924Board.org

[McGyver]

Yes I want to use old connectors and pressure sensor, but the rest of it will be new made PCB with 937 config. But if I have some more time I want to draw logic scheme so almost all internal elements could be replaced with some easy programable microprocessor, and all of that should fit DITC box so externally should look identical as old unit but after takeing out PCB it could be easly connect to PC and all maps could be changed - or we use 3 different programs like US/ROW/GT easly changable with one button.

It's going to be really wild spaghetti


It's definitelly needs to be sorted somehow... in logic way
_________________
931 82' - actually with 924 engine - turbo engine rebuild in progress.
SOLD: 924 81' N/A- with turbo gearbox "dogleg" - great but mysterious car
www.mauser98k.internetdsl.pl - if someone like german rifles (English version avalible)

[stevekat]

Sounds cool!

Regarding pressure sensor...could these be failing on some of our units and we just don't know it? ie: our DITC units provide ignition control, and car runs, but the unit not affecting controlling timing in the proper way.

Any way we can actually source a pressure sensor to take this unknown out of the equation, or rebuild the original sensor?

Not sure how they work, but if there is a diaphragm in the sensor, one could see how they might crack, fatigue, fail after 30 years and tens of thousands or more actuations, particularly with the gases, oil, temperature that might make it to the sensor through the pressure line.

Also, do we know if these sensors sense pressure and vacuum or just pressure.
_________________
"Never get out of the boat. Absolutely goddamn right. Unless you are goin' all the way."

'81 924T, US version, CGT Intercooler, UTCIS-PT, Forged Fuchs Flat Dish 6's, Factory Recaro's.

[McGyver]

Yes the pressure sensor can be rebuild. It has two opposite springs inside(green or picture). It has rubber seal diaphgram (red) and coil on one end (pink). Inside coil we can find some kind of Iron core.
I can't tell how it works right now but I try to find it out soon.

One thing... if rubber inside is ok - in most cases should be!! and coil is ok, than pressure sensor can't be damaged and should work properly.

On photos you can see what is inside - without second spring - I didn't noticed it ealier when I disassemble it.

And the answer on another question... Pressure sensor detects vacuum and boost and I can confirm that with 100% sure. This 2 springs are the answer.
Anything else?


_________________
931 82' - actually with 924 engine - turbo engine rebuild in progress.
SOLD: 924 81' N/A- with turbo gearbox "dogleg" - great but mysterious car
www.mauser98k.internetdsl.pl - if someone like german rifles (English version avalible)

[RC]

Great work your`e doing McGyver. It`s not an easy task reverse engineering something like this. You`re a braver man than me laying out and making new PCBs, although personally can`t really see the point. For our small group of international 931 owners running the stock system there should be sufficient old units (with PCBs) floating around that could be overhauled.

Since this is not a true digital system but relies on basic logic gates with I assume the same PCB I also presume the difference between units should only be some resistor values and possibly some cap values. A side by side comparison can be made, even a good photo will show resistor colour codes.

That pressure sensor is interesting, not a conventional type MAP sensor as I imagined, they`re too old for that.
The only way I can see that sensor providing a varying analog output is by inductance. But that`s only if the system reads and responds to varying vacuum and pressure. Possibly it only reads either vacuum or boost. Depending on the direction of coil winding the moving magnet will give either a + or - spike on pressure and the opposite on vacuum. This can switch logic gates accordingly. Scoping the output will reveal that and a look at the ignition curves in FSM may give some indication.

Sure the 931 guys will appreciate your hard work. However personally believe that unless someone has a desire to keep everything genuine as Porsche made it 30 years ago it is considerably easier, vastly superior, and probably cheaper in the long run to throw the things in the bin and simply change over to a modern programmable ignition system. Imitate stock 931, 937 curves or whatever beyond. Perfectly tailored for individual boost, turbo, engine mods, IC, fuel, etc without accepting Porsche`s obsolete compromise.

[gegge]

McGyver: I think your work is a major breakthru!

Any idea how much boost the sensor can register and handle?

I order to improve, you have to understand. And that is what this is about. I belive that Porsche got right from the beginning and if the DITC works - why replace it? And if you can tweak it - even better!

An example: Search the pelican/rennlist forums for 911 CDI ignition and find out just how much the members appreciate the investigation and research for the benefit of others. The 931 can get the status as a classic if we do some of the work and keep it close to stock.

6-pin (SC and Turbo):
http://forums.pelicanparts.com/porsche-911-technical-forum/203100-6-pin-sc-turbo-cdi-unit-repair-documentation.html

3-pin (1969- ):
http://forums.pelicanparts.com/porsche-911-technical-forum/226517-history-bosch-cdi-toubleshooting-info-parts-list-changes-schematics.html

In short: 911 got CDI ignition from 1969, thats right - MDS!!!
_________________
Carl Fredrik Torkildsen

924 Carrera GT -81 (replica)

CGT IC, GTS turbo, UTCIS, Fuchs & R888, Leather Recaros, LSD, LEDA suspension...

[McGyver]

Tooday I took DITC unit with me to my job to take a look what was wrong - it has just two burned traces and few elements was destroyed. I replace everything and restore burned traces, and after that I connected 12V power supply, and after few checks I'm almost sure that unit I have here back to life.

So now I want to make some test in workshop... I can't find anywhere how flywheel sensor works. Maybe anyone know??
I want to simulate signal from this sensor to make DITC run. It's the only condition needed to operate.
Eventually I can put this DITC in to my 931 - with 924 engine Fortunately I've got flywheel sensor in it. So after connecting it to DITC and give some power... I should be able to check what's going on with output to coil unit.

So for now if anyone knows how this flywheel sensor works - please let me know. For now I know only that there's 5V on sensor connector.

Any infos about what is on input pins and where will be really helpfull Or I find it in my way - which could take some time.
_________________
931 82' - actually with 924 engine - turbo engine rebuild in progress.
SOLD: 924 81' N/A- with turbo gearbox "dogleg" - great but mysterious car
www.mauser98k.internetdsl.pl - if someone like german rifles (English version avalible)

[gegge]

Did you read page 16-18 from the Audi Quattro introdution that I sent you? There are an explanation of the sensor and a graph of the signal, just subtract the reference signal from the speed signal and it will look like a dameged sawbalade.
_________________
Carl Fredrik Torkildsen

924 Carrera GT -81 (replica)

CGT IC, GTS turbo, UTCIS, Fuchs & R888, Leather Recaros, LSD, LEDA suspension...

[McGyver]

Yes I read that, but you have to notice Audi Quatro have two flywheel sensors - one is reference mark - work with pin 1 on flywheel and second is speed sensor which works with all pins on flywheel.

In 931 we have only one sensor which could work as speed sensor. But how this unit know when is good time to produce spark?? There have to be something which tells DITC unit what is engine speed and where is pin 1 on flywheel but all this is in just one sensor somehow...

How this flywheel sensor is connected? on which pins are ... ground/voltage input/output

PIN 15 is ground
PIN 14 shows 5V DC
So pin 13 have to be signal - and it could be only AC becouse of that capacitors in input.


I think when I give that impulses to pin 13 i should receive something on output PIN 3 - going to ICU.
_________________
931 82' - actually with 924 engine - turbo engine rebuild in progress.
SOLD: 924 81' N/A- with turbo gearbox "dogleg" - great but mysterious car
www.mauser98k.internetdsl.pl - if someone like german rifles (English version avalible)

[ideola]

I could be wrong, but my understanding of the speed sensor was that it was used for the electronic speedometer, and had nothing to do with timing; and that the reference sensor was used strictly for engine timing. The engine speed would be calculated based on the aforementioned sawtooth wave generated by the reference sensor.
_________________
ideola's garage
Unique Products, Used Parts, Group Buys & Downloads for the Porsche 924, 944 and 928
Visit our CarDomain site

[gegge]

If you check the S2 flywheel you will find that one of the tooth is missing and replaced with a stainless one, look for the weld. That is the reference mark - non magnetic.
_________________
Carl Fredrik Torkildsen

924 Carrera GT -81 (replica)

CGT IC, GTS turbo, UTCIS, Fuchs & R888, Leather Recaros, LSD, LEDA suspension...

[gegge]

[McGyver]

[gegge]

At 7 o´clock, a metal insert.

_________________
Carl Fredrik Torkildsen

924 Carrera GT -81 (replica)

CGT IC, GTS turbo, UTCIS, Fuchs & R888, Leather Recaros, LSD, LEDA suspension...

[flosho]

Is there a way to recreate the base ignition map so that we could actually chart it out and "put it on paper"? Then also be able to modify it more agressively?
_________________
1981 Porsche 931 -- "Escalation of Commitment"
-Megasquirt 1v3.0 EFI/EDIS conversion, 250# springs, 17" turbo twists, 26.8/18 sways

[McGyver]

I think it's possible to do it. But I can't tell how long take to do something like this If we can understand completly how DITC works and what is what we can make custom ignition computer using modern map-sensor and some microprocessor with some simple program - emulate logic gates in this times are quite easy.
I started to make component list for standard DITC and when it'll be complete maybe someone will compare it to 937 unit or some else like Swedish... just to make few configs for different HP.

I think is really possible to make full working copy of DITC 937 unit for less than 20 Euros - new PCB and all elements - and old pressure sensor and front connector plate. I think update 931 unit to 937 it could be easier - just change few elements - but it could damage original PCB so it depends what risk someone wants to take.

Maybe will be possible to upgrade PCB to 937 config without adding addional board but add it to main unit. There's many possible upgrades, but first ... we have to understand it and some documentation will be good way.
_________________
931 82' - actually with 924 engine - turbo engine rebuild in progress.
SOLD: 924 81' N/A- with turbo gearbox "dogleg" - great but mysterious car
www.mauser98k.internetdsl.pl - if someone like german rifles (English version avalible)