Suzuki DF250S pumping fuel into air intake

[Jeff J]

I am a mechanic by trade but new to boats. Most things I work on are not fuel injected either. The other day I towed in a rental boat that wouldn't run. The driver said they were just idling around when it died. I couldn't get the primer bulb to pump up so I assumed an air leak somewhere. Two days later I changed the fuel hose and primer bulb the engine started right up. It was a little rough so I advanced the throttle a little leaving the lower unit in neutral. The motor smoothed out but after a minute or so the RPMs started increasing on their own even after returning the lever to idle. I noticed fuel on the water so I pulled the cowl and saw the top of the engine was wet so I pulled that cover which has a fuel line going to it and what appears to be a temperature probe. The cover had fuel sloshing around inside it when I pulled it so I ran the engine with the cover off for a few seconds and witnessed fuel being pumped through the hose and pouring into the air intake manifold from that hose. Judging from the grime on and inside the cover this has been going on to some degree for a while.

I assume there is a reason behind pumping raw fuel into the intake screen housing but the logic escapes me on an injected engine nor do I know which part should be changed to rectify it if needed.

I have been looking for a service manual to download or buy but the free one I found is incomplete. The $90 manual option I found doesn't cover this serial number (25004F-210000 range) so I am reluctant to buy it.

Thanks in advance,
Jeff

 

[99yam40]

where is that fuel coming from?
if from the VST then the float is not closing off the fuel when the VST is full.

extra fuel dumped onto a gas motor floods it, not raising the RPM
you have to have fuel and air in the proper ratio to the motor to run properly.
adding fuel without adding extra air also make the ratio out of wack

 

[Jeff J]

I don’t know what a VST is nor did I know anything with a fuel injection system would have a float in the system. The fuel line to the airbox traced back to a small shiny gadget with 2 wires mounted on the top left of the engine. I should have chased the wires, they may go to what I believe is a temp probe in the intake. If they do then the shiny gadget is likely to be some kind of enrichening valve or primer. Like I said, I don’t know much about boats. I assumed an air leak in the fuel lines on the boat because the primer bulb wouldn’t pump up but after seeing fuel getting pumped into the air intake I assume the reason I had to tow the boat was it loaded up and died. Then would not start because it was hot and flooded. But I am just guessing and the local Suzuki mechanic hasn’t returned my call. I just need it fixed. It would also be nice to know why I had an uncommanded rpm increase sitting in the slip before letting the renters use the boat again.

I did finally find a manual searching for “maintenance manual” instead of “service manual” but don’t have it yet. $90 and paper.

 

[99yam40]

VST is the Vapor separating tank.
it houses the high pressure fuel pump that feeds the injector rail

 

[Jeff J]

Thank you, I knew there was a high pressure pump but didn’t know about the VST. I will have to trace the hose down from the shiny gadget (evap purge valve, if I am reading the diagram correctly) to see where it goes. Assuming that is the problem, are there ways to check out the VST other than replacing and seeing if the system stops dumping raw fuel into the air intake?

 

[99yam40]

I have never worked on a DF250 so not much I can say about it,
I have no idea where the pump is on your motor
just thinking about how injected Yamaha motors are set up with a VST.
those are serviceable by taking them apart

 

[Jeff J]

I have been doing a lot of internet reading and studying parts manuals. The fuel is coming out the evap purge hose. Most things I read suggest a problem with the float in the VST (as mentioned above). This boat is 3 miles from the nearest ramp. I would like to drive it there rather than arrange for a tow. What would be the harm in capping the evap purge hose for that run? The other options would be to trim the motor up so fuel doesn’t run into the air stacks and pours over the top of the motor (which it has been doing anyway) or disconnect and let it pump fuel into the lake.

 

[99yam40]

that fuel running everywhere can catch on fire,
does not sound like a good way to go.
very bad to watch your boat burn as you jump overboard

these kind of things is why6 you should sign up for Seatow or other policies.

or ask a friend /neighbor to pull you to the ramp.
3 miles is not far

 

[Jeff J]

That’s why I asked about capping the hose. The evap purge valve isn’t open full time.

 

[Jeff J]

Just hanging out over the water looking at this thing. The evap purge valve is normally closed. It doesn’t seem to let air pass with the electricity off and from reading how purge valves work in general it seems just unplugging it should keep fuel from dumping all over the place. Seems like a reasonable fix to safely get it loaded and hauled to the shop but, I am not a boat mechanic.

 

[vroom ZOOM]

the ecm should have an electronic control to start and stop the lift pump which fills the VST. You can hear the lift pump run when you first turn on the ignition before starting the engine. Check that it stops when the VST is full.

 

[Jeff J]

I drove it to the ramp and hauled it to the shop this afternoon. I don’t know that I have any faith in the shop I took it too since he told me on the phone he had never heard of raw fuel being dumped into the air intakes of these engines but we’ll see if he can fix it. I put “fuel coming out of the evap purge hose” on the work order. I tipped the motor up a bit so the excess fuel wouldn’t flood the engine at idle while loading on the trailer.

 

[Jeff J]

By the way… This one pumps fuel out the evap purge hose an into the intakes or across the top of the engine depending on how the motor is trimmed. The pattern suggests the evap purge valve is working since fuel only comes out when the motor is running and flow is intermittent. I pulled the hose off the top of the VST and got sprayed with fuel there but once the pressure was relieved it didn’t give anymore (motor off).

I have 15 rental boats to manage (8 pontoons and 7 ski boats). Three have Suzuki motors, four have Yamaha two are Mercury outboards plus three Mercruisers and three Volvo Penta. I have learned much about boats in the last 3 months and have much more to learn. The only code reader I have is for Yamaha simply because I own an F70 and it was giving me trouble a year ago but I haven’t checked to see if it will talk to the bigger Yamahas. I am not fond of the idea of taking my laptop to the dock anyway. I am not sure of their value either. As bad as my motor was running, it never threw a code (anti-siphon valve gummed up, had one questionable injector and a bad spark plug pretty much at the same time).

 

[Jeff J]

The local Suzuki shop said the VST was shot. They got this one running but I am unsure of their fix. One of the dock hands left the fuel cap off and a renter ran the boat until ignoring the alarms and lights until it pumped water into the cylinders then they called for a tow. While I was purging water from the system I saw the shop had left mount bolts loose on the filter, a screw loose on the flywheel cover and the evap hose kinked. It makes me wonder it they even opened the VST. They also swapped out the fuel cap and now the tank is collapsing every time it goes out. Not sure I want them touching another boat I manage. I ordered a manual a month ago which UPS delivered to the wrong address (I was home and in the yard when they claim it was delivered). I am still waiting for a replacement so I can do some of this work myself.