PFC knock reading

[d6277n]

Hi guys,

Just been out for a blast in the lovely weather and noticed that when the gear change buzzer comes on in second, so does the knock warning light. Commander shows readings of around 30-35 on moderate boost but a peak of 85 which I guess corresponds to the warning. I\'ve done a quick search but everyone seems to have a different answer, so is this dangerous or not? Does it depend on what mood the sensor is in? I can easily avoid red-lining it, but I\'d rather know for sure. AFAIK it\'s got a slightly rich (smells like it too) safe map by SDMinus (Scott).

Thanks,

Chris.

[alexb]

In my opinion the knock sensor reading reported by the PFC is useless on it\'s own without any other way of knowing what\'s going on with regards to air/fuel ratio etc. As a knock sensor is a microphone it can pick up any noise of the right frequency (e.g. a rattling heat shield) and interpret it as knock, and if you read the PFC manual it just says readings over 60 *can* be an indication of knock - not for sure.

My readings are all over the place and I\'ve had readings way higher than 85 on WOT for several seconds which if was really knock would have killed my engine in no time. If you\'re really concerned then I\'d take the car to a good tuner like Reworx and they can check the A/F readings and also if necessary get you a new knock sensor, although apparently it\'s not the sensor but the connector which can be dodgy. Although if you have a "noisy" engine that won\'t fix it

Cheers,
Alex

[Red Leader]

As Alexb says it can pick up readings from anywhere. I had a rebuild 4000 miles ago and get readings of 113. The comp test readings were 8.0 8.1 8.0.
I,m more than happy that the engines ok (built with Carls own hands :Thumbs-up ) So the high readings are coming from somewhere else.
As Carl said if the reads were from the engine it would be a pile of bits by now.

[ro284]

Would a failed passenger side engine mount cause noise to be picked up by the knock sensor? and give high readings?
Bob

[Jono FD3]

I get readings of 68 - 75 with mine (only on first tubby though) as soon as the second one kicks in my knck drops to 13....... figure that one out!!!!

Got another knock sensor to put in now to eliminate that.... then it\'s on to engine mounts etc!!

Jono

[Red Leader]

Both engine mounts were renewed when the engine was rebuilt.
Was thinking gearbox.

[RedRummy]

... when the gear change buzzer comes on in second...

Errmm... isn\'t that the rev limiter kicking in and therefore more like the "stop-bloody-accelerating-NOW" buzzer.

Do you normally wait for the buzzer before changing gear?  :Giggle

[Jono FD3]

Do you normally wait for the buzzer before changing gear?  :Giggle

Thought this is what every one did:spank

[d6277n]

Nah, always thought it was just a gear shift indicator rather than a real warning. That said, I don\'t hang about when it comes on...

Spoke to Gary the other day and he said that when mapping, they set the knock warning deliberately low at around 60 to give a bigger margin of safety. From what people have said, I\'m not worried :Thumbs-up

Ta,

Chris.

[lockwood77]

Errmm... isn\'t that the rev limiter kicking in and therefore more like the "stop-bloody-accelerating-NOW" buzzer.

Do you normally wait for the buzzer before changing gear?  :Giggle

I thought it was the audio equivalent of a shift light rather than the limit itself?

[goldk28611]

I have got a knock reading of 80 from just starting the car!! does this sound like a problem or not?? plus after just driving around - no higher than 5K rev\'s and looked at the knock reading on the PFC commander and this shows a knock max reading of 144!!!! normaly is around 30ish mark....this was only imported 4 weeks ago - tuned by Pip at WGT and compression tested at 7\'s all round. Engine rebuilt 20k KM ago....

Is this something to worry about and get checked out.... ??

i\'ve recently noticed that since these high knock levels my heat light comes on when i put the key in the ignition but goes before starting it, is this connected in any way?

[alexb]

No, you don\'t have to worry. Knock (if it was happening) would only occur on WOT (wide open thottle).And 144 as a number means very little if taken in isolation...

Cheers,
Alex

[gillard28]

The buzzer is not a shift light. Its a warning to tell you that you shold have already shifted gear.
 
Stock twin with stock port should not be shifting above 7000 rpm
 
S

[lockwood77]

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?

[RobbieRX-7]

The buzzer sounds at 7500, thats when i change gear:3gears-rh  Although im sure it aint been working lately and been bouncing off the limiter:Nono!