Pat McPherson

I just got my 1997 Merc 502MPI fired up after rebuilding it this winter...
My problem is setting the base timing.
I bought a Code Mate last year when I was tinkering with my 1999 7.4MPI. It worked great on that engine. The idle got locked at around 1000rpm and I was able to dial it right on.
With this engine it does not seem to work. With the Code Mate turned on, the engine stalls out if I try to idle back.
Without the Code Mate off, I can get the engine to idle nice and smooth at 650rpm.
I check with a light and it looks to be around 0° at 650rpm. The computer has control at this point so I really don't know if it is set OK or not???
The ECU on my 97 502mag is the older style vs. my 99 7.4...
Is there another way to set the timing on the older EFI systems?

Dave_N

Your CodeMate is working fine. The '99 ECM (MEFI3) will raise the idle (like you said) to about 1000RPM when put in base timing mode. The older ECM's (MEFI1) didn't do this, so you have to raise the RPM to about 1400 before you put it in base timing mode. The RPM will drop down, but as long as it doesn't stall , you can safely check and adjust the timing. The timing will not change no matter what the RPM once in base timing mode.

Dave

Pat McPherson

Thanks Dave.
So what do I shoot for?
10° BTDC at 1000rpm?
If I can't get it to idle below 1400rpm what should I set it at?
Thanks again for the help...

Dave_N

Set it to 8 BTDC. It should not matter what RPM, there is no centrifical or other advance mechanism. Once its in Base Timing Mode, its locked.

Dave

Pat McPherson

Thanks Dave!