F115 sneezes at idle

[Yamahauler]

My 02 F115 was in the shop for a month, and as Rodbolt predicted, the injectors needed cleaning. Ran great for two outings. Tuesday I ran the boat up part of the ICW, miles of no wake zones. When I got back to the dock, I noticed a "miss", sounding like a sneeze and an occasional sneeze under the cowling. I pulled the plugs. Three were dry with a very light white coating, one was a little blacker. Cleaned the plugs and it ran better. By the time I got it form the ramp to the slip, it was sneezing again. Please don't tell me it sounds like a burn valve or something similar. Thanks

[rodbolt17]

start with a leak down test,takes 15 minutes.
once your positive the mechanical sealing is ok then fix the fuel system,again.
sucks but its all part of the marine technician govt stimulous plan.

[Yamahauler]

I didn't have a leak down tester so I did a compression check. I know compression checks can be pretty worthless, so, without worrying about the numbers, it did show that the cylinder #1, the only cylinder to have a dirty plug (and it wasn't that dirty) was 15 lbs. low. I really don't want to put it in the shop for who knows how long, I've already missed a lot of fishing. Could I be doing some serious damage if I ran it for the summer and put it is the shop in the fall? Would it be smart to shut it down now and watch the other boaters from shore?

[Yamahauler]

Since no one replied to get the thing to the shop ASAP, I am going to run the motor with one weak cylinder rather than loose several weeks of boating.

[seahorse5]

With nothing to lose, why not run the shock treatment using Yamaha's Ring Free to possibly clean up the intake, rings, etc. Change the oil after running the procedure. The instructions are on the bottle.

[robert graham]

Seriously, a sneeze is usually associated with a lean fuel mixture which can do some serious damage to that cylinder. Maybe better get it fixed before you run it any more. A rebuilt powerhead can run you $2500! Good Luck!

[Yamahauler]

Thanks seahorse, but the tech said he did a shock treatment when he cleaned the injectors a couple weeks ago.

Robert G, you have me rethinking about it running lean. Three out of four plugs were completely dry with a thin powdery coating. Only one showed any carbon at all. Maybe running lean is more responsible for the sneeze than the one low cylinder.

Is that an easy check for a tech or will he have to pull the injectors again?

[robert graham]

He'll have to check the fuel delivery system from the cowl to the injectors, but it'll be better than cooking a piston/cylinder. There was a guy on here just last week with a plugged carb and it fried that piston quick, $2100 for a rebuilt powerhead! These motors really hate lean fuel conditions! Maybe your fuel tank, fuel lines, entire fuel system in contaminated with old, stale fuel? Do you have a fuel/water separator?...if not, better get one. The boat dealer can put one on easily. Good Luck!

[rodbolt17]

2500 dollars wont touch a rebuild on a four stroke F115.
myself, do a leakdown test then test the fuel system, again.
clean the fuel system at breakfast,reintroduce trash at lunch and guess whats for dinner?

[Yamahauler]

Answer: repeat step one?

I do have a 10 micron fuel filter, don't the newer engines have an inline filter in front of the vst? If so, could I install one?

Am I right that the dry plugs are a sign of running lean?

Do EFI two strokes have this much trouble with fuel?

Leak down tester is in the mail.

Thanks

[Yamahauler]

Sorry to ask so many questions at once.

[rodbolt17]

the F115 from about 2006 uses the inline filter between the fuel pump and the VST. yes you can add it to yours.
yes ALL EFI engines are very sensitive to fuel quality and the amount of debris in the fuel.
that sneeze is a backfire in the intake,typically caused by a lean A/F mixture in the intake.

when we first got E fuels in our area we saw fuel system issues we had never even had nightmares about.

one big issue was all the surrounding states had E fuels and we still had MTBE.
so the guy coming down from VA,PA,NJ,NY, OH,WV they would show up, top off the tank here and the next day major fuel system problems.

second thing was older fuel tanks and lines.
once we got E fuels we found that once the E dissolved the old varnish or oxides there is NO way to filter it.
its like dissolving 3TBS of surgar in hot water and pouring it through a coffee filter.
you get no surgar back as its part of the solution.

wont be the first time I have done the entire fuel system once or twice or in one case 4 times before a sliced a fuel line and found it all cracked and ful of the yellow/gray nasty.

[Yamahauler]

Thanks rodbolt, it will go in the shop tomorrow. I wish you would move further north.

[Yamahauler]

The tech just now got around to my motor. Says it is the mechanical fuel pump and seals around the injectors. Does that sound right for the sneezing symptom?