HPDI 250 Fuel Pressure Questions

[Bigtasty]

In the Yamaha Service Manual it says to check fuel pressure at the VST within 5 seconds after start switch is turned on and that the pressure should be 50.8 psi. After 5 seconds the pressure should be 43.5 psi. Then after warming up the engine the pressure while running should be 50.8.

On my engine the pressure within 5 seconds is 100 psi. After 5 seconds the pressure drops down to zero. While running the pressure is upwards of 100 psi.

My questions. Should the pressure regulators be operating within 5 seconds to keep the pressure down to the 50.8 specified? Then how long should it hold the specified 43.5 psi before leaking down?

The manual also says to test the regulators by applying vacuum to the pressure regulators and that at the specified level fuel pressure reduces.

What is the "specified vacuum level"? I can't find it anywhere in the manual.

I apologize for the wordy post but hope that I got my point out there. This has been an incredibly frustrating couple of weeks...

 

[rodbolt]

Re: HPDI 250 Fuel Pressure Questions

you can have one of two issues.
first check the regulator diaphram for leaks. nasty but it can be done quickly with a piece of tubing and your mouth.
there is a filter in the regulator that can clog, if it clogs pressure increases. the filter is on the regulator return side.
the drop to zero can mean a defective regulator,defective high pressure pump or a leaking injector. monitor high pressure fuel at shut down.
could also mean the last one inside the VST crimped the oring between the pump outlet and the VST housing and its leaking internally.
but the 100 PSI issue has to be solved first and the regulator and regulator filter would be my first point.

 

[Bigtasty]

Re: HPDI 250 Fuel Pressure Questions

Okay, so if I put vacuum to the regulator hose connection it should hold vacuum and not leak down. I'm guessing that if it does leak down the regulator is shot and needs to be replaced. Right?

 

[rodbolt]

Re: HPDI 250 Fuel Pressure Questions

if you attach the vacum to the regulator nipple,then yes it should hold. if it does not the regulator diaphram is damaged.