zonblitz

iTrader: (9)

When I installed my PFC a few weeks back and noticed my knock level to be quite high. The engine sounds great, no strange noises and in addition pulls great vacuum, avg 20mm/hg on my defi gauge when warmed up with no a/c on.

I was worried about this so I spoke to Bryan at Rotor Sports Racing in North Carolina (The guys who built my motor and had done most of the work on the car up untill I purchased). Bryan's response was first to help explain what a knock sensor was and how it worked in conjuntion with the ecu/pfc. He also stated that when you add a bunch of aftermarket mods to your fd you increase the noise in the engine bay and that in many cases registers on the knock sensor. My reading at idle is almost nil, but quickly pegs out with any increase in throttle. I have also had the guys at DCP motorsports in New Orleans check it out and from what they can tell my engine has no knock.

At first I wanted to replace my knock sensor to see if that fixed the problem, but Bryans advice held me back from spending the $170 just yet. He said in almost all cases they (RSR) disconnect the knock sensor or just turn it off in the PFC.

I was worried about it retarding my timing as that is counter productive to what my goal was here in the first place.

I went into PFC and turned it off, however it still shows if you view it.

So my question is: Is it still reporting to my PFC or is it no longer figured into the quation, but just still connnected thus showing a reading? Or is it still on and part of the equation?

Also, how many of you run with no knock sensor?

and... how many of you have had to replace yours?


Thanks guys.

afterburn27

iTrader: (5)

IIRC, unlike the stock ECU the PFC doesn't adjust timing or anything when it sees high knock readings. It is just there for your viewing pleasure.

Trevor

As far as I know the PowerFC doesn't use the knock number to alter timing or anything else for that matter.

The number is just there for use by the tuner.

Even then the "normal" number varies from car to car. Mine is actually quite active with counts of up to 57-59 while just cruising down the highway. I thought about retorquing the sensor to make sure its not too tight but it doesn't look too easy to get a torque wrench in there.

And as a side note knock sensors don't usually "go bad" and require replacement at any normal interval.

zonblitz

iTrader: (9)

cool thx guys.

much appreciated.

afterburn27

iTrader: (5)

Actually, they do go bad. The insulation in the sensor can melt from all the heat in the engine bay and can be seen as a 'black goo' dripping over the front spark plugs.

Trevor

Great...mazda's excellent engineers strike again.

Imagine my surprise...

zonblitz

iTrader: (9)

"Actually, they do go bad. The insulation in the sensor can melt from all the heat in the engine bay and can be seen as a 'black goo' dripping over the front spark plugs."

Mine looks like this....

rynberg

The knock sensor is just a piezo-electric microphone. They can go bad.

Knock sensor readings at anything other than pure throttle application are worthless, as the sensor can pick up tranny noise and other noises. Peak readings are no good. Look at the reading under steady WOT, that's where you can get an idea -- better with a passenger doing it!

Trevor

I never stated that they can't/won't go bad...only that they usually don't.

Knock sensors on most vehicles are designed to last 160k+.

afterburn27

iTrader: (5)

Engines on most vehicles are designed to last 160k+ too

badass7

Had this same question. Knock reading on PFC is blasting off out of control.

Either I have a bad sensor or its def. picking up some other noise.

DaiOni

what's important is your tune - if that's within 'safe' parameters, then I wouldn't worry too much about your knock readings. If you've modified and not tuned to suit, and experience different knock behaviours - then you would have, imo, cause for concern.

Sled Driver

iTrader: (9)

Mine does the same thing under no load. Pegs out at 3K rpms.


Good advice, save your money. I replaced mine & had the exact same readings. I even moved it to the rear rotor housing (thinking that it might be something towards the front of the engine) , but still had the same high readings.


As stated the Pfc only shows a value, it doesn't retard spark. When you "turn off" the knock sensor what your actually doing is turning off the warning feature. The exhaust overheat light will flash on your console. It also does this if you max out your injector duty cycle (unless you turn that off)



I have the sensor installed, but the warning turned off. I've replaced mine NO HELP.