dozybee

My early 1985 944 has disgraced itself twice now and been unceremoniously trucked home
after suddenly stopping, engine dead, resting and running for a while more before stopping
again. We managed to park it off road and call the retrieval company.

Did the usual,loose connections,bad sensors,DME relay,earths, etc.,

The ECU number 944.618.111.03 ( 0 261 200 006 ) was tidy within. No hot spots or other problems.
Trying to trace connections revealed that the ECU schematics (1987 ones) were not adequate.

I have trawled the Porsche websites looking for the older ECU schematics to no avail. Does anyone
know where I can get a suitable ECU schematic for this 944 (Pooch).

Assistance would be appreciated.

931guru

http://www.clarks-garage.com/shop-manual/dme-04.htm

dozybee

931guru, I think Ken Fletcher never located the pre-1985 schematics. The site schematics are for a 911 1987 Motronics schematic.
The other turbo one is for a 951? 1988 ECU. Clarks Garage is INVALUABLE for setting up and testing sensors, etc and I refer to it
before using the factory manuals. However if I ever manage to locate some pre-1985 ECU schematics I will apply to add them to
his site if it is still administered.

I am going to look into updating my 944 to the newer MAF and ECU if it's possible. More digging into the forums!.
Regards.

dozybee

Oops!!! I meant Clark Fletcher. Age withers the mind as well as the body!!!

Zirconocene

I completely support the move toward better documentation for these aging cars and look forward to what you can find.

To get your car on the road, however, have you looked at the F9 Tech options?: https://www.ftech9.com/new-products

They're plug and play (as far as I can tell) and will allow for separate upgrades (like a MAF. Again, as far as I can tell).

Good luck

four0four

Have you tried just mindlessly reflowing the solder on the big TO-3 transistors? I did this when I had similar issues, and it uh...worked

That was a late DME, and I think I just did the one that switches the coil, but same idea. Thought being that eventually those joints will fail under thermal cycling. Yours seem better heatsinked, but that doesn't entirely preclude the possibility. You could also run it with the DME open, then point a hot air gun set to a low-ish temp at various parts until it falls over

dozybee

four0four, I have begun resoldering and am astonished at the way the old solder seems to release from the items being soldered. I have suspected the timing sensors as my DME relay LED diagnostic trap
indicated that the ECU appeared to have been ordered to turn off !. I used my lathe, a lawnmower gear, an oscilloscope and a heat gun to cycle the flywheel sensors to test them. Trying to follow the sensor
trail on the PCBs became a nightmare. A heat gun and an oscillating sander could possibly extract a confession from the suspect. Interesting thought !!.

dozybee

My DME relay may have been "chattering" because the driver transistor or wiring may have been reducing the output to the relay controlling the fuel.
I produced this mod to see if a more positive ground to pin 85b will "hold" the fuel relay better. Time will tell. Meanwhile I will search for some old
ECUs for spare bits.

Test circuit

Extra relay

dozybee

This mod did not stop the intermittent stoppages. Instead it has caused to ECU to pick up some interference and caused the
fuel pump to run when not wanted. Avoid!!!

dozybee

I fitted a more robust relay, less coil resistance and it now works properly.
The 944 is idling for 30+ minutes and then stops. After a short cool down
it will run again. Speed/Ref or ECU, that is the question ?? A subject for
a new thread.

931guru

Use a scope to monitor the flywheel sensors to eliminate them.

dozybee

931guru, Got my old O/scope into differential mode (earth isolation) and noticed that the speed signal was marginal.
After 30 minutes it became worse ( Alloy engine expansion away from flywheel ???) and the engine stopped.
I redid the clearances and got a very good signal. The engine now idled for +1 hour so I have a result.

One more question. which transistor on this older board drives the DME relay ????

931guru

Dunno, but since it outputs to pin 20 on the connector, should be traceable.