200 HPDI, calling on Rodbolt or any HPDI expert

[Britfish]

Got my high end RPm loss of power problem back. New filters in Sept, VST, inline, canister and separator. No more than 20 hours added since then, was running great up to last evening.
Couple of questions about fuel pumps.
The gauge I hooked up to the low pressure one idles at 50 psi, then when i open up the throttle it drops to 40, comes back to 45, drops to 40. Is this too much of a variance off the 50 ? Is 50 the correct number it should run at ?
Also, should there be any residual pressure when I turn the motor off? Its goes straight down to 0.
What would be your first things to do ?
As always thank you
Signed: one FRUSTRATED HPDI owner

[boscoe99]

Somewhat related question.

If a variable fuel pressure regulator with a four stroke is needed for acceleration purposes, why is the HPDI fuel pressure regulator variable given that all the medium pressure pump in that model is doing is supplying fuel to the high pressure pump?

[rodbolt17]

boscoe
it does the same dang thanh on BOTH notrors.

its why you young techs have so many issues.


it works THE SAME ON BOTH.

why cant folks simply understand WHY EFI needs a regulator and WHAT does it do.
its stupidly simple.
the ONLY reason we have a regulator at ALL, is strupidly simple.

some engines will fire groups at hard throttle up. some not.
but at the end of the day I really don't care if its a chebby a ferd a lambo.
it ALL works the same.
some techs are to stupid to deal with it.
the ONLY reason for that regulator is to maintain an even fuel pressure.
THATS SIMPLY IT.

[Britfish]

Hey guys, do I need a new LPFP?

[boscoe99]

I understand what you are saying about a fuel pressure regulator for an EFI motor.

It is an HPDI that I am talking about now. The electric fuel pump with the regulator does not directly supply fuel to the motor. It only applies fuel to the mechanical high pressure pump.

Low pressure pumps supply to fuel to the VST and they are not pressure regulated. Why then does fuel pressure need to be regulated from the VST to the HP pump?

The HP pump is the one that will be doing its own fuel pressure regulation albeit at a much higher pressure than will ever be seen out of the VST. So, why does the fuel pressure to the HP pump need to be regulated?

[Britfish]

Now I'm confused what to do next. Usual HPDI issue, high RPM bogging down. All filters are new in Sept along with fuel injectors sent to flagstaff to be "unblocked". Feels like a fuel issue, what should I do ?
Thanks

[99yam40]

is the high pressure and low pressure dropping at the same time as the motor surges/ looses PRM?
If so you need to be looking for what is causing the low pressure to drop.
Is there a low, medium, and high pressure system that needs to be monitored? Just my opinion

Just because you did something months ago does not mean that the same thing cannot be a problem now
and trouble shoot like nothing has been done.

could there be a restriction or air being sucked into the system causing problems?

Hopefully Rod and Boscoe will try to give some helpful info soon

[rodbolt17]

dunno why they decided on 50 psi to the hp system but it wont work well at 40.

your describing a classic loss of rail pressure,

[Britfish]

Would you suggest all new filters again and changing the Low pressure fuel pump ? it hasn't been changed to my knowledge

[99yam40]

Have you monitored the rail pressure and the others at the same time to see what they are doing at the time the problem shows up ?

[boscoe99]

High pressure pump output pressure should be monitored as well.

[rodbolt17]

or
take your left hand, scratch you privates, while simultaneously take your right hand and scratch you head.
dance about for effect.

OR test this stupidly simple system.

can it maintain 50 psi and about 625 PSI at the failure RPM and load?
if it can its not fuel.

goes back to if you don't wish to read and understand a simple system, pony up the cash to get it fixed.

BTW good luck with that.

even the new crop of supposed master techs cant deal with HPDI,OX66 or even the old carbed 3.1L.

[Britfish]

I said in the start of the thread it could not maintain the 50 PSI, drops to as low as 40 when under load.
Need help with the high pressure test, hopefully this weekend.
Replacing the 2 fuel pumps tomorrow (ones before the vst tank).
Think I need a new electric fuel pump in the vst tank ? do they have a life span? should be changed at certain intervals.
I'm done scratching, now I just need help fixing it.

[rodbolt17]

which is why its critical to monitor BOTH medium and high pressures.
if both fall start looking at VST supply issues.
by the fact it can maintain 50 psi when fuel VOLUME requirements are low I would say the medium pressure regulator is ok.
HPDI, unlike EFI, cannot and will not go to group injection at rapid throttle opening, it does increase injector on time to allow more fuel for acceleration.

so we kick it in the rear, VST pressure drops, tells me either the VST fuel level was low OR the VST pump intake filter is clogged.
suddenly the injectors are ON longer, the HP pump regulator closes to maintain fuel rail pressure, the VST cant supply enough fuel at 50 PSI, engine bogs.

a tip.
the VST filter is located just above the VST drain.

take a can of carb cleaner.
drain the VST catching the fuel in a fire marshal and EPA approved container and dispose of properly.
bend the last 1/4" or so of the red spray tube from the carb cleaner about 90*.
insert it into the drain hole.
spray like crazy while moving the tube around.
most times this will clear any film buildup on the VST intake filter.

[rodbolt17]

voltage at the HP fuel sensor should be 2.8-3.2V, P-B, at ALL rpms.