DIY Autotune Optical Trigger Disc Trigger Angle Question/Problem

[Zcardude]

Hi everyone,

 

I'm running an MS2 3.57 running MS2 Extra 3.4.3 on a 1983 L28ET in a 1973 240Z. I just finished completely rewiring the engine with a new harness as the previous install was hack job by the previous owner. I recently did some work on my car, upgrading it to use a diyautotune optical trigger disc as well as eliminating an unnecessary CDI box. I have it running pretty well (just moving it around the driveway so far, haven't driven it fully yet) but had to use a strange "Tooth #1 Angle(deg BTDC)" trigger angle setting. It seems very healthy compared to the previous wiring job: it fires right up dead cold and just sits there and runs, previously it was very angry cold. I was mostly following the information on https://www.diyautotune.com/support/tech/hardware/nissan-trigger-disc/ but I did not create a second input for the cam, I am only doing crank input for now.

 

For my new setup, I am using a "Tooth #1 Angle(deg BTDC)" trigger angle setting of 285 degrees. When I set this angle, my timing light matches up exactly with the calculated spark advance. DIYAutotune recommends 345 degrees. When I tried 345 degrees, the car would not run at all, I think that the timing was just way too far off. Before installing the DIYAutotune optical trigger disc, looking at my old tune, my "Trigger Angle/Offset(deg)" was 52.3 which I believe was also sort of a weird setting.

 

So my question is: Is it normal to have such wildly varying trigger angles from what lots of other people have and what online guides recommend? Does this mean my distributor drive is potentially installed improperly? Does any of this matter if I am able to get the correct advance out of my timing light? I ask because I know the engine is a rebuild that was already running on megasquirt when I bought it and I don't know if this is something I need to resolve. It had some weird ignition problems before but the wiring was a disaster. I want to know where to look next if there are more ignition issues or if this can cause problems.

 

I can post some MSQs if that's helpful. 

 

Thank you!

[Zetsaz]

Doesn't seem unreasonable. Mine is pretty far off the recommended. Your distributor has it's own adjustment built in, and it's possible to install the wheel 180deg off.... and it's possible to install the distributor 180deg off...

You have to remember, that the computer can literally place your timing at any degree you want, especially if you're running coil on plug. You could clock the distribor in the completely wrong direction, install the disc upside down, and still get things to fire if you happen to get the correct #1 tooth angle on your settings.

 

The most important thing is that your base timing in your settings that megasquirt is expecting, matches with what your timing light is picking up.

[Zcardude]

32 minutes ago, Zetsaz said:

Doesn't seem unreasonable. Mine is pretty far off the recommended. Your distributor has it's own adjustment built in, and it's possible to install the wheel 180deg off.... and it's possible to install the distributor 180deg off...

You have to remember, that the computer can literally place your timing at any degree you want, especially if you're running coil on plug. You could clock the distribor in the completely wrong direction, install the disc upside down, and still get things to fire if you happen to get the correct #1 tooth angle on your settings.

 

The most important thing is that your base timing in your settings that megasquirt is expecting, matches with what your timing light is picking up.

 

Thanks! That all makes sense and lined up with my thinking. Since I have the timing light matching what the spark advance in tunerstudio is stating I'm going to call things "fine" for now

 

My biggest concern I think was that if I got too weird of a trigger angle, since I'm still using the distributor with a single coil, I could potentially end up in a situation where the rotor is not in the correct position to fire the proper plug or fire the wrong one or something along those lines. 

[cgsheen]

I think my trigger angle is about what you ended up with. The ECU needs to know TDC is coming BEFORE it actually happens and not just because we set our plugs to fire before TDC. It also needs time to make the calculations before the events are to happen. Like stated above the important part is not necessarily the trigger angle (as long as there's plenty of time before the event is to happen) but that the actual mechanical timing is the same as the reported timing from the ECU in TunerStudio. I don't think you need to worry as we have set up MS2 and MS3(X) boxes to run on both single coil and COP setups on l-series engines without issue in that regard. I think the trigger angle on one single coil N/A 280ZX L28E was in the 240-ish degree range. (if you think of it this way: 285 degrees is 75 degrees before the "event" if TDC is 360 degrees (or the same as 0 degrees in a 360 degree circle). 75 degrees gives the ECU time to calculate and still fire the plug before TDC even if the timing advance is 37 or more degrees.)

 

I think DYIAutotune is pretty careful to state that 345 degrees is a starting point although I too wish they would change that figure - (and it might be based on what someone else told them and not actual experience) - but they do specifically tell you to set the trigger angle such that the timing reported by the ECU matches the engine timing shown when using a timing light. 

 

Another point you might consider. Make sure that the timing marks on your crank pulley actually match the true engine position. Verify compression stroke TDC. Easiest way is with a piston stop.

Edited August 19, 2020 by cgsheen

[Zcardude]

Just checking back in to say this thing is running really good, the best it ever has since I've owned it I think, so I don't think my trigger angle is causing any issues at all. I haven't hot rodded on it yet but it drives very very good and I'm expecting it to pull good as well. I'm very confident that my mechanical timing is correct as I spent a lot of time questioning that before looking at the terrible wiring job (see my post history :D)