Knock circuit question

[boostmaster]

Trying to chase down an issue of no knock retard. I have checked and eliminated the knock sensor itself, the ECM and the ESC module on the fender. What else could I be missing? Just FYI I checked the components by replacing them with known working parts and the knock sensor itself by banging near the knock sensor with a long extension and viewing changes in AC voltage with a DMM. So I know the sensor itself works. But when I plug up the wire and try the same test.......nothing. It's not in the chip either. Could I have a bad Ignition module? Otherwise the car runs ok.

Thanks, Pete

 

[SHADOWII]

Have you confirmed the wiring itself? Have you verified the knock sensor is not over tightened(14 ft/#'s) as this is reported to be a common problem w/it's performance.
Might give John Spina a call from "Caspers", or catch him when he is on the forum.

 

[balanegra]

Pete, if you are tapping on the block near the knock sensor, the engine speed has to be above 1000 RPM before you will see anything on a scan tool. Knock is ignored by the ECM below 1000. Prevents retard during engine starting.


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[boostmaster]

Pete, if you are tapping on the block near the knock sensor, the engine speed has to be above 1000 RPM before you will see anything on a scan tool. Knock is ignored by the ECM below 1000. Prevents retard during engine starting.


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You are correct but in my past experiences when testing key on engine off the ECM shows knock counts. And yes I have confirmed the harness, no problems there. Had that thing completely filet. So my thoughts are that the module is bad not retarding timing.

 

[balanegra]

You stated that you had tested with other known good parts. How could it be the module. With the information you have provided I would look at the ECM itself or the chip. The input circuit of the ECM. Could be damaged or the knock retard could be disabled in the chip.


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[RmvBfrFlght]

One test is to check the voltage the knock filter is sending to the ECM. At key-on, engine-off it should be about 9 volts (it does vary a little). This is at ECM pin B7 (YEL/BLK).

When the knock filter reports knock it allows that voltage to go close to 0 volts. So rap around the sensor while watching the volt meter. The voltage only goes to zero for short amounts of time, but the volt meter should at least budge a little.

This wire originates at the knock filter, pin C.

RemoveBeforeFlight

 

[boostmaster]

You stated that you had tested with other known good parts. How could it be the module. With the information you have provided I would look at the ECM itself or the chip. The input circuit of the ECM. Could be damaged or the knock retard could be disabled in the chip.


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I didn't swap the ignition module though.

 

[boostmaster]

One test is to check the voltage the knock filter is sending to the ECM. At key-on, engine-off it should be about 9 volts (it does vary a little). This is at ECM pin B7 (YEL/BLK).

When the knock filter reports knock it allows that voltage to go close to 0 volts. So rap around the sensor while watching the volt meter. The voltage only goes to zero for short amounts of time, but the volt meter should at least budge a little.

This wire originates at the knock filter, pin C.

RemoveBeforeFlight

Wouldn't this be the same thing:

Just FYI I checked the components by replacing them with known working parts and the knock sensor itself by banging near the knock sensor with a long extension and viewing changes in AC voltage with a DMM. So I know the sensor itself works

 

[RmvBfrFlght]

Wouldn't this be the same thing:

Just FYI I checked the components by replacing them with known working parts and the knock sensor itself by banging near the knock sensor with a long extension and viewing changes in AC voltage with a DMM. So I know the sensor itself works

No, doing the test the way I outlined it also includes the knock filter, the wires & connectors.

RemoveBeforeFlight