Scangauge
Post Fiend
Joined: Dec 2010
Posts: 10,121
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From: Orrville, Ohio
The way I understand it the ICP pressure is the HPOP oil pressure that is driving your injectors. The IPR Duty Cycle displays the amount of time that the IPR is open and closed to maintain the HPO pressure you are seeing. The IPR is a valve that cycles open and closed to allow oil to bypass the galleries in the head that feed HPO to the injectors. By looking at the two numbers in tandem you can get an idea of the health of your HPOP.
Postmaster
Joined: Sep 2007
Posts: 4,195
Likes: 6
From: Medford Oregon
Copied from another site ... 
Power Stroke’s high oil pressure is controlled by the PCM by way of the IPR 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 IPR 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.
Power Stroke’s high oil pressure is controlled by the PCM by way of the IPR 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 IPR 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.
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