Knock sensor question
Thread Starter
Pro
Joined: Oct 2006
Posts: 594
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From: Peoria IL
Knock sensor question
Here's another silly question from a newbee - When I flushed my cooling system last week , I removed the knock sensor to drain the block and noticed that the pin on the sensor was loose - I took the small rubber washer from the bottom of the pin off and found that the ceramic around the bottom of the pin was cracked.The pin is still firmly attatched. Is there anyone out there in the know who can explain how these sensors work , how robust they are , if I can test it to see if it is still working etc . They are upwards of $70 to replace and I dont want to do it if its not necessary.
Please remember I'm a total novice so idiot proof explanation needed
Thanks in advance
Please remember I'm a total novice so idiot proof explanation needed
Thanks in advance
Race Director
Joined: Jul 2004
Posts: 12,706
Likes: 329
From: Scottsdale Arizona
Not a silly question at all. I'll give it a shot.
The way it works is simple enough. The sensor detects pinging (detonation) in the engine and signals the computer, which retards timing to reduce the pinging. I've never pulled one apart so don't know exactly how the inerds work. The way to test these is to put a timing light on a warmed up engine and then "gentlly" hitting the block near the sensor with a hammer to simulate a ping. The timing should retard for a short period of time.
Whether it works or not, I honestly woudn't bother replacing it unless you have huge detonation problems. Unless the car is a daily driver, you'll get more benefit from premium gas.
The way it works is simple enough. The sensor detects pinging (detonation) in the engine and signals the computer, which retards timing to reduce the pinging. I've never pulled one apart so don't know exactly how the inerds work. The way to test these is to put a timing light on a warmed up engine and then "gentlly" hitting the block near the sensor with a hammer to simulate a ping. The timing should retard for a short period of time.
Whether it works or not, I honestly woudn't bother replacing it unless you have huge detonation problems. Unless the car is a daily driver, you'll get more benefit from premium gas.
Thread Starter
Pro
Joined: Oct 2006
Posts: 594
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From: Peoria IL
Thanks for taking the time to post a reply , Will leave it alone and continue to use premium gas - I definately do not use her as a daily driver so the extra cost is not such an issue . The premium will I assume lessen the chance of the pinging anyway right? There is no risk of using a higer than 87 octane rated gas? 
Race Director
Joined: Jul 2004
Posts: 12,706
Likes: 329
From: Scottsdale Arizona
Originally Posted by britvette
Thanks for taking the time to post a reply , Will leave it alone and continue to use premium gas - I definately do not use her as a daily driver so the extra cost is not such an issue . The premium will I assume lessen the chance of the pinging anyway right? There is no risk of using a higer than 87 octane rated gas?
Drifting
Joined: Jan 2002
Posts: 1,606
Likes: 1
From: Las Cruces NM
Your thoughts on how a knock sensor works aren't quite on. The sensor in the block doesn't determine knocks in itself. It sends a signal to an electronic spark controller which determines if it's a knock and how the timing should be adjusted accordingly.
Your knock sensor is busted and needs to be replaced. Now is the best time since the coolant is already drained. It will only make it that much more of a pita and it'll cost more to add in the lost coolant later.
When they break like that, which is how they almost always break, they'll either send more knock signals and you'll lose more timing and gas mileage/performance, or it won't ever send any, and the computer will assume it can advance the timing as far as its tables allow. Either way is not good.
Chris
Your knock sensor is busted and needs to be replaced. Now is the best time since the coolant is already drained. It will only make it that much more of a pita and it'll cost more to add in the lost coolant later.
When they break like that, which is how they almost always break, they'll either send more knock signals and you'll lose more timing and gas mileage/performance, or it won't ever send any, and the computer will assume it can advance the timing as far as its tables allow. Either way is not good.
Chris
