Megasquirt Ignition Options (falling edge, stock distributor, etc)

[Ondonti]

I believe that the MS logs the "requested" advance, i.e. whatever advance is needed for the given conditions after adding or subtracting for temperature, RPM, MAP etc (see the timing equation in the megamanual for more specifics). If that value differs from the "observed" advance, as recorded visually with a timing light, then there may be an issue. Again, if there is a confirmed error %, it may be due to the low data rate input from the 6-"tooth" part of the distributor.

Also, that thread on msextra.com is from '10, and per Ken, the % off value was borderline useless due to no smoothing in the code that derived the % off value. With 2+ years additional work on the MSII-Extra code since that thread/post, I would suspect that if you did a fixed timing and checked it with a light, you wouldn't get much variation.

Would have been nice for him to give an explanation of what the code was doing regardless of its likelihood of giving bad numbers. Another thing that annoys me about MS.
I still don't see why people are or were directly ignoring the setup advice from DIY.

[Shadow24]

Would have been nice for him to give an explanation of what the code was doing regardless of its likelihood of giving bad numbers. Another thing that annoys me about MS.
I still don't see why people are or were directly ignoring the setup advice from DIY.

It looks like he addressed it in a sense on the last post...

As I said, currently the timing error % is so jittery as to be useless. I would not pay any attention to it at all until we get some sort of smoothing in.

It is only telling when it expected to see the next tooth on your wheel compared to when it actually saw it, and says nothing about actual timing accuracy.

In fact, I'll probably remove it until we come up with a better calculation for it.

Ken

What part of DIY's writeup is being ignored?


Sundance 6G72 - If your seeing accurate timing from the MS, i seriously doubt you have anything to worry about

[Ondonti]

It looks like he addressed it in a sense on the last post...

What part of DIY's writeup is being ignored?


Sundance 6G72 - If your seeing accurate timing from the MS, i seriously doubt you have anything to worry about

The point of this thread is to get after the reasoning for running certain settings, not "everything seems fine." Why exactly are/were people (Ed, Nathan, others) deviating from the suggestions of DIY when setting things up on the low data rate 12v distributor. I would be interested to see the same cars running as suggested and compare datalogs. My car does not run at the moment but I would not mind trying both ways if it is running.

I think there is also a statement from Nathan that I read once where he said his timing advance was capped at 37 degrees "physically" but then I see his trigger angle setting is 11 degrees different then what Ed was running or what Joe is running now. How was that limitation determined and heck, I know I can run more then 37 on a stock computer. Ed has been modifying ignition rotors in the past, trimming them down creating a smaller window of timing potential but preventing crossfire. There are or were a lot of out of the box methods going on so I am looking for the science behind it all.
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http://www.diyautotune.com/tech_arti...ar_30_sohc.htm
"MegaTune Configuration for MS-II

Set ignition capture to "Falling Edge," and coil charging to Standard Coil Charging. Dwell will depend on exactly which coil you are using. Cranking trigger time must be set to Calculated. If using MS2/Extra, set the ignition type to Basic Trigger.

Important when using the BIP373: On the 'Ignition Settings' menu make sure to set 'Spark Output' to 'Going High (Inverted)' and set 'Coil Charging Scheme' to 'Standard Coil Charge'."
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[c2xejk]

For the record, I currently have ignition capture set to "Falling Edge".

[Shadow24]

IIRC, nathans "ignition breakup" at higher RPMs was due to lifter collapse... I don't remember if there was any issues with total advance, but I don't think there was any physical limitations then.

[nmw2006]

My original breakup problems were actually lifter collapse caused my running too light of oil (0w20). After beating my head on a wall on that one, I still could not get more than 37* of demanded timing no matter what I did. This does equal 49* when including base. After that point it didn't matter what position the distributor was in, after accounting for the rotational movement with trigger angle, I could not go beyond 37* without high rpm (6500+) breakup.

I was researching trigger angle and found this via Matt Cramer @ DIYAutotune.

Trigger angle is the angle before TDC where the Megasquirt "thinks" it's getting a signal from the CAS. If you have a trigger angle of 60 degrees and a spark advance of 20 degrees, for example, the Megasquirt waits for a signal from the CAS, then counts down the amount of time at your RPM it would take to turn 40 degrees, then commands it to fire a spark. If the CAS signal actually came in 65 degrees BTDC instead of 60 degrees BTDC, the spark would happen at 25 degrees when the Megasquirt "thinks" it's happening at 20.

So the goal there is to make the physical trigger angle match the angle that the Megasquirt is using to calculate its ignition timing.

This means trigger angle has to be calculated for each motor setup. I was using this when messing with my distributor. As a test, I tried rotating it both directions (between the factory stops) which would throw off my base timing. I adjusted for this in my tables and with trigger angle. This is why my trigger angle was different than other peoples.

After all this I still never figured it out and pretty much gave up on revving it that high. I'm probably missing something here so feel free to call out what I was doing wrong.

- - - Updated - - -

Ed has been modifying ignition rotors in the past, trimming them down creating a smaller window of timing potential but preventing crossfire.

This interests me as I was actually wondering if this was happening to me. This is what I meant when I said "physically" limited.

[Ondonti]

My original breakup problems were actually lifter collapse caused my running too light of oil (0w20). After beating my head on a wall on that one, I still could not get more than 37* of demanded timing no matter what I did. This does equal 49* when including base. After that point it didn't matter what position the distributor was in, after accounting for the rotational movement with trigger angle, I could not go beyond 37* without high rpm (6500+) breakup.

I was researching trigger angle and found this via Matt Cramer @ DIYAutotune.



This means trigger angle has to be calculated for each motor setup. I was using this when messing with my distributor. As a test, I tried rotating it both directions (between the factory stops) which would throw off my base timing. I adjusted for this in my tables and with trigger angle. This is why my trigger angle was different than other peoples.

After all this I still never figured it out and pretty much gave up on revving it that high. I'm probably missing something here so feel free to call out what I was doing wrong.

- - - Updated - - -



This interests me as I was actually wondering if this was happening to me. This is what I meant when I said "physically" limited.

I have 0 for trigger angle with falling edge because that always functioned in the past. Basically what you first attempted to run long ago. That did work for me at the time.

What method is used to check base mechanical timing without getting electronic advance in there messing up results? I had set mine up with OEM computer then did MS so I never dealt with it.

[Shadow24]

I have 0 for trigger angle with falling edge because that always functioned in the past. Basically what you first attempted to run long ago. That did work for me at the time.

What method is used to check base mechanical timing without getting electronic advance in there messing up results? I had set mine up with OEM computer then did MS so I never dealt with it.

MS has a "fixed timing" option used to zero in trigger angle and can also be used to set the base timing. it sets the timing at a fixed value and keeps it there until you disable it. you could set it at 0* and see where your timing light shows up at, and adjust the base distributor timing from there. Then once disabled, you would have base + ignition table for advance.

[Sundance 6g72]

I dont even know why I have certain things set the way they are to be honest. I dont think I even followed the DIY article either, I just went for it.

[Ondonti]

MS has a "fixed timing" option used to zero in trigger angle and can also be used to set the base timing. it sets the timing at a fixed value and keeps it there until you disable it. you could set it at 0* and see where your timing light shows up at, and adjust the base distributor timing from there. Then once disabled, you would have base + ignition table for advance.

So if I have 12 degrees base during fixed timing I would use +12 degrees in my offset. Then my timing maps would all be short 12 degrees since I wrote them up with the 12 degrees subtracted.

[Sundance 6g72]

just set it to fixed 12 or 10 or 8 or whatever you want.

then get out the light and check and see where it is on the timing bracket thing by the crank pully. adjust the dizzy or your trigger offset until the light reads 10* (or whatever MS is fixed to)


done

[Ondonti]

So my offset had to be set at 15 degrees. After 9 degrees of offset (fixed was set at 10) it started increasing the value that I was trying to match up with. So I had to match to 16 degrees (was fixed 10) and ended up with 15 degrees of positive offset. I tried moving my distributor counterclockwise but that seemed to make timing bounce around.

So now I am running truely off my table.

[Ondonti]

I was pointed towards this link by a Mod on MSextra.com Apparently MS3 explains basic trigger better then any older stuff did.

http://www.msextra.com/doc/ms3/distributor.html

This is what 87turbodance was doing with his settings in http://www.turbo-mopar.com/forums/sh...ht=rising+edge
but neither explains the "why" of many actions involved in this style of setting base timing (like why you want offset to be in a certain range, or why you are following such and such procedure.).

I did find that when my distributor was turned too far counterclockwise I had erratic timing (and probably crossfiring).

[87turbodance]

With the stock dist you can never achieve the ideal trigger angle without moving the dist out of sync with the coil towers. crank trigger solved this for me. symptoms are breakup at high advance values.

Trigger angles that will get you a running motor wont allow for more then about 34-40 degrees advance before running out of time (literally). the trigger angle must occur with enough time tdc to allow Ms to calculate the advance. MS calculated advance based on time when using a dist. crank trigger uses a combo of crank teeth ---- and time, MS3 uses purely counting crank teeeth.

[Ondonti]

Looking at the same datalog above, I charted out

Spark Advance
Base Spark Advance
Spark Table 1
Idle corrective advance

And realized that with my base timing set at 15 degrees offset, megasquirt is unable to achieve anything less then 16 degrees advanced. This makes tuning idle not as easy and also creates a problem for boost because my planned timing table at low rpms requires less than 16 degrees of timing once it gets around 7psi boost (150kpa) and around 3000 rpms. That timing stays very low until 4500 and then ramps up quickly. 3000 rpms won't be a problem because I would never get much more then 7psi with a large cam installed but 3500-4500 will be a problem as boost ramps up and peaks in that range with the turbo I will again be using in the future. When I set base timing it was happiest at 15 degrees of offset. Now I need to see how far I can reduce the offset. Maybe it will behave better with the tune a bit more dialed in.

Originally in 2010 I had zero offset, my base timing adjustment had been set with an OEM ecu at 12 degrees stock. I then just decided I would subtract 12 degrees from my actual timing map. At this point I have no idea what was going on with my "real" total spark timing then but reported spark values were able to go to zero and over 40 degrees. I hear we only have around 40 degrees of spark adjustment with our distributor so I don't know why I would want 16 to 56 when most of the upper range is unusable...The old firmware datalogs do not have as much information to sift through.

I don't exactly understand why Megasquirt won't allow you to have your timing less than the offset. Now I have to research :P

Messing with something once a year or less makes it hard to remember what exactly is going on with our ignition sync.

[87turbodance]

I don't exactly understand why Megasquirt won't allow you to have your timing less than the offset. Now I have to research :P

Messing with something once a year or less makes it hard to remember what exactly is going on with our ignition sync.

Megasquirt 1 and 2 use calculated periods of time to guestimate spark advance. Megasquirt bases all advance off of a reference point which is your trigger angle. Megasquirt will then calculate how much time to wait past the trigger angle to fire the spark. It cannot fire a spark before the trigger angle because of this fact. The stock distributor acts as a 6 tooth wheel run at crank speed.

If you want to simply things immensely, drill 6 evenly spaced holes in the outside of your damper 60 degrees apart with the first one aligning with a hall sensor when the crank is at 60 degrees btdc on any cylinder. Thread the holes and install 6 1/4" ferrous metals studs/bolts in the damper. Don't forget to loctite them

Configure MS for 6 toothed wheel with a trigger angle of 60 degrees

Then transfer the distributor wiring to the hall sensor and continue to use the distributor but let the crank sensor do all the timing work. Just adjust your distributor however you want to achieve the best spark range. ie set it up so that the rotor is close to the correct spark tower with a crank angle range of 50 to +10 degrees or whatever works out. When you have the distributor timing and the timing pickup separated it makes things soo much easier.

In my experience I could achieve a 60 degree spark angle range without cross talk in the distributor cap. Based on some quick math, I believe you will need to go wasted spark if you need range larger then 60 degrees because of limitation with using a distributor cap.

Bottom line, when you separate the distributor cap from the MS trigger input angle you gain the freedom to choose an ideal trigger angle and an ideal distributor cap position without making sacrifices. With the stock setup and MS you have to sacrifice one or the other to achieve something that works because both are tied together in the same component - you turn one and the other turns too.

[Ondonti]

Megasquirt 1 and 2 use calculated periods of time to guestimate spark advance. Megasquirt bases all advance off of a reference point which is your trigger angle. Megasquirt will then calculate how much time to wait past the trigger angle to fire the spark. It cannot fire a spark before the trigger angle because of this fact. The stock distributor acts as a 6 tooth wheel run at crank speed.

If you want to simply things immensely, drill 6 evenly spaced holes in the outside of your damper 60 degrees apart with the first one aligning with a hall sensor when the crank is at 60 degrees btdc on any cylinder. Thread the holes and install 6 1/4" ferrous metals studs/bolts in the damper. Don't forget to loctite them

Configure MS for 6 toothed wheel with a trigger angle of 60 degrees

Then transfer the distributor wiring to the hall sensor and continue to use the distributor but let the crank sensor do all the timing work. Just adjust your distributor however you want to achieve the best spark range. ie set it up so that the rotor is close to the correct spark tower with a crank angle range of 50 to +10 degrees or whatever works out. When you have the distributor timing and the timing pickup separated it makes things soo much easier.

In my experience I could achieve a 60 degree spark angle range without cross talk in the distributor cap. Based on some quick math, I believe you will need to go wasted spark if you need range larger then 60 degrees because of limitation with using a distributor cap.

Bottom line, when you separate the distributor cap from the MS trigger input angle you gain the freedom to choose an ideal trigger angle and an ideal distributor cap position without making sacrifices. With the stock setup and MS you have to sacrifice one or the other to achieve something that works because both are tied together in the same component - you turn one and the other turns too.

What was the timing adjustment window that you found when doing the falling edge method at 75 deg BTDC?

I am not looking for high timing, but low timing.

BTW, until I found out today about "This cylinder" or "Next cylinder" modes, a lot of this didn't make sense. Anything at low BTDC angles means it has to skip to the next cylinder and for some reason the code won't allow firing before the offset degree even though you are waiting for the next cylinder.

Offset angle of 60-90 allows "this cylinder" ignition and will basically fire any angle the rotor in your distributor is compatible with on the correct cylinder. That means I have to verify the rotor lines up in my planned timing window as you suggest in your writeup.

What about trigger return setup? That sounds like the best of both worlds using the OEM distributor.

BTW, it seems like I need to throw my degree wheel on the crank to really do what they want but then they also suggest "guessing" :P

[87turbodance]

I've tried all the settings and distributor positions I could never get what I wanted. I even tried to reclock the rotor to achieve a better rotor to sensor alignment. Finally I said ---- it and added a crank sensor; best thing I ever did.

[Ondonti]

I've tried all the settings and distributor positions I could never get what I wanted. I even tried to reclock the rotor to achieve a better rotor to sensor alignment. Finally I said ---- it and added a crank sensor; best thing I ever did.

I would be happy with -5 to 35 degrees or 0 to 40 degrees BTDC as a working range. I really have no need for high timing numbers once boost is involved.

What ranges did you actually achieve? I know you wanted more then was possible.

[87turbodance]

I would be happy with -5 to 35 degrees or 0 to 40 degrees BTDC as a working range. I really have no need for high timing numbers once boost is involved.

What ranges did you actually achieve? I know you wanted more then was possible.

Unfortunately, it's been a couple years so I can't remember. You'll have to get out the degree wheel, mark the spark tower positions on the distributor and mess around with MS and your distributor position until you find something that works. I was using MS1 which is a real pain for this stuff. MS2 is better so you might have more luck.

I honestly think you'll spend less time adding a crank sensor... You could probably get away with only adding three "teeth" to your crank pulley which would give you the same resolution as the stock distributor but with the freedom to choose your trigger angle. Six teeth will give better starting performance, though.