PFC knock reading

[CJay]

Re PFC knock readings, I get a figure of 15 when I start the car, and up to 40 off boost, the level never goes up more than 60. I\'ve had this behavior since the PFC was installed and mapped last January so I\'m not worried. My A/F ratio was off and I had this changed accordingly a few months ago, same behavior re knock levels. One day last week, I enabled the 2 sensor graph view with a view to correlating the knock/boost figure, what I noticed is that knock would fly up only when coming off the throttle on boost, the high reading *appeared* to occur when the stock recirc valve dumped boost pressue (its pretty noise in a lazy way with Blitz filters in place). I want to change the knock sensor at some point for piece of mind, otherwise it doesn\'t worry me too much.

CJ

[gillard28]

Is that when the buzzer comes in? Or is the buzzer later? And the rev limiter later than that?
 
If what you say is true, why would Mazda have both a shift buzzer and a rev limiter if you shouldn\'t shift over 7k?

Its not a shift buzzer !!!! how many more times. The rev limiter is there to stop you from over revving and the rotors walking. The stock twin makes no power above 7000 rpm so why go there ??
 
Chart the knock readings and see where it does it. The knock sensor is pretty lame tbh. Any noise will trigger it off. Ie drain covers loss of traction farting etc

[lockwood77]

Its not a shift buzzer !!!! how many more times. The rev limiter is there to stop you from over revving and the rotors walking. The stock twin makes no power above 7000 rpm so why go there ??

That doesn\'t really answer my questions chap - does the buzzer sound at the same time as the limiter? If so, it makes more sense (although I would say the two are not the same, as whenever I\'ve heard the buzzer I haven\'t experienced the effects of a rev limiter).

If the buzzer is lower, what is the point of it other than to tell you to shift up/lift off? (I really can\'t remember at what revs it sounds - also, is the limiter 7500? I\'ve never hit it and I was told mine was set a couple of hundred less on the PFC anyway),

Do you have a manual or something from Mazda categorically stating that it is a rev limiter and that you risk knackering the engine if the buzzer sounds?

Sorry to be pedantic, there seem to be plenty of conflicting statements about the buzzer from various owners here (in other threads too) and it would be useful to have absolute facts in case some of us are threatening the life of our engines!

[gillard28]

Fact: your engine unless ported with a large turbo does not make power above 7000 rpm.
 
Why rev above this
 
The rev limit on the ecu is a hard limiter. that means it cuts the ignition. dont confuse with a soft limiter like in a 2 step.
 
the buzer will sound before the limiter. not saying you are simple but its a lot like drinking untill you are sick. try this
 
7000 rpm ish being nicely drunk
 
7500 rpm buzzer ish being sick
 
8000 rpm ish hard limit passed out
 
9000 rpm ish in a&e
 
I dont have any doc from mazda coz i dont care if you knacker your motor. Howeva i am trying to help the guy who started the thread and advise him
 
S

[lockwood77]

Mate, I\'m not trying to be argumentative, just trying to get a definitive answer. You may well be right about not making power at the top of the range, that\'s not the same as definitely knackering your engine though!

I\'d like to think that Mazda would engineer any warning buzzer to come in at a point before any damage is possible, leading me to think it is a bit like a shift light (although I appreciate that you may be shifting beyond peak power as a result, which is a bit pointless unless the power after the peak is still greater than the power in the next gear up at that point...)

I also appreciate that the water temp gauge is testament to Mazda not always following that logic of "alert before damage is possible", which, for me, makes it all the more important to establish the facts.

Anyone with a UK FD have a manual that mentions the buzzer in question?

[RemarkLima]

Fact: your engine unless ported with a large turbo does not make power above 7000 rpm.
 
Why rev above this

It may not make more power but it will drop you higher up the revs when you shift, plus if you\'re half way round a corner those 500 extra revs can be very useful indeed!

Of course, this is more for circuit work IMHO, but the argument stands, the buzzer is the same a shift light IMHO, which is saying "shift now at the latest!" with some margin.

The old MR2\'s we used to race had a redline of 7500, but a hard cut at 8200 and we would take them to 8200 in every gear we could as ultimately it made more difference to hang in a gear and end up higher in the revs then to shift, only fractions but the engines had no torque at all so you needed every last rev.

Personally with the twins you have such a wide band of torque that there isn\'t much "need" to rev high, but revs are always more fun than grunt

[RobbieRX-7]

The stock twin makes no power above 7000 rpm so why go there ??
 

because at those revs, im going fast and i aint got time to look at the rev counter and change bang on 7000rpm. For the sake of 500 rpm\'s i would rarther keep my eyes on the road and wait till the buzzer sounds. Mind you,  i am used to it now and change a split second before the buzzer sounds.:driving

[GEO147]

Sounds to me like some of you guys give your motors dogs abuse. I have my 7 3 months now and have never heard the buzzer in question, nor do I ever want to.
Maybe if I was after robbing a bank or sommat I might hear it. But for driving on public roads 6k rpm gives all the power necessary imo but everyone is different!!

[GEO147]

Re PFC knock readings, I get a figure of 15 when I start the car, and up to 40 off boost, the level never goes up more than 60. I\'ve had this behavior since the PFC was installed and mapped last January so I\'m not worried. My A/F ratio was off and I had this changed accordingly a few months ago, same behavior re knock levels. One day last week, I enabled the 2 sensor graph view with a view to correlating the knock/boost figure, what I noticed is that knock would fly up only when coming off the throttle on boost, the high reading *appeared* to occur when the stock recirc valve dumped boost pressue (its pretty noise in a lazy way with Blitz filters in place). I want to change the knock sensor at some point for piece of mind, otherwise it doesn\'t worry me too much.
 
CJ

I experience the exact same symptoms re knock. 90% of the time its when I come off the gas under high boost.
 
Bye the way, I only have my PFC in a little while and my knock levels are monitored with the bar thingy. How do you get the PFC to show the actual numerical readings?? Sorry if this is a muppet Q but my manual is in Jappo!!
 
Thanks.

[RemarkLima]

Sounds to me like some of you guys give your motors dogs abuse. I have my 7 3 months now and have never heard the buzzer in question, nor do I ever want to.
Maybe if I was after robbing a bank or sommat I might hear it. But for driving on public roads 6k rpm gives all the power necessary imo but everyone is different!!

 Not really IMHO, once up to temp and working with good oil there\'s no reason why the engine shouldn\'t be able to rev to the redline, it\'s within toleranceances so all good

[GEO147]

I will have to take your word on that one as I will prob never redline mine, just dont have the balls for it, too much of a worrier!
 
Bye the way, how do you get the PFC to show the actual knock numbers instead of the bar graphic thingy??

[CJay]

I will have to take your word on that one as I will prob never redline mine, just dont have the balls for it, too much of a worrier!
 
Bye the way, how do you get the PFC to show the actual knock numbers instead of the bar graphic thingy??

George, its considered a good thing to regularly redline a rotary, apparently this helps to reduce carbon buildup. A lot of owners swear by redlining the engine each time its driven, personal preference really.

In terms of the knock reading on the PFC, you can\'t change from the bar to a numerical value, you can however change the display to show peak readings of each displayed counter, this will give you max knock reading over the course of your journey.

FYI, PFC instruction manual in English available here:

http://www.irishrotary.com/downloads/fc_commander_fd3s.pdf

CJ

[gsb876]

Theres one thing you guys have missed,

A while ago i had a quick play with a Celica on a private road and the knock reading hit 159 which should be det :2Confused  however after some serious worrying i had a word with Mark (Blitzboy) as he races the FD\'s so should know about knock readings, and the thought was that should the exhaust backfire when letting off then the knock reading will go through the roof as it upsets the sensor in a major way.

So if you get a stupidly high knock reading try to remember if the car backfires when coming off :Giggle

[GEO147]

I get a lot of backfiring!
 
Thanks guys thats some good info. I might redline my 7 today to aid in the carbon situation. I had heard this already! The only problem is that my car tends to loose traction alot higher up the rev range, especially in this weather!!
 
Have any of you guys ever done that water cleanin thing?? Where you attach a line to a nipple on the engine like boost gauge, but the other end goes into a 2 litre jug of water, you rev the engine and it sucks up water, which steam cleans your engine. Water just evaporates and exits out exhaust port?

[RemarkLima]

TBH I only redline it every now and then and certainly not every journey, I try and give it a bit of a thrashing every now and then and the should make the odd trackday and sprint this year which also gives it a good clean out!

Have any of you guys ever done that water cleanin thing?? Where you attach a line to a nipple on the engine like boost gauge, but the other end goes into a 2 litre jug of water, you rev the engine and it sucks up water, which steam cleans your engine. Water just evaporates and exits out exhaust port?

Sounds like a recepie for hydraulic lock (where the engine can\'t compress the liquid it\'s taken in and something else important gives way instead).

Unless it was a very fine mist of water, like Water injection...