The Problem: The car suddenly died and even though the injectors were still pumping there was no spark or a very weak spark.
The Diagnosis: All the sensors (especially the TDC and RPM sensors) were good and the grounds had been checked. Studying the archives at www.roadfly.com revealed that the ground path for the coil (thus energizing the coil) was controlled by a power transistor in the MOTRONIC computer. The solder joint for the transistor would break causing the transistor to shut off or give intermittant function.
The Fix: I spent $8.45 at Radio Shack for a soldering kit and took the following pictures.
I have experience doing this plus I had already bought another ECU. Have a parachute before you jump...
On my ECU there are two plastic retainers, four Phillips screws and two smaller slotted screws. Note that the
two small screws tighten into the phenolic body so will be easy to strip out if you overtighten.
Here the tabs are shown bent up.
Once you have the ECU cover off, remove the screws. You will need to pry the center pin of the plastic retainers up so the c/b can be removed from the bottom plate. The circuit board is not very stiff so pry next to the pins to reduce flexing. Shown here upside down.
Under the plate is a plastic insulation sheet. In this picture you can see the transistor.
The soldering iron is directly above the left joint that was broken. This picture was taken after all three transistor joints were re-soldered.
In this picture is a close-up of the transistor on the left and on the right is possibly a rotary switch (the grey square with black extention on the upper board) that controls certain igniton and mixture profiles detailed elsewhere.