496 Mag/HO Newbie Help! Please!
 

Hi guys, I am new to the forum however I have always lurked around reading up on your good info! I have a problem with my 2002 29' Envison with a 496 mag. I have had a worry free 100 hours of service over the past seven years but now things have gone amiss again! When I bought the boat new in 01 I had to have mercruiser replace the motor since it was one of the very first editions and I broke off all the pushrod tops! My experience was a little jaded since the local performance marine shop here in Tulsa screwed it up royally! The boat ended up in Stillwater (short drive) where the techs replaced the motor. The shop is now out of business and I am a little leary of who to take it to!

Now for the meat of the problem! I do have LS motor experience in my hotrod but nothing on boats! I was running pretty close to wot last summer when all of a sudden the boat took a nose dive (single drive). It felt as it someone jerked the throttle back and I lost about 600-700 rpms. The boat starts and runs but has no power under load. I finished the weekend off and parked it for winter in the shop! I can hear the fuel pumps kick and my exhuast is always open. Could the computer have thrown me into 'Guardian' mode? Is there a possibility it is the dreaded crank sensor everyone talks about? Is there a way to test the crank sensor? Also what is the proper scan tool for this motor and where can I get one? The boat did not come with the smart craft readout and I am getting no warning beeps from the boat. Thanks for any help you can give me!

Shawn Tillotson
Split Decision Customs
Owasso Oklahoma

I felt I needed to add some info on the problem for the best help possible!

* No audible alarms, just the normal beep when the key is turned on

* Running in normal operating temp

*Normal oil pressure

*All fluids are checked out

*Had an new seapump put in about 45 hours ago at the dealer in lake of the ozarks

*RPM normal at WOT is 4950, currently will not exceed 4400.

*Lack of power occurs all the time, from try to get up an plane and at plane

*Motor sounds a little rich at idle, not as crisp as usual (possibly a coil?)

Thanks again for any help!

Fuel pressure? Do you think you could be running short on gas at higher rpms? There is an in line strainer on the side of the pump that caused me some trouble.

I wouldn't even guess without scanning it. Pay the diag fee (usually 1 hr) and see what the ecm has to say.

You should get an alarm if it were in Guardian Mode. If you are not getting an alarm, a scan may not tell you much. You might try changing the fuel/water seperator and checking fuel pressure.

After reading his post again I doubt it's the fuel issue I talked about as he says it isn't coming out of the hole either. My problem was she ran fine for a few seconds til she started starving for gas and would run but just seamed off of what it should have. After you would bring it back down or shut it off it could recover and would run fine again until you got back in it. This was also an 01 ho and if my memory serves me right my preasures would run around 42 psi and then drop to about 8.

First off, fixing a computer controlled engine without a scanner is like using a computer without a monitor. It can be done, but its not efficient.
Stupid question, have you checked your throttle cable? Is the throttle working properly?

Here is the rinda scan tool:
http://www.rinda.com/marine/marine.htm
I think its about $400
I'm going to buy one this summer

The throttle and cable attachment at the motor was the first thing that I checked. All seem to be going in the full range of motion. 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? I will check the fuel pressure when I get over to the shop, but it will have to be a static check with snow on the ground here there will be little chance to get to water. I have no strainers in the fuel pumps after fighting a huge fuel pump problem after the new motor in 2001. Ended up my pumps were getting clogged up from fibers coming from a leather welding glove in my fuel tank!!!!

A side note question.

How were the fibers from the welder's glove getting past the water seperating fuel filter that the fuel flows through first before getting to the first fuel pump?

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).