Testing Knock Sensor
Thread Starter
Intermediate
Joined: Dec 2004
Posts: 34
Likes: 0
From: Joplin Missouri
Testing Knock Sensor
DataMaster showed no Knock Count and No spark retard. Changed Knock Sensor and no change. Checked wiring, it looks ok. The car is knocking when hot and going into overdrive. Was wondering how to check the knock sensor system, is it the sensor itself or the wiring or the connector. Looked for an hour for the spark control module, finnally found out my 91 L98 doesnt have one. So its gota be either the sensor, connector, wire or the ECM. Can I unplug the sensor and check voltage without screwing anything up? Not sure where to start. Dont wanta make things worse. Thanks
Drifting
Joined: Mar 2005
Posts: 1,923
Likes: 0
From: GA
Originally Posted by stonemo
DataMaster showed no Knock Count and No spark retard. Changed Knock Sensor and no change. Checked wiring, it looks ok. The car is knocking when hot and going into overdrive. Was wondering how to check the knock sensor system, is it the sensor itself or the wiring or the connector. Looked for an hour for the spark control module, finnally found out my 91 L98 doesnt have one. So its gota be either the sensor, connector, wire or the ECM. Can I unplug the sensor and check voltage without screwing anything up? Not sure where to start. Dont wanta make things worse. Thanks
Only way I could think of to test a knock sensor would be to hook it up to an oscilloscope and see if it registers anything when you rap on it.
Thread Starter
Intermediate
Joined: Dec 2004
Posts: 34
Likes: 0
From: Joplin Missouri
Watched DataMaster while tapping on the block and sensor itself, Nothing. Now when I installed the sensor I didnt know you were only suppose to tighten it to about 15 ft lbs. Could I have damaged it by over tightening it???
Melting Slicks
Joined: Jun 2004
Posts: 3,032
Likes: 4
Originally Posted by stonemo
Watched DataMaster while tapping on the block and sensor itself, Nothing. Now when I installed the sensor I didnt know you were only suppose to tighten it to about 15 ft lbs. Could I have damaged it by over tightening it???
Is the chip stock? maybe a previous owner put an aftermarket (custom or otherwise in), that always reports 0 knock.
Thread Starter
Intermediate
Joined: Dec 2004
Posts: 34
Likes: 0
From: Joplin Missouri
No aftermarket anything. The knock sensor worked before. Just started getting crappy mileage. So I tuned it up (plugs, wires, cap, rotor, O2 sensor) but still no difference. No codes. Just pings a bit when crusin around. The car still runs good though, idles great and plenty of power, though im a little scared of gettin into it with the pinging. Surely theres a way of testing the wiring and connector to see if thats the problem. Hate to go buy another knock sensor, but I will ... The small daughter board that Morley was talking about, is that replaceable or do I have to change the whole ECM?
Melting Slicks
Joined: Oct 2002
Posts: 3,193
Likes: 1
From: Cincinnati Oh
It's been a while since I went through the Factory Service Manual (Where's CFI-EFI???), but I would think you'd eventually get a code if the knock sensor and/or wiring is bad (the ECM periodically checks this).
However, I would try to check continuity of the wiring between the sensor and the ECM first, then go through the FSM on the diagnostic steps. Rule of thumb: check all the stupid, simple stuff first. So clean all connecting terminals, make sure you double-check ANYTHING that you might have messed with before this changed, etc etc.
If it pings around town, that suggests a timing problem which will be different than (but related to?) the knock issue. Could be EST controll or some other thing...
What have you tinkered with recently?
EDIT: You DID double-check your plug wires, right? Really easy to get those backwards - and that causes bigtime pinging under part throttle (ask me how I know!).
regardless, double check those wires again.
However, I would try to check continuity of the wiring between the sensor and the ECM first, then go through the FSM on the diagnostic steps. Rule of thumb: check all the stupid, simple stuff first. So clean all connecting terminals, make sure you double-check ANYTHING that you might have messed with before this changed, etc etc.
If it pings around town, that suggests a timing problem which will be different than (but related to?) the knock issue. Could be EST controll or some other thing...
What have you tinkered with recently?
EDIT: You DID double-check your plug wires, right? Really easy to get those backwards - and that causes bigtime pinging under part throttle (ask me how I know!).
regardless, double check those wires again.
Thread Starter
Intermediate
Joined: Dec 2004
Posts: 34
Likes: 0
From: Joplin Missouri
Wires are correct, checked them several times. Dont have a Factory Service Manual. Just the Chilton and Haynes manuals, and they dont really tell me much. As far as checking continuity between sensor and ECM, not sure where on the ECM to check. If I disconnected the sensor and turned the key on would I get voltage at the connector? And would It screw anything up to do this? Doesnt the EST controll get its signal from the knock sensor and then adjust the timing? Does the Ignition Module in the distributor have anything to do with the electronic timing advance? I havent tinkered or messed with anything. Did the tune-up to try and solve this problem. It helped some but DataMaster still shows only 1 knock on start and 1 one shut down, nothing in between. Well im gona go stare at it some more and see if anything has changed. Any other suggestions would be greatly appreciated. Im kinda lost here. 
Thanks
Thanks
Drifting
Joined: Mar 2005
Posts: 1,923
Likes: 0
From: GA
Originally Posted by stonemo
DataMaster still shows only 1 knock on start and 1 one shut down,
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
2027 Corvette vs The World: Every Model vs Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
2027 Corvette Buyer's Guide: Everything You Need to Know!
Joe Kucinski
10 Things C8 Corvette Owners Hate (But Won't Tell You)
Joe Kucinski
10 Best Corvettes Coming to Barrett-Jackson Palm Beach 2026!
Brett Foote
Every Corvette Grand Sport Explained! (C2, C4, C6, C7, & C8)
Joe Kucinski
Grand Sport & Grand Sport X Launch Alongside All-New 535hp LS6 V8!
Michael S. Palmer
5 Reasons Bad Drivers Crash & 5 Ways to Avoid a Costly Mistake!
Joe Kucinski
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 32
From: The Top of Utah
Originally Posted by stonemo
Dont have a Factory Service Manual. Just the Chilton and Haynes manuals, and they dont really tell me much. As far as checking continuity between sensor and ECM, not sure where on the ECM to check.
RACE ON!!!
Thread Starter
Intermediate
Joined: Dec 2004
Posts: 34
Likes: 0
From: Joplin Missouri
Nope, Morley, no knock counts. Driving down the road, when it starts to ping real bad, still Datamaster shows no knock counts. And CFI EFI I will have to break down and get a Factory Service Manual as you suggest. Never really had any problems that the chilton or haynes manuals didnt cover. The link that you posted to Helminc.com for the service manual, did I see that right, $95 bucks for the manual? Plan to keep the car for a long time (LOVE MY VETTE) so might as well learn all I can about it. Will invest in one. But in the mean time, should I get another sensor and try it. Was reading in the forums about some electronic parts that were bad straight outa the box. Could mine be one of those? Thanks
Team Owner
Joined: Oct 2000
Posts: 96,443
Likes: 9
From: Fort Knox, KY
Cruise-In IV Veteran
Cruise-In VI Veteran
Cruise-In VII Veteran
Cruise-In VIII Veteran
You can buy a genuine Helms manual a bit cheaper than that here..
http://www.factoryautomanuals.com/home.php
http://www.factoryautomanuals.com/home.php