[urq] Two in a row and a bonus mark

[QSHIPQ at aol.com]

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Warm or cold, IME the standard procedure for cking ignition components
reveals this problem.
For the rpm sensor itself:
"connect ohmeter between turminals 1 and 2 of unplugged connector
  *  specification 1K ohm
If specification OK
-   Connect ohmmeter between terminals 1 and 3 then 2 and 3 of unplugged
connector
  *  Specification = infinite ohms

If specification not ok
 - replace rpm sensor
If specification OK
- Check wiring and connectors betweeen sensor and control unit as follows
-  using ohmmeter, check between terminals of speed sensor  connector C and
contrrol unit connector A

T1 conn C  >  T29 connn  A
T2conn  C  >  T11 conn  A
T3 onn  C  >  T28 conn A
 ---  Specification = approx 0 ohms.

If specifications not OK
 -  CHECK FOR OPEN CIRCUIT IN WIRING BETWEEN ENGINE RPM SENSOR AND CONTROL
UNIT"

IME with starting problems eventually traced to frayed wiring on the rpm
sensor, the resistance is usually found in inconsistant ohm readings.  These
can vary depending on the temperature of the car at the time of the test.
I've also found that the rpm sensor code is usually triggred at somepoint
during the testdrive, usually on initial download of codes.  Put another way
(by a 16 year audi tech) - a good shop should keep an extra rpm sensor around
-  if the rpm sensor replacement doesn't resolve the problem, the wiring from
the connector to the computer should be suspect, per audi service training.

More:
If it's a hard or intermittent no start, the no start should have triggered
the rpm sensor code (5 seconds crank, then download codes), then follow the
above procedure.  IME with this problem, everytime the idle dips from
intermittent rpm sensor reading, the code is stored.  Phil, IMS, the shop
that found the original problem scoped out the sensor to find the problem.
If the signal failed at some point (or in the no start condition) a repeat of
the above test should have gotten an inconsistent ohm reading on the above
connector tests.  IME2, the ohm readings on test2 don't need to be far off 0
to have a problem.  In continuity to the computer 3 ohms resistance is
significant.

I'm intrigued that this couldn't be found with standard audi service
procedures to this sensor.  What "non-standard" procedure was necessary?

Scott Justusson





In a message dated 9/28/02 12:17:33 PM Central Daylight Time,
philp at isham-research.com writes:


Why is it that a problem I've never seen before hits me twice in as many
months?

Patient 1 was a 1990 Type 44.  Patient 2 was a late 1987 MB ur-quattro.

In both cases - weird non-starting problems traced to a crankshaft speed
sensor with a damaged
shield wire.

After much effort in both cases, I might add.