Saturday, October 3, 2015

Yamaha FX fuel smell sputters on idle and runs poorly

Hi all,

had this problem with my ski

We took it out and after starting it up noticed it did not want to run too smoothly at low speed and had fuel gas smell.

I ran the ski that day anyway and had it opened up seemed to be running fine but still at low speed and idle it was not smooth, had gas smell still.

First of all start with the basics here

Did you have the water hose on without the engine running?
If you did you probably pumped water into the engine through the exhaust.

You will now need to take the spark plugs out and turn the engine over to get the water out of the cylinders, you may have to do this a few times be careful not to cross thread the spark plugs and use aluminum anti seize on the spark plug threads to prevent them from seizing later
Do not over tighten the spark plugs

Are the spark plugs clean and in good shape? You could have a fouled plug
Are the spark plug wires firing I mean is there spark?
make sure that there's no oil around the spark plug wire shorting it out or another problem w spark

My plugs were recently changed so I suspected something else....

Later when I got home I took the plugs out, there was allot of gas on one of the spark plugs, I removed the coil wires from the area and turned the engine over, allot of gas came out of that cylinder also. Compression was good.

Took out the injectors with fuel line connected one of the injectors was staying on constantly squirting fuel into the cylinder.

WARNING be careful here with spark! gasoline fire explosion hazard especially if there is gas squirting around when you start and ignition spark coils are connected dangerous!!!!
Recommend disconnecting the coils if your going to have fuel spraying and the ignition on turning the engine over.

So I first swapped the injector to another one and the same cylinder had fuel constantly coming out of the injector. Back traced the wire all of the way to the ECU only thing it could possibly be was the ECU in my case since I was reading the voltage coming out of the computer to the injector.

I bought a new ECU from Powersports plus online in MI (?) that was the most reasonable one I could find but still a very expensive part so don't fry yours.
I had considered buying a used ECM for $400-500 but since I use my ski out away from shore allot in the ocean not in a lake or river where there's shore nearby... I decided to go with the new one instead.

Side note from below- afterinstalling the new ECU I sealed the box and the grommets around the wires going into the box with silicone sealer to keep water out of there.

After new ECM- the injector that was staying on was behaving fine and the engine ran 100% better

Ski History-
I bought this ski used and it needed a new motor, the original motor sat up with salt water and was pretty far gone. The cylinder head had oxidation in the combustion chambers of the head, the head was not usable, the cylinder had corrosion etching in the cylinder walls and would need boring.

I had Snyder's machine shop in Waipahu bore the block out to the new bore oversized pistons .100 the biggest we could go to clear up the cylinders
They also measured and polished the crankshaft and rods, install the new pistons on the rods

After I got everything back I did the short block and ordered a remanufactured cylinder heard from SBT in Florida, it looked great and was fine.

To make a long story short(er) I did not take apart the electrical box
On this ski the electrical box has the ECU engine control unit or computer starter solenoid and other goodies inside.

Apparently there was a small amount of water inside of the electrical box which may have shorted out the ECU, this later after about 40 hours caused the one injector to stay open or constantly squirting fuel inside of the cylinder.

If you do get water inside of your ski sink it or turn it over in water fills up the engine area you may want to just check this electrical box.

After installing the new ECU I sealed the box and the grommets around the wires going into the box with silicone sealer to keep water out of there.

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