01 Yamaha F115 missfire

[Scott K]

My first trip in my boat this spring, my boat missed like crazy, after a little diffing, I found out I started off this season with a gas tank full of water. I pulled the floor up and and siphoned it all out, at that time I wondered how it got in there, but didnt think much of it. Then after a couple rain falls before I used it, and put gas back into it, I put $60 worth of gas into it, between 1/4 and a 1/2 tank. Well it it still missed. I checked the fuel filter, and there was more water in the separator. So I pulled the floor back up, to access the sender and removed it, sucked out 3 gallons off the bottom, and monitored it for a couple days. It didnt separate. I figured the water got into it from the sender so I siliconed where the sender mounts on the top of the tank, and went and tried it again. Still misses. I have no water in the filter/water separater. So I am going to try 4 new plugs tonight.

If that doesnt fix it, what is the chance the water did damage to an injector, or a cylinder?

What should compression be in a 01 Yamaha F115 ?

Is this something that hooking a scan tool to it, would it be able to tell me which cylinder is missfiring? Or should I just reach back and unplug injectors to find out which cylinder isnt firing? What do marine shops typically charge to hook a scan tool up to it?

One other question, I have always bought Yamaha 4 stroke oil for it, but I was wondering is it any different then just a top name brand oil for cars?

[Hookmaster]

I can't help you on the misfire but I started using car oil in my 1999 Yamaha F100. I didn't have any problems but switched to marine 4 stroke since the outboard operates at such higher rpms.

[tlbigstump]

There's a very good chance you have water in your vapor seperating tank. You will need to drain it and flush fresh gas through it and also all fuel lines running under the motor hood. Most likely your injectors and engine are fine. The VST houses the electric fuel pump so it sucks from the bottom of the tank and is bringing water to the injectors. Also if there is water in the VST more than likely your electric fuel pump will take a dump on you somewhere on down the road, they rust up fairly easily. Be very carefull running the engine after draining the VST, because of fuel spillage and vapors rince it out and let dry, you don't want a bonfire in there.Also stick to Yamalube, I know it's dang expensive, but it's formulated to run at 6000 rpms all day at only 120 degrees, where auto oils arent.

[boatfixer]

You can run any oil that meets the specs. There is nothing special about any brand oil. Truth be known, there are more brands out there, than the manufactures making and meeting that spec. In other words, the excactly same oil can be found in several differently badged containers.

[Scott K]

Well I changed the oil with Quicksilver 10w30 4 stroke Marine oil, it was less then half of what the dealer wanted for Yamalube. I was going to get the Pensoil Marine oil, but grabbed the quicksilver instead.

Last night I changed the spark plugs, oil and filter, and removed the injectors and looked at them, and sprayed carb spray in them then blew them out (I know this probably didnt do anything) then went and tried it out, for a short time, 5 seconds, I thought I had it, but then it went back to missing/bogging down. So I reloaded it back up and went home. It only misses under load.

I will try cleaning out the VST today, and maybe flush the injectors before I take it back out. Is there an easy way to drain the VST?

[boatfixer]

Penz would have been fine.

Look towards the bottom of the vst. U should see a brass screw and a small tube.

[Scott K]

Should I just remove the VST and clean the filter for it while I am working on it?

Is Quicksilver ok as well?

[boatfixer]

QS is just fine.

Cleaning it would be fine also, like u said, filter too

[Scott K]

Thanks! I will tear into her shortly. Hopefully I can be up and fishing tonight.

[Scott K]

Well I took the VST apart, there wasnt any water in it. Just a small amount of grimmy stuff in the corners. I cleaned it out well, cleaned the hoses out, flushed the injectors, hooked it up to the garden hose, and left it idle for about 5 minutes, then reved it up, and it fell on its face and died. Now I cant get it started. It seems like it is starving for fuel now. I havent had a chance to check if the fuel pressure has dropped, or if the hi pressure pump is running. I tried squeezing the fuel ball and I can see the water separator is full(of gas), but it doesnt make it start. I plan on getting out there to check fuel pressure, injector pulse, and spark after supper.

Before I worked on it, it atleast ran, and would restart if it actually died.

[Scott K]

Well I got the no start kinda figured out. The fuel line is sucking air. I replaced the primer ball assy. But of course, that wasnt it. It is either in the reserve lever, or the hose in the tank. It got dark, so i quit working on it. I will be checking out the valve and suction hose tomorrow. Maybe this was my whole problem?? Well other then the water in the tank from the beginning.

[Scott K]

Well I figured out the no start. The fuel line was sucking air from my gas tank, so I took it all apart, and vacuum tested all the lines, and the pickup hose in the tank. No vacuum leaks. So I set the pick up in a jug of gas, and it sucks it right up. I guess $60 in gas isnt enough to keep gas on the bottom of the gas tank towards the back of the boat where the pickup tubes go into the tank, while parked in my driveway

OK, I feel like a DA!

But now I still need to figure out if taking everything else apart and cleaning everything, and replacing spark plugs, and the primer bulb assy actually fixed my missfire. But maybe I will put a little more gas in the tank before I do.

Mental note:

Lets see $60 equals about 16 gallons of gas, with a 42 gallon tank, so about a quarter tank of gas while parked in my driveway, isnt enough to start it in the driveway.

[Ufatz]

Fuel pressure regulator. Pull old off-put new on. Problem solved.

[Scott K]

I wanted to take it out for a long ride before I posted it was fixed. I am really not sure what exactly was the fix for the missfire, but I flushed the injectors, and cleaned the entire fuel system. But it is fixed!

[boatfixer]

Good to hear its running good again!