What exactly does a Knock link sense
25 September 2002, 10:27 AM
#5
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You are talking to some one who doesnt know much about engines and stuff. I am a little paranoid at the mo about piston slap and the like so was thinking that if this was the sort of thing the knock link would detect then i would get one.
25 September 2002, 11:31 AM
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i'd assume its the same as factory fit knock sensors on some cars.
if so then it is a device which picks up the start of pinking. in a factroy fit it then retartds ignition till pinking stops so saving engine from damage. i'd assume its the same idea. years ago dave walker (him from CCC) tried an aftermarket kit on a sierra with a 2.0 pinto engine and was able to swing the timing to something like 34 degrees further advanced than standard in search of the max power figure and still had no pinking. obviously the engien wouldnt start due to kick back but it proved how effective the device was. in an ideal world with good mapping and consistent fuel quality they wouldn't be needed but they're often fitted as a precaution. in a sophisticated system they allow every cylinder to have different ignition timing so they all run at their best figure.
if so then it is a device which picks up the start of pinking. in a factroy fit it then retartds ignition till pinking stops so saving engine from damage. i'd assume its the same idea. years ago dave walker (him from CCC) tried an aftermarket kit on a sierra with a 2.0 pinto engine and was able to swing the timing to something like 34 degrees further advanced than standard in search of the max power figure and still had no pinking. obviously the engien wouldnt start due to kick back but it proved how effective the device was. in an ideal world with good mapping and consistent fuel quality they wouldn't be needed but they're often fitted as a precaution. in a sophisticated system they allow every cylinder to have different ignition timing so they all run at their best figure.
25 September 2002, 12:12 PM
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OK.
A knock-sensor won't detect piston-slap. But piston-slap you can hear anyway at startup (your car will have seemingly turned into a helicopter) & only need be worried about if severe & is there when hot (not common).
The thing that you should be worried about & what an aftermarket knock sensor will tell you about is knock - pre-ignition. This causes severe stress to the engine, and can be caused by many things, the 'most popular' being using the wrong grade of fuel (your 'choice' or the petrol station having filled up the wrong tank or the fuel has degraded), but excessive heat, etc. can do the same. When knock is detected, it blinks at you, and that's that. Remove foot from accelerator
The car already has its own knock-sensor; it will retard ignition to try to prevent it, and failing that, will drop boost so that it should be cut out entirely (at the cost of performance). However... it only does this after quite a bit of knock, and so it's better to know what's going on in the first place. If you have just filled up, set off & the knock light keeps blinking, either take it easy for the rest of the tank (refrain from high boost which is where knock is far more likely to occur) or stick in some octane booster.
I think that covers everything?
A knock-sensor won't detect piston-slap. But piston-slap you can hear anyway at startup (your car will have seemingly turned into a helicopter) & only need be worried about if severe & is there when hot (not common).
The thing that you should be worried about & what an aftermarket knock sensor will tell you about is knock - pre-ignition. This causes severe stress to the engine, and can be caused by many things, the 'most popular' being using the wrong grade of fuel (your 'choice' or the petrol station having filled up the wrong tank or the fuel has degraded), but excessive heat, etc. can do the same. When knock is detected, it blinks at you, and that's that. Remove foot from accelerator
The car already has its own knock-sensor; it will retard ignition to try to prevent it, and failing that, will drop boost so that it should be cut out entirely (at the cost of performance). However... it only does this after quite a bit of knock, and so it's better to know what's going on in the first place. If you have just filled up, set off & the knock light keeps blinking, either take it easy for the rest of the tank (refrain from high boost which is where knock is far more likely to occur) or stick in some octane booster.
I think that covers everything?
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