F115 Rough at All RPMs

[rlmarz814]

I can't think of how liquid fuel could get into the airbox
other than the VST vent hose from it overfilling





I'm not following - what are you saying here?

After finding a wet plug, I had concerns about starting it with excess fuel in the cylinders. I pulled the plugs and disconnected the injectors after which I turned over the engine to clear out the cylinders of any excess. What I would consider a significant amount was expelled from there.

[rlmarz814]

No, that's blowby. Fuel evaporates way too quickly to just be sitting in the intake silencer. You already confirmed good compression, but how is the engine oil level?


If you have YDIS and a spark tester, you can do it by yourself very easily. That would be my next step.

It may have been a fuel/oil mixture, but based on color and viscosity it was mostly fuel. I'm not talking residue or a few drops, there was enough to pour out. Compression was good when last checked, and oil level was fine a week ago. I didn't check yesterday. Is the thought here there may be significant blowby hence the sheen in exhaust/content in intake silencer?

My YDIS is unfortunately too old a version to do the spark test so I'll have to do it the old school way.

[rejesterd]

It may have been a fuel/oil mixture, but based on color and viscosity it was mostly fuel. I'm not talking residue or a few drops, there was enough to pour out.

My YDIS is unfortunately too old a version to do the spark test so I'll have to do it the old school way.

Ah ok, then that's likely coming straight from the cylinders (which you confirmed by turning the engine manually). I would still check the oil level because if it's high, then you'll want to change the oil asap to get the fuel out of there.

But yeah, sounds like one or more cylinders are just not firing at all. Too bad about old YDIS not having the spark test. You could still do it by yourself by jumping the battery directly to the starter motor, but it's probably safer to get a helper.

[rlmarz814]

Something just occurred to me. When turning the key to on, not start, the fuel rail pressure obviously went up from the electric fuel pump kicking on. Does the system 'prime' the cylinders, as in does the fuel injectors give a shot. If I remember correctly, the fuel rail pressure went up then faded down to zero again. It would provide evidence towards a possible stuck open injector is my thought. I'm going down to the boat today to test spark, and also plan on pulling the fuel rail off with the injectors still installed, turning it over to see what the injectors do into a cardboard box.

[TownsendsFJR1300]

Something just occurred to me. When turning the key to on, not start, the fuel rail pressure obviously went up from the electric fuel pump kicking on. Does the system 'prime' the cylinders, as in does the fuel injectors give a shot. If I remember correctly, the fuel rail pressure went up then faded down to zero again. It would provide evidence towards a possible stuck open injector is my thought. I'm going down to the boat today to test spark, and also plan on pulling the fuel rail off with the injectors still installed, turning it over to see what the injectors do into a cardboard box.

The fuel line pressurizes but should not open injectors with the engine not running. It doesn't prime cylinders like say "Prime Start".
Fuel injection itself richens the fuel mix when cold by the ECU, just like a newer car..

Injectors will open when the ECU opens them, when needed. A leaking, stuck open injector can allow raw fuel into the combustion chamber, past the intake valve.

As noted earlier, there SHOULD NOT be any fuel in the silencer. Raw fuel would not be blow by, blow back, in the silencer, period...

Again, as noted before, there should not be any raw fuel in that silencer. I'd be looking real hard where that's coming from..


High oil level that smells like fuel, getting into the oil, confirms fuel leaking (from somewhere-likely an injector),

[rlmarz814]

With all injectors unplugged fuel rail pressure shoots to 40# and dies off. Going to swap out injectors and retest.

Confirmed as well that she is in fact "making oil" via dipstick.

Spark test to follow.

[TownsendsFJR1300]

Yep, you got a leak(injector likely) somewhere..

[rlmarz814]

Pulled the fuel rail back and #3 injector was very evidently open. Replaced it with one of my originals that I cleaned and it held 40# of pressure at the rail.

I dipped her and after running it hard to decarb her a bit, she seemed to be running great.

I'm going to do an oil change and take her for a run to see, but I just don't feel out of the woods/have my confidence back.

It was more than likely a case of old injectors just getting gummed up/poor effect of idling for hours. When I cleaned them it obviously was subpar and they gummed up again after 3 good runs. Swapped them with the remans and one went shot out the gate. Ugh.

I've got an appointment Monday and I plan on just asking him to give her a once over and clean bill of health. Oh and get that injector replaced....

[TownsendsFJR1300]

That's great news..

Make sure the fuel is fresh, might consider running Yamaha's RINGFREE..

It is a top end and fuel system cleaner. I use it in EVERY gas machine(SUV included) I own and work on..

It's not cheap but way cheaper than replacing one injector, carb cleaning, etc and IME, works excellent..

https://www.shopyamaha.com/product/d...?b=Search&d=34


Not noted on the bottle but a SHOCK dosage is 2oz / one gallon vs regular usage of 1oz/10 gallons
(it's not a fuel stabilizer)


.