Knock Sensor Picking Up Signal Unhooked(Help)

[spadepro22]

Been trying to track down my knock issue today so we did some trouble shooting. We unhooked the knock sensor from the connector and turned the threshold down to 1200rpm and when I pat the gas ecm link is showing 3.2 counts of knock. With it plugged up correctly and I rev up at idle(car on) its showing 15 counts. I know that it is phantom, but what would cause it to pick up knock with it unhooked? Even cut the knock sensor wire from the ecu(pin 9) and it still picked up knock. The wire was connected back to the ecu properly. The ecu looks fine and was checked out by the guys at ecmtuning when I upgraded to v3 back in November. Does the shield around the wire need to be connected/grounded to something because it stops by the ecu were the plastic covering stops and the white wire appears.

 

[hotrodssnova]

The knock sensor will default to a set amount when unhooked. Try unbolting it from the block, hooking it back up to the harness, and set it up in the firewall. Then you will know if its good or not. No knock would say its good. If you get knock while its on the firewall, I would say replace.

 

[spadepro22]

The knock sensor will default to a set amount when unhooked. Try unbolting it from the block, hooking it back up to the harness, and set it up in the firewall. Then you will know if its good or not. No knock would say its good. If you get knock while its on the firewall, I would say replace.

What do you mean by setting it up in the firewall? Also I had a flairly new knock sensor that we hooked up to the harness and put in the hole where the biss screw is just trying thinks and it still did the same thing. I don't think its a knock sensor issue itself, but a wiring or signal issue.

 

[luv2rallye]

The shield around the knock sensor wire must be connected to chassis ground. It may not be right at the ECU pin 9 but farther back towards the sensor somewhere according to the diagrams (it doesn't show where). Connecting the shield to ground near pin 9 would be ok too though.

 

[spadepro22]

The shield around the knock sensor wire must be connected to chassis ground. It may not be right at the ECU pin 9 but farther back towards the sensor somewhere according to the diagrams (it doesn't show where). Connecting the shield to ground near pin 9 would be ok too though.

So I should cut the plastic back some from around the wire so I can add wire to the shield and ground it? Also is there a ground I need to check for besides the shield? What pin if so or where to look to make sure its grounded?

 

[luv2rallye]

The diagrams show a black-white wire in the knock sensor's 2 pin connector which connects it's shield to another separate shield that is around the white wire going to the ECU. Somewhere (perhaps through harness, again diagrams don't show where) it also connects to ground along with the shield around the O2 sensor. I suggest verifying (with multimeter ohms setting) that the connection is good to chassis ground from the ECU end of this shielding (bend the wire around while measuring to check for electrical breaks). I would also then measure the connection to ground from the knock sensor's shield wire (as close as you can to the sensor itself - perhaps sticking a pin through it's insulation and again bending the wire). Of course you may also just have a bad knock sensor.

You shouldn't have to connect the shield to ground at the ECU end although you can if you wish. Other grounds on the ECU should be pins 101 and 106.

 

[spadepro22]

Same thing was happening with two knock sensors. We even cut the knock sensor close to the ecu and it still picked up knock. This is a list of things we tried yesterday in this link.

http://www.dsmtuners.com/forums/tuning-engine-management/461123-low-timing-still-knock.html