cigrocket

iTrader: (3)

My buddies planned fast without hesitation, so you definitely have an issue going on, I assume it is going into some sort of guardian mode. Plugging in will hopefully figure it out.

bigredbaja

my boat is not a Baja but I am on my third 496 boat and I experienced the exact same thing last spring with my current 32 Sunsation....took for ever to get on plane port motor would barely break 4000 RPM. Changed plugs that evening on both motors and fixed the problem boat runs as it should now and have not had any more issues. I experienced a similar problem on my 288 several years ago except you could hear the single engine make a popping noise out of the exhaust. Check it with a scanner just to be safe but plugs are a safe bet.

BUP

iTrader: (9)

gen 3 COOL FUEL and the paint and the injectors --- 1000 percent one of the issues on top of other issues with these 496s.

The 496s all have common issues thru out the years.

2006 OEM had gen 3 cool fuel but again engine serial number will show exactly the parts installed.

engine serial numbers are a must

if in fact GEN 3 cool fuel is on this app - I would bet there is some of the issues with the rails the fuel pumps - the regulator the injectors - I bet on it and for the ones I have taken care of on this board they surely know as well in the 100s of videos I have provided them.

c0ncEpT

Any alarms? Check for a partial guardian mode. 80-90% allowed power would probably only let it get to the mid 4,000RPM's

Knot 4 Me

As stated above, could be as simple as plugs. I had two reduced RPM issues with my 496. Once was the number 2 plug wire fell off the plug. Second was at 300 hours one of the plugs shot craps. Both times RPMs at WOT were down about 300 - 400 RPM. Regardless if it turns out to not be plugs I'd replace them anyway as they are due. I'd do the wires as well given the age. BUP can set you up on the wires. Cheaper and better than Merc.

BUP

iTrader: (9)

Thanks ^^^^^^ have all that plug wires and the plugs ready to install.

Do not rule out the GEN 3 cool fuel paint peeling and injectors

when was the last time the fuel filters have been changed and the water collector checked ???

Will agree plugs and wires

AND the crank position sensor

and lets not forget the dreaded IAC and the IAC needs the proper on time maintenance needed to keep that alive and the PCM alive.

Bad IAC and or restriction in the IAC system will knock out your pcm. FYI no bull

cigrocket

iTrader: (3)

BUP

iTrader: (9)

Just wanted to add -- There can be misconceptions about scanning marine engines - Just some info to pass on --- A scan will not show any fuel related issues nor will it show fuel pressure and only half the time will show a completely bad IAC and there is a reason for that - does anyone know why ? Yes there is a reason why that happens.

A scan will not show a crank sensor signal going weak / bad until it goes completely bad with NO start - no tach or stalls the engine on its own. Its not going to show weak spark output either. Its not going to fault code for incorrect timing.

Next info - The very first gen 496 s did not have crank and cam sensor fault codes -

Since the IAC is one of the most failed - what is the parameters of the iac at start up and at IDLE and off idle to full throttle for this 496 ? How does the 496 IAC operate and what is it call for operation ? This can help to figure out if the IAC is an issue or not

Scanning will not show a fault code if all those parameters are off for the IAC and like I said, a completely bad IAC will not show all the time..

Maybe some trivia for whomever to play along and think about, Hopefully help figure stuff out when scanning because there is alot more to it than looking for any fault codes listed..

'Just throwing out some questions if anyone wants to play along.

Is the IAC a sensor and is the IAC a 5 V ref part ?

how do you check if your guardian mode ?

what is the fault code and fault number for drive lube bottle

what does it mean when a fault code list Hi or Low ?

What would cause a MPR output fault ?

what does this fault mean MAP idle err

WHY does an overspeed fault code show at 3500 rpms when the MAX recommended engines rpms for the 496 HO is 5000 K rpms and for the 496 MAG is 4800 rpms ? How can that overspeed fault ?

How many fault codes are there for Mechanical T & S PCM 555 for the 496 ? Is there more fault codes for the 496 HO than the 496 MAG ?

Just to get some thinking about what can show up when scanning and possible to focus on.

cigrocket

iTrader: (3)

Wasn't saying that plugging in was definitive. I was just saying that some things can be eliminated and narrowed down. Baseline information. Then I usually start with easiest/cheapest and work from there. I would look at fuel and water separators,plugs, and wires after scanning if nothing found.

Mikeb6871