SM4 trigger accuracy with more or less teeth?

[RAC]

I think this was covered in the old Autronic forum. I think i remember Ray saying any more or less than 8 teeth on the crank wouldn't gain you any better timing accuracy?

If you were to make your trigger setup from scratch for a 4 cylinder with the "best" timing accuracy in mind that the SM4 can do what would you do?

I see some systems out there use every tooth even if on a 60-2 setup.


Thanks Raymond.

[MRMRacing]

If it is a normal engine and not "light mass crank" like two strokers I would go for two teeth where one is loacated your total advance + 10 degrees, normally around 50 deg BTDC. If I would push it further 4 teeth or 8 teeth can be used. I would stick with the gear tooth sensor. The 2 teeth is the simpliest setup. 4 teeth can still use pulse per cycle ic you set Trigger events cycle to 8 (if using the tacho o/p you must use 8 cyl tach here). Else you can set it up as divider which is little more comlicated.

[rzsupra]

will i need any mods to my standard star-wheel crank trigger on a 2jz before i put the motor back together?

[RAC]

I didn't know you could use more than two teeth on a pules per cycle setup. My old 1.02 chip doesn't have a divider setup option i don't think.

So you could use 8 teeth on pulse per cycle and set the trigger events to 16, but the tacho would need some recalibrating?

That seems too simple.

[MRMRacing]

Yes that is correct with the trigger events. I had one 60-2 6-cyl engine. That car (Volvo) has a 4-cyl tacho (even the 5-cyl 850 has 4-cyl tacho). So I ended up setting the motronic setting as per 4-cyl car and only fuel & ignition as a 6-cyl. So the tacho O/P is dependent on the trigger events.

On the early chip with no divider settings you can do so but the trigger events maximum is 16. 4-cyl engine can have max 8 teeth at crank and 6-cyl 12 teeth.

[MRMRacing]

will i need any mods to my standard star-wheel crank trigger on a 2jz before i put the motor back together?
No, but what chip do you have in SM4?

[rzsupra]

not sure but ray hall supplied it 'set up' for the 2jz , i guess that means its loaded with the cal map and appropiate chip ?

[Ian]

There are a few other things that need to be considered before everybody starts fitting multiple extra teeth to all their cranks.

All Autronic ECUs do a Load measurement at the same time as the Cylinder Pulse that occurs at the Cylinder I/P Lead angle. When the Trigger Events / Cycle value is the same as the number of engine cylinders (a normal configuration) then a Load measurement is taken at the same relative point on every cylinder. For example if the Cylinder I/P Lead angle is 60 deg then a Load measurement will be taken at 60deg BTDC on every cylinder. This means the Load value will be most stable because manifold reversion pulses, etc will also be occuring at the same relative times on each reading.

If you increase the number of Trigger Events / Cycle then the ECU will also be taking additional Load measurements. If you double the Trigger Events / cycle there will be two Load measurements per cylinder NOT at the same relative positions. If you have a 4 cyl engine with 60deg Cyl I/P Lead there will be alternating Load measurements at 60deg and 150deg BTDC effectively on each cylinder. If there is a significant reversion effect in the manifolding this may appear as an unstable Load reading (which some other ECU's seem to have as standard). This will also affect Manifold Rate fuel trims if the cal is using that in a Trim table.

Extra Trigger Events / Cycle could also have a similar effect on Ignition timing. A lot of people are aware that if you set a flat ignition table and watch the timing with a timing light when you suddenly accelerate the engine with no load you will see an Autronic retard the first pulse and then be correct for the rest. This is with one pulse per cylinder. If you do the same test with other ECU's and one pulse per cylinder you will see the timing retarded the WHOLE time the engine is accelerating. If you fit three pulses / cylinder to these engines for the other ECU's the retard effect nearly goes away.

The Autronic has a very good predictive timing algorithim that works with one pulse / cylinder. Engines do not run continuously smoothly even though they appear to. They slow down on compression strokes and accelerate on combustion strokes. Introducing extra Trigger Events / Cycle could destabilise the predictive timing in a similar way to the Load calculation. Using a camshaft driven Cylinder pulse has the same effect (seen as timing scatter). All Autronic CPU's up to SM4 v1.05 (& all SMC /SM2) do the prediction the same way.

For RAC with v1.02, if you increase you trigger Events / Cycle but are not using all four ignition outputs you can set one of the unused outputs as a tacho pulse with the correct number of pulses

[RAC]

Thats some really nice info there Ian. Whats the difference from 1.06 on compaired to the 1.05 and older chips?

By the sounds of that i'll leave it as it is. I would of only been doing it for fun anyway. Do you know how the Autronic deals with the early subaru trigger setup, i take it they would only use two of the 6 teeth?

[RAC]

For RAC with v1.02, if you increase you trigger Events / Cycle but are not using all four ignition outputs you can set one of the unused outputs as a tacho pulse with the correct number of pulses

Thats really neat that. I just had a play with a costom ignition setup and never knew it would be that easy. You could use that for lots of interesting things.

[Ian]

For the purpose of this thread the v1.06 and onwards have an additional parameter called the Digital Angle Filter. When set to Fast it operates the same as earlier SM4 & SMC / SM2 CPU's. When set to Slow the prediction is averaged over more Cylinder Pulses to minimise scatter.

Also when using dwell the v1.06+ has a wider tolerance than v1.00-v1.05 before applying dwell extension. It is a complex scenario because the dwell pulse may be initiated several Cylinder pulses before the timing point to achieve the desired dwell time. If the engine speed increases suddenly (after initiation of the dwell pulse) and the output is triggered at the correct position the dwell pulse will be shorter than planned. Depending on the coil minimum dwell requirements the short pulse may undercharge the coil resulting in a missfire. Under certain circumstances the SM4 (and the old dwell boards) will extend the dwell to a minimum value to ensure a spark, which will be slightly retarded, rather than risk a spark missfire. In pre-v1.06 CPU's the tolerance was found to be a bit conservative so it (the tolerance) has been widened in v1.06 and later to achieve better timing accuracy when accelerating.

For the 6 tooth Subaru crank the Autronic uses the 65deg teeth for all timing. The Subaru uses the 10deg teeth for cranking position. When cranking it turns the dwell on with the 65deg tooth and off with the 10deg tooth. Maybe the Subaru ECU couldn't calculate the engine position accurately at cranking so it needed an extra tooth at the cranking ignition point. That then raises the question of ECU's that require cylinder pulses at the cranking position - how good are they if they need a tooth there?

[MRMRacing]

Nice posts Ian, this is the information we like to see here!:p

[MRMRacing]

There are a few other things that need to be considered before everybody starts fitting multiple extra teeth to all their cranks.

All Autronic ECUs do a Load measurement at the same time as the Cylinder Pulse that occurs at the Cylinder I/P Lead angle. When the Trigger Events / Cycle value is the same as the number of engine cylinders (a normal configuration) then a Load measurement is taken at the same relative point on every cylinder. For example if the Cylinder I/P Lead angle is 60 deg then a Load measurement will be taken at 60deg BTDC on every cylinder. This means the Load value will be most stable because manifold reversion pulses, etc will also be occuring at the same relative times on each reading.

If you increase the number of Trigger Events / Cycle then the ECU will also be taking additional Load measurements. If you double the Trigger Events / cycle there will be two Load measurements per cylinder NOT at the same relative positions. If you have a 4 cyl engine with 60deg Cyl I/P Lead there will be alternating Load measurements at 60deg and 150deg BTDC effectively on each cylinder. If there is a significant reversion effect in the manifolding this may appear as an unstable Load reading (which some other ECU's seem to have as standard). This will also affect Manifold Rate fuel trims if the cal is using that in a Trim table.


So on my 6-cyl motronic engine with trigger events set to 4 (have no spare ign O/P since I use the mux) it will read the load 4 times each fully cycle. Meaning the measurements will not be equal to all cylinders.

One other customer to me with a bike was recomended 8 teeth at crank for good accuaracy, and now I understand why he has so unstable readings that he asked for a filter on the load. Now he has two teeth and works fine.
To solve this problems with tacho the way to go is a add scalable tacho o/p on the SM4 (if you want proper load meassurments).
Will ad that to my wish list.

[Chris]

I respectfully defer to me' learned colleague, as usual.

Chris

[Ian]

So on my 6-cyl motronic engine with trigger events set to 4 (have no spare ign O/P since I use the mux) it will read the load 4 times each fully cycle. Meaning the measurements will not be equal to all cylinders.

That is correct, as you have used that 4th ignition output there is no easy fix. Apart from either recalibrating the tacho, going to waste spark or making a 3-2 pull-down circuit the only other thing I can think of is to put a 2-tooth pulse generator on the crank or a 4-tooth one on the cam.

Is there not a version of the Ford V10 that has 36-1 on the crank which means you have to set it to a non-matching pulse count?

[Chris]

Is there not a version of the Ford V10 that has 36-1 on the crank which means you have to set it to a non-matching pulse count?

I failed to immediately see the full implication of his 4 TEV/C. A hasty retreat was called for.

Chris

[MRMRacing]

Here is tested what Ian said regarding ignition timing during acceleration.
In this pic I simulated an accelration, one signal i sync pulse the other ignition 1 o/p. The setup is pulse per cycle and set to sequantial ignition, I/P lead trimmed so the ignition matches the sync signal ever 720 degrees. Ignition is set to -Ve.

This pic is during accelration, here is the first ignition in phase, then little late for two sparks and then in phase. The first ignition is at 1200 rpm and the last is 5000 rpm, I doubt an engine can acceleate this hard but timing is still ok.

[RAC]

The third one looks to have moved more than the second one in relation to the same falling edge of the sync signal ?

Maybe i'm missing something?

[MRMRacing]

you where right, it was wrong pic uploaded, I have edited the file and it is now ok, thanks for pointing this out.

[Chris]

I cant read the time axis. What is the acceleration rate ?

Chris

[MRMRacing]

Just above 4100 rpm/s.

[Chris]

Just above 4100 rpm/s.


I have some datalog here somewhere of a speedway four cylinder at 12000 rpm/s

Chris

[MRMRacing]

This value was manually calculated since the rpm increas was 4100 rpm on 1 sec. I have seen high values in datalogs earlier.

[Ekman]

For RAC with v1.02, if you increase you trigger Events / Cycle but are not using all four ignition outputs you can set one of the unused outputs as a tacho pulse with the correct number of pulses

So only ignition outputs can be used to drive tacho??

[MRMRacing]

O/P 8 is normall used as tacho output, but ignition or fuel can be used if not used (for fuel or ignition). The injectors or ignition O/P is set up under the tab "Advanced" in each menu.

[RAC]

I had a look at my timing with a timing light tonight with all maps at 20deg, At idle it drifts around a little more than i would like.
At 1000rpm and the timing set to 20deg it will drift around from 18-26deg and this is happening all the time, you can here the rpm changing with the timing change. The error gets smaller with more rpm and it does retard about 2deg for an instant when the throttle is blipped. Anything over about 1500-2000rpm and the timing is within 1deg.
I've alway had a little problem with idle smoothness and this may be part of the problem.

The engine is a 2.5L 4cyl subaru with a 6kg fly wheel.

I would like to try more crank teeth to see what the result would be. A newer chip would be nice too.
No ones got a second hand 1.06 foalting around do they?

[Ian]

18-26 degrees :eek:, no CPU was ever that bad !!! That seems more like the ignition was running off another table like the idle table.

Don't worry about extra teeth until you have changed the CPU.

[RAC]

Ha Ha no this is with "ign angle mean" reading constant 20deg when testing, every map, main, idle, overrun and air temp corrections all set to 20deg. If i blip the throttle from 1000rpm it will retard the timing 10deg befor sorting itself out. If i do that at 2000rpm on it will only retard about 2deg befor sorting itself out again.

I tried to take a small video clip of it but it didn't turn out too good.

[RAC]

Here's a little video of the timing set at 20deg flat in the ecu. It seems to get better with less advanced but is still bad.
There's even a good 1-2deg jitter at any rpm.

It also looks better in the video as the frame rate plays around with it a bit i think.
http://i14.photobucket.com/albums/a350/megrac/th_DSCF4560.jpg (http://s14.photobucket.com/albums/a350/megrac/?action=view&current=DSCF4560.flv)

I want to wait till next chip comes out befor i upgrade but then i spose i'll want the next one to ha ha.

Is there anything fancy planned for the latest ?

[gti]

Yes, I do have some used 1.06 chips.

[Kelly2264]

This is a very good and informative thread. :D

I don't have an SM4, I have a SMC v1.92.

I was running a 60-2 crank trigger setup and I'm in the process of changing it over to a pulse-per-cylinder arrangement. I had performed the high speed (internal resistor mod) to the SMC, but was still having issues with sync/cyl percentage. It was rock solid at 38 degrees during cranking, but during running it would bounce all over the place and sometimes go as high as 103 degrees. I was told that the SMCs don't like the multipule pulses from the 60-2 and that I should change it to the pulse-per-cylinder setup.

I haven't got the setup on yet so I'm hopeful that after reading this thread I'm going in the right direction. I should have it running next weekend.

By the way, it is a four cylinder with 2 timing "triggers" now.

[RAC]

Yes, I do have some used 1.06 chips.


You have pm if you didn't already see it ? :)

[MRMRacing]

still having issues with sync/cyl percentage. It was rock solid at 38 degrees during cranking, but during running it would bounce all over the place and sometimes go as high as 103 degrees.

I did not do so many SMC motronic triggering, but this seem not okay. I beleive you mean sync/cyl above when you wrote degrees so I would first check the polarity of the inductive trigger. Check with a scope you got the positive wire connected to the+Ve red wire on the reluctor.

[Chris]

I have only ever done one 60-2 on a SMC V1.92. It was faultless. What was the engine ?

Chris

[Kelly2264]

What was the engine ?

It is an aircooled 4 cylinder Type 1 VW. The crank sensor is from a Porsche 996 (reluctor) with a reluctor interface. The "cam" signal is from a modified Golf Dist. (hall) (it has a single window in the dist. from a Vanagon).

I believe you mean sync/cyl above when you wrote degrees

You're correct, I meant percent. I had gone over most of the wiring issues (what could be wrong and what was right) with Ray. But, this one thing seems to be "hounding" me. I PM'd a couple of AC VW guys on the old forum and some suggested getting rid of the 60-2 for they had had problems in the past with this and SMCs. It's not that difficult to change it over, so...

[gti]

I did a couple of Peugeots using the Bosch 60-2 trigger with SMC. It reported sync error when the engine was being cranked, and it took a bit longer than normal to start - longer cranking time. Other than that, it ran OK. Sensor polarity is most important. If you get it wrong, it gives you all sorts of problems.

[Kelly2264]

Thanks for the input guys ! :)

I will definately be rechecking my polarity to insure it is wired right way around.

[Hening]

I did a couple of Peugeots using the Bosch 60-2 trigger with SMC. It reported sync error when the engine was being cranked, and it took a bit longer than normal to start - longer cranking time. Other than that, it ran OK. Sensor polarity is most important. If you get it wrong, it gives you all sorts of problems.

What engine model did you work on Peugeot? Does it have cam sensor?

[yrkesman]

What kind of things does wrong sensor polarity cause?

[MRMRacing]

I can think of many........if it is a multi-tooth trigger the ignition can move with rpm, If 60-2 (or other missing tooth) it can result in sync errors during crank/start/run, engine will only run to a certain rpm before missing or just random errors. I remember one other brand that stated "If polarity is wrong some weird things may happen" !

[Wroom]

To be a bit "electric", but yet slightly simplistic: The sensing coil in an inductive pickup is wound so that it has one "hot" connection and one "cold" connection. The same goes for the signal receiver in the ECU. It has one "hot" connection that is sensitive, and one "cold" side that is less sensitive and primarily there for closing the "current loop" in the "differential signal pair" from the pickup coil.

So one can not just swap the positive and negative side on the sync inputs. But rather must figure out if the trigger edge is positive of negative. Some manufacturers detect trig events with bumps, and others detect with holes in the timing disc. This tells if the correct trigger edge is positive or negative.

Also, The correct detection edge on an inductive pickup is always the second edge that occurs, (that is, when the bump or hole leaves the pickup), since the first edge will always be much weaker since there will be less "magnetic flux" going from an unenergized state, than going from one energized state to an energized state of the opposite polarity.

Looking at the signals with a scope, one will see that the "hot" signal is slightly bigger in volts than the "cold" signal.

The "hot" signal must be connected to the positive sync input.

The trigger edge that one configures for the sync input in the cal file must be that of the second edge on the hot side.

Hope this explained more than it confused. ;)

[Kelly2264]

Thank you!

I thought that was a very good "simplistic" way to describe the events that take place. :cool:

[RAC]

I've been having a bit more of a play with this timing thing. Its most deffantly a piston acceleration problem, with more timing its worse and less timing its not so bad but still way out.
This is because more timing must be having a greater effect on piston speed on the power stroke.
With only two crank teeth for a 4 cylinder engine you would think there would be a need for an engine mass/cylinder cc size filter in the software.
I can see a 2L subaru with the stock 12-13kg flywheel wouldn't ever have a problem. But when you have a 2.5L with 600cc pots and a 6kg flywheel i think this is where the limit may be?
I wouldn't have thought a faulty chip would cause this as everthing else works fine?

Also if i was to have more teeth on the crank trigger cant the autronic know its still only a 4 cylinder and only still sample the load at the normal place in stead of every tooth, this seems a bit odd if it cant ?

[MRMRacing]

Ian recomended you to change chip, and yeas Ian decribed how the Sm4 senses the load, each "cylinder event". So for doing it right you shall use a divider to still have 4 events cycle. So for this you need a chip with divider meaning 1.06 or newer......

[RAC]

I've had a donation out of good faith and will have a 1.06 to try and i'll report back on the out come.

[RAC]

Well the 1.06 has solved the problem. The timing is bang on and i mean bang on 100%.
What a difference the idle is about 10 times smoother. I've even been able to setup the Ign delay time and see the difference. Should be good to go out and see how it drives but my clutch died the other day:mad: I have a new one i'm hopping to fit this weekend.

Very pleased :D

A big thanks to gti :cool:

Also a big thanks to Ian

[gti]

Glad that the chip helped!
Happy tuning.