YucatanAudi

<center><img src="http://www.autohausaz.com/secure/PartImages/0261231036.jpg"></center><p>Pulled the codes and got Knock Sensor (<b>a_CQ</b> was right on). It always 'looked' ok... but when I went to wiggle the wire near the connector, it was obvious the cable was badly deteriorated and cracked. Just sitting there, it looked clean and fine. So, I ordered a new one (around $44 at AutoHausAZ) and slapped it on there.

WOW... it's like I have a whole new engine. I always thought it was doggy cuz of the Auto Trans. It still isn't any speed demon, but the smoothness, quietness, and additional power - all just from replacing the knock sensor is really a surprise.

For the cost, I'd say anyone who has any question at all should just replace it. When I got mine off, the plastic covering the sensor ring itself was cracked too, but not visible when it was on the engine. Likely, it was totally dead or sending totally bogus signals to the ECU all along - for way too long.

Also, I replaced the Fuel Pump Relay. No indication that the old one had ever been replaced. So, for a few bucks, to insure that didn't become a problem, I replaced it. (Fuel pump and filter replaced last year.)

And... just to pass on the goodwill, here's some info on Knock Sensors from Audi:

MIL ON - DTC 2141, 2142 or 2143, Knock Sensor
90audi08

Subject: <b>Vehicle loses power</b> (Supercedes 89-01, dated Jan. 31, 1989)

<b>All engines with knock sensor ignition </b>
Model(s): from 1984 to 1991 - Group: 28

Number: 90-03
Date: December 31,1990
<b>Condition:</b>
^ engine loses power, performance is reduced (possibly intermittently)
^ OBD light (On Board Diagnostic) comes on while driving (if equipped)
^ fault codes 2141, 2142 or 2143 are stored or displayed (if equipped)

<b>Possible Causes:</b>
^ poor connection (corrosion, loose etc.) between knock sensor and harness connector
^ knock sensor has incorrect torque
^ engine block surface that contacts knock sensor is not clean
^ poor ground wire connection on intake manifold
^ knock sensor assembly has internal damage, broken or fatigued wiring or terminals
^ moisture in control unit
^ engine oil level too low resulting in higher than normal levels of mechanical noise or vibration

<b>Service solutions:</b>
^ check engine oil level, top up if necessary
^ activate fault memory (if equipped) and follow the procedures outlined in the Repair Manual for that vehicle, refer to Repair Group D2 for later models
^ ensure that correct control unit is installed in vehicle, replace with correct control unit if necessary

CAUTION:
Do NOT mix 49 States and California control units. They must be installed in matched pairs.
^ check the condition of the knock sensor and knock sensor harness connector terminals, if loose or corroded repair or replace as necessary

Note:
New terminals (gold plated) must be installed in the harness connector if a new color coded knock sensor is installed (see chart on next page).
Power Timing Contacts (brand name): Part number N 903 35207

CAUTION -- Do NOT apply dielectric grease when using these terminals.

^ remove knock sensor from engine block
^ inspect contact surface; clean as necessary and reinstall knock sensor
^ carefully <b>torque</b> knock sensor to specifications:
engine codes NF, NG and 3A: 20 to 25 N-m (15 to 18 ft.lb.)
engine code PT: 20 N-m (15 ft.lb.)
engine codes KH, MC and 7A: 10 N-m (7 ft.lb.)

For engine codes NF and NG^ inspect ground wire connection on intake manifold, clean and tighten if necessary
^ ensure that stud for CO tap tube clamp is clean and securely fastened
^ check for knock sensor assembly internal damage as follows
^ raise engine speed to approximately 3000 RPM
^ grasp knock sensor wire at a point 20 to 70 mm from the harness connector
^ carefully bend knock sensor wire by pulling up and down while twisting slightly
^ if the wiring is damaged the OBD light in the instrument cluster will light up

If YES
^ replace knock sensor harness connector terminals with new gold plated version
^ Part No. N 903 35207

^ replace knock sensor assembly with new color coded version

...................... Color
<u>Engine code ...... code ..... Part number</u>

3A and NG ........ Blue ..... 054 905 377

KH .................. Black .... 034 905 377F

NF .................. Green .... 054 905 377A

MC w/one ......... Black .... 034 905 377F
knock sensor

MC w/two ......... Red/ ..... 054 905 377C/D
knock sensors .... White

PT .................. Black .... 054 905 377A
................................ 077 905 377A

7A .............................. 034 905 377B/F

^ check ignition control unit for signs of <b>moisture</b>

If present
^ determine source of moisture and eliminate
^ inspect ignition control unit for internal moisture

If present (internal moisture in Ignition Control Unit)
^ replace ignition control unit
^ inspect ignition control unit harness connector for moisture or damage, clean and dry connector if possible

If connector damaged
^ repair or replace as necessary
^ install waterproof protective shroud
^ Part number 447 905 293
If all checks up to here OK (engine codes NF and NG)^ install new ignition control unit (Blue Dot) as follows

For vehicles built before the following VIN numbers:
Audi 80/90 VIN 89 - KA249248 Audi 100 VIN 44 - KNO81879
Install the following ignition control units:
49 State: Part No. 443 907 397C
California: Part No. 443 907 397E

For Audi 100 vehicles built between the following VIN numbers:
VIN 44 - KN081879 and VIN 44 - KN250000
^ install the following ignition control unit
^ Part number 443 907 397L

For Audi 100 vehicles built after the following VIN number: VIN 44 - KN250000
^ install the following ignition control unit
^ Part number 443 907 397M

CAUTION
Part numbers are for reference only. Always check with the Parts Department for the latest information.

520

Glad we could help Thanks for all that info too