Wheelerbob

I hope this is not a old question but I could not find any info with the search. I have an 09 and have a superchips tuner, I had pinging every now and then on the 87 tune so I switched to the tow tune on 93 octane fuel. I think I heard a ping today but am not sure so I started monitoring my knock voltage with my Aeroforce guage. I am seeing knock voltage fluctuate between .1 to .2 at idle .4 to .6 cruising and under hard accel .8 to 1.0. My question is what voltage is normal and at what voltage does the ecm consider it a knock ( ping ). This is the first time I have heard anything since I switched to 93 and the tow tune. If this is in the wrong section I'm sorry, any info would be appreciated.

ronjenx

Most of the sensors get 5 volts to operate on. I assume the knock sensor does. too.
The voltage from the knock sensor will not be zero due to engine background noise, even when there is no knock.
Your low readings are probably from that background noise.

I could not find a voltage for the knock threshold.

Can you go back to the tune that gave you the knock? See what the voltage is when it occurs.
Is "Knock Retard" a value you can see on the AeroForce gauge? Watch it if you can. This, with the voltage readings, will give you an idea of the knock threshold voltage.

Wheelerbob

The aero force reads knock sensor voltage, I could go back but I'd have to go back to the 87 tune and 87 octane as well, this will take a couple tank fulls to get back to pure 87 in the tank. I was hoping that someone out there knew what the ecm was looking for to save the time and hassle of switching back.

Wheelerbob

anyone? anyone?

GoodysGotaCuda

Actually most make their own voltage and are piezo-electric sensors. I'll have to dig through my books and see if there are any values.

To the original poster, until then I'd suggest watching the ignition timing and see if you notice any spikes or signs of it dropping when its pinging until you get the info you need. Most factory specs just aren't littered around the Internet for sensors like that. They vary a lot between different engines so it would be hard to say what is correct without getting the information from jeep. Just my opinion.

Pinging on the 87 tune with 87 is very common with the super chips. I haven't had any issues with 91 or 93 on the tow tune. I also lost the ping with 89 octane on the 87 tune. (@ 2500ft or so elevation)

Doc_D

I'm pretty sure the SuperChips allows you to monitor the knock retard which is probably more reliable than trying to watch the knock sensor directly. They might use a pretty complex algorithm when evaluating that voltage and determining what does and doesn't constitute knock. It could vary by RPM for example. It might be averaged over a certain number of cycles and then be compared to a percentage threshold. They could look at very small time periods during the actual ignition events and ignore other time periods, etc.

For what' it's worth your observations of the knock sensor voltage pretty much mimick mine and I do not believe I am experiencing any knock or pinging.

I drive a manual and notice a hesitation on throttle tip in after a shift in both stock and tuned form. Many manual drivers notice this as well. It coincides with a major reduction in timing advance (like -3.0 degrees total timing). I talked to the Superchips guys and they say this is Chrysler's algorithm for throttle rate timing reduction. Chrysler basically looks at the rate of throttle change and will retard timing for fast changes. I notice when the timing is that retarded there is almost a rattling noise that sounds similar to knock or ping but it is not. I wonder if this could be what a lot of people are complaining about.

ronjenx

What I meant was, most of the sensors on the JK get 5 volts to work with. I wasn't sure about the knock sensor.
After a little research, I agree the knock sensor is piezo-electric, making it's own voltage, but don't see that anywhere in the factory service manual, which is pretty good at describing all the other sensors.

The only mention of "piezo" is when it talks about the 2.8L diesel injectors.

Wheelerbob

UPDATE!!!! Ok I finally got some time to play with my superchips to check my actual knock retard as suggested. I drove around today for about 1/2 an hour and did several wot runs and did not register any knock retard at all. I guess the thing I thought I heard I did not hear after all. Anyway thanks for the help.