Knock Sensor Question

Hello Andre,

I have recently installed a 'stand alone' G1 Knock Block to be used as an audible aid with my G4+. Due to the fact that my engine (Nissan VG30ET) has limited locations for a second knock sensor, I decided to stack the 2 bosch (2 prong) sensor on top of each other and use one bolt to fasten them into the block. I took some care in lightly sanding the engine block so that the 1st knock sensor had smooth surface to mount on and then I lightly sanded the top of the 1st knock sensor, closest to the block, so that the 2nd knock sensor had good metal contact.

I am currently trying to dial in the individual cylinder gain. Some details - normal operating temp, medium throttle, wasted spark ignition, knock sensor located over #3 cylinder. The issue I am having is that sometimes the (#1/#4) is 2 to 3 times higher than (#2/#4) & (#3/#6). I turn the engine off for a couple hours, start it up to the same details above and (#2/#4) is 2 to 3 times higher than the other two or (#3/#6) is 2 x 3 times higher than the other two.

At full throttle the engine noise is much more consistent. However, I hold some concern about the accuracy of full throttle when the G4+ bounces around at medium throttle. Why do you suppose this inconsistency is happening?

I look forward to your reply.

Best regards,

David

Hello Phram

Mounting knock sensors correctly is important and not overly difficult. Mounting two of them on top of eachother is not something that will increase accuracy, the opposite is likely the case and no car manufacturer to my knowldedge has ever done this. In fact, you will be better off using only one sensor per mounting point, make sure the mating surfaces are true, tighten the centre bolt according to spec with a properly calibrated torue wrench (~2.6Nm). OEM locations are usually pretty good, half way or higher up the bore on the exhaust- opposed side of the block. Make sure that there is no mechanical tension to the wires coming from the knocksensor induced by cableties pulling the wires to tightly.

Always start with the basics; make sure the injectors are balanced and run some RedLine SI-1 through the fuel to clean up the valves and combustion chambers.

For simplicity of installation, I would personally recommend using the G4+ onboard knock control strategy. While it is similar in functionality to the knock block, with the knock block installed you have a separate module and more wiring to rely on.

Mounting the two sensors on top of each other is definitely not ideal. If this is your only option I would run a single sensor as you will likely see better results. It's difficult and time consuming in a tight engine bay such as a VG30, but it's worth it. I would find the factory knock sensor location and mount your sensors there. The VG30 isn't an engine I'm hugely familiar with, however most V6 engines have the factory sensors mounted in the valley under the intake manifold.

Once you have the mounting sorted you may find your knock readings start making more sense. As always when configuring knock control I strongly recommend confirming knock is occurring via the audio function.

Thank you for your quick reply.

One point to clarify is that I am using the g4+ knock control in tandem with the stand alone knock block.

Yes, I agree that stacking the 2 sensors if far from ideal. Accessing the valley to.mount the second sensor is ideal but does require pulling the plenum and intake off. At the time that it is necessary to to do so, I will promptly move the second sensor.

That said, I believe that the issue is solve. I found that the Bosch plug for the ecu was defective where one of the plug wires was not secured to the plug pin and the plug was not secured tightly to the sensor. After replacing the plug, the ecu is now picking up a manageable signal. This was a good find.

Again, thank you for your assistance.

David

I'm glad you found an explanation for your problem. Just so I understand correctly, are you using a single knock sensor as an input to the ECU and the second for the G4 Knock Block? Are you simply using the knock block for audio detection?

Hello Andre,

Thank you for your reply.

Just as you have said, I am using one knock sensor for the ecu and a second knock sensor for the knockblock audio to my headphones. The knockblock is giving me a good audio sound to my ears.

It may be important to note that the installed knock block is not a G4 but rather an older version knock-block made by Link, (black Box 3 channel (6hz, 7.5hz, 9hz) with an gain knob). It states in the install instuctions that this device must be used by itself because it modifies the knock signal which would interfere with the ecu detection. I tested this statement by first trying to use one sensor for both devices. The result was the audio output to my headphones worked but the ecu was not hearing anything. Hence the need for 2 knock sensors.

Please offer some insight as to why stacking the knock 2 sensors, in the manor I described earlier in this thread, may be less than ideal?

I look forward to reply,

David

While on the topic of knock - I'm a 'knock-newby' ... I've google'd and youtube'd what knock should sound like to the human ear via a knock sensor amplified to headphones.

Does anyone have a good source of what knock sounds like through headphones?

this is my listening device via the OEM knock sensor(in the process of building it now):

https://uprev.com/documentation/Knock%20Listen%20Device.pdf

Thanks in advance!

James

There are some good audio examples of knock here: http://www.plex-tuning.com/products/plex-knock-monitor-v2-0-new

and here: http://theknockbox.com.au/the-knock-box/sound-recordings/