SPN 731 FMI 0 on M6DI

[23LSVOwner]

Don't know if it helps, but I know a tech and discussed this with him and he gave the following info:

 

Knock Retard at limit (731:0) is 99% caused by fuel which almost always involves a high ppm of water content.  On lesser occasions, there are some labs that we have pulled where the fuel was dirty (sediment).  On even rarer occasions, we have seen engine oil overfills cause this DTC.

The ethanol in E10 fuel will absorb water which can typically range up to 800 PPM.  As a guideline, our water tolerance is 1000 PPM for ethanol based fuels up to 10%. (anything over 10% Ethanol is a no-go).  Non-Ethanol based fuel, the max PPM tolerance is 0 ppm because those fuels do not have the chemical make-up to absorb water content.

Water and sediments are more dense than petrol which means that it collects at the bottom of the tank.  The bucket the fuel pump sits in is approximately (according to tank and pump size) 2/3rds to half way up from the bottom of the tank.  The pump works inside the bucket to move fuel to the engine.  When the fuel level is over the bucket, its already there to be pumped.  When the fuel level moves below the bucket, the fuel gets pulled in from the socks, moved to the bucket, and then back to the engine.  Basically, in a nutshell, when the tank gets low, it is pulling all the water/sediment/etc off the bottom of the tank and sending it back to the engine which in turn can cause the engine knock.

Edited June 29, 2021 by 23LSVOwner

[dwc032]

54 minutes ago, 23LSVOwner said:

Don't know if it helps, but I know a tech and discussed this with him and he gave the following info:

 

Knock Retard at limit (731:0) is 99% caused by fuel which almost always involves a high ppm of water content.  On lesser occasions, there are some labs that we have pulled where the fuel was dirty (sediment).  On even rarer occasions, we have seen engine oil overfills cause this DTC.

The ethanol in E10 fuel will absorb water which can typically range up to 800 PPM.  As a guideline, our water tolerance is 1000 PPM for ethanol based fuels up to 10%. (anything over 10% Ethanol is a no-go).  Non-Ethanol based fuel, the max PPM tolerance is 150 ppm because those fuels do not have the chemical make-up to absorb water content.

Water and sediments are more dense than petrol which means that it collects at the bottom of the tank.  The bucket the fuel pump sits in is approximately (according to tank and pump size) 2/3rds to half way up from the bottom of the tank.  The pump works inside the bucket to move fuel to the engine.  When the fuel level is over the bucket, its already there to be pumped.  When the fuel level moves below the bucket, the fuel gets pulled in from the socks, moved to the bucket, and then back to the engine.  Basically, in a nutshell, when the tank gets low, it is pulling all the water/sediment/etc off the bottom of the tank and sending it back to the engine which in turn can cause the engine knock.

Thanks for that info!!  I have forwarded your post to my dealer. I have said since the beginning that it has to be either water in the tank or some sort of sediment. We will see what he says. 

[dwc032]

Just spoke with dealer. There draining and pulling tank and inspecting it for debris. 

[bcoppess23]

Has anyone else had this issue and been able to confirm the cause?  I had this happen to me once last week at the start of our trip at Norris and didn’t have issues with it the rest of the trip. However, I did notice that my surf speed wouldn’t hold and would not get above 10.2 mph running the speed prop. I’ve never had issues with this prop fully loaded wakeboarding.  I had to change up to the torque prop and even then, it would still not get up to speed for wakeboarding with front and center full plus rears at 50% and 8 people in the boat.  
 

After our trip, took it to the dealer and they reprogrammed the engine with the latest calibration, changed oil and lake tested without issue. Took the boat out today, the error came back. Checked oil and it seems fine.  We fill up at a BP on the way to the lake and haven’t had issues in the past there. 

[bcoppess23]

Bringing this conversation back up as I am still having issues with this code and seeing if others have had other issues with it..

After my dealer drained the fuel, put a new fuel filter on last year, I didn't have issues.  Start this year out and it ran fine a few trips out and then at the 4th of July weekend, this error returned and has been coming back each trip out.  It seems to happen when the boat is working hard.  Malibu took a fuel sample and sent it off to be analyzed and it showed 1300 ppm of water in the fuel where tolerance is 1000. 

I have a hard time that I keep getting water in the fuel from the station.  So as a result after the 4th weekend, we drained the tank again, put a new fuel filter on and then put over 63 gallons of rec 90 fuel in the boat.  That next trip out, the 731 error came on.  I was able to get a service tech on the boat while on the water to try to replicate the issue but as soon as the diacom was hooked up to the boat, the error would not throw.  My dealer is running a pressure test to see if there are leaks in the fuel system anywhere.  

 

[AWADD09]

On 7/28/2022 at 11:09 AM, bcoppess23 said:

Bringing this conversation back up as I am still having issues with this code and seeing if others have had other issues with it..

After my dealer drained the fuel, put a new fuel filter on last year, I didn't have issues.  Start this year out and it ran fine a few trips out and then at the 4th of July weekend, this error returned and has been coming back each trip out.  It seems to happen when the boat is working hard.  Malibu took a fuel sample and sent it off to be analyzed and it showed 1300 ppm of water in the fuel where tolerance is 1000. 

I have a hard time that I keep getting water in the fuel from the station.  So as a result after the 4th weekend, we drained the tank again, put a new fuel filter on and then put over 63 gallons of rec 90 fuel in the boat.  That next trip out, the 731 error came on.  I was able to get a service tech on the boat while on the water to try to replicate the issue but as soon as the diacom was hooked up to the boat, the error would not throw.  My dealer is running a pressure test to see if there are leaks in the fuel system anywhere.  

 

My 22 25 LSV with M6di just threw this code last night while we were surfing.   Boat just throttles down, then will try to throttle back up again.  While I have used 93 octane from pump on occasion I mostly use 91 non ethanol from marina across the lake.  I am bringing it in tomorrow will follow up once it is solved.  

[bcoppess23]

3 hours ago, AWADD09 said:

My 22 25 LSV with M6di just threw this code last night while we were surfing.   Boat just throttles down, then will try to throttle back up again.  While I have used 93 octane from pump on occasion I mostly use 91 non ethanol from marina across the lake.  I am bringing it in tomorrow will follow up once it is solved.  

Yep same thing on the behaviors.  The dealership and I are doing some lake testing Friday afternoon to try to replicate the error.  They did a tank pressure test and it checks out.

[AWADD09]

This is an example of what happened with me.  It around 18-20 seconds in.  

[bcoppess23]

16 hours ago, AWADD09 said:

This is an example of what happened with me.  It around 18-20 seconds in.  

Yup, that is the same.  I have dealt with this two years in a row.. comes on for a moment, rpms drop, it goes away, rpms resume.

[dwc032]

I forgot to update everyone on how this same issue was resolved by my dealer.  So I had the exact same issues as you guys.  Dealer changed fuel filters drained tanks and still did it.  They had an old crusty tech in the shop that said sometimes a bad water pump bearing will create enough knock to set off the knock sensor off.  I was like ok no idea what you just said, but what do we do from here.  They took the water pump off and inspected the water pump and found the bearing was bad.  Water pump was replaced at 100 hours and the boat now has over 250 hours.  I have had zero problems since the water pump was replaced.  Hope this helps everyone.  

[bcoppess23]

Thanks @dwc032!  I was on the boat Friday afternoon with the service manager and tech and we were not able to replicate the issue and I still do not have high confidence that it is resolved.  So, I will keep this in mind if the issue does come back to present itself.  I will be running only Rec fuel for the remainder of the season to rule out fuel being the issue.

[bcoppess23]

On 8/5/2022 at 4:01 PM, dwc032 said:

I forgot to update everyone on how this same issue was resolved by my dealer.  So I had the exact same issues as you guys.  Dealer changed fuel filters drained tanks and still did it.  They had an old crusty tech in the shop that said sometimes a bad water pump bearing will create enough knock to set off the knock sensor off.  I was like ok no idea what you just said, but what do we do from here.  They took the water pump off and inspected the water pump and found the bearing was bad.  Water pump was replaced at 100 hours and the boat now has over 250 hours.  I have had zero problems since the water pump was replaced.  Hope this helps everyone.  

Which pump, the raw water pump or the engine circulation pump?

[bcoppess23]

So after the error codes starting again this year at the 4th of July, I've had nothing but problems with the motor.  The last time I was on the boat this summer, just cruising out to where we were about to start boarding, the Knock Retard error came on followed by a cylinder misfire (happened July 4th weekend), and a CAT damaging misfire (new code).  I parked the boat and swam for a couple hours and then started the boat back up and the knock and cylinder misfire came back on our way back to the ramp.  Took the boat to the dealership where it has been since.

The boat has been at the dealership most of the summer and they have been trying to work through the decision tree process with Malibu.  It has finally come down to Malibu is recommending that a new motor is required.  

Some events that have happened through the testing process:

• When a diacom would be placed on the engine and lake tested under normal use, the boat would be fine.
• A new ECM was installed, plugs, coil pack, wires, etc.  
• Techs noticed that the boat was pulling more fuel on one side of the fuel rail
  • I asked what the fuel consumption was prior to the new ECM and it appears that this was an issue prior to the new ECM
• Dealer performed compression test and leak-down test and results have been fine

Will keep you posted on next steps.

[ndahlberg12]

This code popped up on our final run yesterday after putting 10 hours on the boat over the weekend. Boat went into limp mode but came back up to speed, we headed for the ramp and loaded up. Code is showing on the inactive side, trying to determine is this is worthy of heading to the dealer or if it fuel related as several have noted, anyone else had the pop up recently?

[bcoppess23]

I'd suggest trying to add something to help raise the octane in the fuel, try running rec 90 at the next fill up.  Call the dealer and see if it is something they need to look at or if you can continue to use it as it is inactive.  If it persists, then, for sure take it in.  They will likely take a fuel sample and then go from there.  Best of luck.

[csleaver]

Contaminated fuel is the most likely cause of the fault code, but I have seen the code occur with an engine that had a damaged flywheel drive plate caused by a propeller collision. 

[ndahlberg12]

6 hours ago, csleaver said:

Contaminated fuel is the most likely cause of the fault code, but I have seen the code occur with an engine that had a damaged flywheel drive plate caused by a propeller collision. 

How do you typically handle the situation if it is contaminated fuel? 

[wdr]

For an DIY, the easiest route for me was to gravity drain it. Turned out it was actually bad plug wires, cylinders 7 and 8. I dropped the nose, inserted the hose and let it drain into a 55 gal drum. If you pull the return line and don’t see obvious signs of bad fuel, that is probably not the issue. JM2C

[csleaver]

I do basically the same.  Remove the floor and the fuel sending unit, then use a portable low pressure electric fuel pump and some hose to pump the fuel out of the tank into a drum or other appropriate container for disposal.