..July 2012..
I did the full install of the wasted spark ignition on the engine biturbo, the injection being still done by the OEM IAW Weber ecu of the biturbo. The coil I used was the Bosch 3x2.
I had run the Vems ignition through the distributor for about 3000 km. I made the OEM Microplex Marelli ignition ecu (2 oem ecus : one for the injection, one for the ignition) to run in // with Vems and I got a switch to commute the origin of the firing signal to the coils (there are 2 on the biturbo). I did so for two purposes:
1) to keep the benefit of the knock control of Microplex
2) to start the engine faster in a quarter of a turn with the Microplex instead of the 2 revolutions and more( yes 4 pi) given by Vems.
There has been some discussion about this sluggish start here http://www.vems.hu/wiki/index.php?action=find&find=MembersPage%2FFPhil%2FInstall where one might say that DIS was the cause of it. However without DIS I get the same results and even worse because of the wasted sparks
Wasted spark
Wasted spark for this odd engine is not obvious. The best that one can do is to pair cylinders in such a way that one cylinder is TDC and the other one is 30 deg admission. This could work since, taking account the spark advance, the gas quantity and the pressure in the second cylinder should be low enough for the spark not to ignite.
I previously done some successful testing by firing 4 cylinders through the DIS and 2 directly wasted spark from the Bosch coil.
Results
- Bench test
The test is done by increasing from zero the level of the z012 triggers signals.
One sees:
- the 2 sec trig from the cam pulley per each revolution (4 pi)
- the 6 pairs of prim trig per each revolution: 3 pairs are on the crank pulley 90-30-90-30-90-30
- odd firing 150-90-150-90-150-90
- first fire after 2 revolutions (and more)
-> It is unclear to tell which sec trig from the cam pair is used
-> I checked another config: TDC delay after trigger 10 deg, spark delay 30,0,30,0,30,0 which should give the same. For some reason, the fire comes 30 deg sooner.
- Test with distributor (,no wasted spark)
On the first picture the firing given by Vems (4 pi) is not used since the engine is quicklystarted by the Microplex(same as on bench)
On the second picture
- the first fire (f1) is given by Vems after 4pi (and more)
- the next fire is at f1+150+90
- other fires are a kind of mess for a while but everything comes in order after 2 more revolutions
-> the firing @ f1+150 might be missing because it was off the DIS finger. Indeed Vems probably computes the next time to fire from the time interval of the last two prim triggers, since these triggers are 120 deg apart and the acceleration is high, the time to fire may be off the DIS finger.
-> All together the engine truly start up takes 8 pi +
- Test with coil 3x2 and wasted sparks
The first try was done with 7 deg spark advance at 399 rpm during crank and 22deg at 1000deg 1bar .... The engine says "bang"
Next try done after increasing the crank spark advance to 25 deg
I did not got the bang in that case but the trigs and the fires seem out of sync, engine appears to slow down even when the fire is not too badly timed.
The reasons for these failures were that the high Vems delay to fire when cranking adds up to the 30deg delay of the wasted spark during admission and makes ignition to occur on the paired cylinder.
Finally, still increasing the spark advance during cranking (25 deg @ 299 rpm, 35deg @900 rpm )I was able to start the engine
Do you have a *.triggerlog of this (or similar) real startup ?
- We could replay that on bench from .triggerlog format (not from .jpg).
- 2 REF for good start
http://www.vems.hu/files/MembersPage/Maserati/v3.3_u003856-2012-08-01-11.56.58REF.triggerlog
http://www.vems.hu/files/MembersPage/Maserati/v3.3_u003856-2012.08.01-18.47.05REF2.vemslog
http://www.vems.hu/files/MembersPage/Maserati/v3.3_u003856-2012-08-01-18.47.12REF2.triggerlog
- 1 triggerlog for bad start
Trying to improve the start, I reach this final config:
http://www.vems.hu/files/MembersPage/Maserati/v3.3_u003856-A-2012.08.01-19.18.13REF2.vemscfg
(45 deg @ 400rpm!!! see REF2 files) which is obviously non tractable.
Aiming to get a reasonably good ignition control, better than the Marelli Microplex(6803 processor), I think that
- the 720 deg delay before the first fire should be reduced
- Vems delay to fire during the acceleration of the cranking due to the few (3) trigs used for the computation should be corrected
- wasted spark ignition is too much border limit to be used on this odd engine
Some computation to explain the hard startup
A rough computation shows that the actual Vems strategy for cranking may no allow a clean start
I believe that Vems computes the time of the next firing from the time interval (Told) of the last 2 triggers (120° apart).
Let the starter cranks at 300rpm. When started with the Microplex ecu, the engine reaches 800 rpm quite fast say in 600deg (5x120) So the speed increase of 100 rpm each 120deg phase.
Hence after the first fire, speed has increased by 30% (100rpm) at the next 120 deg trig. Which means that this 2nd trigger is 30% or 36 deg sooner than expected (or more in the case of firing with the 30deg spark delay)from Told.
So at best the startup is messed up, at worse, with wasted spark, the paired cylinder is ignited at 60 deg on admission (30+36 - 7 advance)...
This issue may occur for other coil-type trigger set up with too few triggers on the crank. This could be the case for all Marelli ignition for which each firing is commanded by one specific trig on the crank and a timer.