So I'm having an issue with one of my motors. All fluids ,pressures and gauges are reading fine it for some reason when I first take off I get an alarm and the one motor goes into guardian mode. My scan tool says engine over speed. I'm only at like 3500 Rpms. Today it happened at 4200. My scan tool says engine over speed. I already changed out the neutral safety switches and no dice! I'm stumped! Any ideas???? Thanks!

Are you keeping an eye on your tachs when this happens? Almost sounds like your spinning a hub or coupler. I use Powertech props with cushion lock hubs and when they slip, even for the short time till they lock back up, the overspeed sends it in to guardian mode.Good luck!

Tachs are staying even at 3500

not enough info here - need year model and engine serial #. All set ups go off of engine serial #.

a 2001 496 is not the same as in 2004 nor in 2008 nor in 2010 - they all have the same block but many things change during engine serial # runs ie: fuel set ups, crank and cam gears and sensors, ignition coils, PCM programs, Shift in gear switch, DTS, Catalyst and so on and so on.

Anyways if you have a 2004 year model engine or close to that timeframe, it should have a shift in gear switch - if it does, IMO it is bad or shorted or out of adjustment causing your problem.

here is why if you do have that switch.

The engine is in forward gear running down the lake but the input the PCM receives from the shift in gear switch is incorrect as saying (output) in Neutral - so these ECM / PCM 555 controllers set an overspeed fault code in Neutral at around 3500 RPMs and put it into Guardian mode as well. Guardian Mode will not allow the RPM's to advance any further.

back to the question - early early 496 2001 thru 2003 did not have the shift in gear switch. Not knowing what you exactly have - the SIGS is my best guess to your problem.

It's a 2003. Where would that switch be located?

On the shift cable bracket . Look up Mercruiser parts to what it looks like and look up per your engine serial #.

2003 still does not tell me if you have one or not. 2001, 2002 did not have them at all, I think late 2003 did if not it was 2004 model runs. it all goes by engine serial #. This is the same in the auto would a 2001 Vette engine is not the same as 2014 engine OEM factory stock.

I do not have one. One thing I did find is water pressure on that motor islow compared to the other

Ever figure out what happened here?

Having the same issue on my 2005 6.2s. Replaced the shift switch on the trouble engine and still getting over speed. Not so sure about the wiring going up to it, it has been spliced but I don't know what I need to see on my multimeter to test it.

Hi all,

I have the same overspeed alarm on my engine (496 ho) as from 4000 rpm. Any idea of what it could be?
Engine was reaching 5000 rpm normally. Now max rpm is 4500...
temperature is good 69-70 degree celsius.

Many thanks for your help!🙏