Thread: 90 optimax ~ won't run

not an expert, but should have an alternater to provide the spark. DC power is needed until the engine runs long enough for alt to kick in, which sounds like is not happening for you. Could be the choke not working properly, or you're not setting the choke properly at cold start. Has the motor sat for a long time not used, things could be fouled out/plugged up (not sure if efi or not). Bad/stale gas ??

I'm pretty sure these new computer controlled motors require a good fully charged battery. First thing, get a good battery on the motor.

The battery has nothing to do with the motor running. All it does is provide power to the starter for the motor to start and it must spin the motor at least 300 RPM for the stator to put out enough for the motor to run. However, never disconnect the battery while the motor is running as it will damage your charging circuit.

Just to back up my earlier post, I found this on another forum.
"Recommended Battery
A 12 volt marine battery with a minimum Cold Cranking amperage rating of 750 amperes or 1000 (minimum) Marine Cranking amperes should be used."
Perhaps they have changed their specifications.
A deep cycle battery with a rating of 1,000 MCA may be harder to find than a marine starting battery with that rating.
The general impression of the OptiMax engine is that below a fast idle speed, say 1,000-RPM, the engine is a net consumer of current. That is, it needs more current to run than it can generate from its charging circuit, therefore it is draining the battery at those speeds. It also appears that these engines are very sensitive to voltage, and if the supply voltage drops much at all below 12-volts, the engine will not run properly. This is probably why they specify such a huge starting battery for them. They need to have a stiff supply of 12-volts to get started and running and idle speeds.
The Optimax engine has a lot of electrical devices. It has electrical fuel injectors AND electrical air injectors. It has twice as many injectors as other fuel-injected or direct-injected engines. And it has an electrical fuel pump (which all fuel injected engines tend to have because they have a pressurized fuel rail).
Because you are using your OptiMax for trolling, you may be running it close to the point where its charging current and its electrical demand are about equal. It would be interesting to actually measure the charging current at your favorite trolling speed.
In any case, stick with a strong battery and you will avoid problems. The principal job of the battery on your boat is to start the engine, so I'd get a battery that was designed for that job as my primary battery.
It is possible to have two batteries of different type aboard, but you need to have some plan to charge and maintain them. I would use a voltage-sensitive relay (VSR) type charging combiner. That is a whole different topic. If you want to discuss VSR relay set ups, let's start a new thread, and let this discussion stay focused on the 150-HP Optimax as its TOPIC suggests.

Thanks for all input. Shellback, thanks for all the detail. I have a desiginated cranking battery; its fine. Narrowed it down to fuel side. Trip to shop for a laptop test in order. Is not the first, probably wont be last. Once again, thanks for all yalls help.

Yes the Optimax needs a properly charged battery at all times. The E-tec can run without a battery once started, but still needs a large cranking battery to get it started especially in freezing temps.

Optimax need over 9 amps to keep it running install a new battery and problem will go away

Hey I would like to know what the shop says about this. I have the same engine....