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Engine Sputtering...still

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So my 2010 Mercury Optimax 90 is still giving me fits. I have had the injectors cleaned and flow tested, fuel rail is cleaned as well. VST is flowing good and no water in the fuel anywhere. Fuel & air pressure is good and cylinders have great compression. So the issue of fuel delivery is now officially over. I took it to a mechanic who verified everything above and his assessment is that it's an electrical issue although exactly where is the real question. I changed the plugs and ensured all boots were on securely and I checked the fuses (that I could easily) and no issues there. Now my question to the brain trust is, where else should I be looking? Mechanic mentioned check the ignition and the basics (grounds and the like) and I'm going to do that when I get a chance after the weather is a little more favorable (cold & wet today). Thank you in advance for any suggestions you may have or provide. Although the good news is that the motor itself is in great shape for an almost 10 year old 2 stroke.
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Optimax may be over my head as I typically work on carbed engines.

Some easy things to try:
Find a dark area or night and run it, look for any electrical arcing.
Make sure all your fuel lines, filters, plugs are tightly fitted as it could be an air leak, can shoot carb cleaner around any gaskets as well to see if the sputter goes away too.
 

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Discussion Starter · #4 ·
Still paying for this one or else I'd have already swapped. Bad thing is there is only one "certified" Yamaha shop in the Austin area and there is no way in HELL I'll buy from them...again. I'm not sure they truly performed all of the "checks" they say they do on this boat as that is where I purchased it. Oh, and the "warranty" I purchased through them was a waste of money too, every time I took it over there for what should've been a warranty issue I was told it wasn't.
 

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Question on that, if that was an issue would my electronics have issues as well?
No. Those engines need a battery with 1000 MCA capacity. Once it starts to drop too low, the engine will begin to exhibit issues, though usually a voltage alarm will sound. Battery cables are an extremely common culprit.

Did you ever hook this up to an external tank and see if the problem replicates? The check valve on the tank could be an issue. Also, has the mechanical fuel pump been replaced?
 

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Discussion Starter · #8 ·
The tank has been ruled out as the culprit as the issue remained on the portable tank. They have not been replaced since I have owned the boat but again my mechanic check everything fuel delivery and we're good on that end. He mentioned he spoke to another fellow mechanic and they have seen similar issues and they've all been electrical. The finding where is the problem we're now facing.
 

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The only way you can be certain your existing tank isn’t still a problem is to hook up a known good tank with good fuel line and fuel and run it.. If your trouble is still fuel that second tank will be a sudden magic cure. If the problems still occur then you can at least be sure it’s not fuel related.

At that point you really need a master tech since there’s quite things that might be causing electrical trouble - from your wiring harness all the way to your battery...
 

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Discussion Starter · #10 ·
The only way you can be certain your existing tank isn’t still a problem is to hook up a known good tank with good fuel line and fuel and run it.. If your trouble is still fuel that second tank will be a sudden magic cure. If the problems still occur then you can at least be sure it’s not fuel related.
Issue still existed with portable tank and E free fuel.

At that point you really need a master tech since there’s quite things that might be causing electrical trouble - from your wiring harness all the way to your battery...
The tech that I had it at last is a master tech with over 30 yrs experience. He did tell me that to diagnose the electrical it would take time. He is still researching on his end and that is where we are.
 

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Discussion Starter · #12 ·
If I back off it runs fine. It seems that once I go over 3000 rpm it starts.
 

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Definitely check the battery switch and cables. I had a similar problem on my offshore boat and it ended up being the battery switch. There were no visible signs of damage to the switch but once I replaced it, never had the problem again. Even if that’s not the problem it’s a cheap and easy part to swap out yourself.
 

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Discussion Starter · #15 ·
So the switch appears to be good, alternator connections are good but I cleaned them anyways. Battery terminals are clean. I looked at every fuse block I could find (on the motor) and no fuses are blown. I'm still working through the connections in the console. FTR, Mako wiring is the absolute shittiest I have seen. I think rats would run from the nest that it is, so I'm trying to clean it up while I'm at it. I'm going to replace the filler hose and vent hoses tomorrow assuming I don't run out of daylight again. So far all connections I have looked at appear to be in working order and dry. Going to look at the sending unit as well and ensure everything is tight and clean. Batteries are out and I'm going to charge them individually and check the voltage on them too. I'm considering replacing the battery switch but haven't decided yet because I don't necessarily want to swap out good parts...yet. I plan on completely dismantling the boat in late Jan or Feb because there are some other issues I want to address as well so if I can get it working for the time being I'll be happy.
 

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Going back through your post history, your troubles seem to have started when you changed the separator. What material is the separator housing? Is it black painted aluminum? Is the coating flaking off? If it is, I can almost guarantee that you are sucking air at the housing/filter interface. Opti electrical issues will rear their head over a wide range of operating conditions and will usually give a voltage alarm. Since you stated the problem only occurs over 3000 rpm, I'm still thinking this is fuel related. Also, you mentioned the VST pumps fine. Does it keep pressure at speed? That's a dynamic test that must be performed with the engine running UNDER LOAD, not just at 3000 rpm. A slight drop (and even a fluctuation) will indicate the need for high pressure pump replacement.

In any case, pictures please. Lots of them. Electrical, fuel system, everything.
 

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Discussion Starter · #17 ·
The mechanic ran it on the dyno and had gauges on the fuel & air, which were good. Within 10 psi of each other which is what Mercury states it needs to be (90 fuel, 80 air) He was able to replicate the issue but again no drop in psi. Thus his thinking of an electrical issue. Filter housing is not painted where the filter is and I use a dab of 2 stroke oil on the gasket when putting the filter on. I have actually ran with a filter bypass and still received the same result. I'm still working through all of the electrical and hope I can find it's something simple or just a ground that is loose. One time at BPS they did something with the sender (can't remember exactly) and my hope is that maybe they didn't tighten something all the way but again that is just a hope.
 

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The mechanic ran it on the dyno and had gauges on the fuel & air, which were good. Within 10 psi of each other which is what Mercury states it needs to be (90 fuel, 80 air) He was able to replicate the issue but again no drop in psi. Thus his thinking of an electrical issue. Filter housing is not painted where the filter is and I use a dab of 2 stroke oil on the gasket when putting the filter on. I have actually ran with a filter bypass and still received the same result. I'm still working through all of the electrical and hope I can find it's something simple or just a ground that is loose. One time at BPS they did something with the sender (can't remember exactly) and my hope is that maybe they didn't tighten something all the way but again that is just a hope.

Fuel sender or fuel pickup? Did you add the water separator or change it? Which came first the problem or the filter change?
 
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