OX66 Turning off at high RPMS

[OverTimeAgain]

I've seen very little information on this online in regards to this motor.. So I figured I would make my own thread and put my findings. Maybe help someone else down the road.


Please give any input if you have dealt with this!


I've got a 2000 225 ox66. A year ago when I first bought the boat/motor I was out really opening her up, and it just turned off at 65mph/5500 rpms. I thought nothing of it and carried on. Have taken it out once a week since and run it all rpm range,no issues.


Since then the only that has changed is a new cranking battery and a full one year service, and raised jackplate 1.5".



It started again! Except now it is a repeatable issue. At WOT my motor is turning off, once I past 5000 rpms, might turn off at 5300 or 5800.

I've noticed a little hiccup is the first indicator, like it'll hiccup then immediately after it turns off. No alarms, no lights, motor is still peeing good. Checked primer bulb and it seems a little soft, but nothing crazy. After it dies it will crank right back up with no hesitation. You can even catch it if you're fast enough, little hiccup and take foot off and it'll stay running, but it happens so fast.

I drove approx 20 miles on it yesterday, I have no issues at all when I'm under 5k rpms. Maybe a tiny bit of hiccups occasionally but i could be paranoid.


Going to test low pressure pumps tomorrow and make sure there is no vst filter clogs. If that's not it, going to the mechanic next week.


Hopefully he will have answers.

[21XDC]

Fuel pump diaphrams would be the first change for me... Only $120ish for all 3 and easy to do yourself. I had a similar gremlin, It was the fuel pump relay switch...

[rat0502]

Friend of mine had one that acted like that. After replacing a lot of parts, it ended up being the fuel line from the bulb to the motor. Was not ethanol compliant and the inner liner collapsed restricting flow. Check fuel lines and primer bulb.

[OverTimeAgain]

I have the ethanol compliant fuel lines, they were replaced shortly before I purchased the boat. The primer bulb appears to be in good shape.

I always run ethanol free and ring free.

Although it is good to hear that this does appear to be a fuel restriction issue, and an issue that others have encountered.


Personally I suspect something like what 21XDC said. I checked all my mechanical pumps diaphragms this morning and they all appear to be in good shape. Next step will be inspecting vst filter and electrical pump components

[ClarkBird]

Need to try and determine if it’s fuel related, or ignition. When you say it “cuts off” what does the motor actually do ? Is it like turning the key off for a second, then back on? Or, is it a gradual stumble with a loss of power? Two very different scenarios.

[Bass Junkie]

Need to try and determine if it’s fuel related, or ignition. When you say it “cuts off” what does the motor actually do ? Is it like turning the key off for a second, then back on? Or, is it a gradual stumble with a loss of power? Two very different scenarios.

This^ By hiccup, do you mean it sputters some then dies or it shuts down like you turned the key off or pulled the kill switch. The latter would seem like something electrical but if it's sputtering just a little and then killing it sounds more fuel related.

[OverTimeAgain]

Honestly it's hard to tell. It happens very quickly. I think it hiccups just a tiny bit, and just once and then turns off.


First few times it literally felt like someone just turned the key off, and the motor turned off at 70mph. Now that it happens everytime I have come to recognize the way it "feels". It's still unavoidable, tiny little catch/bump in engine noise/throttle and off she goes.




My mechanic initially said it could be a loose wire, so I checked all my connections and everything seems good. Now I'm thinking fuel, whatever it is it seems to be rpm based. Planes out instantly, runs all day at 50mph 4.5kish rpms. If I push it up I can hit about 60mph/5k rpms, as soon as we start getting into the serious rpm/speed range it just turns off

[TwinStick]

I just went through finding a problem with my ox66. I did a lot of reading, everyone said if you have a problem with an ox66 it's fuel related or an 02 sensor.

[Amistad Tackle]

Fuel pump relay more than likely. Replace it.

[skeeterBill200]

Uh-Huh ^ what he said

[OverTimeAgain]

How do I check just the fuel pump relay? I'd prefer to make sure that's the issue before I spend the money.


Although it is encouraging that 3 people are suggesting fuel pump relay!

[M1RT]

While you're at it, replace the O2 sensor. Symptoms of a bad/clogged sensor can be a hiccup and then reduction at max RPM. This is not what you're experiencing but it is good preventative maintenance.

[Amistad Tackle]

This is a known issue with the ox66. Its not an expensive part. If you are really curious run a volt meter to the leads on the pump and use some wire to run the meter to where you can watch it. My guess is your relay is cutting power to the fuel pump. I’ve seen relays that intermittently work. It will drive you nuts. On a 2000 model you are due for a new one.

[Amistad Tackle]

If that doesn’t cure it you likely have some other electrical issue that is cutting power to your fuel pump. My bet is a new relay will solve your problem.

[OverTimeAgain]

Checked my low pressure pumps today. Unbolted them from the block slightly and squeezed primer bulb.. Two of them leaked fuel drastically.

Replacing all 3 on Friday and going to take boat out on Saturday so we will see.

[Amistad Tackle]

If it’s shutting completely down at WOT it’s not the low pressure pumps, but if they were leaking they need to be changed also.

[Amistad Tackle]

Shutting down at WOT may have popped the fuel pump diaphragms. Again, I’ll say the relay is tripping to the off position.

[OverTimeAgain]

Uodate: replaced all 3 low pressure fuel pumps and my boat runs better than it ever has. Cranks instantly all day and I can get up to 6k rpms again.


Thanks all who provided insight! I'll probably be buying a fuel pump relay soon, because apparently those suckers will randomly die as well.

[Amistad Tackle]

I have never heard of the OX66 completely dying at WOT from low pressure fuel pumps. Loss of rpm at WOT and idle rough yes, but never flat out dying. I guess there's a first for everything.

If it turns out being the relay come back and let us know.

[JoeFriday]

I have never heard of the OX66 completely dying at WOT from low pressure fuel pumps. Loss of rpm at WOT and idle rough yes, but never flat out dying. I guess there's a first for everything.

If it turns out being the relay come back and let us know.

Me either. That's usually the fuel pump relay. Guess we've got yet another data point.