300 Promax dropping cylinder(s)

[Mr. Demeanor]

I have a 300 Promax with a MadEFI intake.
Been working through this setup and have a constant problem where it will run a good number then if I slow down and try to speed back up will be about 5mph slower. Today I actually felt it drop off power. Its not any of the sensors, spark plugs, or the ignition ECM. Other than coils is there anything else I should check?
The weird part is if I idle around a but it will jump back up on plane and pull to the top speed at full power but if I slow down to half throttle and try to speed back up, its just flat.
I have a set of coils to try next. Only other thing I can think of the alternator not making amps.

[Mr. Demeanor]

I might be dropping a couple cylinders because Ive been down one before and it wasnt much on a boat like this. Down about 100hp doing the math.

[Chaz]

Best way to find the needle in a haystack is cowl off test wheel on , back the trailer in the water and make it replicate the problem . Be ready with the ohm meter to check the stator and CDM modules (coils) when they warm up .
If I remember correctly , you can have one go bad and it will effect others in line much like you are describing .
I don't have a book on the early models or I'd send ya a cheat sheet . If you can make it do it , you'll find an open , or off 1000 ohms . Grounds or dead shorts usually smell burnt and don't make it back to normal numbers when they cool off .

[Mr. Demeanor]

Ive got a complete set of coils so I may just swap them all and then if that fixes it figure whats bad later.

[Mr. Demeanor]

Btw I replaced the air temp sensor and it did solve done if the problems.

[Chaz]

Ive got a complete set of coils so I may just swap them all and then if that fixes it figure whats bad later.

Unless you know their history , it might be wise to sit and ohm test them to see if all six of them pass before installing them …. stranger things have happened .