F115 Rough at All RPMs

[rlmarz814]

2000 F115TLRY

Timeline: Idled for quite an extended period of time (fishing) on the second to last run of the season and noted she seemed a bit rough by the end. Commenced end of year maintenance to include: Water pump, lower unit oil, spark plug swap, engine oil, on engine fuel filter as well as fuel/water separator, added stabilizer.
Took her for one last spin before putting her away and she ran rough enough for me to notice. Slight shake, and RPMs would surge on occasion. At the end of the day she had trouble starting next to the dock. Unfortunately I was leaving for deployment the next week and laid the boat up.
Got back, replaced fuel filters since I had them, and cleaned the VST tank and filter. No apparent issues in there. Pulled the plugs and found them all satisfactory.

First run since the first corrective actions and she started right up and seemed fine at first. Once running she was a bit rough at idle, and shaking when in gear. Still was able to get on plane and run at higher RPMs, but still something definitely amiss.

I hooked up YDS today at idle. One thing to note is Code 28, though I'm not familiar with how that would/could cause issues. I'd like to run a separate tank to eliminate fuel issues but don't have one immediately available. Other thoughts/suggestions stemming from the extended idling potentially causing the issue would be IAC valve or injectors.

Data:
Shift position switch Irregular 28
Pulser coil Normal 13
Water temp sensor Normal 15
Throttle position sensor Normal 18
Battery voltage Normal 19
Intake temp sensor Normal 23
Intake press sensor Normal 29
Intake air passage Normal 37
Engine stop lanyard switch Off 44

Engine speed 875 r/min
Intake pressure 545.3 HPa
Intake pressure 16.46 inHg
Atmospheric pressure 993.5 HPa
Atmospheric pressure 29.4 inHg
Ignition timing ATDC 3 deg
Battery voltage (12-16) 15.3 V
Throttle valve opening (0-90) 0.8 deg
ISC valve opening (0-100) 65 %
Fuel injection duration 2.34 ms
Water temperature (below 90) 46 °C
Water temperature (below 194) 114.8 °F
Intake temperature (below 70) 19.6 °C
Intake temperature (below 158) 67.3 °F

I've got some limitations on retests/diagnostics (I have to dip the boat) but standing by to try out what we can think up. Thanks in advance.

Ron

[99yam40]

Shift switch might be that you tried to start the motor when not in neutral or the ECU is not seeing the proper position of gear when started.

I would check compression or do a leak down test on all cylinders.
get a rail pressure measurement to make sure that stays in spec.

then send injectors off to be tested and cleaned

[rlmarz814]

I'll take a look at the wiring for the switch. I just did the VST tank and could see how it could have been beat up from that.

Compression check is doable next week; will report back on that.

I would think the YDS would give a fuel rail pressure readout but what I provided is everything I'm given. Not sure if that is a function of faults with my YDS software or the age of the motor.

[rlmarz814]

Had an opportunity to get down to the boat today.

Wiring for the Shift Position Switch appeared fine. I'll scrounge around and check how to test it.

Compression was good. 140# and consistent on all cylinders.

Pulled the IAC valve after a recommendation to find it clean as a whistle.

I'm going to see if I can get an external tank just to rule out my fuel, and after that I guess we're onto injectors?

[rejesterd]

Yeah, I would send the injectors in to be cleaned. It's happening at all RPMs, so in that case, it might be better to work backwards.. Injectors > pressure regulator > VST pump > VST filter... Your YDIS report looks normal to me, but of course it doesn't tell you about fuel pressure. That's something you'll want to get set up to measure at some point.

[rlmarz814]

Cleaned the injectors and she's running great again. I had the tank open to replace a fuel sender the beginning of the year, so I know the tank is for the most part free of visual contaminants, but obviously something clocked them up. Whatever it was that clogged them up I suspect can be contributed to the long period of idling as well.

Break.

Any idea how to reset the shift position sensor code? It is still locked in and am unsure if I should just replace it or try to reset the code. Thanks in advance folks.

[rlmarz814]

Well the problem has reoccurred. I had about 3 good runs before she started getting rough again. I've been meticulous about draining the fuel water separator and the on engine filter with nothing as results. I swapped out the injectors for rebuilt ones and it ran fine for about 20 min before becoming incredibly rough again, especially at lower RPMs. Of note, it seemed to be running rich/not completely burning fuel based on exhaust fumes.

[rejesterd]

If it is indeed running rich, then the possibilities I can think of are:

-weak spark (due to a bad coil or ECM)
-stuck open pressure regulator
-stuck open injector
-vacuum sensing line(s) disconnected or leaking
-air adjusting screws on the air intake are not right

Since you have YDIS, that makes spark testing easy with a spark tester. Make sure every plug wire is producing a spark that can jump the gap specified in the service manual. The manual should also tell you how to test the pressure regulator. Seems that you've ruled out injectors, though it did make a difference initially (so that's more evidence that this is fuel-related). I have no idea how to methodically set the adjustment screws properly, but again, hopefully the manual would tell you.

[rlmarz814]

Did a bunch today in an effort to dial it in further.

- Ran her off an external tank to rule out fuel/fuel delivery issues. Still ran like crap so isolated the issue to the engine.

- Both pressure/electrical tested fuel filter, mechanical fuel pump, and electrical fuel pump all sat. Injectors electrically sat. 38-40# at the fuel rail.

- Ran a vacuum test on the fuel pressure regulator and did not have noticeable/definitely not trending decrease on fuel pressure. Definitely a data point. It did cause it to stall at one point. It has a bit of corrosion on it to, but I want to be sure before biting the bullet on that pricey number.

- Shift position sensor seems bad based on continuity but I don't see it having an effect.

- Multimeter crapped out before I could check coils/spark or the ISC and TPS sensors, but based on YDS readings I don't believe the sensors are the issue.

- Lastly, the engine exhaust was most definitely making a sheen. I would think it would take a bunch of unburned fuel to make a visible sheen. To be honest I'll be pulling the prop/lower unit vent screw tomorrow to verify I didn't lose the prop seal and rule out oil. When it rains it pours. This was occurring at idle.

I appreciate all the help gents. Every mechanic down here is 4-6 weeks out but at this rate a professional might be the answer.

[rejesterd]

38-40 might be slightly high (though I don't have the service manual for the 115, so I can't confirm). So yeah, maybe the pressure regulator is bad.

But if you are still seeing a code 28, I wouldn't ignore that. The shift position switch actually shuts down ignition to some of the cylinders when it's engaged. It's only supposed to do that when shifting from in-gear back to neutral. But if it's constantly engaged, that might actually be your problem.

[rlmarz814]

Service manual calls out 40# at idle so I'm consistent there.

Based on schematics and the test for it, the shift position switch only provides input when shut (continuity) so I might be missing how that could affect idle when it is open.

[rejesterd]

Service manual calls out 40# at idle so I'm consistent there.

Based on schematics and the test for it, the shift position switch only provides input when shut (continuity) so I might be missing how that could affect idle when it is open.

It could affect idle if the switch circuit is closed all the time. You can test that by unplugging the switch and see if idling in neutral improves. Just don't try shifting when you do that.

[rlmarz814]

Tested the shift position sensor and it was bad (continuity check when closed) so it was replaced with no effect. In the process, when I pulled the air silencer, there was a bit of fuel in it. I'm convinced one of the cylinders just is not firing. I pulled the plugs again, disconnected the injectors, and turned the engine over to which fuel was definitely kicked out. I'll be testing spark once I can get a hand to help me do so. The sheen also was present, but more an more I'm believing I've also got a busted lower unit seal and it is not just unburned fuel alone.

[fairdeal]

In the process, when I pulled the air silencer, there was a bit of fuel in it.

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

I pulled the plugs again, disconnected the injectors, and turned the engine over to which fuel was definitely kicked out.

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

[rejesterd]

when I pulled the air silencer, there was a bit of fuel in it.

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?

I'm convinced one of the cylinders just is not firing.

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