RB26 hearing cracking noise/static on knock audio above 6000 rpm

Have a strange issue while trying to tune a RB26 today while listening for knock on a Plex V2 knock monitor.

Once I reach about 6000 rpm on a dyno run, I could hear some cracking noise in the knock audio which sounds a bit like static. I doubt it is knock though as I can reduce ignition timing by 10 degrees and it is still there. This is not the first time I've heard this. I have worked on another RB26 awhile back (both are GTR R32) and I could hear the same noise. The knock sensor is attached to the cylinder head now while stock location was used on the previous engine.

Does anyone have an idea what the noise could be? I will try and get a recording of the sound tomorrow. It makes me feel very uncomfortable when ever I hear the noise while trying to get the ignition tuning done. Thank you!

I'm betting on ignition noise on your power lines -- how the the Plex V2 powered?

It's currently powered via USB on my notebook. Not sure how I powered it on the previous RB26 I worked on though as it was quite awhile ago. Would the ignition be interfering if it is not powered by the car's electrical system? Or is the notebook itself sensitive to the EMF from the ignition which in turn effects the power that it supplies? I'll try connecting the knock monitor to a separate battery tomorrow.

It the notebook plugged into "mains" power or running off of batteries? Trying an external battery is a good idea.

You might also make sure the routing of the knock sensor wiring is as far away from the coils / HT leads as possible.

Notebook was running of batteries so there shouldn't be interference form the outlet.

A strange thing happened though, I could hear the cracking noise the whole day while tuning under both the 7k band pass and 10k high pass. But when I finally decide to connect every up for recording, the noise disappeared. I did have to turn down volume knob on the unit (the physical dial, not the preamp in the settings menu) or the input on my PC for recording the sound would clip. Maybe I had the volume dialled up too high and the output was also clipping on the knock monitor itself and created the noise? Will try again tomorrow.

I had a problem a very long time ago with an emulator on an old nissan - it would get glitches above certain rpm.

It turned out that the spark plugs were not resistor plugs (eg bcpr7es) and the non resister plugs were causing electrical noise that affected the emulator - but not the factory ecu with an eprom in it - It may not be the case for you but could be worth adding to the list of things to check maybe?

Hello all,

I am resurrecting this thread if that's ok...

I am having what seems to the same issue, very very annoying! like the previous, it occurs mainly above 6000 rpm. To check if it was interference, I placed a non mounted knock sensor close to the stock front location. I heard no interference at all. This leads me to believe it is somewhat mechanical. I am 99% it is not knock as I have significantly retarded the timing and it is still there. My questions are?

1: Could it be clearances on the valve train? It shouldn't be... (Tomei poncam 260's, degreed and lash clearance when installed)

2: Old valve springs? First sign of valve float? Running stock and over 30 years old...

3: Have I done something wrong? Could it still be RF interference? (listening via Link Knock block, one sensor on stock front location, one mounted to front cylinder head bracket, both have the high rpm crackle)

Thanks in advance!!

Nick

Certainly OK since you are having a similar experience.

I like your test so far and agree that likely means it is mechanical.

If it might be valve float on the exhaust side you can try revving the engine in that range in neutral so the high exhaust pressure present during high airflow while in boost isn't present ,and see if the noise is the same or not. Testing at low load vs. high load might turn something else up as well.