I am getting a Low Fuel Pressure Warning on my Lowrance system when I blast off. The motor will surge a couple of times like it is being starved for fuel and then kick out of it. It runs like a top after that. Any ideas?
Thanks<br /><br />
Modified by DocG at 7:40 AM 7/26/2010<br /><br />
Modified by DocG at 7:41 AM 7/26/2010
Modified by DocG at 7:41 AM 7/26/2010
Phoenix 2021 721 ProXP
250 V8 ProXS
Low fuel pressure warning is normally an indiation of a filter problem and there are a bunch of them on a Yamaha. Prime suspects are VST and the medium pressure fuel filter (the can after the VST). However, since it "kicks out of it" and then runs good it may be you need to sync the throttle valves? Could also be a low pressure pump issue.
Have you tested the fuel pressure at the port near the VST? Should be between 39.8 to 51.2 psi (higher is better).
Test the pressure and if you have not cleaned or changed the VST filter lately that would be a good ideas as well (and then recheck the pressure after you clean/change to see if it goes up).
anybody have a picture of the port to test the pressure?
<table width="90%" cellspacing=0 cellpadding=0 align=center><tr><td>Quote, originally posted by Team Stratos »</td></tr><tr><td class="quote">anybody have a picture of the port to test the pressure?</td></tr></table>
Look at the first and third picture in the link below and it sits right on top of the VST sticking out to the front and looks like a valve you put air in and has a black screw cap on it.
http://www.bbcboards.net/zerothread?id=66928
Got it. Thanks. Isn't that also where you bleed out the air when replacing the VST filter?
<table width="90%" cellspacing=0 cellpadding=0 align=center><tr><td>Quote, originally posted by Team Stratos »</td></tr><tr><td class="quote">Got it. Thanks. Isn't that also where you bleed out the air when replacing the VST filter?</td></tr></table>
It is used to bleed off the pressure in the VST and check fuel pressure and bleed air when you change the VST filter and try and fill it back up with gas.
DocG, How is your HPDI behaving at idle?
It runs fine at idle and great at top end. I am going to sync the throttle valves later this week at the dealership and see if that is the issue. All filters have been changed. I believe once the computer is hooked up it will tell the story.
Phoenix 2021 721 ProXP
250 V8 ProXS
<table width="90%" cellspacing=0 cellpadding=0 align=center><tr><td>Quote, originally posted by DocG »</td></tr><tr><td class="quote"> I believe once the computer is hooked up it will tell the story.</td></tr></table>
Don't count on it!
Why is that? It couldn't be that the throttle valves are out of sync? If not I am at a loss, I have changed and tested everything else.
Phoenix 2021 721 ProXP
250 V8 ProXS
The computer will not show any pressure from the meduim pressure fuel pump. It will show a low pressure for the High pressure pump which will be normal if the problem is with the meduim pressure pump.
The meduim pump could be bad or there is an o-ring on the discharge side of that pump that could be the problem. Have you run a pressure check on the meduim pressure pump? When you turn the key on it shoud read 50psi and 5 seconds after the pump shuts of it should leak down no less then 45 psi.
When you get the boat back after nothing is found on the computer connect a pressure gauge to the valve on top of the VST using a long hose so you can run the boat while watching the gauge. Run the hose out of the cowling on the port side where the blank is for the trim switch.
You pressure should be at least 50psi while running and never drop below 45.
Not sure where David is coming up with this 39.8 psi because it is not in any HPDI manual that I have read. But I could have missed one I guess.
<table width="90%" cellspacing=0 cellpadding=0 align=center><tr><td>Quote, originally posted by spider1 »</td></tr><tr><td class="quote">
Not sure where David is coming up with this 39.8 psi because it is not in any HPDI manual that I have read. But I could have missed one I guess.
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It's on page 3-5 of my service manual. I had always been told the 50psi figure also, but this is a direct quote:
"Fuel pressure (medium-pressure fuel line) 280-360kPa (2.8-3.6 kgf/cm2, 39.8 - 51.2 psi)"
My manual is for the 2.6 liter HPDI and was purchased earlier this year from an authorized dealer who confirmed it was the most current version (along with the supplement). Supplement says the exact same thing too.
David there you go. I have not see a manual for the 2.6. Not sure if that is the difference or not by my manual for the 3.3 does not give a range like that.
It says that the pressure should be 50.8 and after 5 seconds it should be 43.5. Says nothing about a range for these two pressures.
By the way David I was never douthing you just saying that I have never seen the pressures that you have stated thats all.
<table width="90%" cellspacing=0 cellpadding=0 align=center><tr><td>Quote, originally posted by spider1 »</td></tr><tr><td class="quote">David there you go. I have not see a manual for the 2.6. Not sure if that is the difference or not by my manual for the 3.3 does not give a range like that.
It says that the pressure should be 50.8 and after 5 seconds it should be 43.5. Says nothing about a range for these two pressures.
By the way David I was never douthing you just saying that I have never seen the pressures that you have stated thats all.
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No problem.
I was just quoting what was in the book. Go figure (and I would go with the 50psi as it's what every Yamaha tech I've ever talked to or seen a post from says).
Supply side fuel flow problems sometims are a cause of suction side fuel restrictions; even thogh pressures are correct at the VST!! so with this due yourself a favor and check the draw side as described by euroman in his many posts. From my side, pay careful attention to the inernals of the many (not up to yami, merc or omc specs) pickup tubes in fuel tanks. simple and basic checks at least for piece of mind. Keep in mind, the fuel system starts at the fuel tank- vent-bottom entry point of tube-thru anti-siphon-thru all hose barb fittings ( use good thin wall ones, not auto store junk) and up the line to the motor. Not to exhaust the issue, I find most of the problems outside of the motor. Thanks, David.
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