Low Fuel pressure issues - 1992 Grady-White Marlin w/ twin 2002 Yamaha 225 4 strokes

[bob marlin]

Here is a short history of the boat and motors before explaining my problem. I purchased this boat in 1996 and am the second owner of the boat. I replaced the 2 stoke motors in 2003 with 2002 Yamaha 4 Strokes. The boat and motors have been yard maintain for most of the time. Since I have owned them I have had no real issue with either the boat or motors until now.
The boat went in the water the beginning of this summer (June 17 2019) and immediately had problems getting the port motor over 3000 rpm. I contacted a local marine to assist with this issue. After they diagnosed my problem they determined it was a fuel pressure issue. I had replaced as normal maintenance the water separator filters and fuel filter. This did not seem to help the problem and the marine at this point suggested replacing the filter (screen) in the VST tank along with the HI-Pressure pump and cleaning the tank. At this time they also replaced the spark plugs at my request do to the fact they were two seasons old. Boat went back in the water and ran fine for a day. The next day it went back to the port motor not getting above 3000ish rpm. This started what was to be a full summer of 'Try This It Should Help'. Some of the attempts to correct this were, running the motors on remote tanks to eliminate gas or fuel line issue at the gas tanks. Remove water separators at two different times to check fuel content and quantity in the filters. Also checked electrical, both at the console and in the motors to rule out possible issues with the computer and ignition switches. Check throttles as well to make sure there was no problem with linkages to motor. During one of the sea trial the mechanic thought I might have spun a prop so I brought it to a local propeller repair shop and had a new hub installed.
This continued for the entire summer at which point I decided it was time to get another marine involved. The marine technicians at the new marine ran the motors as well as pressure tested the fuel system and came up with the same conclusion that the problem is lose of fuel pressure. There recommendation is take care of the motor first, i.e. check the reassembly of the VST tank as well as fuel lines. Secondly remove the floor and replace the fuel lines from the tank back to the motors. Also removing the Grady White installed primer pumps and replacing with hand pump assembly.
Also what I thought was an important item mentioned to me by this new marine was before spending time and money to correct this issue was to check for possible corrosion that the late model Yamaha's were prone to. They pulled the thermostats off to visually inspect and determined it was minimal.
If there is anyone out there that has had similar problems with there boat/motor fuel system I would appreciate their experience and fix.

P.S.
This was my first full summer of retirement and was looking forward to boating on a daily bases, NOT.

 

[seasick]

The exhaust corrosion issue will not show up by inspecting the thermostat housings. If the mechanic told you differently, you may want a second opinion. A spun prop may result in higher revs but not lower ones, Again, if the mechanic told you that low revs may be a spun prop, you need a different mechanic.
If you ran on portable tanks and still had the problem, that would eliminate a lot of plumbing issues depending on where you connected the tanks.If the portable tank was installed after the primer bulbs (directly to the motor) and you still had issues, that pretty much eliminates, hoses primer bulbs, water separator, anti-siphon valve and tank pickup. A simple check of those components can be done by swapping the fuel lines from the motor to the primer bulbs. If the problem changes to the other motor, you have a plumbing issue. If it stays with the same motor, problem is in the motor itself.
Does the motor surge up in revs and back down or does it just sort of limit out at 3000 revs?
I don't know how the mechanics tested fuel pressure but you need to do so at the fuel rail test connector at idle and with the motor under load at higher revs. You might be able to do that at a slip with the boat well tied off.
You may have something as simple as bad low pressure pumps or a bad lift pump if there is one. I don't think there would be on that boat. Bad low pressure pumps are fairly common
It would have also been useful when the plugs were changed to see how the old ones looked. You may have an ignition issue like a bad coil or bad injector.
You could have a defective throttle position sensor (TPS). I think that would show up if the diagnostic data is downloaded from the motor (you should have a diagnostic dump anyway to see if there are issues that the ecu has detected. Testing the TSP is not too difficult if you are familiar with basic operation of a digital volt/ohm meter.

 

[bob marlin]

The corrosion that was mentioned to me was viewable at the top of the block through the thermostat housing. I'm told it is do to the steam generated from the heat of the motors and it settling at the top of the block. The mechanic showed me the same type of engine with a corrosion issue which he reluctantly repair at the request of the owner. This entailed pulling the motor apart and welding the corroded area on the aluminum block which is difficult in its self let alone making sure the existing material is clean enough to accept a weld.
The protable tanks were used but at the time the motor was not running correct which may have been do to the build up of particles already at the filter points. This to me would not have been a true reading with the portables if this was the case. I dont know if that would allow me to rule out from the motors back. The portable tanks were connected right at the fuel filter in the motor.The motor does not surge, it gets to a certain rpm 3500 max and will not go any higher. In fact if you try to throttle beyond this the rpms will drop. This also seems to effect the starboard motor which will not exceed 4000 rpms.
The reason fuel pressure test I can verify the method. The previous test was done at the dock with the boat in neutral and not under any in gear load.
The low pressure pump is the only fuel pump that was not changed.
The motor had been diagnosed multiple times after each failing attempt to correct the problem.
Thanks for the feed back. I have not yet been given a written invoice on what the marine plans on doing and the associate cost, will post it when received.

 

[seasick]

I see. The corrosion you were referring to is the upper head issue and not the lower exhaust corrosion issue. I missed that fact.

The fact that the other engine also looses revs is interesting. Have you tried running with the gas cap off? It's a long shot but a restriction in the tank vent can cause the fuel flow to reduce as the pressure in the tank goes down. The fact that the issue occurs and is repeatable at the slip and not in gear is also interesting. If you repeat that test but in gear, I would expect the problem to occur more quickly and more dramatically since more fuel is being called for.

A partial blockage of the pickup tube is also possible but you don't often see that unless there was or is some serious debris or gunk in the tank

 

[DennisG01]

If I've read this correctly, you ran the engines with a portable tank but there was something else going on or it was just in neutral? Or something like that where the portable tank test was not done completely/properly?

Start with the portable tank test. That will eliminate a lot of variables and either point to the boat-side fuel system or the engine fuel system.

Has anyone checked for codes? Has either marina run with their diagnostic computer hooked up at the same time? I'd normally lean towards thinking this is not an electrical issue, except for the part where you said the RPM's just stopped at 3,500. That sounds like you're saying the RPM's stopped too quickly to be a fuel issue.

 

[bob marlin]

The portable tank was run with both motors but only after I took the boat out running on the house tanks to make sure the probably was occurring. I then came back to the dock and connected the portable tanks directly to the fuel filter supply. The issue with this test is if there was debris in the high pressure filter/screen creating the low rpm the connection of the portable tanks during this period would not entirely be running through a clean filter/screen, I'm thinking. I suppose to test the motors with a portable tank you would need to know that your starting off with a normal operating motor which is difficult to do in this case. Once the low pressure filter/screen was cleaned it would take a day of running before the problem reoccured. With that said you would not have enough fuel in the 5 gal portable tanks to run the boat long enough to get to the low rpm condition if it was going to happen with the portable tanks.
Codes have been check almost every time I came back from a test run and the issue was not resolved.
I think we pretty much ruled out electrical issues. The rpms at different times would fluctuate from low of 2500 up to 3500. If you tried to throttle through the low rpm condition it would reduce the rpm more, almost like choking out a motor.
As I mentioned earlier after the original replacement of the low pressure pump and cleaning of the VST tank the boat ran fine the first day getting 5700 rpm out of both motors. The next day coming back in from a haft day out the motor reacted with the low rpm issue once again. The marine is suppose to get back to me today with a break down of how they plan on correcting the issue. Unfortunately its seems like some of the potential fixes they discussed with me were already attempted by the first marine to no avail.
Thanks for your thoughts.

 

[DennisG01]

So you don't consistently have the issue? That does make it more challenging. However, connecting a portable tank to the boat-mounted fuel/water separator is fine - or better yet, connect it direct to the engine. Either one of those will eliminate alot of variables on the boat side. Keep some extra fuel with you in jerry cans if needed? Maybe T the portable tank into the fuel line so you can quickly change over to the portable tank when the issue arises. Or, heck, you can probably pull the main fuel line off the F/W separator and put the portable line back on quick enough while the engine is running.

But, another thought - and we're going to back to something that Seasick mentioned as well - have you tried running with the fuel fill cap off? This will eliminate the tank vent fitting/hose - which can cause fuel starvation. Especially since, as you mentioned (and Seasick noted), it happens to both engines.

Another thing is that the fuel lines - especially if older - could be failing internally. This essentially can cause a partial blockage to fuel flow... again causing starvation.

 

[bob marlin]

The portable fuel tanks were connected directly to the motors and the same results occurred with the low rpm. I have not tried running the boat with the fuel caps off. We did check as best we could any blockage within the vents overflow and it appeared clear.. One of the possible fixes as discussed with the new marine is to replace the fuel lines from the tank back to the motors due to the age of the boat and possible deterioration of the hoses. During this replacement it was suggested to me to eliminate the Grady White installed in-line fuel pump primers and replace them with the standard primer bulb. I was told that this could be another place for debris to build up.
Has anyone replaced their fuel lines and how big of a job is it. I reviewed a few u-tube videos on line and it doesn't look that difficult.

 

[seasick]

If you have the inline fuel pumps, they can be an issue but I would suggest bypassing one at a time. Install the primer bulbs but get good ones, the Yamaha OEMs are about $30
Changing the fuel line into the motor can be a challenge at times. First of all, make sure you get the correct fuel hose. It is probably 5/16 and not 3/8. Again but good quality hose rated A15. The hose from the primers back to the tank are 3/8 inch, same advice. Get good stuff. I am not convinced that the lift pumps are your issue. I just don't understand why when one motor bogs and you give it gas, the other motor bogs too. That has to be something that is common to both motors.
When you tried the portable tank, didn't you bypass the in-line fuel pumps?
Good luck with the search and let us know what the fix turns out to be. I am at a loss.

 

[g0tagrip]

I had a similar issue with my starboard engine. I have 2007 F250s. The problem I had was the engine would back down to 3000 rpm intermittently. When the engine backed down we were getting a "check engine" indication on the rpm gauge. If you cleared it then we could power back up, but it would happen again but not always. My son finally figured out how to call up the engine diagnostics, we got a Yamaha diagnostics code chart from on line, and it called out "24". that code was engine cam position sensor. I could not determine which one of the three was bad so we changed all three and viola motor works perfectly. The sensors are on the back of the engine, easy to change but not cheap, about 200 bucks a piece.
I would get the Yamaha Fault Codes for your year engines from cdielectonics.com They have a tech support phone number: 1-866-423-4832
Good luck.

 

[Harpoon]

A few years ago I had a case in which I had 2 bad spark plugs out of 6..... you mentioned he replaced the plugs. I was loosing my mind trying to trouble shoot. This was found in 5 minutes with a spark plug tester - by a pro.

 

[DennisG01]

The portable fuel tanks were connected directly to the motors and the same results occurred with the low rpm.

OK, that helps. That means everything upstream of where you connected the portable tanks is NOT the issue. Why is the marina suggesting replacing fuel lines when they are not the culprit? Forget about vents and such, as well. Assuming you used new/good fuel in the portable tanks, that also means fuel quality is not a possible culprit.

When you connected the portable tanks to the engine... where? Before or after the on-engine filter?

Now, you can look to engine stuff.

You mentioned you checked codes but didn't say if there were any?

What was going on with the fuel pressure while the issue happened?

 

[bob marlin]

If you have the inline fuel pumps, they can be an issue but I would suggest bypassing one at a time. Install the primer bulbs but get good ones, the Yamaha OEMs are about $30
Changing the fuel line into the motor can be a challenge at times. First of all, make sure you get the correct fuel hose. It is probably 5/16 and not 3/8. Again but good quality hose rated A15. The hose from the primers back to the tank are 3/8 inch, same advice. Get good stuff. I am not convinced that the lift pumps are your issue. I just don't understand why when one motor bogs and you give it gas, the other motor bogs too. That has to be something that is common to both motors.
When you tried the portable tank, didn't you bypass the in-line fuel pumps?
Good luck with the search and let us know what the fix turns out to be. I am at a loss.

The port motor is the more noticeable of the two but the starboard motor during all of this will not exceed 4000 rpm. It to will drop off if you try to exceed 4000 rpm. I was told by the first mechanic that this is typ. when one motor drops off the other will not compensate and will stay at a lower safe rpm.
I should be getting the report from the marine on how they plan on addressing all of this soon if not today. They wont start working on it until sometime in Jan. Will let you know when the problem is fixed.
Talk about being at a loss, this has been an on going issue all summer. I should have tried a different marine mid way through the summer but had invested to much time and money with the first one to pull the plug.

 

[DennisG01]

January?!?!? Where are you located?

 

[bob marlin]

January?!?!? Where are you located?

Milford CT.

 

[DennisG01]

Milford? And they can't look at the boat till January? That's a pretty popular boating area - and a nice area, too. My brother's family is there. I take it they are just too backed up with winterizing right now?

 

[bob marlin]

Milford? And they can't look at the boat till January? That's a pretty popular boating area - and a nice area, too. My brother's family is there. I take it they are just too backed up with winterizing right now?

I just spoke with the marine and was given the work order and there plan of attack. First item, Disassemble VST tank, check filters/screen and clean as needed. NOTE, this was done once already by the first marine and the High Pressure fuel pump was replaced. Also while VST tank is disassembled check injector srceens and injectors at the same time. Reinstall VST tank with new o-ring.
Secondly remove all fuel lines from the two gas tanks and install new lines from the tanks to the motors. Remove Grady White electric primer pumps and install new primer bulbs.
They can also start on this next week if I approve the invoice.

 

[DennisG01]

If it was me, I'd be focusing on the things I mentioned above. It makes no sense to start disassembling things and/or replacing without first narrowing down the variables more. I feel like I may be repeating myself here, but why does the marina want to replace fuel lines when you/they verified the problem happened with a portable tank?

 

[seasick]

Regarding the issue with the other motor lowering revs when the first motor kind of bogs down: Is there a RPM synchronization feature that is turned on?
I originally thought it was a VST issue and it may still be. There is a screen on the output fuel fitting, I believe. I also agree with Dennis that changing the fuel hoses is not something that I suspect as being an issue based on your tests with the portable tank. The fuel rail pressure test is also critical to see if the fuel regulator is working.

I really hate when a mechanic suggests that a whole bunch of things get replaced. It often means they have no idea what the problem is.

So two questions: Why does the mechanic think that the limited revs on one motor causes the other to lower revs? Ask...

Are you sure that when the problem occurs, the revs slow down or do that go down, back up, back down etc.That is a typical VST type of symptom.

 

[bob marlin]

Regarding the issue with the other motor lowering revs when the first motor kind of bogs down: Is there a RPM synchronization feature that is turned on?
I originally thought it was a VST issue and it may still be. There is a screen on the output fuel fitting, I believe. I also agree with Dennis that changing the fuel hoses is not something that I suspect as being an issue based on your tests with the portable tank. The fuel rail pressure test is also critical to see if the fuel regulator is working.

I really hate when a mechanic suggests that a whole bunch of things get replaced. It often means they have no idea what the problem is.

So two questions: Why does the mechanic think that the limited revs on one motor causes the other to lower revs? Ask...

Are you sure that when the problem occurs, the revs slow down or do that go down, back up, back down etc.That is a typical VST type of symptom.

The original mechanic stated that to protect the motor that is running fine and not put undo strain on it when the other motor is having issues it will not exceed a certain rpm. The problem occurs every time you run the motor and the rpms do not fluctuate they just max out at 3500. But in the case you try to throttle beyond 3500 the motor will start to choke out as i mentioned earlier.