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Author Topic:   1999 Mercury OptiMax Sputters at Full Throttle
ukuslayer posted 05-27-2011 10:18 PM ET (US)   Profile for ukuslayer   Send Email to ukuslayer  
Hi Guys. I am having a problem with my 1999 Mercury Optimax 225. When I hit full throttle the engine sputters and drops in RPM.

The problem seems like an electrical problem as it only happens at full throttle. I can cruise at 3,500-RPM for twenty minutes with no problem at all, and the engine purrs very nicely, so I don't think it is a fuel delivery problem. So far I have checked all the plugs, and they look good. I checked all the ignition coils with a multimeter, and they all check out OK per my shop manual. Found two spark plug wire boots with slight tears in them and replaced them with new wire sets. Found two boots on the spark plug wires that connect to the coil were loose ,so I re-glued them onto the coil with Loctite 454 per my shop manual. No alarms at all on my four way panel gauge.

I found a wire to my #3 fuel injector that the insulation was chaffed through to the bare wire, and the wire was black. I cleaned that up as best as I could and wrapped with electrical tape for now. I have the new AMP connector on order and will replace it as soon as I get it. I have to replace the whole connector because the chaffed part of the wire is right up against the connector and can not be re-spliced.

I think what is happening is that as I get to the higher range of RPM that wire to the #3 injector can not handle the electrical load and the injector is malfunctioning. As I said at lower RPM there is no problem. I have gone through all electrical connections and this is the only problem that I found. Other than this problem the engine runs great and very smooth.

Any thoughts or recommendations would be great.



jimh posted 05-28-2011 09:04 AM ET (US)     Profile for jimh  Send Email to jimh     
If you suspect that cylinder #3 is not getting proper fuel, be cautious about running the engine. If #3 is running lean it will have high cylinder temperature that could lead to problems.
ukuslayer posted 05-28-2011 01:33 PM ET (US)     Profile for ukuslayer  Send Email to ukuslayer     
Thanks Jimh,

Yeah I am waiting on the part to repair that before I take the boat out again. Hopefully that is the problem. If not it will be back to trouble shooting with my manual. I ohm tested all my fuel and air injectors on the engine yesterday and they all check out OK.

ukuslayer posted 06-01-2011 11:30 PM ET (US)     Profile for ukuslayer  Send Email to ukuslayer     
Well I replaced the connectors and the plug for the #3 injector on the starboard fuel rail. The engine had a definite change in the way it sounds. I never really noticed the change in sound when the problem started. I hope this takes care of the problem. I hope to get the boat in the water either tomorrow or Friday for a test run.

The problem has been frustrating but I have also learned a lot by going through my service manual and really going over every connection and tracing out the wiring harness and all its components. For anyone out there with out a Service manual I highly suggest getting one. Will re post on my test run later.



leadsled posted 06-02-2011 08:15 AM ET (US)     Profile for leadsled  Send Email to leadsled     
It's possible the inner liner of your fuel line is collapsing at high speed from the suction. The ethanol fuel can cause the inner and outer fuel lines to separate and the inner liner will collapse at a certain throttle speed. It happened to mine and I replaced a lot of stuff first. The fuel line was less than two years old so I was sure it was not the problem. If you rule out your injector rig another portable tank and hose to see if it the problem goes away. Good luck.
ukuslayer posted 06-02-2011 11:29 PM ET (US)     Profile for ukuslayer  Send Email to ukuslayer     

Thanks for that info. I will definitely check that if the problem persists after I take it for a test run. Even if what I did takes care of the problem I like getting feedback from others on problems they have had and how they were resolved.

How was your engine acting when the fuel line was collapsing? Was it slowly losing Power or was it a quick and very noticeable drop in RPM's as throttled up? Again thanks for the response.


ukuslayer posted 06-02-2011 11:33 PM ET (US)     Profile for ukuslayer  Send Email to ukuslayer     
As you throttled up. I what I meant.
ukuslayer posted 06-02-2011 11:34 PM ET (US)     Profile for ukuslayer  Send Email to ukuslayer     
Is what I meant. My fingers are not working tonight.
leadsled posted 06-03-2011 06:30 AM ET (US)     Profile for leadsled  Send Email to leadsled     
It would be fine one day, then the next day at just above planing speed it would miss and buck if I tried to go faster. If I backed off it would run fine. I have a kicker motor so I would continue to pull my lobster traps at a slow speed and it would run fine until I got above a certain speed. The next day it would be fine. Two days later the same thing would happen. The next day it would be fine.Over time I went and changed plugs,filters, fuel pump.Because I paid 3 bucks a foot for the fuel line less than two years ago I thought it couldn't be the fuel line. Finally I changed the fuel line and it's be fine for two years now. I guess the inner liner would partialy collapse esspescially when the line was warm and plyable.
ukuslayer posted 06-04-2011 02:41 AM ET (US)     Profile for ukuslayer  Send Email to ukuslayer     
Well I took it out for a test run today and the problem is still there. I got to about 4500 RPM's and it started bogging down.

Leadsled I heard from another member here by PM and he was saying exactly what you are. I think that is my next direction I will be following. If anyone else is following this thread and has some suggestions as to what I should check I will sure appreciate the feedback.

Right now I'm thinking either the fuel line somewhere or one of the diaphragm valves on the fuel rails. There are three,
one is called a tracker valve one is a fuel pressure regulator and one is air pressure regulator. Very frustrating as many problems can have similar symptoms.



HawaiianWhaler posted 06-04-2011 05:44 AM ET (US)     Profile for HawaiianWhaler  Send Email to HawaiianWhaler     
ukuslayer - Suggest you rule out the obvious/easy possible causes before getting into the less likely/harder to determine possible ones.

It's easy to check out fuel restriction as a possible cause, so do that first. As already suggested, you can try a portable tank with a separate fuel line to determine if fuel starvation at full throttle is the problem. If that results in good high speed operation, there's one more step to try before concluding that the inner lining of your original fuel line is collapsing, and that is to determine if the restriction is part of your original fuel tank installation.

That's easy too. Just use the separate fuel from the portable tank in place of the installed fuel line. If the high speed stalling still occurs, then you likely have a fuel flow restriction on the tank side of the fuel line. Take a good look at the check valve in the tank's outlet fitting. That's my bet as a likely cause.

After that, you can get into the fuel pump providing insufficient pressure at high speed and the even less likely electrical/ignition/computer engine management issues.

Good luck.

ukuslayer posted 06-05-2011 05:34 PM ET (US)     Profile for ukuslayer  Send Email to ukuslayer     

That is what I'm going to do next. I have a friend with an empty tank and am going to borrow it and hopefully get the boat out on Monday or Tuesday.

Another question for the Mercury crew out there. If I am not getting any alarms and I have verified that the alarm system is working would it still be useful to have it hooked up to a Diagnostic terminal? Appreciate all the responses so far.



martyn1075 posted 06-06-2011 05:42 PM ET (US)     Profile for martyn1075  Send Email to martyn1075     
I had the same problem with the same engine. It turned out to be a few bad connections that were lose and it was causing a problem. Hopefully not the problem but the fuel injectors have had issues for that age model. While owning the same model you had I replaced two faulty injectors before I sold the boat with engine. If its the connector then that would be a reasonable fix but the injectors are a bit costly. Mercury offers a new fuel injector to replace the older style ones. They do the exact same thing but it was one the bugs Mercury worked out over the years for the Optimax line.
ukuslayer posted 06-09-2011 01:16 AM ET (US)     Profile for ukuslayer  Send Email to ukuslayer     
Update, Thanks Leadsled you definitely sent me in the right direction.

I was in the process of hooking up the remote tank when I pulled the fuel line off the engine. On my engine, the fuel line hooks up under the cowling directly to a 5/16-inch barb plugged-in to the fuel inlet for my first fuel pump. When I pulled off the fuel line and looked inside I could see that the inner lining was completely deteriorated. I pumped the primer bulb while holding the end in a container and about a two-inch piece of the inner liner came out with a lot of other very small pieces. I then removed the internal spin on filter and poured that in to a paper towel and got about a one-inch ball of the inner liner in tiny little slivers. I have not had the boat out yet, but I am thinking this was my problem. I am going to cut that line open as I am curious to see what the middle sections and the primer bulb look like inside.

That fuel hose was a Mercury fuel hose and primer bulb assembly that I bought only about two years ago. Next I am going to pull the hoses off my RACOR to check them. When I changed the RACOR element there was no debris in the bottom of the bowl which is why I think the problem was after the RACOR and before the engine in the Mercury hose assembly. I hope to get the boat in the water tomorrow for a test run and will post results when I do.



ukuslayer posted 06-09-2011 01:24 AM ET (US)     Profile for ukuslayer  Send Email to ukuslayer     
Martyn1075--Yes, I know about the injectors. I actually replaced all the old air injectors with the new blue model ones. From what a mechanic told me the little tips on the black ones could fall off into the cylinder while underway, and the result was catastrophic engine failure. Rather than take that chance, I searched e-bay and replaced all six, as I found good deals on them. Way too expensive to buy them brand new. Thanks for the input, though. I have also gone through about every electrical connection on the engine over the last month or so.



ukuslayer posted 06-09-2011 10:07 PM ET (US)     Profile for ukuslayer  Send Email to ukuslayer     
Problem Solved. After replacing the fuel line and primer bulb assembly from the racor to the engine it fired right up and hit 5300RPM's with no problem all the way across Kaneohe Bay. Cruised around for about an hour at 4000RPM's with no problem at all. Very happy to have the engine running properly again.

Just to be sure I replaced the fuel line all the way to the crank case mounted fuel pump. I figure after that pump the fuel system is pressurized and the fuel lines should not be collapsing on them selves. I plan to replace all the fuel lines on the engine in the near future but for now it sure is nice to be able to get her up to speed!!!


martyn1075 posted 06-09-2011 10:35 PM ET (US)     Profile for martyn1075  Send Email to martyn1075     
Thats great to hear. Sensitive machines aren't they. One part that is on its way out and it flat out speaks back at you.

John McBride posted 06-09-2011 10:58 PM ET (US)     Profile for John McBride  Send Email to John McBride     
I just rebuilt my Mercury 5 HP kicker on my sailboat and it would stay running only if I pumped the bulb every 45 seconds or so. The fuel line was doing the very same thing so I replaced all of it. She runs like a top now.

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