Knock Sensor question
Le Mans Master
Joined: Jul 2007
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From: Tampa Florida
Race Director
Joined: Sep 2000
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From: The Top of Utah
I have never heard to "knock on the knock sensor". I would be afraid of breaking it. A light rap with a small hammer on the block, head, or other firmly attached engine part should do the trick. The rapping simulates the "knock" the sensor is supposed to detect. If the rpms don't drop in that test, however, the knock sensor isn't the only possible cause.
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Advanced
Joined: Jun 2004
Posts: 56
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From: Fort Worth Texas
If you've got a digital volt meter you can check it without the engine running. Set the DVM to 2V, and insert the positive into the end of the sensor and ground to the chassis. With the key in the on position, the DVM should read something other than zero, now tap on the exhaust or block and you should see the reading jump if it does, it's working, if it doesn't, replace it. (That's how the FSM says to check them for my 93). Since you have a 91, you only have one down near the oil pan gasket.
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Race Director
Joined: Sep 2000
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From: The Top of Utah
The knock sensor installs in the block, water jacket, drain plug hole in the Gen I engines. It replaces the right side drain plug on mine.
My knock sensor was working overtime. it would send knock signals (false knock) when there was no knock.
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Race Director
Joined: Apr 2003
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From: moraga ca
I have never heard to "knock on the knock sensor". I would be afraid of breaking it. A light rap with a small hammer on the block, head, or other firmly attached engine part should do the trick. The rapping simulates the "knock" the sensor is supposed to detect. If the rpms don't drop in that test, however, the knock sensor isn't the only possible cause.
RACE ON!!!
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Race Director
Joined: Sep 2000
Posts: 17,298
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From: The Top of Utah
Why climb underneath the car or otherwise distort myself to hit the knock sensor with a screwdriver handle? The hammer and the block are too handy to go to any special effort for nothing.
"My knock sensor was working overtime." Emphasis on the "was". The fix was even easier than removing it and wrapping the threads.
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"My knock sensor was working overtime." Emphasis on the "was". The fix was even easier than removing it and wrapping the threads.
RACE ON!!!
Burning Brakes
Joined: Oct 2009
Posts: 773
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From: Minneapolis MN
My advice is just replace if its original.If original its almost 20 years old & there is sometimes crud that sits in there(from coolant).Plus the sensor is not expensive.Also not a bad to remove so it does not seize in block from never being removed.If sensor is new or fairly new everyone already gave good ways to check sensor.Check for codes & wiring to sensor & connector that goes into knock sensor.Not a bad idea to replace all sensors on vehicle if vehicle has 100,000 miles or more & sensors are original but nobody does this beacause its expensive.
Race Director
Joined: Apr 2003
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From: moraga ca
Why climb underneath the car or otherwise distort myself to hit the knock sensor with a screwdriver handle? The hammer and the block are too handy to go to any special effort for nothing.
"My knock sensor was working overtime." Emphasis on the "was". The fix was even easier than removing it and wrapping the threads.
RACE ON!!!
"My knock sensor was working overtime." Emphasis on the "was". The fix was even easier than removing it and wrapping the threads.
RACE ON!!!
Melting Slicks
Joined: Mar 2008
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From: Delta B.C. Canada
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Race Director
Joined: Apr 2003
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From: moraga ca
Yes, once you've unscrewed the knock sensor, the coolant on that side of the block (and the radiator) will drain out. You will have to refill it. Make sure the motor is cold, drain the radiator first, replace the knock sensor (pan under the sensor because the coolant will be gushing out), replace sensor and coolant and hopefully you will be ok.
Race Director
Joined: Feb 2004
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If the coolant is fresh, and you don't want to flush or swap it, be ready with the new one, (and a drain pan) and spin out the old, and quickly spin in the new. You cn plug the hole with your thumb, and then start the sensor by hand. Last time I swapped one, I only lost about a cup of coolant.
Race Director
Joined: Apr 2003
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From: moraga ca
If the coolant is fresh, and you don't want to flush or swap it, be ready with the new one, (and a drain pan) and spin out the old, and quickly spin in the new. You cn plug the hole with your thumb, and then start the sensor by hand. Last time I swapped one, I only lost about a cup of coolant.
Been there, done that.
Race Director
Joined: Apr 2003
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From: moraga ca
Pete, the only problem with the look away method is that you can't find the hole to screw the sensor into. Then the stuff runs down your arms and your shirt gets drenched with coolant. Much better to wear swim goggles. Get the NHRA approved ones.