Sydwayz

iTrader: (1)

Take the flame arrestors off.
Leave the engines off.
Pin the throttles on the dash.
Are the monoblades opening all the way to perpendicular with the tube of the intake plenum?

You can also use the Rinda scanner to check what the Throttle Position Sensors are telling the computer. I would check this also.

I had some weird RPM problems this summer, and it turned out to be a bad Crankshaft Position Sensor. No codes were thrown.

airjunky

iTrader: (2)

And I think some 496 ho ecms will cut the rpm around 3000 or so if it thinks drives are not in gear

BUP

iTrader: (9)

Only if his 496 has the shift in gear switch as the PCM then can see if it is in gear or not. The poster never posted his serial #'s. Hense 2004 / 2005 is the year it was entered into the motor in which all marine apps and their parts and their service procedures go off of serial # runs. A 2001 496 is not the same as 2004 / 2005 496 nor is 2008 496 same as either and nor is 2010 496 the same either. Fuel systems changed. coils changed, intake manifold gaskets changed, exhaust system changed, shift in gear switch added and so on. Engine serial # tells what exactly he has and the set up.

What is your fuel pressure readings thru out the rpm ranges ? Is this boat saltwater app ? It is a small chance but possible that something that does not link both engines together making both engines have the exact same issues at the exact sametime.

Common logic says, Fuel related or a voltage or a corrosion problem of some sort. Do you have the shift in gear switches ? They would be located on your shift plate but still hard to believe that both went out or are misadjusted at the exact same time. The earlier crankshaft sensors where a problem child a lot as well even for the auto / RV side using a 496, I would believe that one. I would check your fuel pressures for testing purposes to either rule it as a problem or not.

next while scanning the engines what is your available power showing on your scan tool ? if it says 100 % then you are not in guardian mode. Do you have any warning horns - ever ? Also the sensors in the exhaust manifolds would be another area to look into, they are called EMCT = exhaust manifold (circuit) temp sensors.

IMO I REALLY think you have a 5 v sensor circuit problem or the wire harness(es) of your 5 v sensor circuit being the problem. Or your fuel tank / gas was junk & crap ran thru both motors causing fuel related problems to both motors at the exact same time causing your issues. Or the sensor(s) in the exhaust manifolds bad. EMCT

dbkski

iTrader: (1)

Hey BUP is this what you are looking for?

sutphen 30

I know on the earlier models you could just unplug them and go,,is this the same on the later?