Need Help Diagnosing 150 Optimax Issue

I’ve got a 1999 150hp Opti. It’s been rock solid till now. Here is the issue: it will not go over about 2500 rpm when under load (in the water and throttling up). The motor begins to shake and sputter hard, possibly in limp mode, I’m not sure. It’s been hooked up to diagnostics and no codes show up. When out of the water and put on a boot there are no observable issues – it throttles up like there is nothing wrong. I’ve bypassed the gas and tried a different battery with no luck. Anyone have any ideas? Or have a recommendation for an honest mechanic that can fix this? Thanks in advance for any help.

Yes you are in limp mode what are you getting for beeps from the controls? A warning buzzer should be sounding when it gets into limp mode.Tthe first thing I would check is if the oil reservoir on the engine is full. Next the on board fuel filter for water, check the belt and airpump. then plugs and lastly injectors and coils. Usually injectors and plugs will not cause it to go into limp mode. When was the last time the waterpump and thermostats were changed?

No beeps or buzzers, it just shakes and sputters. Oil seems fine. The water impellers have low hours on them. The pump has never been changed. The pee coming out of the engine is strong.

They call them optipops cause they are known for blowing up. Hope you don’t need a new power head. That’s anywhere from 4 to 6,000 good luck. I think my brothers motor is doing the same thing. He’s in Mexico now but when he calls today I’ll see what he found.

Call Eddie Lybeck 320-676-3611 there has never been a Opti made he can’t fix.

Odds are its a fouled plug.

dirk-w. wrote:

No beeps or buzzers, it just shakes and sputters. Oil seems fine. The water impellers have low hours on them. The pump has never been changed. The pee coming out of the engine is strong.

Are you saying that the water pump has never been changed?

If so, while it may put out enough water at idle it probably isn’t picking up water like it should on plane and a 1999 motor is WAY overdue for a new water pump regardless of hours on the motor.

First check the line from gas to motor- they have a problem with the inside of the hose closing down on itself- have been in 2 boats that have had this happen. Simple fix.

Family pontoon has an opti we have had to replace all 3 cylinders- expensive part but easy to do yourself.

Bassn Dan wrote:

If so, while it may put out enough water at idle it probably isn’t picking up water like it should on plane and a 1999 motor is WAY overdue for a new water pump regardless of hours on the motor.

And all new fuel supply hose with a new bulb placed vertical. Is there an internal filter? Is it running on last year’s gas? Tried pumping the fuel bulb while it is stumbling? Is the vent open on the fuel tank?

p4walleye wrote:

First check the line from gas to motor- they have a problem with the inside of the hose closing down on itself- have been in 2 boats that have had this happen. Simple fix.

Family pontoon has an opti we have had to replace all 3 cylinders- expensive part but easy to do yourself.

Forgot about the fuel line issue this could very well be the issue the inside of the hoses start to flake off. If this is the problem be sure to change fuel filter

mattgroff wrote:

They call them optipops cause they are known for blowing up. Hope you don’t need a new power head. That’s anywhere from 4 to 6,000 good luck. I think my brothers motor is doing the same thing. He’s in Mexico now but when he calls today I’ll see what he found.

This is usually caused from people not letting the Opti`s warm up before putting the hammer down. The tolerances are so tight on the Carb 4 motors, the pistons expand faster then the cylinder wall so you get what is a called a cold seize. This problem is more operator error then engine problem.

I did replace the fuel lines and bulb – forgot to mention that. And I bypassed the gas in the boat with fresh gas, and the battery. While the water pump may be old the motor is not overheating. It would run all day at 4000 rpms if it was sitting on the trailer. I’ll replace the water separating fuel filter and check the plugs next. That’s the problem with no beeps and codes, it becomes hunt and peck….

Start simple, fuel filter and plugs. If the fuel line did start to come apart it could be plugging the filter. Also not good to run an outboard on the muffs much above idle. As you have noticed running on the muffs and actually pushing a boat are very different, reading the plugs will tell you a lot about how its running.

start with easy peasy, fouled plug is a very real possibility. my e-trap comes around everytime. but it’s not a merc.

start simple, then open wallet. these engines run in theeee cleanest enviroment possible so start with plugs-n-oil-n-water, electronics/parts last.

been there.

fieds

I had similar opti problem.
Motor would run great than kick down to lower rpm.
After trial and error my mechanic called mercury.
They replaced a bad coil.
Opti runs like new now.

Good luck

My fishing partner had the issue with his 115 Opti and it’s bad coils. Merc backed his issue over 3 years I believe. I remember he had the issue 2 years in a row though. The dealer would replace 1 coil one year then another one the next year when having the same issue of no power. I thought that he talked them into replacing the 3rd one then as well.

If it turns out to be the coils replace them all at once.

coils sounds like fairly common issue