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motor runs fine when first started, just had two bad injectors replaced. When motor gets up to temp will run all day until you kill it and wait about ten/15 minutes. It will start back up but die after running for about 10 seconds. It sounds like engine is running out of fuel. you then have to wait about 30 minutes or so and engine will start right back up and run fine. Kill it and you have to go through the same thing over again. The high pressure fuel pump is new. All filters are new, no ethanol is run in motor. Bulb can be pumped but that doesn't help. Dealer service thinks it may be low pressure fuel pump but they really don't know and I don't want to buy a $500 fuel pump on a hunch.
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the guys who know the answers will no doubt be along shortly, but I'm going to throw this out there to see if I've learned anything:
the check valve on the VST vent has failed open -
How to check that?Comment
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there are two check valves.
one is for maintaining fuel pressure to the VST inlet and is located beside the lift pump.
the other is for VST venting and located at the top port airbox.
if the VST vent is allowing vapors to enter the airbox it could cause a hard restart on a warm motor.
its easy to simply unplug it from the airbox and see what happens.
that motor,if the VST is full, will run a few minutes with the lift pump unplugged.
I doubt its a lift pump issue.Comment
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Thanks, I will give that a try. I tested the low pressure fuel pump and it's fine.Comment
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How does it work?
To be factually correct they are not check valves. One is a pressure relief valve and the other is an orifice air valve.
The pressure relief valve opens to reduce the pressure output of the lift pump when the pump cannot pass fuel to the VST, because the inlet valve in the VST closed. It is closed because no further fuel is needed in the VST. The fuel is looped around the lift pump when the pressure relief valve opens. When the float valve next opens fuel takes the path of least resistance and flows to the VST. The pressure relief valve then closes because the pressure of a spring in the relief valve is greater than the fuel pressure.
The other valve (the one between the VST vapor and the intake manifold) opens when VST vapor pressure exceeds the pressure for which the orifice air valve is set. It will then vent fuel fumes into the air intake manifold. Too many of those fumes and the motor will not run, or run poorly, because of an overly rich air/fuel mixture. The valve can fail and cause this condition but also so can fuel that is not being cooled properly (clogged fuel cooler) or fuel that is too volatile, such as winter blend fuel that is being used during the high temperatures of summer.
More than most will want to know but see diagrams below:
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You have to wait for the motor to cool down a bit before it will start again. And it will fire right up.Last edited by justincblades; 06-06-2015, 10:26 AM.Comment
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Perhaps a motor that has cooled down for a while will have less fuel vapors remaining in the air intake system. Fuel vapors will dissipate over time.
As noted by Rodnut, why not unplug the orifice air vent and connect a piece of hose to the hose that comes from the VST to which the air vent was formerly plugged into. Route the added hose to outside of the motor in some fashion and see what happens. There may be some rubber grommets in the bottom of the cowling that you can use or you can remove the plug that can be used when relocating the pan mounted trim and tilt switch.Comment
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Ok so checked all that. Nothing. Fuel pressure is around 40-44 when at an idle. Motor runs perfect. Killed the motor waited 10 minutes and it will start back up for about 10 seconds and die like it is still running out of fuel. Checked fuel pressure at fuel rail and still 40-42 psi. Purged and fuel is in fuel rail. When you try to start it again it spits and sputters immediately then dies. After that it just spins over not even firing off at all. Waited 25 minutes and it started up immediately with no hesitation. I am at a loss.Comment
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Not for arguments sake but for the sake of discussion, which I enjoy and use as a learning tool, sometimes parts are labeled based on the purpose they serve even though internally they may very well be the same or similar.Originally posted by fairdeal
I think of a check valve as a valve that functions to allow a media to flow in one direction only. Like the check valve in a fuel primer bulb for instance. It "checks" the flow of fuel in one direction but does not "check" the flow of fuel in the other direction. The checking mechanism (a flapper type valve in the case of the primer ball) can freely open and close and does not have any mechanical means to hold it closed or to cause it to open at any given pressure. The pressure on either side of the valve will usually be very close to the other side.
A pressure relief valve on the other hand normally has a spring loaded valve that keeps it closed. Pressure will be needed to unseat the valve so that the media can flow. Depending upon the strength of the spring the valve will only upon when the pressure of the spring can be over come by the pressure of the media acting upon the valve and the spring. Think of what many call a "poppet" valve. It is a pressure relief valve. When the water pressure rises to the design value the valve will open and allow water to flow through. Pressure will be high on one side and almost nil on the other side of the valve.
An orifice air valve is a pressure relief valve of sorts in that it might have a spring to help keep it closed but the spring pressure will usually be very low.
Yes, I am painfully aware of Yamaha calling the same part by a different name. One engineer does not agree with another engineer and whichever one is doing the writing/calling uses the terminology that he wants to use. Sorta like me wanting to call a part a pressure relief valve whereas Rodbut may want to call it a check valve. I try to stay with Yamaha terminology if and when I can so that hopefully we are all speaking the same language.
But, I balk at calling a throttle control box a binnacle, calling an anti-ventilation plate a cavitation plate, or calling battery cables a wire harness.Comment
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Did you disconnect the orifice air valve and route the VST vapor pressure hose over board?Originally posted by justincblades View Post
One thing that I note is that your fuel pressure seems to be too high if it is 40 - 42 when the motor is idling. Specification calls for 44 psi when the key is turned on with the motor not running. With the motor running and at an idle the fuel pressure should drop into the high 30's. Too high of a fuel pressure means too much fuel flow through the injectors and too much fuel being looped back through the fuel cooler causing the fuel to heat up more than it should.
Isn't trouble shooting fun?Last edited by boscoe99; 06-06-2015, 03:24 PM.Comment
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Pressure drops to around 38-40. Is there a regulator on the system? And yes I did try re routing the hose. It is definitely a heat issue as it takes longer if the cowling is left on vs off. Or at least it is tied to heat. If you kill the motor and start it right back up it doesn't die and will run fine.Comment
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Yes, there is a fuel pressure regulator on the motor. The regulator is plumbed to the intake manifold so that as pressure in the manifold lowers the fuel pressure will lower. Conversely, as the manifold pressure increases then the fuel pressure increases.
Think about all of the temperature related variables. Block might be running hotter than normal (but not hot enough to trigger the alarm) and transferring excess heat to the VST, fuel cooler might not be cooling the fuel as well as it did when it was new (clogged water passage way), lift pump might be working on the fuel moreso than normal causing the fuel to heat more than normal, the gasoline might be overly volatile, etc., etc.
When the motor is hard to start after it has sat awhile have you tried to open the throttle a bit (say half way) and then engaged the starter to see if anything changes? If it is an overly rich air/fuel mixture the open throttles will help to clear the rich mixture out more quickly, hopefully improving the start. Be ready to come back to idle as soon as she lights off so as to not over speed the motor. Or, pull the kill switch, open the throttles wide open and crank the motor for about 10 seconds. Then put the throttle back to neutral, plug in the kill switch, and see how she cranks, starts and runs.
Don't be fraid to speriment.
In the old days of carburetion it was easy to flood a motor. The trick to starting it was to hold the gas pedal to the floor. Crank the motor until she started. I am told, but don't know for sure, that if the gas pedal is held to the floor in an EFI automobile that the fuel injectors will be told by the ECU to stop working. When the motor starts and you let off the gas pedal the injectors will then be told to work. The ECU is smart enough to take the position of the gas pedal into consideration when it decides how much fuel to provide to the motor.
Now, is a Yamaha EFI four stroke smart enough to do this as well? Need some sperimentation to find out.Last edited by boscoe99; 06-06-2015, 05:17 PM.Comment
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Once it dies (like it is not getting fuel, it seems like injectors are not putting fuel in. Or it is completely out of gas. It does absolutely nothing no matter where throttle is. There is fuel pressure in the fuel rails and high pressure pump primes up. To me it's like the injectors stop working ( all of them). I know it's not flooding either. Pulled plugs and they are clean.Comment
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Sooo many terms = confusing, but most get the idea.. Check valve prevents back flow, and pressure reducing valve is significantly different in design, but generally the point is made when referencing the nomenclature. Different manufacturers love their own sometimes crazy terms just for the sake of having their own special identity even though everybody copies the other guy.I think you are having vapor lock issues..Try venting fuel vapor to atmosphere and not back to the manifold. Might help.Comment
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