T9.9 dies sudenly when out on the water - fuel tank related?

[Stanley Cup]

Great forum and great information here. I am a long-time customer of boats.net.

I wanted to make this post to confirm I am on the right track. I have a sailboat with twin T9.9 four-stroke engines, both year 1995. They are fueled from a single 27 gallon Tempo plastic TP27S tank (no baffles as far as I know), tank is also 17 years old. Al hoses are 1/4 inch I.D. The configuration is: Tank --> hose --> Racor filter/water-seperator --> hose --> t-connector --> 2 hoses, one to each engine.

In the run from the t-connector, to each engine, it is: t-connector --> hose --> bulb --> hose --> connection to engine

This year, I have been having problems with them dying unexpectedly. I'd warm them up, go out and sometime during the trip, an engine would die. I would need to pump the bulb to get fuel back into the line, then it would be OK. But it might die again later. This was happening to both engines, but not at the same time.

First thought was an air leak in the lines. I changed the entire run of gas lines from the tank to the engines. This did not help. But I now have new gas lines, which is good!

I checked the tank vent. It is fine.

After a frustrating day on Sunday with this problem (really rough out there) and massive trouble-shooting effort yesterday, here is what know:

- Sitting in the harbor, if I disconnect the fuel hose from the engine and use the bulb to pump fuel into a large, clear container, it flows regularly, with no problem. This tells me that the fuel flow from tank to bulb is OK when calm.
- Sitting in the harbor, I ran both engines in neutral for 30 minutes at varying RPMs 2000-2800. Nothing died. This tells me that fuel flow all the way from tank to engine is OK when calm, and it tells me that the fuel pumps on the engine are probably OK.
- There was a little water in the separator before I started the trouble-shooting yesterday, there was none there after running the engines for 30 minutes in a calm harbor. The filter does not have crud in it.

From all this, here are my conclusions:

- This problem only manifests itself when the boat is bouncing around on the water
- filter - working ok
- lines - ok
- engines - working ok
- fuel coming from tank when calm - good and clean
- fuel coming from tank when tank is sloshing around - NOT OK

One more piece of information - my tank is now about 1/4 full.

My feeling is that the problem is caused by one or more of the following:

- water may be in the tank and it gets ingested when the fuel sloshes around
- foreign matter may be in the tank that somehow blocks the pickup hose momentarily when the fuel sloshes around
- the pickup hose may not be sitting in pure fuel, for some reason, and it is sometimes sucking air when the fuel sloshes around


What do you experts think of my analysis and conclusions?

Next step is to fix the problem , but I wanted confirmation I am on the right track.



.

[99yam40]

Sounds good to me.

Need to drain and clean tank and flush lines out is my thoughts.
If you do not want to replace the tank, make sure it is not deteriorating due to the ethanol fuel or age of tank.

Should be able to monitor fuel pressure/vacuum to see what is happening.
Could be a cracked pick up tube

[marinermikes]

That 27 gallon tank should have baffles in it to keep the fuel from sloshing around when ruff. See if you can check inside the tank to see if they are still in place.

[Stanley Cup]

Thanks for the replies, really appreciate it. I'll look into the baffles.

[Stanley Cup]

I bought a small 3-gallon Moeller tank, along with the barb to use it to feed gas into a 1/4 I.D. hose. Then, I disconnected the fuel line from the tank on the boat and put it into the full 3-gallon tank. I did this so that I could go out without using the main boat tank, as I want to clean that before putting it back into use. Also, this would confirm 100% that the boat's tank is the sole source of the problems.

Guess what ... same problem! Engines run fine in idle in the harbor, at both low and high RPMs, but they die after a few minutes when bouncing around on the water, and when they die, you can feel that there is no fuel in the bulb. If you pump the bulb to get fuel, you can start the engines and they run for a bit, but then eventually will die, then you have to repeat the process. Also, the bulbs never get completely rock hard. I had two people with me on the boat, and the only way we could keep the engines going is to continue to pump the bulbs while I was motoring on the bouncy lake. They reported that the bulbs would get harder then softer then harder then softer.

This is very frustrating. What do you experts think is the problem and solution?

[99yam40]

Monitor fuel pressure/vacuum.
Apparently your assuming the pumps are good with out testing was not a good idea.
a piece of clear tubing put between pumps and carbs just for testing should show if air is being sucked into the system

I am wondering if you should have 2 lines all the way back to the fuel filter and not a tee, maybe one pump is sucking air back from other motor or connections