Is it possible to repair the "Computer" (ICU)

[Marc Boucher]

As Suggested by Huw, here is the recap of the problem and the tests performed so far:

Car: Audi 100, 1990, I5 NF engine, non-turbo, non-quattro, CIS-E-111 (California)

Problem:  Car cranks but won't start.

History:  Car was driving, and suddenly shut off, unable to restart.  Towed to nearest garage which (correctly) noted no spark and (questionably) "solved" the problem by splicing the brown-white wire leading from the hall sender to the Ignition Control Unit, and grounding it to the engine block.  This drove fine, but I noticed car was idling faster than before, ISV not working.  Based on comments in this mailing list, and the simple fact the repair was not correct, I've set off to find the real problem, and correct solution.

First step, remove the ground wire that the garage added to the hall sender, thus restoring the previous no-start condition.  After this:

Tests Conducted So Far:

All fuses verified.

Throttle switch testing performed as precursor to ECU output tests.  
Result: Resistance between pin 1 and 2 when throttle closed = 0.2 ohms
Resistance between pin 1 and 2 when throttle opened = infinite
Resistance between pin 2 and 3 when Wide Open Throttle = 0.2 ohms
Resistance between pin 2 and 3 when NOT Wide Open Throttle = 0.2 ohms
Conclusion:
Throttle switches functioning.  Can proceed to ECU Output tests.

ECU Output Tests Results:
 ECU is sending 100mA to Differential Pressure Regulator, regardless of state of throttle body.  FAIL.
 ECU is cycling carbon canister solenoid valve on and off, regardless of state of throttle switch.  FAIL.
ECU does not activate Idle Stabilizer Valve, regardless of state of throttle switch.  FAIL.
ECU activates Idle Cold Start Valve, cycling it on and off for 10 seconds, regardless of state of throttle body.  FAIL.

ECU Fault Code Listing:
After cranking engine for about 7 seconds, the codes that came off were
4444-no codes recorded
4444-no codes recorded
0000-end of diagnostic output
2122-Engine speed sensor signal missing, signal used by Ignition Control Unit
0000-end of diagnostic output

Wiring tests of Ignition Control Unit:
Unplugged the Ignition Control Unit and verified via ohmmeter the following connections:
Ground to PIN 22 in ICU cable.  PASS.  Connection good.
Ground to PIN 20 in ICU cable.  PASS.  Connection good.
Tony had mentioned a 3rd ground wire to the Ignition Control unit, but I could only find two PINS that should be ground on the schematics.
Connection from brown-white cable of hall sender (which had previously been spliced) to PIN 10 of ICU.  PASS. Connection good.

Wiring tests of Fuel Injection Control Unit:
Unplugged the Fuel Injection Control Unit and Verified via ohmmeter both ground connections:
Ground to PIN 36 in Fuel Injection Control Unit cable.  PASS.  Connection good.
Ground to PIN 18 in Fuel Injection Control Unit cable.  PASS.  Connection good.
Tony had mentioned a 3rd ground wire to the Fuel Injection Control Unit, but I could only find two PINS that should be ground on the schematics.

Additional Notes:
Both the Ignition Control Unit and the Fuel Injection Control Unit were properly installed inside elastically closed plastic bags.  The terminals (the plugs) of each unit were shiny with no hint of corrosion.  I noted just a spec of something in one of the sockets of one of the plugs and on further examination it was some type of grease.  Point is that I believe that these units were cared for in terms of ensuring they didn't get wet, corrode, and that the electrical contacts were not degraded (at least inside the car).


Thanks Again to all for any suggestions as to what I could test or try next.

MC