Mercruiser ECM 555 Timing

[Boater Jim]

I have a 2003 Maxium with a 5.0 MPI Alpha Mercruiser. It is controlled by a 555 ECM. I seem to have an issue with the timing. I have a scan tool and the scan tool tells me the timing is going to as much as -12 BTDC at idle, but mostly about -4 BTDC. I have confirmed this with a timing light, so the scan tool is correct. With the engine off and the key on, the base set point is 8 BTDC, which is the correct base set point. So my question is this....is it normal for the ECM to retard the timing that much at idle? IMO it should never fall below 8 BTDC. I have been told by someone that referred to himself as an expert on the 555, that this is in fact normal, but I really think I need a second opinion. BTW, as you ramp up the RPM's the timing will advance to as much as 20 BTDC so it seems to follow a normal timing curve, just that at idle it goes to -12 BTDC. And with the timing that retarded, the engine run rough, at top end it seems to run great!
Any suggestions / ideas?

Thanks

BoaterJim

 

[achris]

I also have a 555 ECU, and a couple of friends the same. yes, not uncommon to see the timing moving around a bit. The other idle dependent item is the IAC. Make sure the IAC is working properly, and maybe pull it and give it a birthday (clean the spindle with carb cleaner and replace the IAC muffler)... If the IAC is all good, ignore the 'erratic' idle timing and go boating and enjoy.

Chris.....

 

[Boater Jim]

I also have a 555 ECU, and a couple of friends the same. yes, not uncommon to see the timing moving around a bit. The other idle dependent item is the IAC. Make sure the IAC is working properly, and maybe pull it and give it a birthday (clean the spindle with carb cleaner and replace the IAC muffler)... If the IAC is all good, ignore the 'erratic' idle timing and go boating and enjoy.

Chris.....

Chris,

The IAC is new, as are most all of the other sensors and ignition parts on the engine. I wish I could just ignore the erratic idle, but when the boat stalls pulling out of the slip, it makes things a bit chaotic!

Jim

 

[alldodge]

There are 2 Bulletins out about HVS distributor. One which shows how to precisely clock the HVS on a ECT motor. The one attached list issues with misfiring, no start or shut down.