Question regarding GM/Saturn ICM ignition timing MSII v3.57

[jracer99]

Hello,
I need to just confirm some settings. I am a little nervous that my ignition timing is not exactly what it says. I am a little curious about my trigger offset being 52 degrees. Does this seem right? I have played with the setting up and down from 52 and the engine runs best here. Otherwise the engine would run very rough at other settings.

I have the settings for Gm DIS in mega tune like this page says but I am running the VR ignition trigger input from my ICM. http://bgsoflex.com/megasquirt.html

I am running forced induction and want to be very sure of my timing. My coils and spark plugs are not exposed so a timing light is not going to help me here.

The car seems to be running very well and I am getting excited. I went on my first country road tuning session yesterday.

I have played with my ignition timing maps at idle to check if it had an influence and it does. For example at idle I kept retarding the timing in the map and the engine would sound different and the air fuel ratio would get richer. This is normal behavior I would imagine since it is not burning as much of the mixture when combusting so late.

The main thing is, when my map says 25 degrees of advance I want to make sure that is what the engine is getting.

Any help is appreciated.

[jracer99]

I did some more data logs and analysis and came across an interesting issue which may have solved my question.
I was doing an RPM sweeps in neutral to adjust my VE maps and noticed a strange misfire at about 3000 rpm and up. I noticed that because my map sensor value was jumping around quite a bit in the data log. My maps are pretty smooth and my air fuel ratio is decent, so I am steering toward a timing issue.

Out of curiosity I decided to try ignition capture as falling edge instead of rising edge and set the trigger offset to 0 degrees. Top dead center right?

I did another RPM sweep and it ran much smoother and the data log looked a lot better.

Could I have been looking at the wrong edge for ignition capture?

I don’t have any form of timing indicator on my crank shaft pulley for a timing light so I am really hoping this is right.
Any ideas?

[Matt Cramer]

You really will need to put a timing indicator on your crank pulley to check the trigger angle; not much of any way to get around that unfortunately.

[jracer99]

Bummer, I don’t have any timing marks on the outer surface of my timing chain cover for reference. I am going to have to pull it all off and get inside then mark TDC on the crank shaft then put it back together then mark the cover at TDC. Then what do you recommend? I can’t get marks on the crank pulley, no room, just enough for the belt.. Should I bust out my trusty protractor and mark them on the chain cover? I don’t even have spark plug wires. The coil towers sit directly on the plugs. I can rig something up for wires but the timing marks ar stumping me.

Any suggestions ?

[jracer99]

Ok, after further investigation and about ready to pull my whole front engine cover off, I noticed a couple of groves on the timing chain cover with a 15 above one and a 0 above the other which resembled TDC. I am glad I saw this because it may have saved me a lot of time.

I ran a test and am hoping some one can confirm it is accurate. I only have the 2 marks mentioned above. 15 degrees BTDC and 0 degrees TDC

I set my spark advance maps to 15 degrees BTDC since that is the most advanced indication I have on the cover. With the timing light, the notch on the crank pulley read a little advanced before the 15 degree BTDC mark on the timing chain cover.

I used the trigger offset feature in megatune and kept bumping the timing back with the minus button. With my spark advance at 15 degrees BTDC in megatune and my notch on my pulley lining up with the 15 degree BTDC grove on the timing chain cover, I now have a trigger offset of 11. Is this an accurate way to do it?

I checked it at a few different engine speeds and it was accurate and stabile

Thanks for the help

[Matt Cramer]

Looks like you're all set now. That's the correct way to set your trigger angle all right!

[jracer99]

OH yeah! sweet! Its running really good now. I just cant wait till the weather gets nice here now.

Thanks