Can someone explain ignition concepts? (long)

[Guest kerristallax]

I'm working on a friend's Megasquirted 240z turbo and we're having some difficulties getting it running. This is DAT240Z's car, for those of you that remember the lengthy ordeal we were going through this past June / July.

 

We're running DIYAutoTune's MS-I v3 unit, firing the coil directly from the vb921 module out of LED17. MSnS-Extra version 024s13. Ignition output is inverted, since I have read that it needs to be or you will fry the ignition output, if not more than that. Been there twice already... It did, however, start with the old setup and spark output not inverted, before things got toasted.

 

So back to where we are today. It has fuel and spark but won't start. I've read here and on msefi that there is some sort of difference in timing between inverted and not inverted. Could someone please explain specifically what that difference is? When I set the timing and distributor position as described in Moby's original sticky, it sounds like it is very close to starting, but it never quite does.

 

 

More on ignition concepts:

I decided that it might help us to run a setup more like what is out there and closely documented, so I grabbed a 4-pin HEI module from Autozone and attempted to wire things up how it is described in Metro's setup.

 

Spark output is still set to inverted -- should it be?

 

The HEI module itself is bolted onto the inner fender wall, and connected to the same battery ground as pin W. No spark with this configuration.

 

 

My questions on ignition concepts, then, are...

The coil -- fires when +12v is connected to positive and -12v is connected to negative, correct? Or is there more to it than that?

 

What does the 5v source + resistor combo that is connected between pin G on the HEI module and the ignition output (whether it's LED17 or FIDLE) from MegaSquirt do?

 

What is the difference between spark output inverted and not inverted? I had thought that INVERTED would cause it to switch ground in order to fire the coil, and NOT INVERTED would cause it to switch power. If that is the case, then I can see why the diagram I posted wouldn't work -- there's never power to the coil at all.

 

Looking in the MSnS-E manuals I found this:

Spark Output Inverted Choosing spark output inverted YES or NO is VERY IMPORTANT. This is determined by the way you drive your coil(s) When the spark coils are directly driven from the ECU (VB921 FETs are used) you will choose Inverted = YES. Get it right or you will risk damaging components as well as getting wildly inaccurate timing.

[randy 77zt]

the + side of the coil should still have 12v running from the key switch-this will supply the coil and hei module.the 5v + 1k resistor is called a pull-up circuit.the relay board grounds that terminal on the hei module to fire.when the g terminal isnt grounded that is the time the coil is charging.so the g terminal sees 5v unless grounded by the relay board.the 1k resistor is there to limit current from the 5v supply on the relay board.i have a circuit like that in my fidle relay sockit on my ms.it drives the stock 81zxt transistor on the stock 81zxt coil brackit through the yellow wire from zxt efi system.

[Guest kerristallax]

Hi Randy,

 

Thanks for the response. I think that makes sense -- so is this how it should be wired?

[randy 77zt]

more than likely but dont quote me because my set up doensnt use gm hei module.my set up uses the wire that would end up on g terminal triggering stock zxt power transistor through yellow wire on power transistor.ms requires much online study.

[mobythevan]

Yes, that is correct, "key on 12v" connects to coil pos/HEI B

[z-ya]

If you are getting spark, it is not the VB921. If you want to go through the exercise of trying an HEI module, it can't hurt. You are fixing the symptom, not the problem though.

 

Did you verify with a Timing light that cylinder #1 is firing somewhere on the timing tab? If you can't see the timing mark on the pully anywhere on the timing tab, then your timing is off. change the timing angle in MT until the timing you measure with the timing light matches you crank timing setting. You may want to pull the fuel pump fuse to prevent it from firing. Once you have the timing calibrated, put the fuel pump fuse back in, it should fire right up.

[Guest kerristallax]

Z-Ya,

 

I understand that this attempt with an HEI module, even if it does work (not proven yet) is not getting to the root problem. It is an attempt to fix the symptom. At this point, I decided that I would like to run the "most common" MS setup so as to have the best chance of success and getting help from other users.

 

I have spark now with the HEI module, so theoretically it should just be a matter of getting the timing right. I'll get back to this once I get the new flywheel for the car. The ring gear finally called it quits today. It had a bunch of teeth missing already, and has gotten so bad the starter just spins freely.

 

OK, so -- calibrating the timing:

I set the trigger angle to 60 degrees, and then rotate the crank to approximately 60 degrees before tdc. Then I adjust the distributor until the middle LED stays on MegaSquirt. And then I should be able to do the actual calibration. Right?

These settings are with the PC not connected to MS, so ignore the fact that they are all wrong. Now then, which is the correct field to change in order to adjust for the timing being off? Trim angle? (wild guess)

I want to be able to use the Ignition Advance map from the 24s9 sticky if possible, since we don't have a budget for dyno time.

[mobythevan]

No, not trim angle. Trigger angle is the correct setting to change.

 

TRIM ANGLE is used to adjust the entire spark map by a trim value for some kind of testing purpose, but not used to calibrate your timing.

[Guest kerristallax]

Alright, so you move the trigger angle up or down until your cranking timing matches, say, the 10 degrees set in cranking advance angle? Sounds simple enough.

[randy 77zt]

i had to adjust my trigger angle because after checking my set up with timing light i was 8 degrees late.my magnets were installed in my flwheel at 60btdc and every 60 degrees.so i set my offset to 52 and it worked as checked by the timing light.if you are doing a turbo engine this is critical.