496 Mag/HO Newbie Help! Please!
03-10-2008, 03:10 PM
#11
Registered
Do a comp check...Sounds like a rocker nut backed off or a broken push rod...That will kill the power and you would be running on 7 cyls. That would not throw any codes either. (it might be and easy fix. Pull the valve cover and fix it)
03-10-2008, 05:26 PM
#12
Registered
When this first happened I was running perfectly at 4900 rpm , but as I said it was as if someone threw out an anchor. There was an immediate RPM loss that I have not regained since. Is there such thing as soft faults vs hard faults on an 01 496? Will soft faults not sound an alarm an put it in a minimal guardian mode?
With a hard alarm (constant beep) there can be an additional reduction in Available Power, and depending on the fault, it could go as low as 0% (engine shutdown).
You said that the WOT RPM dropped to 4400, which is exactly where 90% Available Power would put you. However, you should get an alarm and your performance at idle would not be affected. But don't get me wrong, I completely agree with the guys above who say that a scan is the best place to start.
I think you would have heard it if you had a rocker nut back off or broke a pushrod, but you could have dropped a cylinder for some reason, either mechanical, ignition or fuel.
03-10-2008, 05:58 PM
#13
Gold Member
Gold Member
Not a CKP, you would have a no start condition if the CKP was toast. It sounds like a non-critical sensor has "failed in range" meaning you will have no alarm, but possibly have a sticky code set which has limited your RPM range and does not sound an alarm. Could be a CTS, or an ETS, but definetly not a CKP.
If you want a scanner for yourself get one from:
http://www.rinda.com/marine/marine.htm
Get the Mercruiser Scan Tool, and you can scan your motor, and all your buddies motors too, as well as reset your IAC's, and perform a variety of other diagnostic and maintenance issues.
If you want a scanner for yourself get one from:
http://www.rinda.com/marine/marine.htm
Get the Mercruiser Scan Tool, and you can scan your motor, and all your buddies motors too, as well as reset your IAC's, and perform a variety of other diagnostic and maintenance issues.
Last edited by Trippin; 03-10-2008 at 06:00 PM.
03-11-2008, 01:22 PM
#14
Platinum Member
Platinum Member
Join Date: May 2003
Location: newbugh ny
Posts: 2,177
Likes: 0
Received 0 Likes
on
0 Posts
Take a second and check your plug wires. My boat had the same symptoms last year and it was because a plug wire had fallen off the number 4 cylinder. Most likely not the problem but easy enough to check and eliminate. I also had a fuel pressure problem when my boat was new (bad booster pump) and I could not even begin to get my boat on plane with low fuel pressure (17 lbs. as it was trying to roll onto plane).
03-11-2008, 01:38 PM
#15
Registered
Join Date: Jul 2005
Location: Tulsa, OK
Posts: 1,729
Likes: 0
Received 0 Likes
on
0 Posts
Being in Owasso, I would say take it up to Morton Marine. They are mostly a bass boat dealer, but also sell runabouts with the merc 496 and HO engines. They are a certified mercruiser service center. I had them winterize my boat in 2006, and they also helped out with getting my boat on its new trailer in 07. They have always treated me right and are good guys. If your engine is stock merc, take it by and have them run a scan.
If it isn't stock merc, I'm not sure who I'd send you to. My engine builder, Brad Smith, is in Joplin, and does a huge amount of high end marine engines. If you want to go that far, give him a shout.
If it isn't stock merc, I'm not sure who I'd send you to. My engine builder, Brad Smith, is in Joplin, and does a huge amount of high end marine engines. If you want to go that far, give him a shout.
03-11-2008, 08:45 PM
#16
Charter Member
When a Fault Code is set there should be a soft alarm (two beeps per minute) and there will also be a reduction in Available Power (Rev Limit) to 90%.
With a hard alarm (constant beep) there can be an additional reduction in Available Power, and depending on the fault, it could go as low as 0% (engine shutdown).
You said that the WOT RPM dropped to 4400, which is exactly where 90% Available Power would put you. However, you should get an alarm and your performance at idle would not be affected. But don't get me wrong, I completely agree with the guys above who say that a scan is the best place to start.
I think you would have heard it if you had a rocker nut back off or broke a pushrod, but you could have dropped a cylinder for some reason, either mechanical, ignition or fuel.
With a hard alarm (constant beep) there can be an additional reduction in Available Power, and depending on the fault, it could go as low as 0% (engine shutdown).
You said that the WOT RPM dropped to 4400, which is exactly where 90% Available Power would put you. However, you should get an alarm and your performance at idle would not be affected. But don't get me wrong, I completely agree with the guys above who say that a scan is the best place to start.
I think you would have heard it if you had a rocker nut back off or broke a pushrod, but you could have dropped a cylinder for some reason, either mechanical, ignition or fuel.
__________________
[img][/img]
[img][/img]
03-11-2008, 11:09 PM
#17
Registered
Join Date: Jan 2007
Posts: 1,667
Likes: 0
Received 0 Likes
on
0 Posts
I think you would have heard it if you had a rocker nut back off or broke a pushrod, but you could have dropped a cylinder for some reason, either mechanical, ignition or fuel.[/QUOTE]
I had a rocker nut back off completely and there isn't a sound except a very slight rough idle. Only loss of rpm down about 300 -400. Motor "carried" very well as a friend put it. Would even plane and run very fast on 7 cylinders.
I'm not at all saying from a distance that this is your problem. I am saying however, that it could be the problem and your description matches my past symptoms.
Good luck & borrow a scan tool
I had a rocker nut back off completely and there isn't a sound except a very slight rough idle. Only loss of rpm down about 300 -400. Motor "carried" very well as a friend put it. Would even plane and run very fast on 7 cylinders.
I'm not at all saying from a distance that this is your problem. I am saying however, that it could be the problem and your description matches my past symptoms.
Good luck & borrow a scan tool
03-12-2008, 03:07 AM
#18
Registered
Thread Starter
Join Date: Mar 2008
Location: Owasso Oklahoma
Posts: 6
Likes: 0
Received 0 Likes
on
0 Posts
Being in Owasso, I would say take it up to Morton Marine. They are mostly a bass boat dealer, but also sell runabouts with the merc 496 and HO engines. They are a certified mercruiser service center. I had them winterize my boat in 2006, and they also helped out with getting my boat on its new trailer in 07. They have always treated me right and are good guys. If your engine is stock merc, take it by and have them run a scan.
If it isn't stock merc, I'm not sure who I'd send you to. My engine builder, Brad Smith, is in Joplin, and does a huge amount of high end marine engines. If you want to go that far, give him a shout.
If it isn't stock merc, I'm not sure who I'd send you to. My engine builder, Brad Smith, is in Joplin, and does a huge amount of high end marine engines. If you want to go that far, give him a shout.
03-12-2008, 03:08 AM
#19
Registered
Thread Starter
Join Date: Mar 2008
Location: Owasso Oklahoma
Posts: 6
Likes: 0
Received 0 Likes
on
0 Posts
Sunday I will pull the valve covers off and see what I can see, I just hope the gaskets are reusable. I am also going to pull the plugs and ohm the wires also and also check the fuel pressure statically sitting in the shop with the motor running.
