Apexi Power FC High Knock Sensor Readings

[s14_sport]

Ok, So I'm slowly ironing out all issues with my swap. Except this one seems to be a *****.

I've been getting randomly high knock sensor levels on the PFC. Trying to figure out what it could be related to, but, can't. I'm wondering if any of you guys have any ideas on this one.

RB25DET in S14, basic mods, PowerFC, Q45 TB, Z32 MAF, rebuilt strengthened turbo, FMIC, walbro 255 FP and PowerFC has a fresh tune on it.

So on a cold day I start up my car and let it warm up. Just during idle I will see a max value of sometimes 89 on the PFC. I'll drive the car around the block very carefully and at random times it spikes up to like over 100 and sometimes 200 for no apparent reason (not laying on the gas pedal at all).

I spoke to my tuner and he said just ignore it because it is most likely not related to the engine and could be coming from something else near the engine.

So I tried to drive and ignore it and I'll give it alittle bit more gas and when I do that it hardly knocks at all. I'll get a random spike >100 sometimes when I LET OFF the accelerator.

I know the tuner says ignore it, but, I can't...its driving me nuts....

[240z4u]

What do you mean by "it hardly knocks at all" if you can hear it knocking thats not good.

That said, when its cold my knock numbers are high.

Seems like something is showing false knock, hard telling honestly. Maybe just try changing the sensors?

Evan

[s14_sport]

when i say "it hardly knocks at all" I'm always referring to the levels I see on the PFC....levels don't go up to past 20-30. Which is where it should be at all the time...

I do have some spare knock sensors in my garage which I want to try changing.

[240z4u]

Rule of thumb that I have heard is under 40 knock and your golden.

Does it happen at any specific point that you can replicate? It could be hearing a number of different things.

Evan

[Darius]

Mine has hella loud valve train noise because of the hack job valves I got from Ferrea and mine does not idle above 2 or 3 knock points. There is no way you are getting true knock spikes of 100 at idle unless you have valves hitting pistons or you rebuilt your engine and the pistons are hitting the quench pads on the head. At those levels, you should physically be able to hear the engine pinging if it is true pre-detonation knock.

I would immediately shut my engine off if I saw a knock value above 20 at idle. Yeah you might be okay with a value of 20-40 at WOT and 5500 rpm, but not at idle. In fact, I would pull back a degree or two of timing with that value.

First thing you want to do is make sure your knock sensors are firmly in the block. The torque setting is only 21 Nm or ft-lbs so its not a whole lot. Then, try to find anything that might rattle against the block or head and make noise. Loose bolts, clamps, or the engine vibrating against the firewall or pipes against the body. Anything could resonate and cause the knock sensor to freak out.

[gawdzilla]

knock sensors going bad probably, or picking up way too much noise. i think it's impossible to have real knock while idling, no matter what your timing is. extreme advance or retard will probably make the motor shut off entirely. i'd try changing out the knock sensors since you have spares.

the "under 40" rule of thumb really isn't great to follow. every motor is different, and every setup is different. on my old setup i would see 40 a lot and it was fine. on my current setup if i see 25 I start to be concerned, so i set my CEL To flash at 25 now.

[Darius]

There was just a post in the datalogit user group about making det cans (detonation cans) and how to make them yourself out of copper tubing. That will be the best way to tell when your motor actually starts knocking because your ears will hear the difference.

[240z4u]

Those guys were hooking up knock sensors to laptop mic inputs too from what I understood. Pretty interesting stuff, I have been following along with the FC users group stuff too.

Evan

[s14_sport]

good advice guys....thanks.

I'm going to first check the sensors and see if they are loose. If not, then switch them out with the spares I have.

240z4u "Does it happen at any specific point that you can replicate? It could be hearing a number of different things. "

The thing about it is that its completely random. It doesn't happen at any specific point in the map, rpms, or whatever. It could happen at 1200rpms or 5000rpms....sitting in my driveway idling or on the road under load.

[240z4u]

Yeah i was just wondering if you could relate it to something specific. Sound like a dying sensor like the guys above suggested.

[Cjmartz2k]

x2 for sensor.

I've got solid metal motor mounts, and stuff in my trunk. Sometimes when I get wheel hop launching, it'll read really high knock if I don't take all the crap rattling around in my trunk out first. Remember, you knock sensor is just a microphone set to listen for a specific range of frequencies, and a lot of other stuff can make that noise.