mosesw

Hello,

I have a 2004 24' Ultra Stealth with a 496 HO. I am having an issue with the motor shutting off on me, it happens at different times and speeds. This weekend I was pulling a wake board and when I throttled down to pick them up it just shut off. The motor cranks, I can hear the fuel pump kick on but will not start. I got towed in, I anchored up and waited about an hour low and behold it fired up. The rest of the day it ran fine. Then when I was pulling up to the trailer it died again and had to swim it in.

The problem seems to be during slowing down or throttling down. As it has done this a hand full of times while pulling up to the shore to anchor up. I took it to a mechanic they thought it was a water line (they replaced) and the kill switch was not flipped up. I know the switch was up as I switched it on and off several times to ensure it was not it.

I load tested the batteries last year (good), I did not see any loose connections.Any suggestions?
Kind of knew to this any help would be greatly appreciated!

Questofpower

Idle air control (IAC) common failure on the 496HO had to replace one of mine last year. A very easy fix, takes about 10 min the replace, get a gasket as well. The clue is you are having a problem coming back to idle or powering down, that's its function. A friend of mine works for merc, and has done testing on these for about 4 months recently, the spring fails in them, merc has asked hitachi (thats who makes them) to use a better spring, but I am not sure where that is sitting right now. Anyway search 496HO IAC on OSO and you will find the same problems you are describing.

What happens is the spring sticks or breaks and then the unit over heats.

[ATTACH=CONFIG]502863[/ATTACH]


If you look at the one on the right you will see a little piece of plastic sticking out on the bottom right hand side this is the failed one. This is melted plastic. The one on the left is new.

mosesw

Thank you Questofpower. I will look at this today.Would this keep the boat from starting back up after shut down? Or could this just be the cause of shutting off?

Questofpower

It's possible if it is stuck in a funny position, are you hearing any really faint 2 beep alarms? By the way you have to pull the 496 plastic cover off and it is located at the very back of the motor under some wiring.

mosesw

Yes, I am hearing a 2 beep alarm every 1-3 minutes. I did not time them out, but it is definitely within in this time frame.

Sydwayz

iTrader: (1)

More than likely IAC.

But I highly recommend buying a scanner for that engine. It is money very well spent. More info on this thread:
http://www.offshoreonly.com/forums/g...-525-help.html

Reckless32

2 chirps every minute is called a "soft alarm" meaning a non-critical issue so the engine lets you know about it AND will reduce the engines performance by 10% hence if you went up around 4k rpm's or more it probably started to hiccup as it won't let you go that far. Plus if you did it go full alarm and you would have to back it down to around 1100 rpm for it to go back to 2 chirps.

Typically the symptoms happening down in the low or idle rpm range will be the IAC. Very simple to change and is located up top at the rear of the motor towards the starboard side near the throttle linkage. Follow the hose from the intake back to the IAC. Only remove the top and not the spacer.

The IAC like on any vehicle, is a worm gear that opens/closes allowing/not allowing air flow into the intake to assist with idling. Yours sounds like it shot but not completely yet. Wen it is it may start for about 60 seconds then the motor will stall out and yes you will have to wait a bit to even get the 60 seconds again. If you were a twin setup you could easily swap it out to confirm it.

There are three things specific to the 496 an owner should keep in stock (in addition to other ready service parts) on the shelf in the shed or in the boat when on a roadtrip along with the associated hand tools and those are:

1. Fuel separators
2. Boost pump
3. IAC (idle air control)

mosesw

Thanks Quest, Sydwayz, and Reckless32.

I took the boat over to the local mechanic and they hooked up to the scanner / computer. They were able to clear the first code (Sea Pump), said it was a loose connector. Should I just replace the IAC even though it is not throwing a code? Again thanks for all your help!

Fault# Description Active Source
36 Sea Pump Pressure Circuit High YES PCM03
94 Pitot Pressure Circuit Low YES PCM03
75 Fuel Level 1 Circuit High YES PCM03
118 Steering Position Circuit High YES PCM03
191 Fuel Level 2 Circuit High YES PCM03

TWIN-SPINS

yes replace iac

Questofpower

I still would, none of those should be shutting the motor down, putting it into guardian mode yes, but it should not shut it down. The IAC is going to be the most likely cause. Have you had any over heating issues?