Can't get 4-1 wheel working properly

[Bubba Zanetti]

Hi,

I am helping my friend on his MS instalation on Fiat 1.6 SOHC turbo engine.

We already get that engine running very well without turbo on MSnS-extra code ( fuel only) and tuned it with LC-1 (<100kPa area only) and after cca 1500 km's we were satisfied with results, we decided it's turbo time - so now MS of course has to control ignition part...

After reading a lot about wheel decoder stuff we decided to try 4-1 wheel for ignition :

Setup is like this:

- VR sensor is std Fiat with bolt-on bracket - it fits perfectly on SOHC block with 0.5mm tooth-sensor distance, it gives around 190mV (0.19V) AC on cranking,

- for VR conditioning circuit we used std Fiat little module - it's designed for VR dizzy with 4 teeth so it would be OK for this application, frequency wise at least,

- after conditioning we connected one 2.2K pull-up resistor to +12v and we got very nice and stable signal on cranking - Megatune is showing around 300-310 RPM,

- output from Megatune is going to Magnetti Marrelli ignition module with coil - on cranking we got some very large spark, so that part is also OK ,

So what's the problem then you may ask?

Well, problem is in 4-1 wheel decoder settings in Megatune - on cranking we almost get the engine running , but it always just backfires and never really starts - it seems like we are very,very close with timing but can't get engine running.

To clarify things, here is pic of 4-1 wheel position when mounted on crank:




My questions seem so simple and maybe stupid , but I have to ask:

1. Is my CAD drawing showing correct teeth numeration ?

2. What would be proper Megatune spark settings for such wheel on 4 cyl. engine with one coil & dizzy?


P.S.

Code is MSnS-extra 026i on v2.2 MSboard, FIDLE is used as spark output, Megatune 2.25b627 version.

[newtyres1]

If your pickup on the drawing is moved 120 degrees clockwise or 60 degrees counter clockwise then it should work correctly. You need a trigger 60 degrees before TDC of a cylinder that you want to fire, you don't want to trigger on the no.2 tooth, set the spark to trigger on no.1 and no.3. I am not experienced so wait for a few more replies. At the moment you're probably 60 degrees retarded.

Ian.

[Bubba Zanetti]

Hm, I see what's problem - with 4-1 wheel unfortunately you have only few possible ways of mounting VR sensor.

So, if we mount VR sensor 60° anti clockwise, situation on engine will look like this:


Trigger A on tooth 1:




Trigger B on tooth 3:




And wheel decoder settings in Megatune should be set like this:




I am just not sure if this settings are correct - can I set cranking advance to 0° ?



Of course, I probably need to disable spark map & trim angle and put everything to 0° until I finish with timing settings ?


P.S.

I suppose that one coil with dizzy could work with such settings - or maybe I just need to install two double coils with two spark outputs (A & B)?

[jsmcortina]

Set the cranking advance to 10BTDC not -10.

I wouldn't put the spark to zero, most engines don't like to run with timing at TDC. For initial startup you might want to put the Fixed angle to 10 so you can then strobe the timing and tweak your trigger angle.

What code version are you using? Looks rather old.
You _may_ have better results with a newer version. Make sure you use the "024 style" wheel decoder with later codes.

You can use either wasted spark or a distributor, the code supports both. If using a dizzy then set a single spark output, if using wasted spark then set sparkA and sparkB.

James

[Bubba Zanetti]

2 jsmcortina:

Single coil output? If you mean using FIDLE as Spark output - that's what we used.

MSns-extra code is 026i - but I can't see why should new code version work and old version couldn't - of course I understand if I start the car and get some rpm spikes and wierd decoder behaviour that maybe new code will be without such bugs , but in this case our car want even start...

But I'll certainly try some fresh code - after all, it's far easier to change code then VR sensor position .


Today we tried newtyres1 idea: to mount VR sensor 60° anti-clockwise - unfortunately, it was impossible to mount VR sensor in this position because proximity of alternator belt

So , we tried another even simpler idea - to change position of crank pulley - we removed pulley and tried to make slot for pulley mount 60° clockwise - but we were in hurry and of course we somehow made slot in wrong position - VR sensor is now inline with 1st tooth at 120° BTDC

But I remembered that in MT you can put angles larger then 60° with some additions, so I put 75° + 45° as adition - and again nothing, car coughs, backfires, goes shortly to 500-600 RPM, but never really gives that familiar sign that it will start and make us happy in 12 PM...

I then slowly went through settings : 2 degrees of timing up/down , then +/-4 degrees, +/-10 degrees - again nothing. Changing trigger angle also gave nothing, of course. Changing cranking angle didn't help either.

Hmmm, we didn't have our timing light but we did have our old dizzy with VR sensor that worked in this MS instalation before - so we mounted dizzy, put engine in phase, set Megasquirt to "Fuel only" and it started without problems - so engine, fuel system and fuel maps are OK...we then leaved same dizzy in that position and set ignition to "Wheel decoder" and connect VR sensor & everything else set as before - again nothing, car just don't wan't to fire up with 4-1 wheel...

If we couldn't get that wheel to work - can we just grind off 2nd tooth (tooth in the middle) so we are left with only 2 tooth 180° apart and use MSnS-extra in "Single coil-distributor mode" ?

Is there anyone with such configuration that actually works?

[Bubba Zanetti]

It works !!!!

After trying all combinations with trigger angles and stuff - we gaved up from software changes and tried our last resort- changing again crank wheel position, but this time to correct angle

So we carefully modified crank wheel so sensor is aligned with 1st tooth at 60° BTDC, as close we could get with handsaw and a file .

We also removed single coil and decided to mount 2 double coils that are driven by two Magnetti Marrelli 7-pin ignition modules.

LED 17 was used as Spark output A, and LED 19 as Spark output B.

On our first cranking - nothing. Hmm, we first check module outputs - they were not firing spark plugs...but LEDs were blinking in alternating pulses... I then suspected that LEDs are maybe "sucking" too much current so I removed LEDs and put jumper in their places - then we cranked car - and bingo , we got idle !

Very weak and unstable, but it's at least some idle - so we then played with trigger angle settings and spark map untill we got smooth idle and easy engine start-up.

Tnx everybody on help - I almost couldn't sleep last 3 days because I was thinking all the time why this simple wheel doesn't work...now I am aware that position of VR sensor is obviously extremely important with such wheel...way more important then we ever expected.

[newtyres1]

Hey, that's great news, bet you're real happy now!

Ian.

[alfa75ba]

Hi,

I have similar engine, FIAT 1,4 SOHC and I recently switched to crank sensor setup (Hall sensor, 2 triggers) but kept the distributor for spark delivery.
I had the same backfire problems. Trigger on 60 deg, finger pointed towards spark on cyl. no1.
The problem was in distributor gearing or something, for some reason it is offset 180 degrees.
That means, when trigger on 60 deg BTDC on crank ( measured on cyl. no.1), the finger in the distributer should be pointed to the spark lead no.4

The easiest way is to unhook the distributor cap, deattach it from distibuter, rotate it 180 degrees and put it back down on distributer.
Everything then works like charm.

Of course, when getting rid of distributor (like dual coils wasted spark) that problem should disappear, which is also my next step.
I only need to mount the third trigger on the crank pulley.

One question:
Are there any noticable gains on FIAT SOHC when switching from standard Webber-Marelli coil to dual coil wasted spark system?

Regards, Drazen

[Bubba Zanetti]

2 alfa75ba:

Hey, always nice surprise to find another Megasquirter from the neighbourhood

Yes, I also feel that dizzy is real P.I.T.A., so I badly wanted to remove dizzy from my friend's MS instalation - and finaly we did it, yeahhhhh

Noticable gains on SOHC engine with wasted spark ?

Hmmm, I suppose that we'll get at least a little bit stronger spark and more stable ignition timing - but of course, only few days passed by and we need many more km's with wasted spark & turbo setup to see it's real benefits...

I'll try to put this instalation in "Sucess stories"- it's always interesting to see such old & cheap car with lot of electronic gadgets, at least to me

P.S.

I am really interested in your MS experiences - you can e-mail me whenever you have some spare time if you want - my e-mail adress is: "veliborv@net.hr" , I'll be glad to share my experience ,

Velibor