Knock Sensor Applications

George M. Dailey gmd at tecinfo.com
Mon Oct 21 02:18:52 GMT 1996


At 06:28 AM 10/19/96 +1000, you wrote:
cut!...
>    If a motor was never fitted with a knock sensor, don't bother. Just
>    set as conservatively or agressively as you dare. 

I fitted a GM TBI system to a early 350 engine. In researching where to put
the knock sensor I discovered several interesting things. GM has put them in
different locations for different engines (even among the same engine).  I
rolled the dice and used a 3.8L sensor on a 5.7L engine (5.7L ESC module).
I put the knock sensor on the lifting tab on the intake. Well, it all worked
just fine. When it comes to luck, I often roll snake eyes! I guess I've used
my luck allotment for this lifetime

>Peter reported once that GM
>spent millions on the problem and no one seemed to pick up on the
>significance of the fact. 

The same can be said for Fuel maps, ignition timing systems, and lumbar
seats.  Just like we incorporate precesion roller bearings in many DIY back
yard designs, few people try to machine there own balls.

>    I believe the OEMs are probably using the output of the knock sensor
>    at points where it is known to be reliable and otherwise being very
>    conservative. It has been reported that GM units over retard under
>    some conditions. This may be the reason.

Can the GM ECM modify its spark timing map to compensate for external
conditions that will affect spark knock, or does it simply advance to
detonation?
Soon it will be time to install the low pressure turbo on the 3.8L MPI with
a 9-1 c.r.
I'm sure spark timing is going to be a real monster.

GMD




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