Odd wheel decoder settings
 

So I'm a little stumped on this one. For anyone that remembers my previous MSII thread, I decided to go back to MS1 for now (I got MSII running, but still decided to switch back for various reasons).

Anyways, I built the MS to DIY specs and whatnot, got the car started and idling, BUT, it only runs on opposite settings from the standard DIYAutotune Settings on the wheel decoder settings page.

To get a better understanding, lets look at this picture:
http://diyautotune.com/images/cartec...eel_decode.gif

If I were to put those settings verbatim on my MS, the car refuses to start, and will randomly backfire. Now, if I change the 2nd trigger active edge to 'Falling', the car will start right up and be fine (I think, haven't driven it around yet).

Another way to get the car to start is to set the 2nd trigger active edge to 'Rising', but reverse the order of Trig Pos A and Trig Pos B, from 2 and 1, to 1 and 2.

I'm curious as to why this is happening and what effect it has (or which setting is better?). I built the MS harness exactly from all the diagrams posted around, but this car has had an interesting life with an EE and I think he may have wired something in backwards.

I've double checked the wire colors for the CKP and CMP signal lines going to MS, but they have been cut at the CAS itself and I suspect wired backwards there?

So, anyone have any idea why this is like this, or what would require these settings to be the way they are?

(I've built another MS to an unmolested Miata using the standard DIY settings and everything was fine, hence my confusion)

Technically, the DIY settings are backwards. IOW, with the software configured their way, SparkA winds up driving the 2&3 coil, and SparkB the 1&4 coil. Sounds like you just found that out the hard way.

You didn't reverse the CMP / CKP wires. It wouldn't run at all in that configuration, ever.

Interesting, I wonder what I did on my other Miata that made their settings work perfect. Oh well.

So you're pretty much saying that either way I have my settings set up (either falling with 2 and 1 or rising with 1 and 2) it should make no difference on how the car runs?

Can anyone verify this is ok? Or better yet, give a good explanation of their meaning?

Thanks!

No one knows this mystery.....? :(

Sorry I didn't get back here earlier.

If you want to do it "right", leave the Second Trigger rising, and do one of three things:

1: Set trigger A = 1, B = 2.

2: Reverse the two ignition trigger wires coming out of the MS- the brown and brown / yellow factory wires relative to pins 31 and 36.

3: Reverse the relative positions of the 1/4 and 2/3 spark plug wires at the ignition coil.

What I'm getting at here is that there is no absolute right or wrong way to do this. Technically, DIY's A/B trigger setup is backwards, in that it causes SparkA to be the 2/3 spark, whereas in OEM terminology, IG1 is the 1/4 spark. So with the wheel decoder set up their way, you have to connect your ignition triggers "backwards"- SparkA drives IG2, and SparkB drives IG1. This is fine, and it's how most people do it. You can observe the backwardness of this simply be removing your CAS and fabricating and installing a missing-tooth VR crank trigger. (Well, not that simple, but you know what I mean.) When you do this, assuming you had your CAS Wheel Decoder set up the DIY way, you then have to reverse your ignition trigger wires, since the VR-based spark signals are inherently correct.

Thanks for your response Joe, I have a much better understanding now. :)

you shouldn't have to rewire/change anything if your settings are:

rising, A=2, B=1
falling, A=1, b=2

assuming you did the standard spark mods on your board.


so it's more than possible you have your spark outputs reversed on your board/harness from what the "standard" is.

That's my guess- brown and brown/yellow reversed relative to the usual.

When I first installed my MAS (I was still using a CAS at that time) I wired the spark outputs based upon what I felt was logical- that SparkA should trigger 1&4 (which are driven by IG1 on the stock igniter) and SparkB should fire 2&3, which are IG2. After much frustration I found this to be incorrect, given DIY's configuration of the Wheel Decoder. So I swapped the wires.

After I tossed the CAS and went missing-tooth, I had to re-swap the spark output wires back to the way I had them originally, since in single wheel missing-tooth mode, SparkA does drive 1&4, and SparkB 2&3, which is really the "proper" setup from a logical standpoint.

Just to revive this thread, I have just built my megasquirt, in piggyback mode with the settings as above (downloaded from MSPNP basemap) I get perfectly good rpm readings.

Since then I've tried my MS1 v3 in standalone and I am getting no RPM reading whatsoever even when cranking (and therefore cant get the engine started), would this setting be something to do with it?

I've double and triple checked my wiring harness so i'm sure its not that. I will try swapping the values in trigger pos A with trigger pos B tomorrow and see if the car starts.

should be the exact same...no difference in the MS mods or settings parallel vs standalone.

Is it possible that one or both of the pullups on the CAS inputs are missing from the MS? This would account for normal operation in parallel mode (with the stock ECU providing the pullup) but no RPM reading in standalone.

Ill check this tonight and let you know how it goes. I installed both pullups but will check the soldering as well. On a default msq the stim shows rpm readings too. If i still can't get it started i'll create a new thread with more details / images / settings.