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Registered User
Join Date: Nov 2003
Location: Naperville, Il
Posts: 496
Knock Sensor Failure Symptoms

What would be the noticeable impact on engine performance if one or both knock sensors malfunction? My understanding is that if the sensor detects knocking it produces an input to the ECU which then retards the ignition timing on the cylinder bank experiencing the knocking. I am "guessing" that such a situation would be short lived and that the timing would be returned to normal quickly once the knock dissipates.

Does the sensor produce a voltage output when knocking occurs? If it malfunctions, can it trigger ignition retardation that persists long enough to be felt in engine vibration or some other parameter?

I did not replace either of the two knock sensors on my 3.6, and am now second guessing whether I should have replaced them during my rebuild.

98 993 C2S - Arena Red/Beige
76 914/6 3.2 Conversion - Estorill Blue/Coral Red
Old 06-05-2016, 01:46 PM
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Registered User
Join Date: Jul 2001
Location: Portland Oregon
Posts: 7,006
Check your knock counts with either a Hammer, PST-2, or PIWIS to see if those values are abnormal or not.
Steve Weiner
Rennsport Systems
Portland Oregon
(503) 244-0990
Old 06-05-2016, 02:16 PM
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KTL KTL is offline
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Join Date: Sep 2000
Location: Frankfort IL USA
Posts: 16,312
Here's a nice article on knock sensors

Engine Knock Sensors, Part 2 - Diagnostic News

Notable info on how it works: Two major knock sensor designs are used today: broadband single-wire and flat response two-wire knock sensors. Both sensor designs use piezoelectric crystals to produce and send voltage signals to the ECM.

Kevin L
Present: '86 Carrera, 89 Corvette Z51 6spd
Past: '87 Carrera, 79 911 SC widebody racecar
Old 06-06-2016, 09:47 AM
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