F115 Electrical Troubleshooting Help

[Cascade Cruiser]

Looking for electrical troubleshooting help regarding my 2006 F115, I think I may have a bad ECM or perhaps a malfunctioning TPS, ISC valve or engine wiring issue. The original issue is summarized in the link below, basically the motor runs fine for 5-10 minutes (including running smoothly above 5000 rpm) until a misfire creeps in and pretty soon the motor will not run above about 4200 rpm without running rough. I believe I've ruled out fuel issues and ignition (ran on separate tank, fuel px good at the rail, serviced injectors, replaced or cleaned just about everything in the fuel sys, plugs and coils replaced).

So on to the electrical components: TPS shows correct voltage at idle (.733V) and on YDS appears to increase appropriately when accelerating. Any suggestions to further troubleshooting the TPS?

ISC appears to be operating normally...engine idles initially at a higher rpm then lowers after a few seconds. Seems to pass the YDS stationary test. ISC clatter can be heard on shutdown. Any suggestions for further troubleshooting this valve?

I can inspect the wiring harness for signs of damage, shorts, continuity, etc, but this sounds like a needle in a haystack. Any trouble areas on the wiring harness that I should pay particular attention?

Finally the ECM. I can swap in another unit from a friend's F115 but I definitely do not want to fry his unit if I have a sensor or wiring issues that has caused mine to go bad. Any suggestions?

Is Yamaha OEM the only realistic replacement option for these components? $1,100 for an ECM and $400 for an ISC is pretty steep unless I am confident it will fix the problem.

Thanks for any insight, this problem is driving me nuts.

[rejesterd]

basically the motor runs fine for 5-10 minutes (including running smoothly above 5000 rpm) until a misfire creeps in and pretty soon the motor will not run above about 4200 rpm without running rough.

What is the compression in each cylinder after the engine has warmed up?
What is the fuel pressure at 4500 rpm within the first minute after starting vs after 5-10 minutes?
Did you do a real spark test (with a spark tester) on every plug wire with YDIS?

And then how do those numbers compare with your friend's engine?

If you've done all that and the numbers are similar, then get the service manual. It will tell you how to test the ECM output peak voltage

[99yam40]

yep, need to know what the rail pressure is doing while the problem is happening to rule out fuel problem

[boscoe99]

What is the compression in each cylinder after the engine has warmed up?
What is the fuel pressure at 4500 rpm within the first minute after starting vs after 5-10 minutes?
Did you do a real spark test (with a spark tester) on every plug wire with YDIS?

And then how do those numbers compare with your friend's engine?

If you've done all that and the numbers are similar, then get the service manual. It will tell you how to test the ECM output peak voltage

Output peak voltage for what? To what?

[Cascade Cruiser]

What is the compression in each cylinder after the engine has warmed up?
What is the fuel pressure at 4500 rpm within the first minute after starting vs after 5-10 minutes?
Did you do a real spark test (with a spark tester) on every plug wire with YDIS?

And then how do those numbers compare with your friend's engine?

If you've done all that and the numbers are similar, then get the service manual. It will tell you how to test the ECM output peak voltage

My compression test showed was anywhere from 125 to 130 psi across the 4 cylinders. I wasn't too impressed with the gauge I was using, or my technique for that matter. I put the fast idle lever all the way up but not sure if that opened the throttle enough to get accurate numbers for the test.

Fuel pressure is about 40 psi at idle and 44 psi at higher rpms. I've only tested the higher rpms on a warm engine because it takes me at least 5 minutes to slow bell out of the marina. The pressure fluctuates a few psi but it doesn't appear to be dropping significantly when the engine runs rough. I have done exhaustive work on the fuel sys at this point, including run the motor off a spare tank, replaced all low and high pressure fuel lines, fuel bulb, low px fuel pump, all inline filters, VST screen, fuel px regulator, VST tank inspect incl breather and needle valve, and fuel injectors serviced. Nothing has resolved the issue. In general the fuel sys has appeared to be very clean.

I have not tested the spark, although plugs, wires, and coils have been replaced. Would a spark test still be beneficial?

I am looking through the service manual and try to tackle some of the electrical troubleshooting. Looks like I will need to learn about peak voltage testing and track down some test harnesses. Thanks for the input.

[Cascade Cruiser]

yep, need to know what the rail pressure is doing while the problem is happening to rule out fuel problem

On one of my test runs with the fuel gauge hooked up to the rail it did appear that the pressure was dropping momentarily from 44 psi when the engine misfired, but it wasn't more than a few psi and only for a split second. On subsequent tests I've convinced myself that the fuel pressure is good. I've watched the gauge fluctuate a few psi while it's running smoothly and then have the same fluctuation while misfiring.

One interesting thing about this problem is that the engine doesn't just drop rpm when it's running rough...the tach will show it quickly increase rpm too. For example, if I accelerate to 4500 rpm and the misfiring starts occurring, the rpms may fluctuate quickly between 4300 and 4700 rpm. Does this sound like a symptom of an electrical or sensor issue? Thanks for the the help.

[TownsendsFJR1300]

I would think the fuel pressure should not be fluctuating..

I'd get that working correctly before chasing other things..

[99yam40]

maybe some one could chime in with what the rail fuel pressure should be sitting at.
moving around means that the injectors would be varying the amount of fuel into the cylinders.
Someone correct me if I am wrong, but the VST pump should be running all of the time, so only way for pressure to vary is running low on fuel in VST or pressure regulator.

I guess injectors could be having a problem, or a connection to an injector, or injector driver?

what kind of tach do you have?
digital or something with a needle ?
a needle might swing some in both directions moving back and forth as the motor RPM changed suddenly.
Just my thoughts

the motor is having a problem, you need to see if spark is going away on some cylinder from time to time or the fuel is causing it.
test what you can

if you use a timing light to check the spark to each cylinder ,you can also see if timing is varying or meeting spec

[rejesterd]

My compression test showed was anywhere from 125 to 130 psi across the 4 cylinders. I wasn't too impressed with the gauge I was using, or my technique for that matter. I put the fast idle lever all the way up but not sure if that opened the throttle enough to get accurate numbers for the test.

Fuel pressure is about 40 psi at idle and 44 psi at higher rpms. I've only tested the higher rpms on a warm engine because it takes me at least 5 minutes to slow bell out of the marina. The pressure fluctuates a few psi but it doesn't appear to be dropping significantly when the engine runs rough. I have done exhaustive work on the fuel sys at this point, including run the motor off a spare tank, replaced all low and high pressure fuel lines, fuel bulb, low px fuel pump, all inline filters, VST screen, fuel px regulator, VST tank inspect incl breather and needle valve, and fuel injectors serviced. Nothing has resolved the issue. In general the fuel sys has appeared to be very clean.

I have not tested the spark, although plugs, wires, and coils have been replaced. Would a spark test still be beneficial?

I am looking through the service manual and try to tackle some of the electrical troubleshooting. Looks like I will need to learn about peak voltage testing and track down some test harnesses. Thanks for the input.

In the manual I'm looking at for the F115 from 2000, it says minimum compression is 135 psi. But you're not that far off, and as you noted, it could very well be higher than that if you re-tested with a different gauge.

44 psi at high rpm is good, but it should be closer to 35 psi at idle just after you start it up when cold. Also, it should be 44 when you turn the key to ON without starting it. I don't think it should fluctuate, but if you don't see significantly more fluctuation when the issue happens vs when it's running ok, then I would say the issue isn't totally related to fuel system components.

One thing the manual's troubleshooting section has is the condition of "erratic engine speed". If the fuel pressure is out of spec (which it is at idle), check the 20A fuse, the main relay, and the ECM's output peak voltage. But again, this is a manual from 2000. At this point in your investigation, it's probably worth buying the service manual for your exact model/year. It might have even better suggestions for troubleshooting.

The spark test could still be beneficial, because you might find that one or more plug wires can't jump the gap specified in the service manual. Usually, you'd notice that issue at idle and not just higher rpms, but it's still a worthwhile test just so you can be absolutely sure that it's not a bad coil or plug wire.

[boscoe99]

The fuel pressure will vary as a function of manifold pressure. More manifold pressure more fuel pressure.

The pressure regulator is plumbed to the intake manifold.

Highest manifold pressure with the motor not running. That is why highest fuel pressure will be seen when the key is just turned on. Start the motor and run it at idle. Manifold pressure will be as low as it can be. Fuel pressure will drop. Open the throttle, manifold pressure rises and so too does the fuel pressure.

[Cascade Cruiser]

I really appreciate everyone's input. So I looked back at the fuel pressure results I've recorded and they are about 37-38 psi at idle (at least 2 psi above spec) and 42-44 psi when running at speed. I will have to check the pressure with the switch ON but motor off, pretty sure it's in that 42-44 psi range. My fuel pressure gauge setup is home built but I think it's more robust than the cheap kits you can buy. However, the line that connects from the fuel rail to my gauge is long (~5-6') so that I can hook it up and run it through the upper cowling vent and run at speed on the water with the cowling on. If I didn't bleed all the air out of the gauge line I think that could explain some of the 1-2 psi fluctuations in the pressure readings, especially considering the fluctuations are the same regardless of the motor running smoothly or misfiring. I am 99% sure the VST is staying full. Pumping the primer bulb repeatedly when it's running rough and immediately afterwards does not resolve the issue, and I've tested or replaced everything leading to the VST. If fuel pressure is the issue then I think it would have to be the high pressure pump (or driving voltage to the pump) or a fuel injector (or injector driving voltage). I'm going to try to track down a test harness to monitor voltage to the high pressure pump while running and see if it is cutting out for some reason. I think the fuel injector voltage would be more difficult to test. Any ideas on how to test the injectors while the motor is running at speed? I may just buy one new injector and swap it in at each position to see if anything changes.

The tach on the boat is digital. I'll see if I can post a video of the malfunction occurring. I will get a spark tester and check spark when the boat is on the trailer and pick up a peak voltage adapter. I'd really like to figure out a way to measure these electrical signals while operating at speed while the misfire is occurring.

[99yam40]

I am not sure about peak voltage readings on an ECU motor.
I realize a CDI motor has spec for peak voltages, but not sure what peak voltages to measure on your ECU drivin motor.

Boscoe corrected my miss thoughts of fuel pressures.


just thinking now
what can affect a motors RPM
Timing
one or more cylinder dropping due to
spark,
fuel, too much or not enough

as I mentioned a timing light hooked to the different plug wires should indicate if spark is getting to the plugs steady while the problem is occurring and tell is timing is jumping around

fuel is not easy to check besides pressure

[Cascade Cruiser]

I've been in touch with the local Yamaha mechanic and he's going to replace the throttle position sensor. It'll be good to have a professional mechanics eyes on the motor as this is the first outboard I've worked on. If the TPS doesn't solve the problem I think I now have a good list of additional troubleshooting ideas:

• spark gap
• timing light to assess spark while running at speed if possible
• peak voltage tests per ch 8 of the service manual (ignition coil input, pulsar coil output, lighting coil, rectifier/regulator)
• monitor input signal to high px fuel pump at speed
• possibly throw some new parts at the motor (sensors, fuel injectors) if the troubleshooting doesn't reveal the problem. The fuel injection troubleshooting section in ch 9 of the service manual that rejesterd refers to mentions the water time sensor and intake air temp sensor as possibly causing erratic engine speed.

Thanks again for the input. I'll report back. It will be a glorious day when this thing runs right if I ever get there.

[Cascade Cruiser]

Update. So I ran last night with a new throttle position sensor. Same issue with the misfire at 4200 rpm. However, I put some Mercury Quickleen in the gas tank and ran the motor for about 30 minutes at 4000 rpm and below. After this point we tried a higher rpm cruise and the motor would run smoothly up to 4800 rpm, with the misfire occurring above that. Something definitely changed, as once the engine is warm I've never been able to run smoothly above about 4200 rpm.

[pstephens46]

If we could get Whaler27 to run some graphs regarding historical outcomes on this forum, I’m betting 85% of running issues are due to fuel issues. Go with the odds and stay on the fuel path. Perhaps you flushed a little funk with the cleaner you added. You could send the injectors by mail to have them cleaned and tested. You may have already done that? I may have missed it. Cheaper than swapping parts.