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Marine Power 8.1L Surging Issue? - Video

jetboating

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I have a 2009 Marine Power 385hp 8.1L (330 hours) and I was hoping to get some advice or guidance for a technical issue I am experiencing.

I have a video of the problem here: https://youtu.be/ho53LJPfhqs

Under load, primarily in reverse, the engine is surging/pulsing from 2500 rpm down to 1500rpm. It doesn't do it as much in forward. I think it's doing it in reverse because the throttle lever has a much shorter throw in reverse than forward, thus applying throttle faster.

I've checked:

- rail pressure (44 PSI at key cycle)
- 38-40 PSI at idle.
- 38-39 PSI at 3500 rpm.
- pulled off vacuum hose while running, fuel rail pressure jumps up about 6-7 PSI.
- checked all spark plugs. They are sooty, dry black indicating a rich condition or weak spark, consistent across all 8 cylinders.
- made a makeshift smoke machine and blew smoke into throttle body, no visible vacuum leaks.

Thank you for any help or advice?
 
I'd be inclined to get the computer scanned....it will show you all of the key parameters (in near real ime) which will allow a better assessment of what's going on inside of the engine. You should also download the service manual so you have a full set of specs as well as the proper troubleshooting sequences.

It could be as simple as the ECT is starting to fail...I've seen a few examples where the sensor data was too cold by 50 degrees which drove the fuel mixture rich....no error code was ever set as the sensor hadn't reached the 'failure thresholds' for the test the ECU ran.....
 
I'd be inclined to get the computer scanned....it will show you all of the key parameters (in near real ime) which will allow a better assessment of what's going on inside of the engine. You should also download the service manual so you have a full set of specs as well as the proper troubleshooting sequences.

It could be as simple as the ECT is starting to fail...I've seen a few examples where the sensor data was too cold by 50 degrees which drove the fuel mixture rich....no error code was ever set as the sensor hadn't reached the 'failure thresholds' for the test the ECU ran.....

Thank you Makomark, I can't find a shop that will take the boat for at least 3 weeks, lol... It's boating season here and everyone is booked up. I have the service manual from marine power already and have been in contact with them as well. I am thinking about just buying my own scan tool but it's a toss up between Diacom and another option called Mefiburn. Mefiburn is quite a bit cheaper. ($350 USD vs almost $800).
 
Understand your predicament....The diacom or the stand alone scan tool is the standard in the marine industry....with the Newer ECU, I'd really checkout the MEFIburn before investing - I understand they work very well with the MEFI1-4 ECUs but don't know of anyone trying that tool with the 'next generation' of ECUs....

Since you've downloaded the service manual, you can go thru the symptom charts....most of the sensors can be checked with a digital meter and the service manual should have a range of values as well as 'at idle' values.....some can also be check by themselves, independent of the ECU. Also, go thru the control loop description and understand which sensors drive the fuel delivery parameters - those are the primary set to check.

A final thought is to approach some of your boating buddies about doing a cooperative buy on one of the Rinda options - cost sharing lessens the bite quite a bit. The good news, even if you can't get help, is that it only takes a couple issues to recoup the investment, especially with current shop rates bumping into $100/hr in many areas...
 
Understand your predicament....The diacom or the stand alone scan tool is the standard in the marine industry....with the Newer ECU, I'd really checkout the MEFIburn before investing - I understand they work very well with the MEFI1-4 ECUs but don't know of anyone trying that tool with the 'next generation' of ECUs....

Since you've downloaded the service manual, you can go thru the symptom charts....most of the sensors can be checked with a digital meter and the service manual should have a range of values as well as 'at idle' values.....some can also be check by themselves, independent of the ECU. Also, go thru the control loop description and understand which sensors drive the fuel delivery parameters - those are the primary set to check.

A final thought is to approach some of your boating buddies about doing a cooperative buy on one of the Rinda options - cost sharing lessens the bite quite a bit. The good news, even if you can't get help, is that it only takes a couple issues to recoup the investment, especially with current shop rates bumping into $100/hr in many areas...

Thank you again for responding Makomark, it seems like the Diacom system is the way to go. I don't think the standalone tool will work as the adaptor needed #94029 (6 pin Mefi 5) doesn't work with the handheld?

Getting into the all manual testing is into a realm I am not too confident in. I do have a digital multi-meter, I can't run the boat out of water as it has a hamilton pump and it cannot be dry-run due to the cutlass bearing needed water as a lubricant. I am the sole boater out of my buddies, especially with a jet boat lol so the cost of the Rinda will be something I bear alone... I could probably offer up scans to other local boat owners through classifieds or something though to help recoup costs.

I will dig into the manual some more. The manual provided by marine power is for the Mefi 4 and not Mefi 5, not sure how much will be different.
 
marinepower does have an MEFI5 manual on the www page though it appears its tailored to the 5.7l engine. The ECU doesn't care what engine it controls...the differences are accounted for in the 'tune' that's programmed into it. you can always compare the mefi4 manual sections to the ones in the mefi5 manual...I doubt there's any major difference in the basics, only in the extended functions the -5 provides over the -4, and then if marinepower implemented them.

I'd say check with the mefiburn people to see if they guarantee functionality....if they do, you don't have much to lose other than time.

After thinking about it a bit, I'd doubt your engine is really that 'new'....GM stopped making the 8.1 long before 2009. A call to the factory with the serial number can tell you when it left there....how long before it went into a hull and the package was sold is beyond their control.

Curious, how does a jet pump work with a cutless bearing...I've never seen that kind of setup? of course, where I'm at you don't see too many jet pumps....
 
marinepower does have an MEFI5 manual on the www page though it appears its tailored to the 5.7l engine. The ECU doesn't care what engine it controls...the differences are accounted for in the 'tune' that's programmed into it. you can always compare the mefi4 manual sections to the ones in the mefi5 manual...I doubt there's any major difference in the basics, only in the extended functions the -5 provides over the -4, and then if marinepower implemented them.

I'd say check with the mefiburn people to see if they guarantee functionality....if they do, you don't have much to lose other than time.

After thinking about it a bit, I'd doubt your engine is really that 'new'....GM stopped making the 8.1 long before 2009. A call to the factory with the serial number can tell you when it left there....how long before it went into a hull and the package was sold is beyond their control.

Curious, how does a jet pump work with a cutless bearing...I've never seen that kind of setup? of course, where I'm at you don't see too many jet pumps....

Got it... There is a plate on the motor that states it was manufactured 12/2009. Also provided the serial number to Marine Power. So the block might be a little older, I think it went through Marine Powers marinization process 12/2009 maybe?. They switched from MEFI 4 to MEFI 5 in the 2008 model year I believe. This model is definitely MEFI-5 and has E67 stamped on the ECU housing.

The cutlass bearing on a Hamilton 212 is made out of rubber and requires submersion in water for lubrication. They do have dry-run kits but they can only be used for a minute or two at idle.
 
I just did a little playing around with the spark arrestor off and observing the throttle body. At full throttle forward it opens all the way... at full throttle reverse it does not. This could be the source of the lack of power in reverse but I don't know if it would cause the surging?

Here is a video: https://youtu.be/ozlsozrSs1E
 
Got it on the cutlass....never been inside of a hamilton jet....was thinking there was a strut somewhere with a shaft.....

anyhow, I don't believe the butterfly opening in reverse is coupled to the surging....lack of power - yes.....
 
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