Where to get EEC-IV ECU specs/schematics.

[Mike Wesley - SLIP]

On Fri, 20 Oct 1995, Hans Steiner wrote:

> My mechanic just told me that the code 41(always lean) code that I am 
> getting is caused by a bad computer.  And a "rebuilt" one costs $225.  So 
> I thought I'd first try to fix it myself, since I would be buying a 
> "rebuilt" one anyway.  So I was wondering whether anyone knows where to 
> get the schematics and/or specs for the EEC-IV ECU.  This has probably 
> been addressed before, and I apologize if I am bringing it up again, but 
> I tried to find the info in past articles, but I didn't feel like 
> browsing though a couple megabytes of past articles.
> 

It's pretty rare for the EEC to go bad, but it does happen. I deal with 
these ECM's everyday and have seen this code pop up for a variety of 
other problems. Since you didn't say which vehicle you have, I'll assume 
you have a dual HEGO system. The 41 is saying the right HEGO indicates 
lean (continuous) and is not switching (engine running test). Do you have 
an exhaust leak, low fuel pressure, bad injector or plug not firing? Any 
of these will show up as lean. Pin 29 on the EEC is the right HEGO into 
the EEC. If you want to trace it all the way back to the CPU (8061) probe 
pin 31 in the 8061. This is one of the analog input channels. There is an 
IC between pin 29 of the EEC and pin 31 of the 8061, but I'm not sure 
what it is (goofy part number on it..obviously a custom EGO chip). It's 
an 8 pin dip on most EEC's. Pin 1 is the input for the right HEGO, pin 8 
is the output to the 8061. Pin 49 of the EEC is the ground for the HEGO's 
and this connects to pin 3 of the 8 pin dip IC. From pin 29 of the EEC, 
the HEGO signal goes through a 22K resistor, plus a 2.2M resistor to HEGO 
ground before going into the 8 pin dip IC. After going through the IC, 
the signal goes through a 3.3K resistor then has a diode connected to VCC 
and a cap connected to analog ground, then it goes directly into the 8061.
Pin 6 of the 8 pin dip, connects to a 5V reference voltage, pin 2 is VCC.
For the left HEGO, pin 43 of the EEC is the input which connects topin 4 
of the 8 pin dip and the output is pin 5. Then it connects to pin 36 of 
the 8061. 
I could have drawn an ASCII schematic, but I'm not that good at doing it!

Mike...