Fordelocks wrote:
Thanks for the reply W W Diesel. I reckon I have ruled a fair bit of that list out but I am open to suggestions.
Air in fuel, it would have been running fine seconds before the fail to start/low rail pressure.
Battery low, only after loads of cranking still won't start on a boost till it decides it's ready.
CPS, I am showing rpm on live data.
5&6 Valves on HP pump, doubt it as I am getting fuel up to the rail seconds before and during the fail to start.
Fuel pressure solenoid possibly yes that's why I posted the question, I am not 100% sure what controls it or how it should behave I find it strange that it is dumping fuel while the rail needs more pressure
Rail pressure sensor is new
Injectors I will pull the returns off and check tomorrow.
There should be almost no fuel dumping out of the Fuel Pressure Regulator on the end of the fuel rail during engine startup.
Maybe these descriptive and diagnostic documents can be of help for your understanding of the Fuel Pressure Regulator operation?
I have included a document for the Cascade Overflow Valve and Fuel Quantity Solenoid Operation also.
Fuel-Pressure-Solenoid-on-End-of-Fuel-RailQuote:
Cascade Overflow Valve and Fuel Quantity Solenoid Operation
OPERATION
The COV has a spring-loaded center spool-piece that has a drilled channel with three passages: one for initial low-pressure lubrication, one for lubrication at housing-pressure , and one for overflow. The valve is operated in three stages based on the level of pressure at the inlet.
Stage 1
When the fuel pressure entering the tip of the COV is between 0 and 3 bar (43psi), pressure is too low to overcome regulator spring tension and fuel flows through the center channel, only . This passage always allows fuel flow through to the pump center-ring and lubricates the pump bearings and internal moving parts. This circuit also allows air to bleed during initial cranking and returns the air to the fuel tank.
The COV is in Stage 1 during cranking, only.
Stage 2
When the fuel entering the COV exceeds 5bar (73psi), but is less than 12.4bar (180psi), the spool-piece moves against spring tension aligning a second passage for lubrication purposes.
Stage 2 can be reached during cranking and initial start up.
Stage 3
When fuel pressure exceeds 12.4bar (180psi), the spool-piece aligns with the overflow passage. This stage relieves the pressure into an overflow circuit that sends the fuel back to the inlet side of the gearotor pump, thus limiting maximum fuel pressure to 12.4bar (180psi).
Lubrication fuel continues to flow through all channeled passages during this stage.
Excess fuel is sent back to the fuel tank through the fuel-return circuit
Stage 3 is reached at over-pressure
FUEL QUANTITY SOLENOID
AKA FUEL CONTROL ACTUATOR
DESCRIPTION
The Fuel Quantity Solenoid valve is located on the back of the front cover of the high-pressure pump. The solenoid is pulse-width modulated by the ECM and meters the amount of fuel that flows into the high-pressure elements inside the high-pressure pump.
The solenoid is inactive up to 30 seconds after Ignition switch is initially keyed to ON position to allow maximum fuel pressure to the fuel rail during cranking and start up. ECM assumes FQS valve control when CPS signal and rail pressure are within acceptable limits
OPERATION
The Fuel Quantity Solenoid valve is a pulse-width modulated valve that controls the amount of fuel sent or delayed to the high-pressure pump elements inside the high-pressure pump. The ECM determines the fuel pressure set point based on engine sensor and rail-pressure inputs. If the actual fuel-rail pressure is too low, the ECM commands the solenoid to allow more fuel to flow to the high-pressure pump. This minimizes the difference between the actual fuel-rail pressure reading and the set point. The ECM will also operate the solenoid to delay fuel, reducing flow-rate, if the fuel-rail pressure becomes too high.
The FQS valve is commanded open by the ECM to allow the high-pressure pump to build maximum pressure (1600bar, 23,206psia), or closed to decrease pressure.
Thus, rail fuel-pressure can be increased or decreased independent of engine speed
The valve also has a fuel tank heat-protection function* that meters the exact amount of low-pressure fuel to the high-pressure pump to prevent excessive injector-heated fuel from returning to the fuel tank.
Temperature of fuel from the fuel tank is measured at the fuel inlet in fuel manager head via a temperature probe in the inlet side of the fuel-heater module.
Fuel System Diagnostic Flow Chart
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