Any way to modulate knock sensor effect?

[uniberp]

My 97 2.2 is the smoothest engine I ever owned, but it runs much better in 2k-2.6k revs with the resistor in place of the knock sensor, which I replaced and torqued correctly. With the knock sensor, it really kind of bogs at 2.2k-2.6k. New front 02 sensor too.

 

Premium gas helps a bit, but is there a way to really test how much detonation is going on and maybe adjust the curve with a varistor or something?

 

I've run techron through, no diff. And the car runs perfect for the first hour after disconnecting the ebattery for an hour and reconnecting.

[nipper]

i have no idea whay the resistor works in place of the knock sensor, as it really shouldnt.

 

The knock sensor is a piezo electric sensor (think microphone). It creats an AC signal, and the ecu examins that signal (the spikes) to adjust the timing to reduce the spikes.

 

nipper

[porcupine73]

Apparantly the ECU doesn't mind not seeing any signal or just a little noise, as long as the circuit resistance is roughly correct.

 

You might be able to reduce the amplitude with a voltage divider. If the knock sensor impedance is 500k-ohms, put a ~500k-ohm resistor in parallel with the knock sensor, and a 250k-ohm in series to the ECU. Then the ECU still sees the same resistance, but the signal amplitude should be 1/2. This might not be enough amplitude for the ECU to detect knock if there is any though.

[uniberp]

Apparantly the ECU doesn't mind not seeing any signal or just a little noise, as long as the circuit resistance is roughly correct.

 

You might be able to reduce the amplitude with a voltage divider. If the knock sensor impedance is 500k-ohms, put a ~500k-ohm resistor in parallel with the knock sensor, and a 250k-ohm in series to the ECU. Then the ECU still sees the same resistance, but the signal amplitude should be 1/2. This might not be enough amplitude for the ECU to detect knock if there is any though.

 

So what you are all saying is I need to hook up a scope to the KS output, match the signal spikes to likely cavitation damage points, and .... duh, nevermind.

 

How about something that would just cap the spikes? Would that be a voltage clamp or zener diode or something, (terms I found)?

[porcupine73]

afiak at any given point in time the ECU either thinks it is detecting knock or it isn't. I don't know if that decision is based purely on the amplitude of the knock sensor signal. If it is based purely on the amplitude, then clipping the signal to below that point would simply mean the ECU would never detect knock (even if knock were present).

 

Not sure if this is helpful but here is the descrption endwrench gives:

endwrench knock sensor description:

The knock sensor is designed to sense knocking signals from each cylinder.

 

The knock sensor is a piezo-electric type element which converts knocking vibrations into electrical signals. The electrical signal is sent to the ECM, which changes the ignition timing to reduce the engine knock or ping. For this system to work correctly, the sensor must first hear the engine ping. The driver of the vehicle may also hear a small engine ping. A delay of approximately 1-2 seconds is normal, depending on the fuel quality, engine load, air temp, etc. At this time, the ECM will retard the timing.

 

This function can be viewed on the Select Monitor RTRD mode. When the knock is eliminated, the timing is gradually advanced to the specified setting. If engine ping is heard again this process is repeated. This will continue until the knock sensor no longer hears the engine knock or ping.

[uniberp]

afiak at any given point in time the ECU either thinks it is detecting knock or it isn't. I don't know if that decision is based purely on the amplitude of the knock sensor signal. If it is based purely on the amplitude, then clipping the signal to below that point would simply mean the ECU would never detect knock (even if knock were present).

 

Not sure if this is helpful but here is the descrption endwrench gives:

 

Thanks. I've never hear the engine knock or ping, but then, I am getting to that age where not hearing has advantages. I will check the fuel filter, like the article says.