Those timing values appear fairly normal. Of all the stock timing tables I've seen Merc tends to reduce timing at the upper rpm and MAP of the table. For instance it might have 34 degrees at 3200 rpm and 70 kPa but at 5200 rpm and 100 kPa it might be 28-29 degrees. These numbers are only shown as an example and NOT actual values you may have on your table.

Bottom line, most cases I've seen timing reduced as you go to the upper RPM/MAP cells as compared to mid range cruise values.

I think you are confused on how timing works on a MEFI ECM. All stock Mercury Marine EFI motors are shipped with 8 deg's base timing (set only in base timing mode). This, base timing is included in the total timing shown in the scan tool or data logs. The ECM does not have a function to know what real world timing is. So if base timing is off, say 4 deg, then the scan tool would show the commanded timing, but your timing would actually be 4 deg's retarded.

So a 500hp EFI does not have 36 degs! In the software, you can change what base timing is, but Mercury has always used 8 deg's.

The one thing Mercury Racing did, and it was only on the 500hp EFI is that ALL 500HP EFI's have the ECM set at 8deg base timing, but all new motors were shipped with the timing set at 10deg base. Meaning when the ECM showed 28deg, it really had 30deg (with timing light).

With your calibration showing 29deg's timing, you already have a modified ECM and 29deg is about all you should run with Euro 95 octane. With your 98 octane, you can run 31deg. To change, just put your motor in base timing mode, and move your base timing from 8 deg to 10deg. This would give you 2 deg more advance. If you want less, just take 2 out.

Note: Any good calibrator will run more timing at part throttle to increase engine efficiency, better mileage, less soot while there is low cylinder pressure and less possibility for detonation. So I see nothing wrong with more timing at lower manifold pressure.

Yes you say it. Hp500 are 28 on software and 36 in real.

I have 29,53 on software and in real. I need 15,5 basetime for 36 real.

NOOO, 28 on scanner, 30 real if timing if base timing is 10deg. If base timing is at 8, then its 28deg just as scanner shows.

You don't add your base timing to your actual timing. The ECM assumes base timing is 8deg. DO NOT RUN 36 DEG TIMING!!!! If you want more, bump your base timing to 10 deg instead of 8, this will give you 2 deg more, but your scanner will still show 29.53.

I have test it with 8 9 10 and 11 base time.

8 base, diacom 29,53 real 29-30
11 base , diacom 40 real 43 nock retards.

Hmmm, a discrepancy...

Yes, that is my problem.

Can it be, first black EFI 1993 are shows "TOTAL Spark Advance" and newer and blue Engines shows "Spark Advence" in Diacom ?

No, it has no way of knowing where the motor is to know actual timing, you would need a crank and cam sensor for that to truly happen. If you are changing base timing 2-3 deg more and your getting that much advance, you've got another issue such as the dist itself. The parameter in GM's software is "commanded timing" meaning its commanded, not actual.

I have ordert mefiburn software from Bob.
I will read all the date from my efi ecms. Than i now more what the engine is programmed to do. My rinda records shows me what the engine do.
If i now more i will tell.

Make sure your ECM isn't password protected or make sure you have the password otherwise you won't be able to get the data you are looking for.