, there is a fault in the high pressure system.
To isolate the heads as a potential large leak: 1) Remove the line from the right head and cap with a suitable plug. 2) Remove the left-hand line and connect an oil pressure gauge capable of reading 3,000 psi or greater to it. 3) Crank the engine while watching the gauge for actual pressure. If the reading is low, the problem lies in the high-pressure pump or the IPR. But to determine which is the guilty culprit, you first need to replace the IPR to evaluate. If that doesn't correct it, the pump will need replacing.
So the next time one comes in with a lack of power, stalling or no start concern and you retrieve fault codes P1211 and/or P1212, you too can work a little magic!
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