350 MAG won't rev past 3400 rpm, sounds like rev limiter

[bortSanders]

350 MAG
serial: 2A191167
2014 SeaRay Sundancer 260, bravo 3
600 hours
rental boat

Won't rev past about 3400 rpms. Won’t plane out, Sounds like the rev limiter kicks on and stumbles. No alarms or any indication of problems on the gauges. I am able to recreate the problem with the boat parked in the slip, drive in neutral.

I caught up on past due maintenance in an attempt to fix the problem:
-correct plugs NGK 5599, OEM Cap Rotor Wires, Water separating Fuel filter (old one about ½ dark-not that bad)
-Batteries are new, clean tight connections
no change

-prop was bent and has since been replaced, no change

I did find a small chafed leak in the vacuum hose from the fuel pressure regulator (elec taped for now), but I figure that should be a low rpm prob not a high rpm prob.

- Fuel pressure at the schrader valve test port between the 2 fuel rails and behind the throttle body: idle = 36-37psi , vac hose of fuel psi regulator removed 46-47 psi. Also the prob occurs with the fuel pressure regulator vacuum hose removed too. Its a MAC tools fuel gauge and I've really only used it a few times, so it should be accurate.

Hooked up Rinda scantool on the laptop:
- I checked for codes: none active. except the "SWITCHED BATTERY VOLTS" code 65 times in the previously active section. I assume thats one of those things you ignore. I might add that this is a rental boat.

-I made a video snapshot of the Parameter Data if anyone can help. The fuel trim at the top right of the screen isn’t visible, but it's equal to the other banks fuel trim. It also has audio to hear the problem.

- note: I also have a noise at idle that I dismissed as valve train noise, but I made a video just in case anyone thinks its a bigger issue...(its the second link)

Any help is very much appreciated. Thank you. No need to sugar coat things.

parameter data:

noise at idle:

 

[Scott Danforth]

the rev limiter is at over 5200 RPM, and it is simply in the program

you have a fuel issue

what is your fuel pressure while you are under load while moving?

 

[alldodge]

First vid link doesn't work

Second vid sounds like a valve issue, have you done a compression test?

 

[bortSanders]

fuel pressure under load: that's a good idea, I will try to get a helper for a test drive

compression test: also a good idea

thanks for the replies, I fixed the link (maybe the forum moderator can clean up my formatting in my original post)

video link:

 

[alldodge]

At the 3300 rpm the
Throttle lever position is at zero
Throttle Blade Position is at 14%
All of the Gas exhaust temp sensors is N/A (Not Applicable)

Something is not reading correctly. Does the software indicate it can read a PCM09 ?

 

[Fun Times]

2A191167 = MERCRUISER 350 B EC 6R 350 MAG BRAVO MPI
Do you know if your engine has "DTS" Throttle Body, Digital Throttle and Shift?

https://www.mercruiserparts.com/350-mag-mpi-alpha-bravo-ec-1a611928-th

A high percentage of the time when an engine is stuck around 3400 RPM that seems like it's on the Rev limiter like this there's something amiss with the Gear Indicator Switch Assembly..Item number 18 or 17, Shift Bracket, Bravo
Shift Bracket, Digital Throttle and Shift / Axius

Are you able to see/watch any gear indicator switch parameters somewhere else within your scan tool software parameter settings to see if it going from neutral gear position to forward gear position ?

 

[bortSanders]

At the 3300 rpm the
Throttle lever position is at zero
Throttle Blade Position is at 14%
All of the Gas exhaust temp sensors is N/A (Not Applicable)

Something is not reading correctly. Does the software indicate it can read a PCM09 ?

Nice, I will check that next time I hook it up. (either tomorrow or the next day)

I'm not sure if this is revelant to you or FunTimes (the forum moderator), but keep in mind that I was revving the boat in the slip in nuetral. Things may change while it is on the open water (I need to find a helper to drive next time).

 

[bortSanders]

2A191167 = MERCRUISER 350 B EC 6R 350 MAG BRAVO MPI
Do you know if your engine has "DTS" Throttle Body, Digital Throttle and Shift?

https://www.mercruiserparts.com/350-...ec-1a611928-th

A high percentage of the time when an engine is stuck around 3400 RPM that seems like it's on the Rev limiter like this there's something amiss with the Gear Indicator Switch Assembly..Item number 18 or 17, Shift Bracket, Bravo
Shift Bracket, Digital Throttle and Shift / Axius

Are you able to see/watch any gear indicator switch parameters somewhere else within your scan tool software parameter settings to see if it going from neutral gear position to forward gear position ?

thanks for your reply. I mentioned to the other gentleman that the boat was in neutral in the slip when I was trying to recreate the problem. Im not sure if that is relevant though, just a reminder.
Im not sure if it has DTS. I will happily check the for the equipment and the scantool for the parameter data. Im sure I can jumper the switch closed too as a test.

 

[Fun Times]

Yes it very important that the boat is in forward gear/underway to know if the the problem under load is still active because just free revving in neutral in the slip would put you against the rev limiter right around 3500 RPM recreating the same similarities you're describing while underway...The thing is your ECM may think you're still in neutral when you're in forward gear should the gear switch selector not be working or adjusted correctly.

The scan tool ought to tell you if the switch is switching telling the ECM what gear it's in.... The only difference here though is normally you'd be hearing a warning horn when you hit the Rev limiter but thus far you don't seem to be which could indicate either it's not a switch problem or the warning horn system isn't working correctly.

Do you hear a warning horn when you first turn the key on before start?

There should also be an output parameter option within the scan tool to turn on/Test the warning horn system to see if the horn will beep for about 10 seconds.

 

[QBhoy]

Hi

It’s almost certain you are in guardian mode here. Something is limiting the engine. Most common cause is the SW pressure sensor. There are others but this is the one that doesn’t always alarm or show up. Other is the crank sensor, but usually behaves differently and stalls randomly.
Your ticking noise sounds very much like mine when the corsa exhausts are closed and the rpm are lower than 1200/1300 rpm. The diverters rattle. Do you have exhaust exits ?

 

[bortSanders]

Yes it very important that the boat is in forward gear/underway to know if the the problem under load is still active because just free revving in neutral in the slip would put you against the rev limiter right around 3500 RPM recreating the same similarities you're describing while underway...The thing is your ECM may think you're still in neutral when you're in forward gear should the gear switch selector not be working or adjusted correctly.

The scan tool ought to tell you if the switch is switching telling the ECM what gear it's in.... The only difference here though is normally you'd be hearing a warning horn when you hit the Rev limiter but thus far you don't seem to be which could indicate either it's not a switch problem or the warning horn system isn't working correctly.

Do you hear a warning horn when you first turn the key on before start?

There should also be an output parameter option within the scan tool to turn on/Test the warning horn system to see if the horn will beep for about 10 seconds.

thanks, I will check and reply back!

 

[bortSanders]

Hi

It’s almost certain you are in guardian mode here. Something is limiting the engine. Most common cause is the SW pressure sensor. There are others but this is the one that doesn’t always alarm or show up. Other is the crank sensor, but usually behaves differently and stalls randomly.
Your ticking noise sounds very much like mine when the corsa exhausts are closed and the rpm are lower than 1200/1300 rpm. The diverters rattle. Do you have exhaust exits ?

Im grateful for your response. Im new to boats but I was an auto mechanic so there is some stuff I am still learning. Im not familiar with the SW pressure sensor. What does the SW stand for?

The ticking noise: I also have to claim my non boat past (but Im learning). As far as I know everything is the way it was from SeaRay (rental boat). The only thing that has really happened that I know of is the lower/unit was replaced at one point.

I should also note that I cleaned up a semi corroded ground point on the back of the motor by the coil. I'm going to do some voltage drop testing from the battery next time I'm on the boat to be sure everything is good.

 

[Fun Times]

Im not familiar with the SW pressure sensor. What does the SW stand for?

Sea Water Pressure Sensor..., Item Number 16 found on the power steering cooler, https://www.mercruiserparts.com/bam/subassembly/31757/15045/270 / the first item number 30, https://www.mercruiserparts.com/bam/subassembly/31757/15045/45

Can you hear your warning horn at all??

 

[QBhoy]

As above. Sea water pressure I’ve known it to alarm and also not alarm. It’s a sensor failure and usually not genuine.

 

[muc]

Not sure why the sea water pressure sensor is being talked about. The scan of it sure looks good to me. And isn't that why we use a scan tool? It will tell us whats good so we don't have to guess.

Here's my recommendation. Get the scan tool working properly. I'm no expert on Diacom with these engines. I would be using G3, but Diacom is what you have and it will work.

Are you sure that the right engine was selected when the scan tool was first hooked up? It looks to me that maybe a DTS engine was selected. (you don't have DTS) I see the scan tool is looking for throttle lever position and not seeing anything. That leads me to think the wrong engine was selected.

Stop revving the engine in neutral. It's abuse and at this point the PCM is doing it's job, trying to keep you from blowing up the engine.

Make sure your Diacom has the latest update. I think it's up to Version 3.09 now. it's a free update from the website.

Then make sure you have the tool set up right. You are missing some data lines from that video you made. At the bare minimum get the in gear read out on there. That's been the best guess so far. If in doubt enable everything.

Learn how to use the scan tool. It comes with instructions. They are right there on the laptop.Once you learn how to use it, you won't need a helper. You can use the record function. Hook up the scan tool, start the engine, hit record and drive the boat for about 20 minutes. Bring the boat back to the dock and stop the recording. You will now have a saved file that can be reviewed. You could also post that file here and anybody who has a diacom can look at it and make knowledgeable recommendations.

 

[thannah84]

Had a similar problem with buddy’s 350 mag. If I remember correctly, he had to change the throttle cable and that whole throttle position/rev limiter had to be adjusted.

 

[bortSanders]

Not sure why the sea water pressure sensor is being talked about. The scan of it sure looks good to me. And isn't that why we use a scan tool? It will tell us whats good so we don't have to guess.

Here's my recommendation. Get the scan tool working properly. I'm no expert on Diacom with these engines. I would be using G3, but Diacom is what you have and it will work.

Are you sure that the right engine was selected when the scan tool was first hooked up? It looks to me that maybe a DTS engine was selected. (you don't have DTS) I see the scan tool is looking for throttle lever position and not seeing anything. That leads me to think the wrong engine was selected.

Stop revving the engine in neutral. It's abuse and at this point the PCM is doing it's job, trying to keep you from blowing up the engine.

Make sure your Diacom has the latest update. I think it's up to Version 3.09 now. it's a free update from the website.

Then make sure you have the tool set up right. You are missing some data lines from that video you made. At the bare minimum get the in gear read out on there. That's been the best guess so far. If in doubt enable everything.

Learn how to use the scan tool. It comes with instructions. They are right there on the laptop.Once you learn how to use it, you won't need a helper. You can use the record function. Hook up the scan tool, start the engine, hit record and drive the boat for about 20 minutes. Bring the boat back to the dock and stop the recording. You will now have a saved file that can be reviewed. You could also post that file here and anybody who has a diacom can look at it and make knowledgeable recommendations.

To clarify: the original complaint was a lack of power, not getting on plane and topping out around 3300 rpm. I did not have a chance to replicate it myself because my time is limited as I have a lot of work to do for my employer. Our renters all had the same complaint.

So I read everyone's responses (thank you for sharing your knowledge) and I got back out to the boat. I updated my Diacom software and I also used a different adapter and hookup point for the cable. So now I have all of the data that everyone was asking for. I also hooked up the tool and went for a quick test drive.

Before the test drive I looked over the basics and some of the questions from the post earlier:
gear shift position indicator ok. warning buzzer sounds and works. The throttle blade in the throttle body opens all the way. Voltage drop was within specs (<5%). No active codes. Some history codes ( I have a video). Hooked up my fancy snap-on vac gauge because I was worried about that valve train noise....

Manifold vacuum at idle = 14 inHg!!!!!
I've never seen a reading that low, (should be above 17 inHg). Then, I turned off the run switch and measured cranking vac.
Cranking vacuum = 1 inHg (should be around 5 inHg I think)
I also made a video of me revving the engine with the vac gauge hooked up as I was monitoring the gauge to look for exhaust restriction. I'd say it passed the test and manifold vac quickly returned to 14 inHg.

So it's clear the engine isn't breathing too well. My next step will be a compression test next time I'm down there. I am suspecting engine mechanical at this point.

I hooked up the scantool correctly, turned on the "record function" and went for a test drive even though I found the low vacuum. I motored out of the harbor, then opened it up for a very short while because the seas were a little rough and then I turned around and it was dark. It didn't seem like it was in a hurry to plane out but I didn't push it. I can make another test drive in better conditions.

Diacom said I have a misfire at cylinder #7. I should also note that the riser on that side seems to heat up slightly faster than the other one (which I think makes sense because all of the unburned fuel is in there).

I would love to hear any feedback or advice. I especially would like to hear some feedback on the Diacom snapshot I made. Thanks

So I made a .rec file but I currently don't have security clearance to upload it. Maybe the moderator can assist. I'm not sure how it's usually done.

Thanks AllDodge, here's the link for the .rec file
https://drive.google.com/file/d/1B9I...ew?usp=sharing

 

[alldodge]

Mis fire on a cylinder means 37hp loss and might have some other issues which is reducing hp

Might use something like google's one drive and place the file there. Then others can go and download it. Set the one file as open so all can see it.

 

[bortSanders]

Vac Gauge

https://youtu.be/J_kktsGHA_g

Here's a link with the Diacom PID's at idle and checking the history codes. I think I should have made a "Diagnostic Report" using some feature with the Diacom software

https://www.youtube.com/watch?v=IHg2_4Rh5xA

 

[alldodge]

Thanks for the vid, I kept pausing and going back to take in all the readings

Engine hours 622
Barometric pressure 29.4
volts 13.4
Misfires on 7 and 8 bad, 2 next highest, 4,6 lowest
O2 sensor A 180
O2 sensor B 102
O2 sensor C 76
O2 sensor D 728

Fault
22 Exh Man overheat port - 13.0V 0.0hr
314 Stbd Cat failed to run properly 14V 352.0hr
355 Stbd O2 fault 13.4V 360.3hr 360.3hr
19 Guardian overspeed exceeded 5423rpm 14.3V 198.9hr
321 Port side fuel lean 1593 rpm 14.4V 204.8hr
390 Strb Stuck rich 1909 rpm 14.5V 370.6hr
3 Sea pump low 0.0 psi 14.4V 401.6hr
9 Guardian 14.7V 199hr
2 Bat voltage low 7.8V 470.3hr engine stall
12 Low oil pressure 2.9psi 951rpm 14.4V 611.8hr

The last one is closest to current time frame

I'm seeing more misfires then just on number 7, just 7 does have the most. Could be a bad cap even though the cap, wires have been replaced.

The new plugs where NOT adjusted for gap??

I would think the O2 sensors should be closer per bank