Hello Zoltan,
thank you for the link - I remember that there was a discussion but forgot completely that Lars sent us a very good report of the DI casette.
It's so important and expressive so that I quote here again:
2screwed wrote:I have attached a file for the pin out of the Ignition cassette. Nr. 4 cylinder is the one closest to the connector. Pin number 1 is used for monitoring the charge voltage to the capacitor (1/100 of the charge voltage gives about 0-4V)
The voltage on the trigger pins is 12V and it triggers on the falling flank when grounded (500mA peak). The trigger must at least be held low for the discharge time of the coil which is about 500us. There must be 2.5ms charge time between triggers to avoid damage to the cassette. The recharge of the capacitor starts directly when the trigger goes high again and the charge time is 2.5ms at 12V battery voltage. It's important to minimize voltage drop in the harness as the charge time will rapidly increase with lower voltage (3ms at 9V). Charge voltage can be monitored the on pin 1.
The misfire signal is a square wave signal 0-12V. There are 2 lines for this, one is for cyl. 1&2 and the other is cyl.3&4. SAAB also use this signal during cranking to find the which cylinder is in the compression stroke and which is in the exhaust stroke. The SAAB Trionic trigs both partner cylinders until it can detect a combustion in one of the cylinders, during this time these two coils get half each of the stored energy in the Cap. You will have a signal some microseconds after a trigger if you have a combustion. This signal is only for combustion detect and has nothing to do with knock.
The raw ION knock signal is filtered in the Cassette to a 7kHz +/- 6V sine wave. The amplitude of the signal reflects the degree of knock. I don't know the voltage levels for light/heavy knock. The Trionic engine management system also has some sort of 7kHz filter on the input. This is the tricky for us since each engine has it's own specific knock frequency. The main factor is the bore size, but I guess other things as the shape of the combustion chamber can influence this as well. The built in filter is not that steep so there will be a signal between 6-8 kHz. The charge pulse gives a lot of disturbance so the trigger must be kept low until the knock info is read. Normally most of this information is found between 10-40º ATDC. If the spark is 30º BTC and the knock info is at 40º ATDC, this means the trigger signal should be 70º long. The Trionic have a "window" for when reading out the knock which I think varies in time depending on MAP and RPM. I'm trying to get more information about knock window timing.
The coils in this system has a liquid insulation material, therefore the orientation is important. You can't tilt the coils more than 45º from vertical without damage to the high voltage winding.
There are some different cassettes, one red and one black for four cylinder engines. They have been in production since 1987, but the ones of interest is from 1992 and up. They are still in production in the 9-5 model today. The black has AC spark, giving longer spark duration. This can improve idle stability and lean condition misfire. There is also a three cylinder cassette, which can be found in 9000 & 900 models with V6 engine. There has never been cassettes without the epoxy potting made.
2screwed wrote:The "quick and dirty" wasted spark solution will not work due to the 2.5ms charge time for the capacitor. And as you say the cassette will not work for your PPP project, only for knock detection, and then just for engines with a bore around 90mm.
Only keeping a real DI (and PCB and some components) in hands I can understand Lars' information - thanks again.
My 2cent Conclusio:
- An unmodified DI is pretty useless for PPP (ISP)
+ The SAAP COP coils could be tested with DIY-CDI as suitable CDI coil.
~ If we can find out the schematics maybe we can cut out just a limited area to solder a shielded wire to exploit the raw ion sense current/signal.
+ A test bench could be biult to trigger a DI module. This might be an interesting information for all SAAB guys to know more of a specific DI failure.
@Schematics:
I got a rough overview circuit of the detection circuit - I'll try to find the traces and components on the PCB.
@Test bench:
Lars describted that the Trigger pins are between sparks at +12V, but when they go to ground then this COP sparks.
I guess it should not be too difficult to modify MSnSExtra (MSII?) 5V (inverted?) output signal to boost it up to 12V.
Can anyone design a quick circuit (cheapest transistor, resistor, 12V Z-diode?) to trigger DI with MS (Stim)?
I got some helpful information of DI documentation/manual, some snips:
»a) ...sends a knock signal from each cylinder to control module pin 38.
From the combustion signals, the control module will be aware of which cylinder has fired...
»b) If there is an open circuit or a short circuit at the knock lead between the ignition discharge module and the control module, diagnoctic trouble code P0327 will be generated.
»c) Firing order is 1-3-4-2, Capacitor voltage=400V, Ionisazation voltage=80V
»d) When main relay operates, power (B+) is supplied to the ignition discharge module which converts 12V to 400VDC and charges a capacitor.
»e) This voltage (400V) is connected to one pole of the primary windings of the 4 ignition coils.
»f) When the engine control module grounds pin9 the other pole of the primary winding of the ignition coil for cylinder 1 will be grounded (via B+...)and the 400V transformed to maximum 40V.
»g) If there is an open circuit in the power supply or a ground connection to the ignition discharge module the engine will not start.
@a:
If one wire can tell ECU information of each cylinder then each cylinder has its own 'signature'.
@f:
Typo? 40V should be 40kV?
@g:
Included savety device - does this (or »b) ) include that each wire/cylinder must be connected - I guess/hope not!
»Horst
