2003 F115 hp 4 stroke problems after 15 minutes of running

[glennbossie]

My motor run great from idle to wot for about 10-15 minutes, then starts cutting out. Tach goes crazy up and down and engine really hesitates, and dies. Sometimes it starts back up, but I usually have to wait for 15 minutes for it to cool down, then it will start and I can run it at idle to get home. If I leave it to cool for a couple hours, I can repeat this whole process almost exactly. I suspect the coils may be acting up when they heat up, but would like some suggestions. I thought fuel issue at first, but it runs fantastic for those 15 minutes.

[TownsendsFJR1300]

Check all battery connections both at the battery and power-head.

R&R them, no just "looks fine".. make sure ALL grounds as well are super clean and tight.

A loose/crappy electrical connection can cause all kinds of issues.


Bad coils won't make your tach go crazy, I'd guess a bad connection somewhere..

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[99yam40]

do you have a tach with alarm warning lights, and do they work?
does the alarm buzzer work.
there is a good chance your motor is over heating or has an oil pressure problem after heating up
rule out the things you can check easily 1st

[glennbossie]

I’ll go do that now. Thanks. I think the tach goes crazy because the engine is jumping up and down when it first happens.

[glennbossie]

My overheat alarm does work, and occasionally comes on when I’m running out of the water with the muffs on. I did have gas in my oil, and changed both the thermostat and low pressure fuel pump. Changed the oil and filter also.

[glennbossie]

I removed all my power leads and grounds from the battery and motor and cleaned and inspected them. Did have some corrosion and my motor hot lead had the nut only finger tight. Took the boat back out on the river, and same problem. Ran at 5krpm on step for a couple of minutes, and then its like someone turned the key off. Motor will only run in idle and a little higher, maybe 2k rpms. Push it any harder, and it stalls and will not restart until it cools down or rests for a little while.

[99yam40]

sounds the same as over heat.
just saying make sure that is not the problem

[glennbossie]

How would you check for an overheat? Should I take it to the fail point, and take a temp reading on the motor? I don’t have temp gauges on the boat.

[99yam40]

I removed all my power leads and grounds from the battery and motor and cleaned and inspected them. Did have some corrosion and my motor hot lead had the nut only finger tight. Took the boat back out on the river, and same problem. Ran at 5krpm on step for a couple of minutes, and then its like someone turned the key off. Motor will only run in idle and a little higher, maybe 2k rpms. Push it any harder, and it stalls and will not restart until it cools down or rests for a little while.

Reading this again , over heat will not cause the motor to die and not restart.

when this happens check for spark.
if all plugs have good spark, then it would have to be too much fuel or not enough fuel to fire the cylinders properly

[glennbossie]

I took my lower unit off and took the water pump/ impeller off and reinstalled it. I had just replaced it last Fall, so it all looked great. I put it back together and ran the muffs on it. The water coming out of the p hole tripled. Sometimes I had to squeeze the muffs to get it to come out. This time it came out strong and straight. Not sure if this will fix my problem, but really happy this works better now.

[glennbossie]

Took it back out for a try. Idled out onto the river and opened it up. Stayed at 5k rpm 25mph and it ran like a champ. At the 10 minute mark it bogged down. I dropped it back and into neutral. Restarted and headed back to the dock at 2k rpms. Anything above that and it would cut out. Stalled completely 100 ft from the dock and wouldn’t restart. Paddled in, put it on the trailer, and tried to start it again, and it started right up. No overheat, p hole water was barely warm. Bulb had fuel in it when it died. What next?

[glennbossie]

99yam40 - What would cause me to lose spark to the plugs under the circumstances I’m experiencing? Coils, ecu? I know I have plenty of spark up until the time it bogs down. It generally will start up again also.
I can’t figure out why after 10 minutes it stops getting fuel, if that’s what’s happening. What would stop fuel after 10 minutes of hard running? The only fuel spot I haven’t looked into is the vst tank.

[99yam40]

all I am saying is check what is easy to check.
a spark tester or inductive timing light should show if there is spark to the plugs.

not sure how to check if cylinders are getting the proper air fuel mix.
but rail pressure to make sure it has in spec fuel pressure.
too low or too high might be a problem

[TownsendsFJR1300]

Can you try running it say at 4K RPM (same time frame) and see if it acts up again?

Just trying to rule out a potential over heat issue.
With the somewhat lower RPMs, the engine isn't quite as hot and may keep running IF NOT OVERHEATING..

I gather from your previous posts, you never got an alarm when the engine "acted up"?

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[glennbossie]

I ran it yesterday at a little over 4k rpms, and same thing. 10 minutes in, it bogs down. As long as I don’t mess with trying it again, I can get back to the dock under 2k rpms. I took all my fuel injectors out again and found 1 with a split rubber ring next to the engine. Replaced it, but no fix. I also checked the p hole water when it bogged down, and it was only slightly warm. Squeeze bub is new, and it had fuel in it. Makes no difference to my problem if I squeeze it. It’s not collapsing either. No alarms at all any time this has happened.
I’ll try anything you suggest, because I’ve hit a dead end. I have not taken the vst tank out and checked the filters yet, but I would think it would happen everytime I tried to throttle up if they were clogged. Is this something the ecu might cause?
Thank you all for giving me some ideas. I really appreciate your time.