F115 Electrical Troubleshooting Help

[Cascade Cruiser]

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.

I did have the injectors sent out and cleaned/tested back in December when I originally replaced all the fuel filters and inspected the VST. However maybe one is still acting up. Ran again today and the misfire is back at ~4200.

[pstephens46]

I did have the injectors sent out and cleaned/tested back in December when I originally replaced all the fuel filters and inspected the VST. However maybe one is still acting up. Ran again today and the misfire is back at ~4200.

Can you still get WOT above 5000rpm initially before the issue occurs? I read that you could at one point.

[Cascade Cruiser]

Can you still get WOT above 5000rpm initially before the issue occurs? I read that you could at one point.

Yes, ran today WOT at 5800 rpm. Backed off to about 5000 and after 5 minutes or so the misfire started occurring. Ran with the cowling off for the first time to measure kV in the spark plug wires. The "misfire" sounds like a loud pop or backfire with the cowling off. This thing is really baffling me. kV on the #4 spark plug wire measure significantly higher than the others (about 40 kV). The other plugs were 30, 30, and 22 kV.

[99yam40]

back fire to me means popping back thru the intake.
to do that either the plug fires before it should, the intake valve is open when it fires(Hanging valve maybe)

or is it in the exhaust?
fuel not being burned in the cylinder so it hits the exhaust and burns there

higher KV could be the plug , plug cap,or plug wire.
have you moved the plugs around to see if that caused it to move
Is KV higher on that #4 all the time?
or just during the misfire?

I know the more compression the more KV is needed to jump the same gap.

I wonder if lean on fuel or rich on fuel will affect resistance to jump spark

[Cascade Cruiser]

back fire to me means popping back thru the intake.
to do that either the plug fires before it should, the intake valve is open when it fires(Hanging valve maybe)

or is it in the exhaust?
fuel not being burned in the cylinder so it hits the exhaust and burns there

higher KV could be the plug , plug cap,or plug wire.
have you moved the plugs around to see if that caused it to move
Is KV higher on that #4 all the time?
or just during the misfire?

I know the more compression the more KV is needed to jump the same gap.

I wonder if lean on fuel or rich on fuel will affect resistance to jump spark

Ran again tonight to do a shock treatment of Quickleen from a 5 gallon gas can. Same issue with the misfire starting after about 5 minutes at high rpm, but things did eventually improve. On the final run back to the marina it held 5300 rpm for about 10 minutes running smoothly. Overall there was probably at least 20 minutes cumulative time running at 4800 rpm or greater with no misfires. I think that would rule out any steady state fuel delivery issues unless there is something electrical or intermittent that affects fuel delivery and causes the misfire.

The hanging valve sounds plausible in regard to the backfire and intermittent loss of power. I suppose the de-carb treatment might help this issue and result in the smoother running we had tonight. Strange that whatever the issue is so intermittent.

I have not moved plugs around to see if it affected kV. The kV on the meter fluctuates quite a bit on all plugs, difficult to correlate directly to the misfire.

[99yam40]

sounds like the only time it starts running well is when running on a different tank with

Quickleen

.
have you thought about there is a problem with your gas in the boat tank

or was the 1st time in your normal boat tank?
how old is the gas and is it none ethanol fuel

[Cascade Cruiser]

sounds like the only time it starts running well is when running on a different tank with

Quickleen

.
have you thought about there is a problem with your gas in the boat tank

or was the 1st time in your normal boat tank?
how old is the gas and is it none ethanol fuel

I'm glad you brought this up because I hadn't thought of that lately. The problem started last summer and since then we've probably been through 5 or 6 fill ups of 20-25 gallons. No ethanol in the fuel here to my knowledge. I've only ever found trace, if any, evidence of water in the Racor bowl and the fuel system seemed very clean when I was inspecting and replacing components. I did run it off an external tank with fresh fuel in the past to try to isolate the problem from the boat plumbing, but to be honest I was focused more on air leaks or flow restrictions and less on fuel quality. Last night was the longest I've run on an external tank (about 45 mins run time). For what it's worth, the last run back to the marina (9 minutes at 5300 rpm) was plumbed back into the boat tank. I will think about this more, prob worth try to clean out anything in the bottom of the tank.

[pstephens46]

I am still leaning towards fuel delivery or quality.

[Cascade Cruiser]

Still trying to track down this problem. Batteries died a few weeks ago so replaced them. I have the boat on the trailer now and fired it up this morning to check the sync on the throttle bodies and TPS. Had the motor hooked up to the YDS and noticed battery voltage was 12.2 volt at idle. Something must be up with the charging system, will start troubleshooting that next. I'm wondering if something was on the way out (rectifier/regulator?) and it finally died. Previously when running with YDS hooked up I've always noticed battery voltage indicating above 14V while running. Maybe this issue will lead me to whatever has been plaguing this motor for so long.

[99yam40]

you said batteries, so more than one battery.
strange to have more than one die at the same time.

good chance you had charging problems for awhile if multiple batteries gave up at the same time.
test lighting coils and RR

low voltage can cause running problems.
maybe batteries just could not keep up the voltage the longer you ran.
strange how it would be at a certain RPM tho

[Cascade Cruiser]

you said batteries, so more than one battery.
strange to have more than one die at the same time.

good chance you had charging problems for awhile if multiple batteries gave up at the same time.
test lighting coils and RR

low voltage can cause running problems.
maybe batteries just could not keep up the voltage the longer you ran.
strange how it would be at a certain RPM tho

One question on testing the RR: my FSM shows output peak voltage measure at the rectifier regulator harness (red to black) to be 12.5V at 1,500 rpm and 13.0V at 3,500 rpm. Shouldn't I expect to see something above 14V? I have a 6 pin test harness on order so I can test the lighting coils and RR.

Agreed, I thought the (dual) batteries were just giving up finally (9 years old!) but it must have been a longer term charging issue. Some of the mechanics at work (aviation techs) were suggesting electrical issues could cause the running issues, although I've always noticed the battery voltage above 14 V on YDS, even while the motor is misfiring.

[rejesterd]

Are you still seeing 37-40 psi fuel pressure at idle? If so, that's too high and you should probably test the pressure regulator, or at least remove it and try cleaning it. If it sticks, that could cause it to over-pressurize at idle, and then not maintain enough pressure when running at high rpm. Although it could be related to electrical components, the only thing that's really made a difference so far is the fuel/quickcleen mixture.

And you did say the numbers fluctuate at high speed. Is it the same for your friend's 115? I know you've done a lot of work with the fuel system, but that 40 psi at idle is too high (if the same gauge is giving you 44 psi at key-on).

[Cascade Cruiser]

Are you still seeing 37-40 psi fuel pressure at idle? If so, that's too high and you should probably test the pressure regulator, or at least remove it and try cleaning it. If it sticks, that could cause it to over-pressurize at idle, and then not maintain enough pressure when running at high rpm. Although it could be related to electrical components, the only thing that's really made a difference so far is the fuel/quickcleen mixture.

And you did say the numbers fluctuate at high speed. Is it the same for your friend's 115? I know you've done a lot of work with the fuel system, but that 40 psi at idle is too high (if the same gauge is giving you 44 psi at key-on).

Fuel pressure was 37 psi at idle when measured previously. I don't have my FSM in front of me to see what the spec should be at idle. I got mixed results measuring pressure at high rpm. On two occasions the pressure was in the range of 42-44psi and steady even when the gauge misfired. Although there was still some flutter in the needle of about 1 psi even when it was running smooth, I assumed that was a normal output characteristic of the pump? On a third occasion I did see the pressure drop 3-4 psi when the misfires occurred, but I'm not sure if I had properly bled the pressure gauge on that test. The pressure regulator has been replaced as part of my troubleshooting. If there is a fuel issue at this point I think it would have to be an intermittent signal to high pressure pump or injector(s), or a pump just intermittently failing.

[rejesterd]

Ok, if you replaced the regulator, then I think you're good there. The spec from the manual I have says it should be 35 psi at idle and 44 at key-on. And I really don't think it should fluctuate unless you change the throttle plate position quickly. So I would do the pressure test again, making sure you bleed the gauge this time.

It does seem like an electrical issue, because it's a very intermittent misfire/backfire. The loud noise indicates that fuel is igniting when it shouldn't be, obviously. That's typically due to ignition/stator/ECM/timing. But the fact is, there was a slight improvement when you made a change to the fuel mixture, and it doesn't seem that your fuel pressure is exactly within spec. So I would say you can't completely rule out the fuel system yet. The HP pump is really the only component you haven't fully ruled out (assuming you really went through the VST, checked the needle valve and everything). In addition to performing the fuel pressure test again, I would take a good look at the wiring for the HP pump, and make sure the insulation is all good.

If you find that the fuel pressure doesn't drop when the issue occurs next time, I think you have to move on to testing the ECM output peak voltage. The manual I have gives this as a possibility for incorrect fuel pressure.

BTW the 12.5 volts spec is the lower limit. So it it's 14.something, that's ok. It just can't be lower than 12.5.

[99yam40]

is that peak volts measured with the proper voltmeter or with a DVA and regular meter.
I also would expect to see voltage at the battery above 13 even at idle