Opti sputters on acceleration

[johnmr12]

I have a 2001 Optimax 225 3.0L DFI, serial #OT305247. I was having trouble going from idle to 3000 rpm. The engine would sputter for about 10 seconds before it would finally get on plane. Once on plane it ran good but my top end RPM dropped from 5650 to about 5300. I tried to figure it out myself but failed. I would try something and go to the ramp to test it. I didnt even have to leave the dock to know if it was going to run right. I just had to put it in neutral and slowly rev the engine. It would hesitate and sputter right from idle on up so I never even had to go above 1500-2000 rpm. after several frustrating attempts, I brought it to a shop. When I told the mechanic my symptoms he said he was almost positive I needed new reed petals before he even looked at it. I left it with him and after he looked at it he said most of my reeds were broken. So he put in the composite reed petals from Boysen I think they are called. Almost $1,200 later I picked up the boat and headed straight to the ramp. It is definitely better than it was, but here is my question. When I put it in neutral and rev it up its just as bad as it was $1,200 ago. Now I realize I have no reason to ever rev it up in neutral but based on my limited knowledge of internal combustion engines, shouldn't a healthy engine rev smoothly whether the transmission is in neutral or drive? I wasn't able to test my top end RPM because the water is below 40 degrees now and it scares me to go WOT because a very long time ago I blew the power head on this engine on a cold January day when I tried to go WOT.

[castforcash]

Never rev an Opti in neutral. What you are experiencing while doing that is guardian mode protecting the motor.

[johnmr12]

Are you saying every opti will sputter and cough if you try to rev it up in neutral?

[castforcash]

Are you saying every opti will sputter and cough if you try to rev it up in neutral?

Yes

[SilverFox579]

In addition to Guardian activating trying to protect your engine from what you're doing, every time you rev that Optimax in idle you are creating neutral overspeed faults that are logged in the computer. NEVER rev an Optimax in neutral - at the least you set a neutral overspeed fault, at worst you could scatter the reciprocating assembly.

As Don says, throttle should only be applied with the engine IN gear going somewhere.

[EuropeanAM]

As Don says, throttle should only be applied with the engine IN gear going somewhere.

+1... And yes, you are now likely CAUSING faults and Guardian.

Engine needs to remain AT IDLE POSITION when you turn the key on, when you start the engine, and when in neutral. Any deviation from that can and does cause faults.

[johnmr12]

I wont ever do that again, but i'm still thinking I have an issue because from what I have read, a properly running engine will actually rev up to a point before a warning horn sounds and the engine reduces the RPM. In my case, it sputters as soon as I pass 1000 RPM and no horn sounds. I dont think it even reaches the speed required to sound the alarm. When I was dealing with my original issue it always ran best on my first run of the morning. Then as the day went by it got worse. Our high temps are close to or below freezing now. I tested it yesterday for about 10 minutes. Im a little worried about running it hard for a few hours in these temps, but if the mechanic didn't fix the problem I sure dont want to wait until April to find out.

[EuropeanAM]

If the engine accelerates properly IN GEAR, there is nothing there to fix (at least not with the engine).

You might still want to make sure your warning horn is actually sounding test-beeps at key-up.

[wmitch2]

Check your secondary fuel pump. It will cause the engine to fall on it's face when first accelerating.

[SilverFox579]

Air temperatures aren't something to worry about with your Optimax, water surface temp can be. I run my Optimax all winter long in NE WA without issue. I have, many times, run with surface temps in the upper 30s. In those conditions Smartcraft instrument/s are, IMHO, mandatory in addition to a healthy dose of operator awareness.

[johnmr12]

Mitch, is the secondary fuel pump the one on the port side next to the water separator?

[EuropeanAM]

Mitch, is the secondary fuel pump the one on the port side next to the water separator?

John... there are three (3) fuel pumps on your Optimax. The pulse (supply) pump, the low pressure pump, and the high pressure pump. Not sure what he meant by "secondary" pump... but I would recommend checking the BASICS:

-Compression Test
-Belt/Tensioner Inspection (tensioner should supply at least 70 lbs/in when checked with a torque wrench)
-Spark Test (and spark plug inspection)
-Fuel Quality, Delivery, and Air/Fuel Pressure Tests

[johnmr12]

Tensioner was good, I have spark but the plugs didn't look healthy. They were black. The fuel and air pressure at the rails is 90 and 80. My compression seemed low. I know it's more important that they stay with 15% but mine were 80, 80,80, 80, 70, 70 from 1 to 6. I was expecting over 100. I warmed the engine up but it's 35 degrees so I dont know how cool it got by the time I pulled all the plugs and tested the first 4. Maybe 5 and 6 would have been higher if I checked them first?

[johnmr12]

I followed all the instructions on here about doing a compression test except one. I forgot to open the throttle. How much of a difference will that make?

[johnmr12]

Im not the best picture taker but those are my plugs. Only 1 has a tan color to the ceramic. The rest are black.

[SilverFox579]

How old are those plugs - hours/months?

[johnmr12]

Those are probably about 2 years old. The guy who replaced the reed petals said I should change them so I bought a new set. But since the work he did didn't solve my problem I'm hesitating to install new plugs before I fix it. Is it possible that he did fix it and I just need to replace those plugs? I have seen far worse looking plugs so I'm thinking they wouldn't cause it to idle this bad. I noticed something when I was running it the other day in the driveway. When I start it up it idles smooth for about 3 or 4 seconds and then it goes south. It sputters and coughs and if I dont increase the idle speed to about 800 or 900 it stalls. It also seems worse than when I last had it on the water so does having all the cowlings removed change the flow of air through the engine making it run worse? I think today I'm going to get the parts needed to run a pressure and vacuum test on the pulse fuel pump and a pressure test on the low pressure pump. Since I have 90psi at the rails am I right in thinking the high pressure pump is good? It looks like the pulse pump diaphragm is controlled by the pressure and vacuum created by the piston movement so if that diaphragm fails might fuel be leaking into the crankcase? That would make it run rich which would result in black plugs.

[buster502]

do you have the factory oem service manual for the engine

[EuropeanAM]

Replace the plugs before going any further work. Quite possible that they are the problem.

[johnmr12]

I do have the manual. I am going to check the mechanical pump and low pressure pump since I have easy access right now.