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Old 08-23-2019, 08:52 AM   #2 (permalink)
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Location: MI.
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P1093 Large Leak; difference between commanded fuel pressure and actual pressure is greater than 20 Mpa. Large leak means there is a leak in the high pressure system. Large leaks go into the return system and flow back to the tank, these are not external leaks.
1) If P0087 is set, solve P0087 first.
2) Similar Diagnostics to P0087

P0087; fuel rail pressure is less than 22.5 MPa at more than 600 RPM, fuel rail pressure too low.

1) Excessive restriction, fuel supply, plugged filter or sucking air. Install special tool J44638 to check vacuum restriction on fuel supply to the high pressure pump. Maximum restriction at WOT (wide open throttle) is 5 inches HG in park. When driving under hard acceleration maximum would be 7-8 inches Hg. If too high replace the fuel filter and retest.
2) If restriction is only a couple of inches vacuum, that could indicate that the fuel supply system is sucking air, use clear fuel lines at the filter head to check for air. Buy Racor Fuel Filter Head Assembly
3) Excessive restriction could also cause a DTC P1093 to set at the same time.
4) Rail pressure should read 1-1.8 MPa with key on and engine off. If out of range replace the rail pressure sensor.
5) Check fuel return from the high pressure limit valve or fuel pressure relief valve. If it is leaking then it will need to be replaced. We have also heard of race plugs leaking, even if you have a race plug, you may want to check for leakage at max rail pressure.
6) With the engine up to operating temperature, use the scan tool to command rail pressure to 21,000 PSI, if the rail pressure will not achieve 21,000 PSI at idle you most likely have a problem with the injectors, especially if you are having a hard start, miss, rough run or smoke and balance rates are excessive. Perform the enhanced injector return test.
7) Disconnect the fuel rail pressure sensor the fuel pressure should be greater than 175 MPa as displayed on the scan tool.
8) If these codes set only on hard acceleration or when pulling a hill with a load, check fuel supply issues first. Then see if rail pressure will reach 21,000 PSI at idle, if it does then the low rail pressure under a heavy load is usually caused by a bad high pressure pump.

Also note that 1 MPa (megapascal) is equal to approximately 145 PSI, 100 kpa is roughly 14.5 PSI.

Last edited by Rvn4me; 08-23-2019 at 08:58 AM.
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