F250 fuel flow problem at low rpms

[shoot-straight]

hello everyone. i am spent, i cannot diagnose the problem with my F250 yammie. apparently it has a fuel pump that runs intermittently at idle which makes problems worse.

issue: i can run all day at cruise, *****ing speed, etc, but if i "putt" around at low rpms (like when i am looking for fish) i will sometimes lose fuel pressure in my hose and the motor will stall. i also will have problems at take off after i have idled for a while. to make it work, i have to re-prime my bulb before take off.

here is what i have done: replaces anti siphon valve on tank, replaced/refitted all connections, used permatex on screw in fittings, replaced fuel filters (they were clean with no water in them). i did not replace the bulb, it was working fine when i inspected it. no signs of fuel anywhere. vent is clear.

any suggestions?

[boats.net]

Try running it on a 6 gallon portable gas tank and new hose to see if problem is in boat or in motor.

[rodbolt17]

then check the valve between the VST and the feed pump inlet.if its leaking that is the symptom you get.
what happens is instead of maintaining about 10 PSI at the VST inlet, fuel will start recirculating between the lift pump inlet and outlet and the VST goes dry.

[shoot-straight]

thanks guys, will give it a shot.

[keyrentals]

Thank you for your help

I want to thank the person that posted on this forum about the vst check valve. I have been working on these outboards since they came out but have no formal training. I had a pair of f250s on a boat that definitely sat for awhile or had used ethanol fuel. In 12 years of working on these outboards I had not experienced a bad check valve. Because of the fuel abuse I believe both of these engines had the failure. I tried everything that usually fixes them and your post pointed me in the right direction. When I opened up the hose to the check valve it was a crusty mess, something I had never seen before, I knew it was the right solution. If you ever need a boat for a week in the Marathon I owe you one, just call me early because we are really busy. Marathon Boat Rentals Inc - Marathon's Most Unsinkable Fleet

[rodbolt17]

DUDE
I was just in marathon last week.
placed some resumes,one at trevanier marina.
I hope to be back in marathon about November.

I had to go down there to fix a 2003 150 for a friend of mine.

was the longest mobile repair job I ever did.
18 1/2 hours from colington NC to marathon and 16 1/2 hours back.
I had road eyes for 5 days .
I did get to eat some fresh grouper and some fresh snapper .
glad ya got it fixed.
that check valve is not mentioned in any training class.
most instructors have no idea why its there.

but its been used since about 2002.

[fairdeal]

Rodbolt - you looking to re-locate to the Keys?

Best of luck !!!

[boscoe99]

Instructors and/or students must not be paying attention in school.

From the Yamaha Advanced Four Stroke training manual, circa 2006, addressing the Yamaha F250:

A circulating fuel line with a one-way check valve has been incorporated around the low pressure pump. When the pump is running and the demand for fuel is less than the output of the pump, fuel will be circulated around the pump to prevent heating and vaporization of the fuel.

Now the confusion may very well be the nomenclature of the part. It is not a check valve per se. It is a pressure relief valve. The SM calls it a check valve as does Yamaha training data. The parts catalog calls it what it is. Maybe there was a translation issue from Jap to English.

A pressure relief valve (PRV) is a type of valve used to control or limit the pressure in a system

A check valve, clack valve, non-return valve or one-way valve is a valve that normally allows fluid to flow through it in only one direction.



If mechanics here in the USA cannot understand the system pity the poor mechanics in third world countries that don't use English or Jap. Imagine how Jap gets translated to Rag Head.

[TownsendsFJR1300]

Tavernier, Florida keys.

I did my open water diving certification there about two decades ago... Gorgeous water for scuba diving!!

SW Florida is very short of Master mechanic's, only one I know of on Ft Myers Beach..

[fairdeal]

... pity the poor mechanics in third world countries that don't use English or Jap. Imagine how Jap gets translated to Rag Head.

oh - that's hardly "PC" .....

[fairdeal]

Tavernier, Florida keys.

...
SW Florida is very short of Master mechanic's, only one I know of on Ft Myers Beach..

thought there was - remarkably - one on Big Pine Key.

I could be mistaken...

[boscoe99]

Tavernier, Florida keys.

I did my open water diving certification there about two decades ago... Gorgeous water for scuba diving!!

SW Florida is very short of Master mechanic's, only one I know of on Ft Myers Beach..

What is "open water diving certification".

When I got my certificate there was just one. It covered any type of diving one wanted to do. Actually, all it got was to get my tanks filled at a filling station. With the tanks filled we could go and do what ever it was that needed to be done. A license to kill if one wished. Kill oneself that is.

[boscoe99]

oh - that's hardly "PC" .....

It is the trump effect.

[TownsendsFJR1300]

What is "open water diving certification".

When I got my certificate there was just one. It covered any type of diving one wanted to do. Actually, all it got was to get my tanks filled at a filling station. With the tanks filled we could go and do what ever it was that needed to be done. A license to kill if one wished. Kill oneself that is.

Open water certification (PADI), your depth is supposed to be limited to 80' as I re-call. (its been about 16 years since initial certification). And yes, you can get tanks filled too.

You can do what ever type of diving you want to do.

But for instance, deeper diving, say to 120', you should be certified to recognize the effects of Nitrogen narcosis. Some charters won't bring you to a deep site (say a wreck in deep water) if your NOT certified "deep". Same with "night diving". Very, very different at night, especially communicating with each other at night.

I'm maxed out on the "civilian" spectrum of diving certifications and stopped just short of instructor (I'm a assistant Instructor) including dive master, rescue diver, deep, night, etc...

If you haven't dove recently, there's also Nitrox diving. There's O2 added to the tank before topping off with regular air. You can either calculate the "deepest you can go" by hand, or enter your O2 percentages into your Nitrox computer. Should you go too deep on Nitrox, you CAN get oxygen poisoning and pass out at depth..

You don't get nearly as tired on Nitrox (6-8 dives per day on a liveaboard is not unusual) vs 2-3 dives on regular air will kick your butt so you have to watch your depth MUCH closer.

My older straight air computer, is VERY liberal with time and will allow me much deeper dives.

[rodbolt17]

yep
wifey dearest wants to get close to Miami.

I did notice a lot of Yamaha product and almost no actually trained professional techs.
the so called island time is about the same in the keys as it is on the outer banks of NC.
so is the importance of training.

I had a dealer support tech at Kennesaw argue with me about that "relief" valve, was told it could not happen.

it can and it does.

but can you tell me what a "cover nut" is ?