250HP OX66 Surging at 3700rpm

[DennisG01]

I'm in PA, my brother is with the boat in ME...

He mentioned that at 3700RPM, the engine surges a little up and down. Sort of like someone was slightly advancing and lowering the throttle a little bit. If he either upped or lowered the RPM by about 100 or so RPM's, it ran rock steady. If I'm correct, the final cylinder deactivation (or activation as the case might be) happens around 2,200RPM. Any ideas?

 

[family affair]

Fuel filters or low pressure fuel pump(s).

 

[seasick]

I'm in PA, my brother is with the boat in ME...

He mentioned that at 3700RPM, the engine surges a little up and down. Sort of like someone was slightly advancing and lowering the throttle a little bit. If he either upped or lowered the RPM by about 100 or so RPM's, it ran rock steady. If I'm correct, the final cylinder deactivation (or activation as the case might be) happens around 2,200RPM. Any ideas?

If it surges when the boat pounds the waves, even a little, then most likely the VST screen is clogged. I am not sure why this is but I have seen in it multiple times.
All cylinders kick in a lot sooner than 2200 revs.

 

[The_Chain]

Yup, bet there one of these three, im thinking VST clog....then LP fuel pumps....but start with the fuel filters, cheap and easy to knock of the list first.

 

[DennisG01]

Cool, thank you guys. All of that makes sense. Other than that issue - and an occasional stall at slow, warm idle (which could be indicative of the same problem), the motor runs great. No issues at other RPM's or WOT. There's a 10 mic pre-filter, too. I'll call my brother and start with the filters. Not knowing Yamaha's too well, yet, we both thought it had something to do with the cylinder deactivation since he said it was like "clockwork" with the hesitation right at 3700 every time.

 

[DennisG01]

Just got off the phone with my brother. Got an extra pre-filter so we'll change that. No extra engine-mounted filter but he's going to give that a good lookin'-over. I asked him to pour out the pre-filter into a glass jar to look at the fuel.

He added some more info... the "surging" is not enough to change speed, he said it sounds more like the engine runs "rough" for a minute or two, then calms down again. Then maybe a minute or two later it will run a little rough again (for a minute or two). This calm/rough thing is not happening quickly - it's every couple of minutes. It is not a "hiccup" - the rough running will continue for a minute or two before going back to normal for another minute or two. It ONLY is happening at 3700rpm.

 

[bluewaterfisher273]

I have twin 225s on my 273 Chase...and this has occured a couple of times with me. I can tell you...a lot of the time it is a clogged o2 sensor. If your fix doesn't work...I would pull the O2 sensor and clean it.

 

[DennisG01]

Thanks, Blue Water. Just soak in gas for a while and wipe with a paper towel? Never cleaned one before. I've got a spare 250HP at home that I can play around with.

I texted my brother to check the plugs, too. Just to help eliminate variables, although I would imagine that the problem would be more evident if the plugs were the issue?

 

[bluewaterfisher273]

I don't see where it would be a plug...but you never know. What you have described has happened to me twice in the last three years. The first occurance was a complete clean of the VST tank as well as putting a new side mount filter on (the little red filter on side of motor) and checking the fuel pumps to eliminate any type of problems with them. I let the local marine shop here to me perform this job on both motors as well as clean both O2 sensors on the motors...and welll $562 later they purrrrrred as good as ever.

The most recent occurance of this was this past fall...which is wahoo season here for us and I was panicing to get the problem sorted. Since I knew the fuel lines on the boat had never been replaced I started at the tank and replaced all the line from the tank to the fuel/water separators and from them all the way to the engine. I put new fuel pumps on the motor that was giving an issue just so that the pumps were changed out for the annual 150hr change. The local mechanic showed me how to take the O2 sensor off and the best way to clean it. Take the sensor out and with a torch...being careful not to damage any other part of it...heat up the build up on it and clean it off. The other part you may want to be sure isn't stopped up is the draw tube portion for the O2 sensor as well.

 

[seasick]

I don't see where it would be a plug...but you never know. What you have described has happened to me twice in the last three years. The first occurance was a complete clean of the VST tank as well as putting a new side mount filter on (the little red filter on side of motor) and checking the fuel pumps to eliminate any type of problems with them. I let the local marine shop here to me perform this job on both motors as well as clean both O2 sensors on the motors...and welll $562 later they purrrrrred as good as ever.

The most recent occurance of this was this past fall...which is wahoo season here for us and I was panicing to get the problem sorted. Since I knew the fuel lines on the boat had never been replaced I started at the tank and replaced all the line from the tank to the fuel/water separators and from them all the way to the engine. I put new fuel pumps on the motor that was giving an issue just so that the pumps were changed out for the annual 150hr change. The local mechanic showed me how to take the O2 sensor off and the best way to clean it. Take the sensor out and with a torch...being careful not to damage any other part of it...heat up the build up on it and clean it off. The other part you may want to be sure isn't stopped up is the draw tube portion for the O2 sensor as well.

The O2 sensor can be placed in a jar with Ring Free. Gasoline probably wont dissolve the buildup. It is important to submerge only the tip up to the top of the holes in the solvent. Do not submerge the whole thing.
There is also a thimble in the hole that passes the combustion gasses from the cylinder to the sensor housing. That thimble or sleeve should be removed and checked to make sure the hole is not clogged.

If you use a propane torch as mentioned and I don't recommend that usually for the novice, you have to be careful not to overheat the tip. If it goes over 600 degrees F you will ruin it and that can be an expensive mistake. Note that if the O2 sensor is clogged, the motor will run rich. That usually doesn't result in surging as you describe but I am always learning new symptoms and causes

 

[bluewaterfisher273]

@"seasick"

I was just simply sharing my experience with pretty much the same motors that the OP has on his boat. I do find it funny how you claim that an O2 sensor wouldn't cause it to surge, however, that has been the culprit of the problem on my boat on two different occasions now. Anyhow, everyone has their own remedies for fixing or repairing things and different methods of how to go about it. The OP was just looking for advice and so that is what a forum is for...sharing your experience with others.

 

[seasick]

@"seasick"

I was just simply sharing my experience with pretty much the same motors that the OP has on his boat. I do find it funny how you claim that an O2 sensor wouldn't cause it to surge, however, that has been the culprit of the problem on my boat on two different occasions now. Anyhow, everyone has their own remedies for fixing or repairing things and different methods of how to go about it. The OP was just looking for advice and so that is what a forum is for...sharing your experience with others.

I am sorry if I seemed to discount your experience. I was talking about my experiences with that symptom and VST issues.
I don't know why the surging would occur at a specific rpm but to be honest, I also don't know what the logic of the ECU is doing at that speed. I would expect that if the O2 were off and was not responding correctly, performance would be affected at various revs not a specific one. Issues at specific revs are often related to issues with the TPS or the tach input signal.
I continue to learn new things about these motors and welcome any and all theories.
Thanks again for sharing your experiences.

 

[DennisG01]

My brother just texted me. The only thing he checked was the engine-mounted fuel filter and said that the ring was not floating. Said the surging has gone away. I don't believe in magic so I'll check all the things you guys have mentioned when I get up there in a few weeks. Just need to get an O2 socket - maybe I'll get lucky and be able to get one from a local auto store. I've never taken one off before, but just by looking at the one on the spare engine, it almost looks like an open wrench may work?

 

[DennisG01]

Ordered a 22mm offset O2 wrench from Amazon for $8. I'll try it out on the spare engine. But, I do want to try and salvage the spare's sensor just in case I might sometime need it. I sprayed it with PB tonight and will do so a few more times before trying to remove... Just in case.

 

[seasick]

My brother just texted me. The only thing he checked was the engine-mounted fuel filter and said that the ring was not floating. Said the surging has gone away. I don't believe in magic so I'll check all the things you guys have mentioned when I get up there in a few weeks. Just need to get an O2 socket - maybe I'll get lucky and be able to get one from a local auto store. I've never taken one off before, but just by looking at the one on the spare engine, it almost looks like an open wrench may work?

Interesting. I had a motor that surged and it turned out that the engine mounted fuel filter housing was not seated correctly and the motor was sucking air. If the bowl is full of gas, the bowl is most likely leaking since the normal situation is a half to 3/4 full of fuel.
With the engine off, pumping the primer hard will usually result in fuel leaking from the bowl. With the motor running the leak stops but the motor starts to suck air.

 

[DennisG01]

Interesting thought. I'll check that, too. Thank you.

 

[DennisG01]

The O2 socket was a little too thick - wouldn't slip past the wall of the "block" that the sensor is screwed into.

I'll try this one: http://www.amazon.com/CTA-2064-Oxygen-S ... sor+socket

Unless anyone has a better suggestion?

 

[lime4x4]

Yeah your probably gone need a thin wall designed o2 sensor socket. The only problem with the thin wall sockets is the have a habit of slipping off if the sensor is really tight. How did the hatch recore go? Haven't worked on my offshore for 2 weeks. We took the searay to Indian river marina for a week just in time for Arthur lol

 

[DennisG01]

Good timing with that trip! :wink: We're you able to get any boating in?

Yeah, I'm worried about the slipping thing, too. I've never had an O2 sensor out before - car or boat. Is it safe to assume that an air gun is not a good idea? In lieu of that, maybe I can put a hose clamp around the socket to help keep it from spreading... just long enough to get the sensor cracked free?

The hatch came out great. But that was the easy part. I ended up doing the entire floor along with a major bulkhead. Came out great, though. Rock solid. Even built a new, matching hatch for where the sterndrive used to be and also built rain gutters into the hatches so no water gets into the bilge. I've got the hatches on hinges so I can't silicone them.

 

[family affair]

Definetly DO NOT use any air tool!

We ground the circumference of a socket down until it fit. Ne problems removing the sensor then.