Ford Knock Sensor and Spark Control

[Jeff Webb]

I've noticed that there's been a lot of discussion about electronic ignition
and spark control systems recently, so I thought some of you might be
interested in my current project.  I plan on designing an electronic spark
control system for my '65 289 V8 Ford Mustang.  My plan is to start out by
simply monitoring engine parameters, and then work my way up to ignition
control and electronic fuel injection.

This summer, two of my friends and I designed an instrumentation system for
my car that monitors manifold pressure, throttle position, air temp, engine
temp, spark advance, spark dwell, and engine rpm.  (I have info and
calibration data on the Ford MAP, ECT, and ACT sensors if anyone is
interested.)  The system uses a 68HC11 to display the data in real time on
an LCD display, or log the data to memory in a battery-backed SRAM for
downloading to a PC.  

My next project is to interface a knock sensor to the system.  From what I
understand, Ford uses two types of knock sensors: one for smaller engines
with knock frequencies of about 6 Khz, and one for larger 4.9L/5.0L engines
that  knock at about 9.5 Khz.  The sensors put out a small voltage signal
(about 1V) that changes with the frequency of engine vibration.  (All of
this info is from Ford Fuel Injection & Electronic Engine Control by Charles
Probst.)  I plan to sample the sensor signal with an A/D converter, and then
analyze the data to figure out exactly how I can determine when engine knock
occurs.  

Does anyone have any other information on these sensors?  Is the output
essentially a frequency to voltage converter, or is the signal a sine wave
with a changing frequency, or is it a raw signal that requires extensive DSP?

I have purchased a knock sensor for a 1990 Ford Bronco 5.0L for use on my
Mustang.  My first problem is mounting the sensor.  I have no information on
the stock mounting location for this sensor, or how critical the mounting
location is. What other engine sounds might occur at the knock frequency?  I
would greatly appreciate any information on this subject.

Thanks,

Jeff Webb
mustang at eel.ufl.edu