Sunsation25NY

200hrs needed a tune up it has been sitting.. Plugs were fouled, starboard side were wet and smelt like fuel. Port side were dry and looked a little better but still poor condition. I replaced plugs and wires also dumped a few pints of seafoam in the fuel and filled up the tank with fresh fuel. The first few hours what looked like steam was coming out of exhaust much more noticeable on the starboard side now it has eliminated. Fully loaded it stumbles getting up on plane and has a slight miss at idle and motor vibration at low rpms. Every time I run the boat it does seem to get a little better like its clearing itself out... I can only get to about 4400-4500 RPM trimmed up with 1/4 tank fuel before the boat would hit 5000 RPM. I have never had any alarms. Any ideas where to start? If I need to buy the Rinda Diacom software to diagnose I will. That's the only way to properly test the ignition system correct? Thanks!

Wasted Income

Do your guardian buzzers beep at key-on? (to self-test so you know they're working?)

If so, are you getting any beeps while running? Might be in guardian protection, allowing only 90% or less power.

My last Sunny with the 496...I didn't realize that the buzzer was broke, and the IAC was bad when I got it. Would only turn around 4400-4500 like yours, then felt like it was breaking up/misfiring....because it was....because of the guardian power limit.

I didn't realize it at first, and changed out a bunch of stuff in the meantime...boost pump, fuel filters, plugs, wires...none of it helped, until I finally scanned it and facepalmed myself. lol.

Get a scanner on it and go from there.

Sydwayz

iTrader: (1)

1) I would buy the www.rinda.com Techmate regardless. You are going to need it one day, guaranteed.
2) I agree on above, are you getting beeps when you start?
3) The Crankshaft Position Sensor can go bad without throwing a code/alarm, and it can rob you of RPM.
4) Are you sure you are running the right prop? If you just bought the boat, it could have any old prop thrown on there for the sale.

Sunsation25NY

Velocity 280 26p bravo one 62mph 4500rpm 16% slip. Under a heavy load getting on plane it definitely sounds like it's breaking up that's the only time I notice it. Prop is nicked slightly I'm going to send it to bblades once I get this figured out. I get a one second beep when I turn the key to the on position that is it. Same as my previous boats. I was going to go with the Rinda Techmate Pro ($500) but I think for an extra $79 the Rinda Diacom ($579) PC software is the way to go much more versatile.

Trippin

In response to your private message. I'm not a mastertech, only multi-line certified, including Mercury sterndrive racing and outboard racing credentials. But I have dealt with another 496 with those exact same issues, unfortunately the #5 & 7 cylinders were compromised. Once I did a compression check on the engine and discovered that problem I quit and informed the customer of the issue. He came and got the boat, disgusted as he had just bought it I think he took it to the lake and cut his losses. Anyway, I would start with basic checks first, like checking for water in the fuel system, the scan tools are nice but they don't tell all. One other thing, quit using sea-foam, cheers!

monster12valve

I would look at the TPS or injectors. I had same issue with a 502... And the builder broke an injector lead off... And it was running on 7

Sunsation25NY

Got the Rinda Techmate Pro.. No faults ran fuel injector and ignition coil test everything came back good.. Pulled the plugs all looked good except cylinder #1 was BLACK. Compression test found cylinder #1 at 50lbs all other cylinders around 140lbs.. No water in oil, no oil consumption, oil pressure at idle = 40psi WOT = 55psi temp stays at 160deg... Before I tear it down what could be the culprit?

Sunsation25NY

OK I'm bringing my thread back to life... My boat ended up needing a valve job. Its running 100% on all 8 now. My spark plugs look perfect. But my WOT RPMs are still about the same.. I can only hit 4600 RPM while others with the same setup hit 5000 RPM. The power feels great getting on plane etc... I have a slight rough idle too, the boat does not stall out. I'm thinking IAC to resolve that. Maybe crankshaft sensor for my low WOT RPM? Once again no alarms to report. Thanks!

BUP

iTrader: (9)

your PM made me laugh anyways. Many things can make a lost for rpms.

First since your heads were done - did anyone test the fuel injectors ?

Which cool fuel do you have ?

Your fuel pressure psi thru out all rpms is ?

Your ignition firing strong and on all 8 -- how is the spark plugs ? and their gap ? coils and wires ? All wires connected solid to the spark plugs ?

Scan testing ? All parameters in spec ? and are they known what they should be by the person scanning ? Just because one has a scan tool and no faults showing means 100 percent nothing.

the TPS reading at WOT is ?

does your throttle plate open all the way completely ?

Crank sensor can 4 sure be an issue for lost rpms

prop correct pitch and condition ?

Hull bottom condition and spotless clean ?

the outdrive in perfect shape no damage ?

hull carrying extra weight ?

Last words ---- The fuel injectors especially in 496 s NEVER come into me clean nor balanced flow volumes. I am telling it straight up --- I have NEVER seen a set of 8 fuel injectors that were perfect again NEVER. They suffer from too many sources that contaminate them especially in 496s. It happens and there is no way around it.

Never was determine your year model nor engine serial number. SO much info goes of off engine serial number that 99 percent boat owners do not know this period. Engine serial numbers are extremely important. Can never stress that enough.

Case in point a 2001 496 is not the same as 2004 nor 2006 nor 2008 nor a 2010. None of those years the 496 was ever the exact same. A 2010 496 is so different than 2001 that at least bare min half the engine does not even have the same parts on it. So many changes throu out the years. But all of this and the changes go off serial number ranges.

OEM stock 496 HO ===== 5 K max rpm rev limits at 5150 stay away from 5150 - these engine stock do not make any power at 5100 and up rpms anyways.

Sunsation25NY

First since your heads were done - did anyone test the fuel injectors ? No

Which cool fuel do you have ? (2002 496) Cool Fuel II - Fuel / Water separator is new. I plan on cleaning the boost pump screen.

Your fuel pressure psi thru out all rpms is ? Can I check this with Techmate Pro?

Your ignition firing strong and on all 8 -- how is the spark plugs ? and their gap ? coils and wires ? All wires connected solid to the spark plugs ? Replaced plugs and wires, gapped to .060". Plugs look great.

Scan testing ? All parameters in spec ? and are they known what they should be by the person scanning ? Just because one has a scan tool and no faults showing means 100 percent nothing. I cannot data log with the Techmate Pro, correct?

the TPS reading at WOT is ? I'll have to check this as well, Techmate Pro?

does your throttle plate open all the way completely ? I actually adjusted this yesterday as i had 1/4" of slack left in the cable at WOT. I did not pull the flame arrestor to confirm yet.

Crank sensor can 4 sure be an issue for lost rpms

prop correct pitch and condition ? Yes stock bravo 26p good shape not perfect

Hull bottom condition and spotless clean ? Hull is clean.

the outdrive in perfect shape no damage ? Outdrive is in good shape, skeg guard on it im thinking previous owner took a chunk out of the skeg..

hull carrying extra weight ? Tested with 1/2 tank fuel two passengers empty cuddy no coolers etc no extra weight

BUP - I appreciate you taking the time to help troubleshoot my issues. I do have the new version Techmate Pro and only used it once to check for codes. I see other people posting live data but I do not believe this is capable? Could someone give me values to go off of so when I scroll down the list of sensors I can confirm everything is within spec? Thank you.