Low Fuel Pressure

[Bulldog 51]

2004 HPDI 150 [vz150tlrc] lost power and would not rev past 5000 rpm under load. I changed plugs and it immediately fouled all six. Replaced all fuel filters and added 10 micron water separating filter - didn't help. Had diagnostics run and tech said screen was flashing red LOW FUEL PRESSURE. It measured 350 psi. Where to start? Almost forgot plugs are still fouling and are wet.

[99yam40]

replace or clean all filters and screens

[Bulldog 51]

That was the first thing I did. Any other sugestions?

[99yam40]

You replaced/cleaned screens in VST? and did that motor have the per filter before the VST?
Did they monitor the medium fuel pressure also to see if that was a problem while the HP fuel pressure problem was found?

Did they give you any info on what the problem could be?

[99yam40]

If low/medium pressure is good and HP is low then maybe the screens inside HP pump are plugging

[rodbolt17]

ok
we know the ECU is not happy.
its tossing a code.
either you dont have fuel in the VST(hull systems or lift pumps) cant get fuel through the vst to the HP pump(vst or medium pressure filter) or your HP pump is clogged.

[Bulldog 51]

I replaced the filter inside the water separator. I replaced the $71.00 canister filter. I cleaned the VST filter [although there was nothing on it]. All the filters I replaced looked clean. I even cut into the canister filter and stretched the cardboard out to inspect and it was clean. I put in new plugs and went to the lake to test. It started fine. It got up on plane pretty good. Ran up to 4900 rpm fine. When it crossed the 5000 rpm mark, it bogged. Letting off the hot foot made it pick back up but, 5000 rpm was tops. I ran about 30 minutes testing. Since there was no improvement, that is when I had the tech diagnose it. He is the one that told me about the "LOW FUEL PRESSURE" flashing warning. He thought it might be an obstruction from the HP pump. He also put in new plugs. I pulled the "mystery filters" with no noticable effect. It runs too smooth at idle and up to 4900 rpm for me to think I have an injector sticking. All of the components I have replaced have been clean and I don't have any oil, crud, or anything on my motor. Could you school me a little on the low pressure pumps. Are there two of them on a 150? When I measure the VST pressure via the schrade valve, am I measureing all of the pumps combined except the HP pump. How can I tell whether or not the low and medium (VST) pumps are right? What effect do they have on causing fouled, wet plugs and how?

[rodbolt17]

that system has 3 pump systems.
low pressure is the two lift pumps that feed the VST at about 7 psi.
the medium pressure feeds the HP at 50 psi.
the HP feeds the fuel rail at about 625 PSI.
at about 550 PSI it starts running poorly.
it also starts running lean and detonating pistons.

[Bulldog 51]

Rodbolt HELP!

OK - I put the fuel gauge on the schrader valve on the VST. I turned the key and the pressure went to 55 psi. It immediately began to fall at about the rate that a second hand moves on a watch to 40 psi. The fall rate slowed to about half but the pressure continued to fall. The primer bulb will firm up but starts going slack at about the same rate but not as dramatic. I can smell raw fuel but I cannot see any leaks. Does this mean the low pressure pumps are bad? Does that explain the other things that are happening?

[rodbolt17]

if the lift pumps are bad then the VST will run out of fuel and then the HP system goes low.
at key on the medium pressure pump runs about 3 seconds.
after that pressure starts falling cause the pump is off.

[Bulldog 51]

If the HP pump is giving trouble, does it make sense that it will run 5000 rpm smoothly. Could this be an injector problem?

[99yam40]

The fuel pressures should be monitored simultaneously to see what is going on, that should tell you what and where problems are

[rodbolt17]

it will run smooth all the way till it wont.
keep running it lean and you will post about another issue.

[Bulldog 51]

Ok, I haven't posted back because I have been turning wrenches during the couple of hours of daylight I have left when I get home.
I put the fuel pressure gauge on the VST and ran it. When it got to about 4800 rpm, the gauge went erratic jumping from 50 down to 30 very rapidly. When I would back off, it would steady back off at 50 psi. I checked the low pressure pumps. They tested good. I pulled the low pressure pumps and the diaphragms were good. Now what? I rigged up and external tank and ran it off that. Steady 50 psi. I started looking on the boat side for a constriction. It turned out to be a faulty anti-siphon valve on the tank itself. What a bear to get to! When I got that replaced I went back to the water and ran. It maintained a steady 50 psi but still would not reach WOT. I sent my injectors to be cleaned and they are back in with a set of new plugs. I will not get to check it out until Saturday. I will post back. My premature question is, "If this does not get me to WOT, could it be anything except the HP pump?"

[99yam40]

ok
either you dont have fuel in the VST(hull systems or lift pumps) cant get fuel through the vst to the HP pump(vst or medium pressure filter) or your HP pump is clogged.

what rodbolt17 has already said