250hp Ox66 Engine Issue

[JohnnyMadisonCT]

The engine is a '98 Yamaha 250hp Ox66 with ~600hours.<br /><br />For the past 400 hours, or since my ownership of it, she has performed flawlessly. Maybe, to my fault, all I've done in the past 3 seasons is change the water pump, Racor Filter (in the boat) and the spark plugs. I have decarbonized her via the "can" method 3 times, but other than that, I've done nothing.<br /><br />The last time out, to my surprise, after hitting an average boat wake, the engine, for just a split second, almost cut out, or lost a few hundred RPM's. They came back within a small fraction of a second, but when you know your motor, you know when something ain't quite righ.<br /><br />This happened on two occasions this past trip.<br /><br /><br />I've done an extensive Internet search, and some feel it could be the VST (Vapor Seperator or High Pressure pump screen...problem). <br /><br />It was so momentary in duration, I doubt it's fuel related as in fuel quality. I would suspect it's either electrical, or VST related.<br /><br />Rodbolt and anyone with advice, I would really like to hear it.<br /><br />Thanks Guys !!<br /><br /><br />JohnnyMadisonCT

 

[rodbolt]

Re: 250hp Ox66 Engine Issue

dude<br /> your killing your motor.<br /> the O2 sensor is WAY overdue for a cleaning and the vapor seperator filter is way past due as well. the hitting a wake thing, if it was something electrical, would be a one shot only deal. the motor would run normally afterwards. you say it is not right. give the symptoms of why it isnt right.<br /> good luck and keep posting. PS you need to do the t-stats and pressure valve as well.

 

[JohnnyMadisonCT]

Re: 250hp Ox66 Engine Issue

Rodbolt: Thanks, please let me clarify.<br /><br />I also did the Thermostats and cleaned/replaced the Poppit Valve last fall, especially after I had a low speed overheat situation.. Both are new this season. I became an expert on that poppit valve and the proper cleaning of the area under the grommit.<br /><br />As for the O2 sensor, wouldn't it show symptoms first before cleaning was necessary? There is no RPM surge, loss in WOT RPM's or anything. Should it still be cleaned?<br /><br />No work's ever been done to the VST tank though. How often and what should be done to this. I would probably leave it up to an authorized Yammie dealer to do it. But please advise as to what should be done so the dealer doesn't ask me... "what do you want us to do?" I trust the Yamaha dealer our way, but expect this type of question.<br /><br /><br />As for my incident, on two occasions, after hitting a boat's wake, the engine just "skipped" in RPM's. No other symptoms were evident. It was like the engine cut out for 1/10th of a second. Otherwise, the engine runs perfectly. No worse for the wear.<br /><br />Could that be a VST issue, especially since it was never serviced in several years now?<br /><br />John

 

[JohnnyMadisonCT]

Re: 250hp Ox66 Engine Issue

Perhaps Ray Neudecker has a comment?

 

[Ray Neudecker]

Re: 250hp Ox66 Engine Issue

Problems which are that intermittent are very hard to find. Rodbolt has him on the right path of checking the things which have not been routinely serviced. A loose connection on the electrical side could produce these symptoms. That problem would normally tend to get worse and less intermittent with time. Most techs find the problems through a careful visual exam of the motor, listening to it and the info provided by the operator. Most of this is not possible over the internet. Here you can only offer possible solutions based on experience with similar problems. Many times all you can do is advise to check the basics such as compression,fire, connections, and non routinely serviced items such as above. I have seen battery connections cause this type of problem and would want to check them, but Rodbolt is right on with his suggestions also.

 

[JohnnyMadisonCT]

Re: 250hp Ox66 Engine Issue

Ray: Thank you. It happened again today, twice. It seems when I come "down" a boat wake, like when the boat surfs a little, it happens, a very shot loss of RPM's, probably 1/3 of a second.<br /><br /> I've personally not had time to look at things yet myself. Gonna look for the obvious batteries, grounds on the engine, temp sendor (as maybe it would cause the engine to go into Slow mode for a split second, etc etc)<br /><br /> I hate these types of problems. I almost wish it would die completely, so then the Yamaha guys could find the problem.<br /><br />John

 

[bernieb]

Re: 250hp Ox66 Engine Issue

Im sure you have already considered ,but "quoting" from clymers yamaha manual it says...on occasion,the engine will experience a misfire only at higher engine speeds and when all ignition components test correctly.Many times the overspeed prevention circuits in the cdi unit or engine control unit causes the misfire. I have a problem with my 250 yamma but I have to wait till october then I'll seek the advice of the pros on this board.How about switching to a different prop(higher pitch)

 

[JohnnyMadisonCT]

Re: 250hp Ox66 Engine Issue

Bernie: My boat never hits the rev limiter. This is happening at 4000RPM's.<br /><br /> Thanks anyway. Anyone else got any ideas?<br /><br />John