No Start: Audi 100, 1990, I5 NF engine, non-turbo, non-quattro, CIS-E-111 (California)

[Marc Boucher]

I've updated the list below with some additional tests and two minor corrections in what I'd typed before.

Additional tests:

Disconnected hall generator and verified continuity of each of 3 wires to ECU:

Red-Black to PIN 4 on Ignition Control Unit : PASS
Brown-White to PIN 10 on Ignition Control Unit: PASS
Green-White to PIN 24 on Ignition Control Unit: PASS

Also performed this test in a 'duplicate' manner by running a second wire from the brown-white to PIN 10.  Still, no start.

Additional or Repeated Ground Tests:

Re-verified that the ground PINS for the Fuel Injection and Ignition Control Unit listed below are all ground.  All Pass.

In addition, performed a physical inspection of the ground points.  
Engine ground behind intake manifold
Engine ground linking ignition to rocker cover
Main engine ground
The only ground that I can't find is described as "a brown wire that attaches to the base of the right side of the "A" pillar.  This grounds Pin 22 on the Ignition Control Unit.  PIN 22 measures that its connected to ground, but I'd still like to find the actual connection and verify it.  The base of the right-side "A" pillar is where the Fuel Injection Control unit is located.  I can't find any brown wires attached to the A pillar anywhere around there.  Anyone have any ideas on how to find this final ground wire?  I did find a major ground attached to the left (driver's side) A pillar almost at the level of the bottom of the driver's window.  This seemed like it was a ground for the dash.   But I can't find a ground wire on the right side A pillar.

Further Tests or Conclusions:
  
1.) At this point, the grounds to the Ignition Control Unit and Fuel Injection Control Unit have been checked and rechecked.  We know the Ignition Control Unit is grounded.   We know that the car starts when the brown-white wire on the Hall Generator is grounded.   We know that the brown-white wire on the hall generator has continuity with PIN 10 on the Ignition Control Unit as per the schematics.  Thus isn't it a reasonable assumption at this point that the ECU system is grounded, and its simply not passing the switched ground onto the Hall Generator or, for that matter, all the other items that it controls (since ISV, Carbon-Canister, Cold-Start, and differential pressure regulator all failed tests)?  IE, isn't it a reasonable conclusion that the fault is indeed in the ECU, and not the wiring?

2.) If the car starts and drives well using the hall ground that the mechanic installed, is there any risk in driving it short distances until I get a new ECU, or get the problem fixed?  In other words, I understand that the ECU (combined Ignition Control Unit and Fuel Injection Control Unit) serves the primary purpose of optimizing performance by adjusting ignition and fuel across a wide range of temperatures, pressures, etc..  Without it, the car won't shut down, its simply going to run rich or lean or idle too fast or slow.  Is this correct?

Thanks again,

MC


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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 = infinite
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 35 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