[BeBe]

Starting a new topic, rather than tagging on the end of an old one with a title that doesn't quite match my issue.



A couple thousand miles ago, I got the Check Engine light. Car seemed to be running fine, but the blink test showed O2 sensor and Knock Sensor #2 codes.



I cleaned the <acronym title='mass air flow'>MAF</acronym>, replaced the O2 sensor, and put some Techron fuel injector cleaner in the tank. That did not make the Knock Sensor code stop ocurring. After I replaced the #2 sensor, everything was fine.



Now I'm getting a code for knock sensor #1. The difference this time is that the car does seem to be running rough. Last time, I can conclude (in hindsight) that the sensor had just gone bad. Now, I'm concerned that that sensor is working and there is something else wrong.



Any suggestions of what to check first, second, etc.?

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[flash]

the knock sensors are essentially piezo microphones. they can be triggered by any fairly high pitched clattery noise. if your valve train is noisy, that could trigger it.

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[BeBe]

How would I "quiet" my valve train? I'm concerned that one of the symptoms is that the car isn't accelerating smoothly and that there's something else wrong (besides the sensor itself).

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[tryan]

Try swapping them and see if the flash code follows.

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[BeBe]

As much trouble as it was changing knock sensor #2 without removing the manifold, I'd rather just replace #1 and see what happens.



Do the knock sensors feed something into the ECU and affect how the car runs (change timing or something)?

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[paulzebo]

Here's the Diag on a knock sensor code. The setting of a code could indicate an electrical failure which can be the sensor, connector, wire or the ECU itself. Tracking these down can be a bear. With a current code, your engine should be running 6 degrees retarded.





Knock sensor 1

Fault code 1-31 - Mounting of knock sensor (observe torque and type of screw)

- Check wiring harness and plug connection in accordance with

wiring diagram

- Reconnecting the plugs helps to eliminate contact resistances

- Check if coolant or other fluids have ingressed in the knock sensor

area

- Replace knock sensor

If the knock sensor is faulty, ignition timing is retarded by 6 degrees on the

crankshaft at a certain engine load.

- DME-Diagnosis/Troubleshooting







Knock sensor II

Fault code 1-32 - Mounting of knock sensor (observe torque and type of screw)

- Check wiring harness and plug connections in accordance with

wiring diagrams

- Reconnecting the sensors helps to eliminate contact resistances

- Check if coolant or other fluids have ingressed in the knock sensor

area

- Replace knock sensor

If the knock sensor is faulty, ignition timing is retarded by 6 degrees on the

crankshaft





Removing and installing knock sensor

1. To remove and install the knock sensors,

unbolt the intake rail from the engine. Refer

to page 15 - 21 to 15 - 22.

The coolant hoses remain connected. The

intake rail remains in the engine compartment.

2. Undo and take out knock sensors. Disconnect

connector.

3. Reinstall with a new genuine M 8 x 30 bolt

(micro-sealed) without washer.

L Tightening torque: 20 Nm (15 ftlb.)

Note

Handle the knock sensor very carefully. The

knock sensor must never drop to the ground

from greater heights as this may damage the

piezocrystal.

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[BeBe]

Would the retarded ignition timing make the car not accelerate smoothly?



Should I clean the plug with some type of cleaner in addition to unplugging/replugging (or replacing) the sensor?

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[flash]

it's never a bad idea to clean any contact with contact cleaner



retarded timing will not make it smoother. it will just make it slower.

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[tryan]

Beckman technology ( repairs mainly merc modules) has a cool little device for checking current load capabilities called a 'drop link probe'. This is a silly video but I am thinking about getting one. http://www.youtube.com/watch?v=qAEg8jcTptg

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[BeBe]

I replaced the sensor and the car seems to run/accelerate better. I did notice that the wire that runs from the sensor to the engine (or wherever it terminates) is in pretty rough shape. I think there was a family of mice living in the engine bay where the <acronym title='previous owner'>PO</acronym> kept it. I already replaced the plug wires because they looked like they had been chewed on.



The outer insulation on the wire leading away from the sensor is compromised. I can actually see copper. I didn't have a replacement, so I just put wrapped some tape around it and reconnected it.



Does anyone know the part # of the wire/harness that runs to the knock sensors? I can't find anything in the parts catalog. On sheet 901-00 (where the sensor is depicted) there is a wire designated as #32, but there is no part # corresponding to the callout in the description table.

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[jfrahm]

You might find knock sensor repair harnesses on Ebay or the like. It might be the same as an injector harness.

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[BeBe]

For whatever reason, I can't clear error codes without disconnecting the battery. Anyway, I did that and have put about 100 miles on the car without the code coming back, so I assume it's fixed. So now I've replaced both knock sensors and I conclude that the knock sensor is only there to sense when the sensor goes bad (and to make the car run poorly after it does by retarding the timing).

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