It regulates the "bleed-off" to control the injection pressure. The HPOP produces much more pressure than is, necessarily, needed depending on conditions. So the IPR leaks the extra (as controlled by that magnetic coil) to lower the pressure. The more its Closed, as represented by a percentage of time, the harder time it's having maintaining the desired pressure.
A forum community dedicated to Ford F-series owners and enthusiasts with a Power Stroke diesel engine. Come join the discussion about performance, bulletproofing, modifications, classifieds, troubleshooting, maintenance, and more!