Just started misfiring on the water at mid range rpms on very last outing in 2024 - end of year so wintered it and thought I’d fix it before launching it this summer. This is a low hours (83.5 hours) sparsely used motor on a 19 ft, Wellcraft centre console, stock aluminum four blade prop.
Now on ear muffs it consistently—
- starts and idles perfectly as it always did
- misses consistently at 2500 prop not engaged
- does not misfire on the lightest of loads (when prop is engaged on earmuffs all the way up to 4000 rpm)
Loathe to launch it with the (prop not engaged) misfiring being 100% consistent.
Checked and tightened all fuel lines and fittings.
Installed a new coil (thanks Amazon), same. Swapped previously removed coil for the other, same.
Adapted a fuel pressure gauge at the rail valve
Reads 52 psi at key on, settles back to 46 when pump stops, then stays at 46 psi after engine start.
No misfire in gear when prop spinning up to 4000 rpm. Gauge is steady at 46 psi. Chose not to go higher at light load.
This is where it gets weird - In neutral misfires start at 2600 rpm. Gauge is steady at 46 psi.
4000 rpm in gear and steady 46 psi indicates to me that fuel starvation is not the issue.
Plugs all near perfect color and only 80 hours old - misfire seems to be all cylinders …….
Starting to look like faulty signal from the ECU re spark or injector command?
One caveat - previous owner upgraded his 115 to this 150 so boat was wired and gauged for a 115 originally. Previous owner advised that the low oil pressure reading was at 15 psi due to the use of the old (115 compatible) gauge. Would it be possible that the 150 ecu sees low oil pressure and interrupts the spark or injector firing?
Scratching my head big time on this one …… any suggestions appreciated …….
Now on ear muffs it consistently—
- starts and idles perfectly as it always did
- misses consistently at 2500 prop not engaged
- does not misfire on the lightest of loads (when prop is engaged on earmuffs all the way up to 4000 rpm)
Loathe to launch it with the (prop not engaged) misfiring being 100% consistent.
Checked and tightened all fuel lines and fittings.
Installed a new coil (thanks Amazon), same. Swapped previously removed coil for the other, same.
Adapted a fuel pressure gauge at the rail valve
Reads 52 psi at key on, settles back to 46 when pump stops, then stays at 46 psi after engine start.
No misfire in gear when prop spinning up to 4000 rpm. Gauge is steady at 46 psi. Chose not to go higher at light load.
This is where it gets weird - In neutral misfires start at 2600 rpm. Gauge is steady at 46 psi.
4000 rpm in gear and steady 46 psi indicates to me that fuel starvation is not the issue.
Plugs all near perfect color and only 80 hours old - misfire seems to be all cylinders …….
Starting to look like faulty signal from the ECU re spark or injector command?
One caveat - previous owner upgraded his 115 to this 150 so boat was wired and gauged for a 115 originally. Previous owner advised that the low oil pressure reading was at 15 psi due to the use of the old (115 compatible) gauge. Would it be possible that the 150 ecu sees low oil pressure and interrupts the spark or injector firing?
Scratching my head big time on this one …… any suggestions appreciated …….