150 HPDI, VST fuel pressure drops from 50 to basically nothing....

[refimike]

I have an 03 HPDI that I have done a lot of work to so far. Recently the motor started to die at anything above 1200 rpm, but would idle fine. Then about a week after that it would not idle for longer than about 10 seconds. Called in a mechanic who measured pressure at the vst schraeder valve and found that at key on it goes to 50 and about 5 seconds after that just completely falls off a cliff down to like 5. He wants to replace the fuel pressure regulator but I just want to verify that this sounds correct because he does not sound very confident that this is indeed the issue and the part is 300 bucks.

Within the last year I have done the following:
Had all injectors serviced by Brucato. all but 1 were able to be brought up to spec, that one was replaced.
replaced all the filters, and the basket filters on the hp pump.
all new plugs and all new coils
new neutral safety swith
new fuel lines
new primer bulb
new racor
new vst filter

YDS showed normal high pressure fuel pressure before this issue started.

The fuel pressure regulator is kinda covered in surface rust and does not ever appear to have been replaced, but I feel like I ran across a post stating that this could be an o-ring on top of the vst fuel pump that causes the loss of vst pressure at the valve. Oh, the o-ring on the vst tank itself is also brand new.

Any help is appreciated. I have added the new pressure regulator and both internal o-rings for the vst pump to my cart over at sim yamaha but don't really want to chase this down just by throwing parts either. Just trying to get this thing up and running as I am trying to sell the boat as I have a new boat arriving in June.


Thanks in advance.

[boscoe99]

If the fuel pump is made to run with the key on (say by grounding the pump via a jumper lead to a ground) does the pressure stay at 50 psi or so, or does it drop?

If the motor is started immediately when the key is turned on (pressure at 50) what is the pressure when the motor is up and running?

[refimike]

50 PSI with key on then falls off to like 5 after about 5 seconds, same thing when it is running. 50 psi then drops to like 5 and engine dies

[boscoe99]

You did not answer my question. Does the pump run with the key on and with a ground lead attached to the fuel pump or not?

If the pump does not continue to run with the ground lead, and battery power is being supplied by the key being on, then the pump is the problem.

If the pump runs continuously but pressure drops it is more than likely the regulator.

[boscoe99]

Trouble shoot. Stop throwing parts, money and wasted labour at the motor.

[refimike]

My apologies, I will test to see if the pump continues to run with a ground lead on it tomorrow. I am at work and I have not tried that.