faulty Knock sensor or detonation?

[GunMetalR33]

Some times when cruzing around my powerfc tells me that the engine is knocking its head off. oscourse if I acellerate then engine warning light comes on. I know this sounds bad but my tuner was in the car with me monitoring the know and said that it was getting really bad when we where going over bumps. He thinks that it is stuffed as the car should not knock when cruzing at 2500 rpm.

Also there is no noticable sound comming from the engine when this is occuring...

What do you guys think?

[meshmesh]

Hmmm..

1. faulty knock sensors

When you first start the car what knock level do you get? I was told that sometimes knock sensors can pick up other vibrations, noises eg: mutli plate clutch rattles etc etc.

[GunMetalR33]

on start it ranges anyway from 20 to 50 on the PFC. I dont think thats right...

[meshmesh]

on start it ranges anyway from 20 to 50 on the PFC. I dont think thats right...

Sounds like it's picking up other vibrations/noises.. because you cannot get knock on startup.

I believe most tuners can check the knock manually (and not via the PFC Hand Controller) by listening via mic's.. see if your guy can do it.

[GunMetalR33]

Yea he said that he could do it but said that it was not needed. He did say that he reakons that the sensor is f88ked but its really hard to drive the way I like too :-} with the engine warning light flashing in your face, its very unsettling...

[Steve]

Have you checked the sensor is plugged in properly? Also, have you checked on the etc menu under sensor check - if a sensor is faulty it will be highlighted.

If I could hear anything coming from under my bonnet I would be very very afraid.

May be time for a second opinion. To just say its a faulty knock sensor, and not swap it out to make sure sounds a bit bodge to me.

Dont even risk it - I was getting knock on a tune of under 190rwkw. My tuner said 'nah, its not high enough to worry about' even though it was getting up around 80-90+ regularly. I got it retuned and it never went over 40.

meshmesh, why cant you get knock when you start the car?

[GunMetalR33]

you cant hear any noise from the engine and its runs really good and smooth. I will do the sensor check at lunch time today. How hard is it to get the the knock sensor it self?

[meshmesh]

meshmesh, why cant you get knock when you start the car?

I'm going by what I am told, and the reason (as I understand it! - and I'm not technically advanced)was there is no timing or something on ignition start up. stand to be corrected.

[Marlin]

I used to hide my FC hand controller because it made me paranoid! But on my 26 with forgies, (about 30% lower all round with cast pistons), the readings hovered around - cold start 40. Full load/big revs 55. Light load & cruise 10.

I do recall when I smashed no.6 piston it was a constant 120, with no audible sound from the engine.

On mine, the check engine light flashed whenever it exceeded 58. After doing a few engines, I would personally never exceed this level without thinking there was something wrong.

I did a test once, wanting to know how sensitive the sensors were. I tapped the sensors with a screw driver as best I could, and no reading at all registered on the controller. So I don't believe hitting bumps in the road will trigger a high reading.

My gut feeling is he's hurt your engine, and is trying to buy a bit of time by sending you away looking for a knock sensor fault.

[Ustasa]

Seen many a faulty knock sensor. I think it is presumptuous and alarmist to say the engine has karked it and the guy is trying to piss you off.

The knock sensor is a piezoelectric device which picks up vibrations at certain frequencies. It is also susceptible to picking up spurious vibrations when it gets a bit long in the tooth. No one engine is the same and hence even batch of knock sensors programmed to pick up knock for one rb25det might be a touch sensitive for another.

Only real way is to listen for pinging on the dyno or with chassis ears (placement is important) and have a safe ignition map in the first place.

Try –3 in the ignition trim and go for a rap down a safe stretch of road and record the max knock value. If it’s significantly different then knock is occuring.

[2rismo]

The immediate above is coming from the guy that tuned my car beautifully and got rid of the sh1t tune that was on it from a major Sydney workshop who shall remain nameless.

Less timing, a touch more fuel and it has been going on the Power FC for 18 months like this.

Take some timing out and see if it fixes it. If it does, get your arse to a DECENT tuner now.

Adrian

[Cubes]

My Rb30DET has a little piston slap when cold and gets maybe knock 6 or 8 on the initial start.

Once idling with the slight slapping that can be heard the knock sits on 1.

knock level of around 100 I can hear the ping.

At 70-80 I get the tell tale sign of detonation on the dyno. Tell tale sign being the slight puff of smoke.

Once warm, I give it a bit of stick, I never get over 30.

Also as a word of warning. As SOON AS the petrol guage gets half way between the last 1/4 and Empty it leans out (I presume) and knocks up to 80-90 if I drop it back and WOT through 3rd.

First and Second I assume don't allow the fuel to swish to the rear of the tank and cause a slight lean condition as there's no traction due to my crap tyres.

[mabru]

Just so I make sure I'm on the same page as you guys, you are talking about the cal knock value. Not the raw value under sensor check? My general rule of thumb is don't let it get over 40 on stock internals. (cal value that is)

[Cubes]

cal?

I will have to check the cal under the sensor check.

I was refering to the Sensor Monitor Section.

So which one is higher the raw or the processed?

[mabru]

Raw is usually higher (much higher) how it cals the monitored value I don't know. The SAFC2 has the same knock monitor and does the same thing. I just wanted to make sure you guys were referring to the displayed monitor value and not the etc, sensor check reading.

As for a bump not causing bizzarre knock readings, it can, if the harness plug is loose it will jiggle over bumps causing wild knock readings then settle back down. Pull the plugs off, clean the connectors and reseat the plugs before worrying about replacing the sensors themselves.