I was wondering if it would be a good idea to replace the 17 year old knock sensor.

I did a little bit of searching and found a few threads but all scattered information From J&S safeguard to ditching the stock knock sensor for a 3 channel unit. I am not sure what this all means so i decided to open up a new thread to clarify some of these discussions and also learn how the knock sensor works and how does is affect timing..

 

Are you on the stock ECU (re-chip or not), PFC or other?

 

Pfc

 

I'm no PFC expert, but IIRC, the PFC doesn't do anything but display the knock reading. It doesn't react to it like the stock ECU.

 

^ Thats correct the pfc does not alter the fuel or timing maps based on the knock value. All it will do if you hook it up is flash the CEL if the values are higher than what you set it to in the commander or the datalogit.



John

 

OK good thread I would like to learn a little bit more about knock and what effect it has on the 13b engine.

first thing what is a high "danger" knock count and what is a low "avg" knock count?

Also which after market knock sensor/system would be good to use on the fd.

 

bump for info.

 

Bump

I just started researching this, specifically the J&S unit, and have not come up with much so far. if anyone has any experience with aftermarket knock sensors/controllers please post here.

Thanks,
Dan

 

Chuck Westbrook (cewrx7r1) has used a J&S I believe. They are simple systems--your mom's Camry has much more advanced control. But they may still be useful if you can get it set up right such that it is only picking up "real" knock.

 

I was thinking the same thing this morning, they do have the option of a bosch sensor which would allow use of the OE sensor for reference/logging, might be helpful?

 

the J&S does work but there are a few gotchas.

the big one is that in the event of knock, it only retards the LEADING timing, and not the trailing. so you have to make sure the thing cannot pull so much timing that the trailing doesn't fire before the leading, which might be bad. its actually a simple matter of making sure there is more split than the J&S can pull timing.

two is that you have to actually believe it when the lights light up.... there was this one time, when BATMAN made my friend pour this clean power stuff in the gas tank. went for a drive and the J&S lit up like christmas, but the car ran fine! while we were wondering weather the J&S was failing, because we'd seen that, the engine popped. just to prove his point, BATMAN (look it up) drained the clean power gas tank and put it in his FD, and it blew up too. +1

pretty sure there was a thread, but it might have been lost, this was like 99-2000

 

thanks for starting a thread on the under-appreciated OE knock sensor.

while it is a bit low tech in today's world, being 1992 vintage, it is one of the most important FD tuning tools. and it is accurate. i was chasing an all of a sudden change in my knock pattern and installed 5 knock sensors. all 5 generated similar readings. (the aberrant knock turned out to be coming from outside the engine...)

knock under load/boost is the acid test as to tune. if your motor is properly tuned and supported (AI etc) knock should drop under boost to under 20. knock can be 40-60 in vacuum.

some say that because rotaries are so fragile you can't/shouldn't tune w knock. not so, but you must move very slowly, and hold the start of a knock uptrend in high regard.

as to the J&S Safeguard Knock system... i have run it since 04. it employs a Bosch knock sensor and it screws into the rear rotor housing's knock port that Mazda thoughtfully provided. there are a couple of models... the one you want only works in boost.

i have mine set to retard IGL 10 degrees and i run an 11 degree split. (no retard in vacuum)

it will literally retard timing ON THE NEXT ROTOR FACE!

when you get into some sort of malfunction in boost and you start to get apex seal breaking knock the reaction must be immediate or your "safeguard" will be of little use in saving your motor. that's why i run it in my car.

combine the Power FC/Datalogit and OE knock sensor gives you a huge understanding on what's going on inside your motor... before it blows.

instrumentation makes up for lack of genius

howard

 

sometimes.... sometimes its the other way!

i do agree though, that the SENSOR is fine (i have seen old/dead ones) but the system its attached too is the primitive part. arghx has posted numerous things on the knock strategies of the newer WRX's and EVO's and they are WAY more involved than the FD was.

the J&S didn't save my friends motor, but it did give us enough warning to take the foot off the gas, which is all you'd need if it wasn't for that lack of genius part....

 

I have a good working J&S for 175 shipped

 

if what you have is the J&S Safeguard unit that works only in boost (it has a boost line connection) and is complete... module, bosch knock sensor and guage...

GRAB IT!

 

When i started this thread i was trying to find out if there was an updated more sensitive/reliable sensor that can be more trust worhy when tuning. question- The later 2002 FDs came with the same knock sensor as our 93-95 ones?

 

i believe so, i do have the 99 parts book, but not in front of me...

another option might be the Rx8 sensor. N3H1-18-921 and the bolt 9979-40-830B. the sensor actually looks like the bosch ones, with the bolt in the center.

the Rx8 sensor bolts to the same place, but i don't know if/how the signal is different. the Rx8 sensor lists for $90, the Rx7 sensor is $270... Mazda has plenty of both, BTW

 

there's a bunch of OEM knock control units out there, i wonder if any would work well to adapt to the rotary.