Optimax engine losing power?

[Cobra427cable]

Ok...I know there is plenty of experience out there and while I am knowledgeable about car and motorcycle engines, boat motors seem to be a different breed so I am seeking help! I have a 135 HP Mercury Optimax engine that seems to be losing WOT performance. I bought the boat last year and it was a dealer demo boat so the actual hours on the engine im not sure but it's a 2008 model. Last year and so far this year up until this weekend, it has been a very good engine. This weekend we took some friends out for a ride and I noticed it didn't seem to have much power at full throttle and would barely get up on plane like it was loaded down. I have had more weight on the boat in the past and not had this problem. Later, I took it out for a spin just by myself and it was much better but still just not quite itself. The RPM's would only get to about 4000 when there was a few people on board and much worse when we tried to pull a tube or wake board. I thought maybe one of the tubes could be taking on water so I pulled all the plugs when I got home and all were dry and had some pressure in them. I pulled the plugs while at the lake and several were a little black but I've seen worse on other engines and they still ran good. I cleaned them up with some sandpaper and reinstalled but it did not seem to help. Actually, I started to notice the engine miss a bit at idle after I did that. Any ideas?? I have not done anything to this engine since I got it so maybe it's due for a few tune up items? Also, kinda off the subject but I was curious...when you put the tranny into neutral and rev up the engine a little, it will only go to about 2000 RPM's and a buzzer will sound and it seems to limit the RPM's to around 2000 RPM's?? What's up with that? I would think it should rev on up to at least 5500 RPM's before it acted like I was over reving?? Thanks for any help in this matter.

[crspang]

Sounds like a fuel delivery problem. Check the fittings in the fuel line also check the vent for for your fuel tank. Could also be a bad fuel pump. Is the primer bulb staying firm at WOT?

[lakerunner]

Bet you have a stuck check valve in your gas tank fitting the line clamps to. I had the same problem and took forever to find it. The fitting has a little check valve and mine would stick and nor let me hold prime

[KV41]

Have you checked your oil tank? If oil is low you will get a buzzer.

[Cobra427cable]

Well, I'll check the bulb and the check valve but I do remember when I primed it this weekend it felt like the bulb was pretty firm in my hand after a few pumps. The oil tank was full when I started this weekend, and it appeared to use the same amount it usually does. The alarm under the dash when I rev up in neutral I don't think is related to my problem. It's just something I've always wondered about and noticed ever since I got the boat. I'll check the tank vent as well.

[lakerunner]

Mine would pump firm also but would loose prime after a while. One thing I did before I found the problem was install a primer bulb at the tank. That way if it lost prime I could raise tanning pad and pump bulb. Look and see if you have a Moller(think that's the spelling) tank

[LTB Racing]

Your alarm is normal...its a neutral overspeed alarm.. as its never a good idea to rev your motor high in neutral ...
It could be any number of things causing your problem however without the right tools and computer it could be tough for you to find the prob at home....you can ck the basics as mentioned above...fuel sample(run it on a different fuel tank if available), ck for a restriction in the fuel system, ck compression, and spark. Also u ck for loose battery connections. Good Luck.

[ORAA1997]

I have 115hp Optimax that has driven me crazy since I bought the boat used last October. After three visits to the dealer for the same problem, they found that I needed a new thermostat. This combined with changing the water pump has worked wonders for mine.

Got a warning this past weekend, but I noticed it was the oil level. Put some oil in it, and it runs great!!!

Hope this helps

[Cobra427cable]

So the engine was running hot and you were lacking in power too? I would have thought the temp alarm would have been going off??

[ORAA1997]

YES, there was no power at all, and I had buzzers going off all the time. Even with 4 light adults on board it would overheat and the RPMs would not go past 3000.

Its at least worth a shot to check out the thermostat. Good luck!!

BTW, do you have a radio splash cover on your boat? Mine is regency as well, and I have to replace the stereo becuase it got soaked. Tried the Sony marine radio cover, but did not work. Too small.

Thanks,

[bruuuuce]

So the engine was running hot and you were lacking in power too? I would have thought the temp alarm would have been going off??

I have the almost exact same issues as you. 3500 is my max RPM if I trim and run long enough I can get it up to 4000 but that is it. I put new plugs and fuel supply line and blub on no luck.

I failed to winterize the fuel system last year, I sprayed the cylinders with fogging oil but didn't drain the fuel system like I did the year before and I suspect that my injectors are dirty.

I ran a tank of fuel/sea foam threw and didn't get any better, my idle is rough and dies also.

Mine is at the boat dealers now getting fixed, I hope to have it back by Friday but not sure he is on board with that plan

[Cobra427cable]

Funny you should ask about the radio. I had another post on here about that. Mine did not come with a splash cover as well and I'm on my second Sony radio and it is all screwed up now as well. There are aftermarket covers that I will look into when Im ready to replace my radio again. As far as the thermostat problem, it sounds a little different than my problem since I have no alarms going off and it doesn't run all that bad. It has a small miss every once in a while at idle and when I open it up, it just lacks the power it used to have. I feel like I am running on 5 cylinders but I can't confirm this. I plan on pulling all the plugs today and ground each one and check for a good hot spark to see if maybe I have a bad coil or a plug that won't fire off well. I ordered some new spark plugs and should have those in by Thursday and I'm going to change my fuel filter as well. Hopefully something will work. Thanks everyone, for all the ideas.

[BobL]

What RPM's are considered "limp" mode on your engine? You think by chance it is going into "limp" mode and the alarms are intermittent? I doubt that is the problem but wanted to throw that out as an idea. I have hit limp mode a couple of times because my intake was clogged and was not getting good water pressure for engine cooling BUT when it went into limp mode, it was obvious because the throttle would not respond other than backing down to neutral.

[slingshot]

I'd do all those things LBT said but first I'd do a full tune up on the OB first. It's hard to troubleshoot a motor otherwise. Remember, the vast majority of poor running engine problems stem from poor fuel delivery or poor spark deliver so figure out which it is using a process of elimination (you eliminate many possible causes with a thorough tune up). Your OB has an onboard diagnostic system but unfortunately the hardware and software for it is proprietary by Mercury who only sells to its dealerships. You might be able to buy it but it's very cost prohibitive (thousands of $$$). If you still can't figure out the problem once you change all the filters, plugs and such you may want to have a dealer at least run a diagnostic on it. Good luck.

[Cobra427cable]

Well, I spent last night doing a little diagnostics on the engine. I removed all six plugs and grounded all of them to the block. I had my wife crank over the engine while I observed the sparks and there was one that had no fire. I then swapped out plugs and still no fire. I then swapped out plug wires and still no fire. The last thing I tried was swapping out coils to make sure it wasn't a bad coonection to that coil or something and once again no spark to that coil. I'm now convinced it's a bad coil but we have a big weekend planned for the 4th and I'm hoping I can find a coil (used or new) before then. I've called the dealership I bought the boat at and of course they are booked up and can't help me right now. They have to be the ones to service the engine or it won't be covered under warranty. Heard these coils are about 160-200 bucks so if I can find someone who stocks them, I guess I'll just have to fork over some cash. I am still going to take it in to be serviced and I will reinstall my old coil and this way I'll have a spare if I ever have another one go out. Anyone had this problem with their Optimax engine? A liitle research on Google and it seems to be fairly common...should be a recall item.