Puzzled on Knock Sensor

[Dustin P]

My 86.5 N/A had a code 52 so I checked for continuity from the knock sensor to the ECU and that showed good.

Naturally, I assume the knock sensor is at fault and replace it. Well, I've still got a code 52.

What has me confused is the whole circuit consists of the knock sensor and the wire going to the ecu, correct?

So, what could be at fault short of the ECU?

 

[ForcedTorque]

Did you reset the ECU when replacing the sensor?

 

[hvyman]

The shielding wire around the knock sensor could be bad.

Id do the rewire and then go from there. Highly unlikely that the Ecu is bad.

Also did you clear the codes and then re check after replacing the knock sensor?

 

[Tuner.87]

continuity test don't always give the best reading. If you have any knowledge of your meter you can do a voltage drop of the knock sensor wiring from the sendor to the ecu. Usually a safe voltage drop for ciruits is no more then .3 volts. You could have continuity but just have a high amount of resistance in the circuit and high would cause a high voltage drop across the wires.

 

[hvyman]

Except there is not 12v on the knock sensor wire. The sensor makes a very small amount of voltage when it hears a knock. It's a resonant type knock sensor.

Also by doing a continuity test and seeing the amount the wire ohms out to you would be able to see if that wire has unwanted resistance in it. Iirc with the older wiring will usually have about .4-.6ohms in it.

The wiring is most likely old and brittle and getting noise into the system.

 

[Dustin P]

I did not reset the ECU but the check engine light was gone for about 15-30 minutes before it illuminated again. During this time, I was allowing the engine to idle in order to warm up. If I recall correctly the CEL did not illuminate until the engine had reached operating temperature. This makes me wonder if the KS wire has too much resistance once warmed up.

I also had a bad TPS which I replaced at the same time and the code is gone for that.

The engine still feels sluggish. It's especially noticeable in about the upper 1/3rd of the RPM range. As I understand it, the ECU automatically retards ignition timing 10* in order to be sure the engine is not destroying itself in the event of a faulty knock sensor circuit so I assume the sluggish feeling is stemming from whatever is causing the code 52.

I probably won't have the opportunity to check the resistance in the KS circuit until Sunday at earliest. Just to be clear, what is an acceptable resistance range?

 

[jetjock]

The wiring can't be drop tested as is. Not enough current. Doesn't mean some couldn't be added though. Imho more trouble than it's worth.

 

[Tuner.87]

that's true didn't think about the fact that there is not voltage through it all the time

 

[Dustin P]

I reset the ECU and the car ran great until it setup the code again. Immediately lost power when the CEL illuminated. Seeing as the KS is new and the only other components of the circuit are the wire and the ECU I'm going to rewire it. I don't think this is an ECU issue so the rewire is really the only thing left to do. Thanks to anyone who took the time to reply to my question.

Looking back it feels like a silly question. It's funny how a lot of times you end up answering your own question in the process of typing it out or even just talking to yourself.

 

[Dustin P]

I reset the ECU and the car ran great until it setup the code again. Immediately lost power when the CEL illuminated. Seeing as the KS is new and the only other components of the circuit are the wire and the ECU I'm going to rewire it. I don't think this is an ECU issue so the rewire is really the only thing left to do. Thanks to anyone who took the time to reply to my question.

Looking back it feels like a silly question. It's funny how a lot of times you end up answering your own question in the process of typing it out or even just talking to yourself.