Auto Service Professional

APR 2018

Magazine for the auto service professional

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18 | ASP April 2018 Technical condition. Note that the high side pressure reached 9.8 mega pascals. e conversion to psi is to multiply 9.8 X 145 equals 1,421 psi. Under WOT conditions at 5,000 rpm this pressure will exceed 2,000 psi. e supply side system supplies low side fuel pressure to the high pressure pump that is driven from the camshaft. is high pressure pump has an integrated control solenoid that is controlled by the PCM. e solenoid is spring loaded open, and duty cycle controlled to close in order to raise high side pressure in the injector rail. Ford uses four lobes on the camshaft whereas the other manufacturers use three lobes on the camshaft. A cam follower is used to mechanically connect the pump to the camshaft. When removing the pump always remove the cam follower and check for concave signs of wear where most likely the cam lobes are worn as well. is would prevent full piston travel of the pump, thus creating a loss of fuel pressure on the high side. is problem is well documented on some European vehicles. In addition, a high side fuel pressure sensor mounted on the injector rail reports high side fuel rail pressure to the PCM. is PID is available on the scan tool. e scan tool will show the command signal to the control solenoid. GM shows this on-time in degrees of crank rotation, although I have seen some aftermarket scan tools convert this to a duty cycle scale (see Figure 3). e top scan graphic is the duty cycle signal from the PCM to the high pressure pump control solenoid in a duty cycle scale. e bottom scan graphic is the command to the high pres- sure pump control solenoid in degrees of crank rotation. At frame 10 we did a WOT power brake. Note the increase in both parameters. Ford and other manufacturers show this value in a duty cycle scale. Depending on your scan tool you may be able to bidirectionally control this solenoid by commanding a higher on-time which should increase the high side pressure. Keep in mind you will have to bring up the rpm as you use this function in your bay. e control solenoids have very low resistance values, around .5 ohms, so the PCM will hammer the solenoid 6,000 times per second (on/off) to limit the current flow. As with the fuel pump control, the PCM simply increases the on-time to ramp up high side pressure. e PCM on both systems supply both the voltage and ground for these solenoids. e circuit codes for these systems are very robust. To limit the current flow the signal is frequency controlled by the PCM. On GM vehicles if the high side pressure line is removed, replace it and do not reuse it. Ford says that if the high side fuel pressure sensor is removed, it must be replaced with a new one. Lean conditions are a common problem from a bad high pressure pump. In addition there have been cases where the high pressure pump leaks fuel into the crankcase, so always Figure 3: The top scan here shows the duty cycle signal from the PCM to the high pressure pump control solenoid in duty cycle scale. The bottom graph shows the command to the high pressure pump con- trol solenoid in degrees of crank rotation. At frame 10 we performed a WOT power brake. Note the increase in both parameters.

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