Can someone explain to me how the factory knock sensor works on our cars? In theory, I suppose it should detect knocking or predetonation and then retard the timing accordingly. If so, then why is the knock sensor not a viable option to other timing retard methods with F/I. Granted, I won't want to risk everything with just a cheap knock sensor, but shouldnt it act like a safety valve of last resort?

 

I have heard mention that the factory sensor reacts too slowly and with not enough timing retard to prevent damage under FI conditions.

 

It's an integral part of the J&S Safeguard timing controller.

 

They can only hear soft pinging, so soft that you would never hear it. It's basically just to provide performance to the user, but save the motor in the event of bad gasoline. Detonation on a FI steup is usually audible and very destructive. It sounds like metal berrings shaken up in a coffee can.

 

A knock sensor is nothing more than a microphone. Your ECU is programmed to literally listen to your engine for tale-tell signs of detonation. Usually between 10-15khz. So it totally depends on the programming of your ECU to listen correctly and to retard as necessary.

The J&S taps into this line and listens also. It doesn't care about external engine noise(you have to calibrate it) RPM or unlike the ECU.

 

Jesseenglish,
Do you know where the knock sensor is located?
Mike

 

It is mounted between the two heads on the top of the engine block near the front. You have to remove the upper and lower plenum to get access to it.

 

Thanks, I may have disturbed it in some way?

 

And the wire is too thin or sensitive, some have even moved it. I don't reccomend that but just so you know false knock has been known to occur with me at the track and on the dyno when I had too much vibrations and was N/A and I was told because it was poorly placed (the stock one.)

 

A little off topic but I recently installed the J&S, and set it to 2degrees RPM retard and 10 degrees maximum individual cylinder retard based on knock. I noticed when I am WOT in 3rd and 4th gears when I hit like 6000 rpms the gar goes "POP" "POP" and stutters like it hit the rev limiter then keeps going through it.
I run 94 octane on a 9lb ATI set up. I mentioned this to John at J&S and he said something about sending it back so he can adjust the DWELL? But I thought it was my plugs since I fouled the plugs before so I replaced them and it still does it..Any thoughts?Does the J&S pull timing that abruptly when it picks up knock???

 

Please read the theory of operation on the J&S website...

If knock is detected on a fireing cylinder then plug will not fire on the next revolution.

This is supposed to be on a cylinder by Cylinder basis..

Regards Amy -

 

If the unit detects knock, it retards the timing for that cylinder, the next time it comes up to fire. It does not kill the spark.

 

YEs, when the retard kicks in and you are in all cylinder retard mode, you can definitely FEEL the car losing power momentarily.

G

 

I have it set for Retard per cylinder max of 10 degrees plus 2 degrees of rpm based retard..But it seems like when i near 6000 (sometimes 5800-6200) It hist the rev limiter prematurely..Same as when I had a fouled plug but my plugs were brand new...John had mentioned something about Dwell time? But do you think I am detonating and the J&S is just pulling so much timing to save my engine that its causing the misfire or is there something wrong with the unit?The symptoms only manifested after the unit was installed...and its only in 3-4-5 gears...

 

Yes but will this be that abrupt that it feels like you hit the revlimiter???

 

Per a VQ FSM:
The knock sensor retard system is designed only for emergencies. The basic ignition timing is programmed within the anti-knocking zone, if recommended fuel is used under dry conditions. The retard system does not operate under normal driving conditions. If engine knocking occurs, the knock sensor monitors the condition. The signal is transmitted to the ECM. The ECM retards the ignition timing to eliminate the knocking condition.

The knock sensor is attached to the cylinder block. It senses engine knocking using a piezoelectric element. A knocking vibration from the cylinder block is sensed as vibrational pressure. This pressure is converted into a voltage signal and sent to the ECM. Freeze frame data will not be stored in the ECM for the knock sensor. The MIL will not light for knock sensor malfunction.

I believe the ECU factory programming is LIMITED on maximum degrees of timing retard possible, so with FI and hot temps/bad gas/etc., you'll need more.

The J&S is sensitive enough to kick in BEFORE the factory saftey measures kick in or your ears can even hear, yet pull far more timing then the OEM programming allowed.

Honestly, for as much money as you guys throw into your engines, I can't see how you couldn't justify $500 just to save a motor even ignoring the performance tuning benefits.

 

Ice....like I said..this thread is MONTH AND MONTHS old...we are beyond this now.

I am using the eManage to retard a very safe amount of timing...its working perfectly....and it only cost me $30 vs. $500

Despite that, I have been an advocated of the J&S for a very long time...do a search on my thread titled "J&S with eManage". It is a great unit, but there are some wiring or technical issues that are blowing coils on the VQ motor. A lot of people don't wanna talk about it. I hope John from J&S can get his unit working reliably with our motor, becuase its an amazing device, and a terrific safeguard against detonation.

Oh, and thanks for looking after my pocket-book....I dont know what I would do without you holding my hand.

 

please expound on these technical issues on the 350z coils blowing??

 

Doh~! Missed the dates.<~~me

Keep them purdy new slugs/rods in one piece now.

 

OK....


The reason is still unknown as to why the coils are blowing. The J&S, and the Greddy Ignition harness (before people put diodes on the lines, and kept the car out of the key-on-engine-off position), both put current on the ignition wires. With our direct ignition system, there is one coil pack on top of each plug, and for whatever reason, they are getting over heated...due to excess current.

If those that blew their coils wanna chime in...go ahead..but in respecting their privacy, I'm not naming names.