Replaced Knock Sensors - How Long for Computer Reset?
 

2001 C5 6 speed stock motor.

I have had some pinging issues and determined that the knock sensors were bad. It was pinging at WOT. Scanner determined that the computer was not adjusting timing when it was pinging. Replaced the knock sensors and now the timing is adjusting but the knock is still there. My mechanic explained that the computer needs a few hundred miles to adjust and broaden settings based on new learning. Does this make sense and can anyone add any more information to this?

Is there something else to consider? Cleaned MAF and did top end cleaner before replacing knock sensors.

Thaks in advance.

Your knock may be something mechanical knocking or carbon issues. The knock sensors are like microphones, as soon as they sense SPARK KNOCK, the computer should pull timing out till the knock goes away. They are tuned to the sound spark knock makes, if your engine is knocking for other reasons you have other issues.

Thanks for the reply... Yes, thats correct... As mentioned, the computer was not adjusting the timing with the old sensors and now it is but there is still a knock. I have only driven it 10 miles since replacing the knock sensors.... Does the computer need to to re-learn since it is now detecting knock and do the parameters need to widen?

If not, whot other mechanical issues could caus ethe pingng?

You could have a lot of carbon on the intake valves/pistons that causes more knock with "flare up" when the carbon get hot. You could try the SeaFoam de-corbonizing treatment-be prepared for the GIANT clouds of smoke. That may help is it the exact same noise you have before the sensors and I "assume" you have a stock tune on the computer???

The knock sensors detect when there is knock. There is no computer learning required. Either you have a bad component or the car is knocking.

Peter

Don't rule out bad gas.

Thanks for all the replies.... Let me clarify.

* I always use 93 octane.
* I have done top end cleaner several times.
* I have cleaned the MAF several times.

Last resort was scanning with a laptop while running the car at WOT through the gears. The prognosis was that computer was not adjusting timing (or anything) when the knock was occuring. This indicated that the knock sensors weren't working so I replaced them. The new sensors are working and the computer is adjuting timing.... Just not enough (yet) to stop the knock.

I have had two local mechanics confirm that the computer now must learn the new parameters required to control the knock. Since no adjustments were being made while it was knocking with the bad sensors and now, all of a sudden, it knocks, the correct adjustments to overcome completely take time to learn since new sensors are actually sending information now.

I was hoping to confirm this with knowledgeable folks on the forum.

You can believe what you want but I have never seen anything to indicate the computer learns the knock sensors and I'd love to know how it could. The knock sensor is the feedback so it has no way of knowing if the feedback is wrong.

This would be like saying the computer learns what the O2 sensor signal means. Wrong because it doesn't. It uses the O2 feedback to adjust the fuel. If the O2 acts up then it can mess with the fuel.

Peter

Wow...love is a strong word...

There is a control module within the PCM that monitors noise pickup from the knock sensors. Over time, it samples minimum/maximum noise levels, background noise, etc. Samples are taken at idle, various rpms, etc. From that data, it determines the high/low noise from normal operation....and only uses the captured data from cylinders at the TDC position(firing). When it senses an abnormal frequency(knock) the PCM will pull timing, until the signal is null (or back to the original sampling). So yes...it does do a learning routine of sorts.

That being said, I would be more concerned why the engine is knocking to begin with.

Thanks, this is the affirmation I was looking for.... Certainly, I have not been able to determine why the knock was occurring and did most of the recommended remedies to prevent it. The fact that knock sensors exist in the motor suggests that knock can occur and the computer should adjust various parameters to correct it. I am hopeful that the control module you are referring to will relearn the normal and abnormal sounds. Without them working, the computer has been assuming the sounds have been normal or not hearing them at all.

Gotta love CF