# 2008 Mercury Optimax 90 - loss of power



## ohiojmj

My 2008 Mercury Optimax 90 won't go above 3000 rpms and stalls occasionally at idle. Any idea what's wrong? Here's some details below. 

After running the Merc for a few miles yesterday on Lake Erie (perch limits!)without any problem at full throttle, I anchored to perch fish for 4 or hours. I started the motor up again and could not get it above 3000 rpm's and it vibrated a little like it was struggling. Returning to the launch slowly and unable to go above 3000, it stalled several times at idle in the no wake zone.

I checked the prop and it spins freely. I've had no prior problems with the motor. I plan to check the plugs and pull the engine fuel filter to see if there is any debris in the gas. I've been to Canada twice this year and filled up at remote places. I keep the gas treated with Stabil at all times plus the recommended treatment for Optimax (quick clean or something like that). I'm suspecting bad gas (water) or something depleting the gas supply.

How can you check if there is water in the gas? I'd like to rule out fuel problem; otherwise it's warranty work.


----------



## ohiojmj

Talked to Tom at Vic's Sports Center and it sounds like a coil. I hear they go bad, but no recalls. I'll let the experts fix me up.


----------



## ohiojmj

My hats off to the guys at Vic's. I dropped the boat off saturday and they had my optimax fixed by tuesday. Nice people to work with! 

It turned out to be one bad coil/switch combo Apparently, Mercury was supplied with lots of bad coils in the last few years. The good news is that there is one coil and switch for each cylinder, so if one goes bad, you can at least run back to the launch. Older Merc's have only one, so you would SOL, so I'm told.


----------



## ohiojmj

Well, it's now 2015 and I have the same problem and likely another bad coil on my 90hp Optimax. I'm posting this so others know what to expect from their Opti if it one day it just runs a little rough, has little power and won't go over 3000 rpm in the safe mode. Wonder if I should pack a spare coil.


----------



## ohiojmj

OK, I checked my spark plugs (new in April) and 2 were dry and one was wet. The wires all looked good and were snapped into place correctly. I'm replacing one of my two remaining original coils and will report my results after installation and test run on a small lake.


----------



## Meerkat

Not to question your bad coil issue for a minute but I had similar symptoms on my Mercury outboard last fall.

In my case it turned out to be a loose spark plug lead which would give the same result as a bad coil. Lead looked fine but it was not pushed in all the way. Only thing I can figure is I must have knocked it loose when taking the cover off at some point.


----------



## c. j. stone

Maybe totally unrelated to your problem but I had an early 2000's Optimax that did the exact same thing. Apparently when there is actual(or even potential of)"overheating", the engine's computer will limit rpm's to keep from burning itself up-and yet get you back in. This happened to me, some water pump repairs and a computer reboot fixed that particular problem.(There were many others!) Happiest 2 days of my life were when I got that engine on my new boat, AND when I saw it leaving my driveway Behind Someone Else's vehicle!!!


----------



## ohiojmj

I'll double check wires, thanks.


----------



## c. j. stone

I also had a bad fuel injector. That significantly impacted my available rpm's and my bank account!(LESS than one month out of warranty-Mercury told me essentially "Tough Beans" when I asked for "some consideration" regarding the $800 bill from the shop!) Hell, I'll just come out and say it--"The Optimax I had just might be the biggest piece of crap Mercury Marine ever put on the market"! JMHO!


----------



## ohiojmj

OK, installed new coil and it runs better in driveway so will test in small lake before erie.


----------



## bountyhunter

I have a 2005 115hp opti ,never had a problem. only time its been in the shop was a water pump tuneup. guess you got a lemmon .


----------



## ohiojmj

Final answer: bad coil! Ran like new on the water this evening. I'm ordering another new coil to replace the remaining original that hasn't crapped out. Only had two problems in 7+ seasons, both coils that Merc knows very well. I'm just happy to have my boat running again.


----------



## billy4prez

Yup, my 2007 115 chewed up 3 of them so far! I am doing my trolling with a kicker now, hope the coils last longer now!


----------



## c. j. stone

bountyhunter said:


> I have a 2005 115hp opti ,never had a problem. only time its been in the shop was a water pump tuneup. guess you got a lemmon .


I guess you're right, although I researched the earlier Opti problems on the net and I surely wasn't the only one!(80% of the probs were injectors). Mercury knew it and kept selling them w/o fixing them! Problem usually happened close to the end(or near!) warranty period expiration dates. There was a "class action" lawsuit over it (which Mercury lost!)


----------



## thebige22

Just experienced a similar problem with my 2007 225 Optimax this weekend. In forward my max RPM was about 2800 and ran a little rough; however in reverse I can get up over 4500 rpm. Did you ever try reverse when you had this problem? I'm trying to diagnose the problem. Thanks.


----------



## ohiojmj

No didn't try reverse. Easily diagnosed my problem, another bad coil, a popular reliability issue with Merc Optimax's over a range of years when they had a bad batch and didn't recall them all and offer to replace unless they went bad.


----------

