Motor troubles. 496Mag HO.

[Biglue]

Hey guys, has anyone ever experieced the following with their 496HO/Bravo 1 set ups?
Yesterday I was running my boat and it began acting up on me. As soon as I get anywhere near 3200RPM it goes into what I have been told as safety mode. It comes out of the hole just fine, it accelerates fine but once it powers the outdrive at those RPMs it does not continue. It will do 3200-4000 RPM in neutral no problem. All the gages were reading fine.
It did it once in Havasu about a month ago. But it went away, I've run it twice since in local lakes and had no problems. Yesterday it came back hard and that was it.
Any advise or info sharing will be greatly appreciated. Thanks in advance guys
Louie.

[THOR]

Big,
call Mercury Racing. They should have some answers.

[phebus]

Take it to a Mercury certified repair facility, and they can scan the motor, and tell you what codes are being thrown, and pinpoint the fault.
When was the last time you changed your impeller? Wouldn't be a bad place to start if you are trying to troubleshoot the problem yourself.

[Beer-30]

Phebus is right. I had a similar problem and found it to be a sensor. The scan tool pointed us right to it.
If it is 2002 or newer, it has a water pressure sensor at the sea pump. If pressure it getting low, it will go into Guardian mode. Changed the impeller lately?

[Biglue]

Take it to a Mercury certified repair facility, and they can scan the motor, and tell you what codes are being thrown, and pinpoint the fault.
When was the last time you changed your impeller? Wouldn't be a bad place to start if you are trying to troubleshoot the problem yourself.
The impeller was changed at the beginning of this season. The temp gage was reading fine and I got none of the audible alarms. The impeller actually went out on me and I'm real aware of what to look out for......borderline sketchy. It was a problem for a couple weeks. What had happened is that the intake hose coming from the outdrive was not wire re-inforced so the impeller was actually collapsing it starving the impeller hence the failure.

[Beer-30]

It should be around $45 to scan it. Going into Guardian mode, it will set a code. If you have shut your batteries off, it will clear the code. Only have it scanned after you have ran it, entered Guardian mode, and not turned off your batts.

[Biglue]

It should be around $45 to scan it. Going into Guardian mode, it will set a code. If you have shut your batteries off, it will clear the code. Only have it scanned after you have ran it, entered Guardian mode, and not turned off your batts.
Crap, I'm pretty sure the batteries are shut off. And yes it is an 02 so maybe the pressure pump maybe a factor.

[FREIND OF AA AND TA]

Mine is going in this week for the same shiat!! They think it is a sensor or the high pressure fuel filter has caca in it. Im curious to see what the computer sais. Stand-by till Tuesday afternoon

[Beer-30]

Mine ended up being real simple - an unplugged sensor. Plugged it back in and it ran great. Mine had a constant "double-beep" ever minute. Then Guardian mode if I got around 4000. Mine doesn't have the sea pump sensor, which was first thought. All fluid levels were good. Was racking my brain, and finally took it to a Merc dealer and had them scan it. Bingo, exhaust water temp sensor code. Looked at the sensors and found the port side unplugged from the harness. I would have saved a lot of time if I had just had it scanned immediately.

[phebus]

Did you change the impeller yourself, and if so, was there a lot of scoring of the pump body? Very common that the brass gets scored, and results in a decrese in pressure even with a new impeller. Also, when you replaced the old impeller, was it intact, or were there broken vanes? If there were any broken vanes, you need to back flush the system to relieve any obstructions to flow.

[Biglue]

Did you change the impeller yourself, and if so, was there a lot of scoring of the pump body? Very common that the brass gets scored, and results in a decrese in pressure even with a new impeller. Also, when you replaced the old impeller, was it intact, or were there broken vanes? If there were any broken vanes, you need to back flush the system to relieve any obstructions to flow.
No I did not replace it myself but I did see the housing when it was apart. It was slightly grooved and the mechanic said it would probably be ok. I haven't been too comfortable with it hense the sketchyness I was talking about earlier. When I service it fir next season, I'm gonna replace the whole thing. Tired of having that on the back of my mind.
Oh and the impeller was not intact. The outdrive was removed and the system was completely back flushed.

[Biglue]

Mine ended up being real simple - an unplugged sensor. Plugged it back in and it ran great. Mine had a constant "double-beep" ever minute. Then Guardian mode if I got around 4000. Mine doesn't have the sea pump sensor, which was first thought. All fluid levels were good. Was racking my brain, and finally took it to a Merc dealer and had them scan it. Bingo, exhaust water temp sensor code. Looked at the sensors and found the port side unplugged from the harness. I would have saved a lot of time if I had just had it scanned immediately.
You know maybe this is something along the same lines. Like I said it did it to me once in Havasu and it went away. Then all of the sudden it reappreard. Maybe it isn't but it has the makings of a classic "disconnected gadget".

[phebus]

I would think if it was an unplugged sensor, it would be a constant problem, and not an intermittent one.

[Biglue]

I would think if it was an unplugged sensor, it would be a constant problem, and not an intermittent one.
I was thinking of it maybe coming loose or something.......who knows.
Beer-30 was saying that if I shut off my batteries it would erase the codes for the scanner is this true?

[phebus]

He is a knowledgable guy, and has been through it before, so I would have to say yes. Luckily, I haven't been through it.

[Beer-30]

I was thinking of it maybe coming loose or something.......who knows.
Beer-30 was saying that if I shut off my batteries it would erase the codes for the scanner is this true?
When we scanned mine, it showed a few other codes that didn't apply to my motor. We turned the perko off, then on and fired it up again. Code was cleared but re-appeared. We found the sensor plugged it in. Fired it up and found we fixed it. Turned the perko off and re-scanned. Code was gone.

[Beer-30]

Thanks Phebus. By the way, added two more Eclipses to Beer-30. Have two more to replace. I notice from a previous thread that you run Eclipse as well. Gotta love'm.

[Biglue]

He is a knowledgable guy, and has been through it before, so I would have to say yes. Luckily, I haven't been through it.
Oh well crap I was hoping to hear that it wasn't true since I'm almost positive I turned the batteries off.

[Biglue]

When we scanned mine, it showed a few other codes that didn't apply to my motor. We turned the perko off, then on and fired it up again. Code was cleared but re-appeared. We found the sensor plugged it in. Fired it up and found we fixed it. Turned the perko off and re-scanned. Code was gone.
Are you saying that after turning the perko switch on they re-appeared? Or did firing up the motor make them reappear? I'm just a little worried because the mechanic will have to go through some higher RPM's to duplicate what I saw.
BTW I wasn't try to sound like I was doubting you buddy. I'm just wondering if the mechanic will even be able to find any of the codes now that the batteries have been turned off.

[Beer-30]

Sorry. Codes are in the "volatile" part of the memory so that they clear after 50 or so starts / or / battery disconnect. Otherwise, they would just collect and keep showing trouble. :wink:

[phebus]

It seems to me that if you had an unplugged sensor, or a bad sensor, the problem would be constant. With the time I have spent on this site, it seems that the vast majority of times that people have had their 496HO go into guardian mode has been due to water temp/water pressure issues. When your mechanic back flushed your system, were all missing pieces of the impeller found? Also, was the pump scored/grooved both front and rear? The front plate can be resurfaced.

[Biglue]

Sorry. Codes are in the "volatile" part of the memory so that they clear after 50 or so starts / or / battery disconnect. Otherwise, they would just collect and keep showing trouble. :wink:
Gotcha. See NO. 19.

[Beer-30]

On mine, as soon as the codes were cleared, we turned key on and it popped up. Fired it also, but code was already there. Once again, mine was a constant "double-beep" . As soon as the key was turned on "beeep-beeep". Then, 60 seconds later, "beeep-beeep".
BTW, on mine, it would rev up to 5000 out of water. Put the earmuffs on and turned on the water. Mechanic put the stick forward and sat it at 5K for a few seconds. It appears that the Guardian power reduction only really applies to a loaded engine. If the ECM senses no load, it doesn't worry about the motor as much. I am not sure of this, but I can tell you that mine wouldn't go much above 3800-4000 in the water without Guardian kicking in. Would hit 5K w/o load.

[Biglue]

It seems to me that if you had an unplugged sensor, or a bad sensor, the problem would be constant. With the time I have spent on this site, it seems that the vast majority of times that people have had their 496HO go into guardian mode has been due to water temp/water pressure issues. When your mechanic back flushed your system, were all missing pieces of the impeller found? Also, was the pump scored/grooved both front and rear? The front plate can be resurfaced.
You're probably right. The housing was grooved slightly. But I don't remember if it was just the the front plate.
Yes we believe all the pieces were flushed back out.

[Biglue]

On mine, as soon as the codes were cleared, we turned key on and it popped up. Fired it also, but code was already there. Once again, mine was a constant "double-beep" . As soon as the key was turned on "beeep-beeep". Then, 60 seconds later, "beeep-beeep".
BTW, on mine, it would rev up to 5000 out of water. Put the earmuffs on and turned on the water. Mechanic put the stick forward and sat it at 5K for a few seconds. It appears that the Guardian power reduction only really applies to a loaded engine. If the ECM senses no load, it doesn't worry about the motor as much. I am not sure of this, but I can tell you that mine wouldn't go much above 3800-4000 in the water without Guardian kicking in. Would hit 5K w/o load.
Same with mine. I could rev up that high as well in neutral.
While it was actually under load the guardian mode kicked in around 3200rpm.

[Beer-30]

There is a manual that Merc doesn't let us non-dealers have - I think it is number 15 or 19. Anyway, it pertains to the ECM and has all the trouble shooting trees and codes in it. It has a nifty graph of what sensors and failures cause what level of Guardian. Mine was limited to "90% power". Sounds like yours may be a bit more serious and it has put you at "75%" or so.
Looks like you will have to run it in the water, and then take it to be scanned. It will help you in the long run, though. No more guessing.

[Biglue]

There is a manual that Merc doesn't let us non-dealers have - I think it is number 15 or 19. Anyway, it pertains to the ECM and has all the trouble shooting trees and codes in it. It has a nifty graph of what sensors and failures cause what level of Guardian. Mine was limited to "90% power". Sounds like yours may be a bit more serious and it has put you at "75%" or so.
Looks like you will have to run it in the water, and then take it to be scanned. It will help you in the long run, though. No more guessing.
Sounds like you may be right. I'll post what outcome I have for the rest of the forum to see. I will call up the mechanic again and get his input and advise.
Hey Guys thanks again for the input. It gives you some direction as to what approach I have to take.

[Beer-30]

Hey Guys thanks again for the input. It gives you some direction as to what approach I have to take.
No problem. Hope all turns out well. Let us know.

[Biglue]

No problem. Hope all turns out well. Let us know.
Sure will bro.

[DeepVee]

Check your batteries and battery cables. My HP500 started cutting out above 4500 RPM's this summer. It ran fine out of the hole up to 4500 then the motor would shut down and come back on, shut down & back on until I backed out of the throttle. I was sure it was fuel or sensor related but turned out my battery cables were loose from changing batteries over the winter. These cables were not jiggle loose; they were snug but I could turn them by hand when I grabbed the cable. I cranked them down tight and the problem went away. Must have been loosing the ground in my case. Good Luck.

[Biglue]

Check your batteries and battery cables. My HP500 started cutting out above 4500 RPM's this summer. It ran fine out of the hole up to 4500 then the motor would shut down and come back on, shut down & back on until I backed out of the throttle. I was sure it was fuel or sensor related but turned out my battery cables were loose from changing batteries over the winter. These cables were not jiggle loose; they were snug but I could turn them by hand when I grabbed the cable. I cranked them down tight and the problem went away. Must have been loosing the ground in my case. Good Luck.
A guy in our party at the lake said the same thing. I just remembered that. Thanks for bringing it up.

[daytona22]

i have the same motor - had a similar problem - small debries got pulled up thru drive into both oil cooler and heat exchanger for motor - took both apart, cleaned out debries, problem gone. motor never showed abnormal temp or oil pressure - restricted flow will heat risers, causing this w/o killing the motor - runs unloaded because it doesn't need the flow like it does under load - merc shops that sell lots of 496's will clean these out any time they do the impeller because it is easy, cheap, and a known problem spot in these motors

[Havasu47]

We are a Merc. certified premier dealership.
Error codes are stored in the ECU. Turning off the batteries will not clear codes. They have to be cleared through a scan tool.
The 496 is very complex and does not always store a code for problems. Everything you have been told to check so far is a possible cause. Check the gear lube reservoir level also.
Good luck.

[Biglue]

We are a Merc. certified premier dealership.
Error codes are stored in the ECU. Turning off the batteries will not clear codes. They have to be cleared through a scan tool.
The 496 is very complex and does not always store a code for problems. Everything you have been told to check so far is a possible cause. Check the gear lube reservoir level also.
Good luck.
Thanks.

[Beer-30]

We are a Merc. certified premier dealership.
Error codes are stored in the ECU. Turning off the batteries will not clear codes. They have to be cleared through a scan tool.
The 496 is very complex and does not always store a code for problems. Everything you have been told to check so far is a possible cause. Check the gear lube reservoir level also.
Good luck.
I must not have seen him clear with the tool (?). Hmmm. Could've sworn all we did was kill power. Oh well.
When we emptied my reservoir to check that sensor, it screamed right away. He should have an instant alarm, if it's a PCM555 like mine.

[SnakeWrench]

Theres a few hundred things it could be. One thing is water pressure. On the 496's, the brass impeller body doesn't like the impeller being changed and it can have enough water to keep it cool but not enough to satisfy the ECU. I have had many, (more than a dozen) failed water pressure senders. I have also had heat exchangers full of rocks that will keep the water pressure too high.
He's another dumb one, the power steering pressure sender has gone bad before and caused a gaurdian, but it doesn't set a hard code. Good luck.
Any other questions, feel free to e-mail me. flyinggreek84@adelphia.net

[Biglue]

Thanks Snake wrench.
Boat is in the shop and will know something later on today.

[PHX ATC]

Sensor.
Maybe a sensor or the wiring harness...check all the "pins" that connect into each of the sensors. I had one crankshaft sensor (actually the portion on the wiring harness that plugged into said sensor) that had a few pins bent from the factory. Merc ended up replacing the engine over this as nobody could figure it out.
Just a thought.
Toby

[Starloans]

I have a 525. I don't know if your Ho has the same equipment but I had the same prob. There is a sensor on the gear linkage right on top of the motor. If the motor has been pulled or worked on this sensor could have been bumped and cause it to malfunction. Basically, there is a button that is in a valley when the gear is in neutural. When you go to forward or reverse the button is pushed in and allows the engine to go above a certain rpm. I guess this keeps from overreving in neutural. If the button is out of adjustment and not being pushed in all the way you will not go fast. :cry: There are two phillips screws for adjustment. Check this sensor. I don't think you can bypass it by upplugging it either. I'm pretty sure the button has to push in. Mine would not go about 3500 rpm. Everything else was fine. Make sure you don't over adjust or the button will always be pushed in and you may damage the engine. Pissed me off bad especially to find it was a simple thing. Let me know what you find. Good luck. No I'm not a mechanic but I did stay at a Holi.......never mind. :smile:

[Biglue]

Hey Beer30. Maybe you were right about the shutting down the batteries. I talked to the mechanic and he couldn't find any active error codes. He may have to put it up to a dyno he said to duplicate what I was seeing. That's the latest on it.

[Beer-30]

Hey Beer30. Maybe you were right about the shutting down the batteries. I talked to the mechanic and he couldn't find any active error codes. He may have to put it up to a dyno he said to duplicate what I was seeing. That's the latest on it.
I was pretty sure that was how mine went. As I said, I didn't watch him 100%. I had left for a moment and he told me he turned the batts off, which cleared it, and it popped up again.
Anyway, I hope he takes it easy on you on the dyno thing. Time on those can get pricey. You guys don't have a nearby body of water to run it?

[Biglue]

I was pretty sure that was how mine went. As I said, I didn't watch him 100%. I had left for a moment and he told me he turned the batts off, which cleared it, and it popped up again.
Anyway, I hope he takes it easy on you on the dyno thing. Time on those can get pricey. You guys don't have a nearby body of water to run it?
The nearest lake is about an hour away. The ocean is 20 minutes away but I don't know about doing the salt with the boat.

[wantacat]

We are a Merc. certified premier dealership.
Error codes are stored in the ECU. Turning off the batteries will not clear codes. They have to be cleared through a scan tool.
The 496 is very complex and does not always store a code for problems. Everything you have been told to check so far is a possible cause. Check the gear lube reservoir level also.
Good luck.
I trust this guy:D:D my boat is actualy at his shop for somewhat the same problem.

[Biglue]

I trust this guy:D:D my boat is actualy at his shop for somewhat the same problem.
What RPM's is your's going into guardian mode at?

[Biglue]

Here is the latest.
The mechanic couldn't find anything wrong or code when he scanned the ecm. He said mybe it was bad gas causing the knock back sensor to act up. We drained all the gas out and replaced with fresh high octane crap........Nothing.
He rigged it up with some more diagnostic stuff and had me push a button when it failed to see if he could scan that for any failures the ecm is not storing. I have to take it back in tonight to have it re-diagnosed.
I'll post the next episode when I have it.
Thanks again guys.