Increased Knock levels after mech. diff install

[Chris32]

Quick question,

For a while now I have thought I have had a dodgy knock sensor. After doing a bit of fiddling with the fuel and ignition maps on the weekend to fix up a bit of knock, I noticed my PFC hand controller is indicating knock when ever my diff locks up ( 1.5way mech.)

Has anyone else noticed this? In a straight line I was getting up to 70 knock on the hand controller, after a bit of playing around I got it down to 35, which I think is acceptable

On my way home driving through the hills, I would glance down and see 60-70 knock again, and upon closer inspection it was picking up knock when my diff locks up out of corners?

Has anyone else had the same issue?

Chris

[Trust33]

Not me but id say,at a guess,that your diff is taking initial torque and your engine is under a stress lock momentarily.All this would come about because where teh tyres used to spin before letting the engine breathe a little b4 it now cant.

Babble!maybee.Never know it could be somthing else not the diff.But if it happened like it did when you say it did then it more than likely is the diff that is causing the knocks.

[Trust33]

Not me but id say,at a guess,that your diff is taking initial torque and your engine is under a stress lock momentarily.All this would come about because where teh tyres used to spin before letting the engine breathe a little b4 it now does not under certain loads.

Babble!maybee.Never know it could be somthing else not the diff.But if it happened like it did when you say it did then it more than likely is the diff that is causing the knocks. :confused:

[R31Nismoid]

^^ what he said.

i guess your getting that little bit extra grip, before it lets go maybe?

Mine was tuned with my new diff at the same time so i have nfi!

but then, that (you would think) wouldnt matter on a dyno in 4th etc ?

interesting too see what comes of this thread indeed!

[Chris32]

Its odd hey!

The problem is my PFC and Diff went in at the same time, so I can't compare too!

It seems strange though, as even when its not under and load, the clunks from the diff show up as knock? I have aluminum sub-frame bushes, as well as alloy tops on my suspension, I wonder if the noise is travelling through and reading as knock. Its quite loud in the car around corners etc

Bit of a wierd one!

[R31Nismoid]

imagine thats happening..

fark what a trip out that would be!

what about from a standing start giving it a rev and a tad of clutch dump?

do it then?

[Chris32]

yeah a little, also when it starts to wheelspin a bit in second with a bit of axle tramp

[yogi000]

might be a different thing all together but i get some really strange knock readings......but then i got back and do the same run and with same revs and knock is really low. and i cant get it to knock on the dyno tooo.

[Tommyk]

My pfc picks up knock from my noisy starter motor. And it only happens on startup !

So it is prone to picking up noises. Whether it is the diff or not, I have no idea?

[dangerous_daveo]

I would posibly be load from the inside wheel and outside wheel trying to go round at the same speed, but it wouldnt be whenever the diff its self it locked up as that would happen at anytime under load, and therefore would show up on say a dyno or just straight line.

It could be a bit of a wild guess, but it could even be a fuel pump/tank/something else problem, and say the fuel moving about, or a bit of a connection or something is coming loose while cornering, and the jolts from the diff are just making it worse. As I guess less fuel would also cause knock correct? And that with the increased potential load would cause more again.

Id say if its a worry the car might be too much on the edge of the tune to start with.

[BigDatto]

Hi Chris,

Everytime my Commander registers a knock level above 15, it's between gears & off-throttle.

So I suspect my knock sensor is picking up drivetrain noise also. I'm not sure where it's coming from, but I think you may be on to something. Any tuners out there know what's up ??

[RB30-POWER]

a knock sensor is just a piezo microphone basically so it can certainly pick up driveline noise as well as just engine noise.

on a standard car with a standard ecu it is calibrated to tell the difference between detonation and other background noise frequencies.

once you change parts from standard its possible to introduce frequencies into the system that the sensor picks up as detonation, when it may not be.

[SLY33]

i had my FC tuned before i put my super-clunky 2-way diff in, but the clunks never register knock to my knowledge. Especially on slow speed tight corners the clunks are very abrupt and shake the car around, but no knock. I also have the same aluminium cradle bushes.

I had a problem with spontaneous knock and thought it might be the sensors, but it turned out to be simply bad fuel. Try some mobil synergy and see if it makes any difference?

[Chris32]

Funny you should say that, I have always run BP, and put some Mobil in last night becasue I was almost out, it doesn't seem to be as bad. I think its just a coincedence though, as I have run mobil before and 100 octane fuel and it does similar. A bit of a placebo effect I think

Still reckon the knock sensor is a bit dodgy. I reckon the guys are onto something with the drivetrain noise, my gearbox is getting old and has a bit of slop in the gears, so maybe its picking up that?

Either way, just ignoring the knock sensor for the time being, I know its not a tune issue

[BigDatto]

Looks like I found my answer here: http://www.skylinesaustralia.com/forums/sh...k+between+gears

(I have a very rattly twin plate).

Hope this helps someone else out.