RaymondH

As title.

SecretAgentMan

3rd gear going **** up sure did.

I don't know about the piston slap - my guess is that it doesn't as the microphones used are bandpass, tuned for a specific frequency (to only listen for detonation).

/J

Sheepsplitter

Can I add to the question:-

Does piston slap cause the ECU to (over a period of time) reduce the timing to protect against what it think is knock?

swan

As above, only if it's in the frequency range that's being checked for knock.

dowser

I suspect the knocklink listens to a wider frequency than the ecu. Fitting different headers can render the factory knock detection circuitry useless (which some would say it always was anyway ), while the knocklink continues to detect.

I'd suggest you'll 'see' piston slap on the Knocklink, but that the factory ecu wont. Only way to be sure is by monitoring ecu though....

Richard

Bob Rawle

The knocklink will see it, so will the factory ecu, some well recognised causes of poor performance include knocking exhaust's and piston slap, even Bosch management can get fooled, A Link ecu will record greatly incresed knock levels from a slappy engine and that uses the factory knock sensor. That tells me that it will. Subaru have a fix involving the resiting of the sensor to get around this sort of thing. (bit dangerous if you got real det though)

SecretAgentMan

Interesting Bob - thanks for your input!

/J

dowser

** Not related to the post, evidently piston slap or heatshield vibrations is enough to set off factory knock correction, sorry **


Hi Bob,

The description of the factory circuitry doesn't tie in with what I've found with different header designs - I assume the ecu itself is filtering either side of a certain 'expected knock' frequency....which is changed when the headers get swapped. Hence my knocklink is the same with any headers (actually, a little quieter with the Maxim - but I guess that's expected ), but the factory sensor goes quiet.

Even with a big tear in my inlet pipe, and using the knocklink's big-red as a shift light (.....), my ecu didn't register knock....

A friends car, with a different design of header, is also quieter than normal - but this one does do knock correction in extreme circumstances (ie; poorly cooled rolling road, aggressive timing map).

Richard

Bob Rawle

The factory ecu doesn't always react to knock even when there is genuine knock and no slap ... certainly I have now proved that to myself beyond a shadow of doubt, slap will trigger higher knock sensor out put levels and will cause a recation, slap can be present and induce a range of fequency, its not all in one place.

Moving the sensor or trying to damp it is generaly not a good thing but if you can ascertain that the problem is caused by a resonance on the sensor oem position then changing to a close alternative could work.

Andy.F

FWIW When my piston had a cracked land, the Knocklink was going crazy even if I lightly tapped the throttle. I couldn't hear anything, even with my head under the bonnet !!

Bob Rawle

Exactly what I mean, early JDM Sti's were quite often fitted with a variety of options and customers could spec in different pistons amongst other things, cars like this (my early STi2 wagon was one) were normally clearly fitted with pistons of larger clearance wrt the bores. Those cars had a much higher background noise than std. My current car registers 0-4 as background, wagon registerd up to 26 as background but when hot nothing could be heard.

RaymondH

Thanks for all your input, men. My Knock Link is very quiet, only showing two green lights under flat out acceleration so I'm happy.

Raymond (now a not quite so paranoid MY98 owner...)

Ted2kAWD

what Perfomace differences would u notice with slap? and what signes are there?

Just got a 2000 Turbo, standard uk. I gues i need some kind of rolling road test to check her out?

ted

Sheepsplitter

Thanks for the info Bob. So would you suggest it was a safer solution for someone with Piston Slap to reset the ECU from time to time, rather than re-site the sensor?
Assuming of course that their original map was changed for a 97-98 RON UK mix.
If the answer is yes, over what sort of period would you expect piston slap to affect performane in a noticeable manner?




[Edited by Sheepsplitter - 1/11/2003 9:20:47 AM]