Mercruiser 2003 5.0L ECM 555 base timing procedure

[delmarjr]

Can anyone inform me if my Mercruiser 2003 5.0L ECM 555 has a base timing procedure or not? I know some of the older models MEFI systems can be put into service mode using a scan tool or a jumper on the DLC connector and the base timing can then be adjusted. But I don't think the base timing is adjustable on my Mercruiser 2003 5.0L ECM 555 system. I guess the computer controls all of the ignition timing. Please provide any answers on this topic that may be helpful? Thanks

 

[delmarjr]

Re: Mercruiser 2003 5.0L ECM 555 base timing procedure

The Seloc manual is not clear because one place it shows n/a for ignition timing specs but another place it says to use a scan tool to put it into service mode to set base timing. But the manual covers many different ignition systems and lumps some of the procedures together. I've found several dicrepancies in the manual for those kinds of reasons. When I check the timing with a timing light it goes right back to just a little to the right (retard) of the mark on the timing cover when moving the distributor either direction. But I do know timing matters because I was a little off when setting the distributor in place and the engine wouldn't idle very well when I turned it all the way in one direction so I put it back on TDC and aligned spark plug terminal #1 in the distributor cap to the rotor and it runs fine no matter how far I turn the distributor in each direction. So it appears to me that the base timing is adjustable but the ECM keeps it in the proper range anyway. If it is adjustable why would it matter if the ECM controls timing anyway? My question is should base timing be adjusted if possible, how and why. Thank you.

 

[newport dave]

Re: Mercruiser 2003 5.0L ECM 555 base timing procedure

Base timing is NOT adjustable on that engine. Turning the distributor has no affect on timing, but it does need to be properly aligned for correct rotor phasing.

 

[delmarjr]

Re: Mercruiser 2003 5.0L ECM 555 base timing procedure

If timing is not adjustable then why is there a mark on the harmonic balancer and a mark on the timing cover? Can you explain rotor phase? What if the distributor was out 180 degrees would the engine still be in time and run fine? I don't think so but I'm not really sure. Please explain.

 

[Don S]

Re: Mercruiser 2003 5.0L ECM 555 base timing procedure

If timing is not adjustable then why is there a mark on the harmonic balancer and a mark on the timing cover?

You do have to have the engine up on #1 TDC when installing the distributor and locating the proper location of the rotor, and it's also needed for setting the timing on carbed engines. GM doesn't make special timing covers and harmonic balancers for each engine. All 5.7's of 2003 use the same ones, carbed or EFI.

Can you explain rotor phase? What if the distributor was out 180 degrees would the engine still be in time and run fine?

As stated above, the distributor has to be installed the proper way in the block and with the rotor aimed in the right direction (Phased) so the ECM can then control it using the crank and cam sensors.