Thread: Yamaha VMAX OX66 fuel injection 225

I have been a certified outboard tech for almost 23 years and I have seen very few electrical problems with Yamaha and almost no bad coils. I'm not saying they don't happen but they are very rare. What are the symptoms with the motor? The first thing to do is check the compression. If that is good then the problem is usually in the fuel system.

Originally Posted by Bullet101

I have been a certified outboard tech for almost 23 years and I have seen very few electrical problems with Yamaha and almost no bad coils. I'm not saying they don't happen but they are very rare. What are the symptoms with the motor? The first thing to do is check the compression. If that is good then the problem is usually in the fuel system.

Thanks for that information, it just start this , will start with no problem and may do good a dozen times, then just turn over and not fire at all , it set a hour or so and started right up. One time won’t start got it back on the trailer took it to the shop and it started every time for them. They say they couldn’t check anything until it did it for them. Put it on a computer or anything til it won’t start for them?


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I had a problem identical to this with an Evinrude once. It turned out to be a bad power pack. I could put the boat in the water and it would start up every time. But if I shut it off and then tried to restart after a short time it would not fire. Let it sit for a while and it would start right up. What was happening after running a while the power pack would heat up. Then shutting it off the heat would cause component(s) or connection(s) in the power pack to swell and not work. After it cooled off the "swelling" would go down and it would start working again. This can be a very hard problem to trouble shoot. Back in my TV repair days we carried a can of freeze with us to spray a suspect component with. A can of it might be worth the investment. Amazon.com: MAX Professional 7777 Blow Off Freeze Spray Electronic Component Cooler, FR-777-777 (10 oz): Office Products

Don't know if a Yamaha is built the same but, my neighbor has a 40 mercury and it would start right off and until it got hot. It would spin and spin and not crank. There is a small tank on the side that has a pump in it and it would be hot to the touch. You could splash water on it for a minute and it would fire right up until it got hat again. We replaced the pump in the tank and it cleared right up and has not given anymore trouble.

If a single coil went out, the motor would still start. In fact, it would still start on 3 cylinders. I would rule out trouble with the high pressure fuel pump and/or the fuel pressure regulator. If the ignition system is the culprit, I would suspect the problem is with the kill switch circuit and not the ignition system itself.

Most of the older OX66 motors didn't have a diagnostic port for the computer anyway. They used a noid light that would flash a certain amount of times then you would look up the code. The ECU had no memory. I would check for bad connections, especially grounds, on all the ignition components. Things like the stator, trigger and CDI unit
(Merc/switch box: OMC/powerpack) failures are very uncommon. Either way, the compression should be checked first then verify the fuel pressure is up to 36-40 psi. I would have you bring it to my shop, if you were closer.

Thanks for the input, Bullet 101 the boat is in Heartland,FL little town of Frostproof FLORIDA or you close ?


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No. I am just outside Knoxville, Tn.