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Another OX66 250 lost rpms <<READ POST #106 FIRST>>

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Another OX66 250 lost rpms <<READ POST #106 FIRST>>

Old 06-27-2017, 04:14 PM
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Default Another OX66 250 lost rpms <<READ POST #106 FIRST>>

Here we go again..

Background, 2001 OX66 250 with about 500 hours
Work completed in March 2017 included:
New LP Pumps, all 3
New Water separator
New on motor fuel filter
New on motor check valve
New HP Pump filter and gasket
New fuel lines entire boat
New Ball
New plugs
cleaned O2 sensor
new water pump

Boat ran great for about 15 hours after March tune up was completed

Ran out about 38 miles, moved around a few times during the day and then while heading back in, about 20 miles from shore I noticed the speedometer had stopped working. I figured it had gotten a piece of grass on it or something.

Then a few minutes later the RPMs dropped from 4000 to about 1000 and the boat slowed to just a few MPH.

As I pushed the throttle forward it sounded like it was bogging down and there was no increase in RPMs.

I removed the cowl and checked oil in engine mounted tank and it was full.

I could only get about 1500 rpms with max throttle, then after leaving the throttle at full it would gradually climb up to 3000 rpms and we would be able to get moving 20 mph for only a few minutes then it would bog back down to 1200 - 1500. It did this several times for the 20 miles we had to go.

I'm thinking that the motor went into some kind of limp mode but maybe not.

Today I drained and cleaned both oil tanks and verified correct operation and operation of the low oil alarm. Everything oil related works.
I found 1 of the new LP pumps was leaking and changed it thinking this would fix the problem.

Checked fuel pressure at rail while running and it seems to be 32-34 pounds but its hard to read with the motor shaking all over the place.
I put the boat in the water and it seems as though I can get 3000 RPMs but it' shakes a lot and it's not happy.

I don't know if the speedometer has something to do with it or not, I would think not.

What am I missing?
What else should I check?

Thanks

Last edited by Edselectric1; 06-30-2017 at 01:36 PM. Reason: updated
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Old 06-27-2017, 05:38 PM
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What fuel do you run
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Old 06-27-2017, 05:41 PM
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Originally Posted by wetneck View Post
What fuel do you run

I run regular gas and use startron. Do you think it's ethanol related? All fuel lines were replaced in March as well as anti syphon on tank.
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Old 06-27-2017, 05:44 PM
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Check compression to rule out any major failure?
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Old 06-27-2017, 05:46 PM
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Originally Posted by Texas 17 View Post
Check compression to rule out any major failure?
Yes, 115 on top 4 and 110 on bottom 2 .
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Old 06-27-2017, 06:31 PM
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The fuel rail pressure need to be checked while the issue occurs. It should remain at around 35 PSI all the time... 32 psi is a bit low.
Find a Yamaha "Winky-Blinky" test light and look for codes to find if a sensor is failing.
Cleaning the O2 sensor is not enough, you must check voltage output afterwards to confirm they are in range.
Check also injectors screens.
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Old 06-27-2017, 06:37 PM
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Originally Posted by mesias View Post
The fuel rail pressure need to be checked while the issue occurs. It should remain at around 35 PSI all the time... 32 psi is a bit low.
Find a Yamaha "Winky-Blinky" test light and look for codes to find if a sensor is failing.
Cleaning the O2 sensor is not enough, you must check voltage output afterwards to confirm they are in range.
Check also injectors screens.
The issue is constant, never really get any "good " throttle. The pressure stays 32ish .Basically just running really bad and can't get above 3000 rpms. Even sounds bad.
The injectors were just cleaned as well.

I really don't get much power right from the start. It's not a loss of power, it's just no power at all.
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Old 06-27-2017, 06:43 PM
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Originally Posted by mesias View Post
The fuel rail pressure need to be checked while the issue occurs. It should remain at around 35 PSI all the time... 32 psi is a bit low.
Find a Yamaha "Winky-Blinky" test light and look for codes to find if a sensor is failing.
Cleaning the O2 sensor is not enough, you must check voltage output afterwards to confirm they are in range.
Check also injectors screens.
Also, O2 tested within range doing the flame test. I will do other tests tomorrow.
Ordering Winky-Blinky as well
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Old 06-27-2017, 07:23 PM
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Definitely sounds fuel related to me
Recheck lp pumps
Check vst contents
Both filter content
If you're not at 36 psi it's not going to run right
I personally won't put reg eth gas in my boat
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Old 06-27-2017, 07:27 PM
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Hey Ed,

Either fuel quality or fuel quantity.
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Old 06-27-2017, 07:32 PM
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Bad spark plug wire/coil will also so do that. Measure the resistance of all 6 coils, if you see 1 or 2 with different ohm reading from the rest, you got the culprit.
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Old 06-27-2017, 07:44 PM
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Sounds a lot like a low pressure fuel pump is bad. I would have someone pump the fuel bulb while you're running under load. If this solves it, that's your problem.

Not likely, but if it's electrical in nature you can unplug the yellow wire behind the ecu to see it anything improves.

As others have said, it's almost always fuel.
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Old 06-28-2017, 03:27 AM
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Originally Posted by Phil View Post
Bad spark plug wire/coil will also so do that. Measure the resistance of all 6 coils, if you see 1 or 2 with different ohm reading from the rest, you got the culprit.
This makes sense to me. It seems like it's in a limp mode so maybe it's only running on a few cylinders.
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Old 06-28-2017, 03:59 AM
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I think we may be looking in the wrong area,

When I had a bad LP pump the boat ran fine, it would have lots of power for a few seconds while trying to get on plane then lose rpms and as a result lose power, and while it was trying to get on plane it sounded good and strong

This time is different, There is no power at all,
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Old 06-28-2017, 04:02 AM
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Originally Posted by Absolute View Post
Hey Ed,

Either fuel quality or fuel quantity.
going to check separator today, maybe I've got some water in the fuel?
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Old 06-28-2017, 05:14 AM
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Run it from a 5 gallon gas can.

Check the vst filter. Any crud on it, no matter how small can cause issues.

Make sure all fuel related items are tight and not sucking air.

Does the fuel bulb get hard?

How often are you using the boat?

15 hours since March? With ethanol fuel sitting. If your not using the boat often enough to change over the fuel frequently, your going to have issues with separation. I don't care what "treatment" you put in the tank.

Use only ethanol free. If your going on a trip that will turn over the gas tank, then sure, use ethanol fuel. If not, ethanol free fuel only.

Any water in fuel?
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Old 06-28-2017, 05:20 AM
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Originally Posted by lmannyr View Post
Run it from a 5 gallon gas can.

Check the vst filter. Any crud on it, no matter how small can cause issues.

Make sure all fuel related items are tight and not sucking air.

Does the fuel bulb get hard?

How often are you using the boat?

15 hours since March? With ethanol fuel sitting. If your not using the boat often enough to change over the fuel frequently, your going to have issues with separation. I don't care what "treatment" you put in the tank.

Use only ethanol free. If your going on a trip that will turn over the gas tank, then sure, use ethanol fuel. If not, ethanol free fuel only.


Any water in fuel?
I'm going to check and clean the VST and try running from can.

The fuel bulb does get hard.

There is no water in the on motor fuel filter and I'm changing the separator today as well.

We use it about every other weekend and run for 1 - 2 hours each time
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Old 06-28-2017, 05:25 AM
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Twins or single?
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Old 06-28-2017, 05:27 AM
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Before you do anything else, check the VST filter.
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Old 06-28-2017, 05:32 AM
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Originally Posted by dell30rb View Post
Before you do anything else, check the VST filter.
When you do check vst, note if the vst was full or empty.

Check the vst float and its needle. Make sure it's all lined up properly and the float is swinging freely.

Make sure the vst needle is not sticking AT ALL!

In fact, if you haven't cleaned the vst components, do so. Clean the yellow gooo off of everything in there.
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