Grounded Knock Sensor (QR25)

[cowboydren@b15sentra.net]

On Fri, Jul 26, 2002 at 06:21:53PM -0500, Daniel Kort wrote:

> I have seen a lot of people post about this, but is it really a good idea?

The stock knock sensor is entirely too sensitive, it seems.  This is the
third suggestion I've seen to reduce it's interference with the car's
performance.  The other two options made a lot more sense than putting
it on the freakin' firewall, though.

> looked at their timing before and after this?  I would be interested to see
> how much timing advance you get with it grounded

The knock sensor does exactly that; sense knock.  The only time the ECU
does anything to your ignition curve is when the knock sensor starts
feeding the ECU information that something's wrong.  If you're running
good gas, the atmospheric conditions are ideal, and you're not trying to
pull a 25 MPH hill in fifth gear, you'll never see the difference, even
watching the ECU in real time.

> compared to a stock car in the same gear.  In theory, it could advance
> beyond what is really safe.

No.  The KNOCK SENSOR has nothing to do with advance.  The advance curve
is coded into the ECU as a map, and ECU only *retards* this map in bad
situations.  It does not *improve* the curves based on "ideal" or
"optimistic" conditions.  That'd be pretty cool, though...if I'm wrong,
do correct me.

> Or is it sensitive enough to still see serious knock when away from the
> block and retard timing?

I have my doubts about how quickly the knock sensor could tell the ECU
that something's wrong when it's not actually in the block.  Knock *can*
go undetectable for a few milliseconds before the human ear can pick up
and respond; I can only assume that the knock sensor, when divorced from
it's home, starts reacting more like the human ear does.  This can't be
good for rod longevity.

--
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