Knock sensor? What does it do?

You don't need to drain the antifreeze if you plan it right. You will loose
a little antifreeze. Just have the new sensor ready to screw in and pull the
old one, hold a finger over the hole and then quickly insert the new one....
Make sure the radiator overflow tank has plenty of antifreeze in it and keep
a check on it for a week.

wrote in message

>I have a 91 GMC pickup with a 350 engine and auto tranny. I had my
> mechanic do a checkup of the underside of the truck and he said the
> knock sensor is broken (the wire terminal corroded off). I asked him
> what it's for. He said it senses a knock in the engine and does
> something to compensate.
>
> He knows I am on a limited income and said I can change it myself if I
> want. He said I just need to drain the antifreeze because it screws
> into an antifreeze coolant port. Unscrew it, replace it, put wire on.
>
> I agree this sounds pretty easy to do, but I cant understand how a
> thing inserted into a coolant path can sense a knock in the engine?
>
> Can someone explain how this thing works.
>
> Thanks
>
> LM
 >> Stay informed about: Knock sensor? What does it do? 

>I have a 91 GMC pickup with a 350 engine and auto tranny. I had my
> mechanic do a checkup of the underside of the truck and he said the
> knock sensor is broken (the wire terminal corroded off). I asked him
> what it's for. He said it senses a knock in the engine and does
> something to compensate.
>
> He knows I am on a limited income and said I can change it myself if I
> want. He said I just need to drain the antifreeze because it screws
> into an antifreeze coolant port. Unscrew it, replace it, put wire on.
>
> I agree this sounds pretty easy to do, but I cant understand how a
> thing inserted into a coolant path can sense a knock in the engine?
>
> Can someone explain how this thing works.


To add to JR's post, the fact that it doubles as a plug for the coolant
jacket is irrelevant. It threads into the *engine block* and detects the
knock vibrating through the entire casing. It really is as simple as
draining the coolant and swapping out. Even if you're quick you'll make a
BIG mess if you don't drain the coolant first.
 >> Stay informed about: Knock sensor? What does it do? 

Hi!

> You don't need to drain the antifreeze if you plan it right. You will
> loose a little antifreeze. Just have the new sensor ready to screw in
> and pull the old one, hold a finger over the hole and then quickly insert
> the new one....

Only do this if you're very, very sure that you won't cross-thread the
sensor. If you do that, you will be in trouble.

Draining the anti-freeze might seem like a pain, but if you're careful you
can collect, filter (very important!) and reuse it. It's cheap insurance
against having to rush through a job only to find out that in your haste,
you cross-threaded the sensor.

William
 >> Stay informed about: Knock sensor? What does it do? 

This message is not archived
 >> Stay informed about: Knock sensor? What does it do? 

On 8 Dec, 07:15, letter....TakeThisOut@invalid.com wrote:
> On Mon, 08 Dec 2008 01:05:50 GMT, "William R. Walsh"
>
>
>
> wrote:
> >Hi!
>
> >> You don't need to drain the antifreeze if you plan it right. You will
> >> loose a little antifreeze. Just have the new sensor ready to screw in
> >> and pull the old one, hold a finger over the hole and then quickly insert
> >> the new one....
>
> >Only do this if you're very, very sure that you won't cross-thread the
> >sensor. If you do that, you will be in trouble.
>
> >Draining the anti-freeze might seem like a pain, but if you're careful you
> >can collect, filter (very important!) and reuse it. It's cheap insurance
> >against having to rush through a job only to find out that in your haste,
> >you cross-threaded the sensor.
>
> >William
>
> Thanks for all the replies.
> It sounds like a pretty easy repair.

It is not

Get a new car
 >> Stay informed about: Knock sensor? What does it do? 

On Sun, 7 Dec 2008 16:13:53 -0500, "Woody" wrote:

>You don't need to drain the antifreeze if you plan it right. You will loose
>a little antifreeze. Just have the new sensor ready to screw in and pull the
>old one, hold a finger over the hole and then quickly insert the new one....
>Make sure the radiator overflow tank has plenty of antifreeze in it and keep
>a check on it for a week.

1. Open the radiator cap (tank cap) and relieve all pressure in the
cooling system first.

2. Replace the cap and tighten it down.

3. Then follow the above instructions.
 >> Stay informed about: Knock sensor? What does it do? 

PeterD wrote:
> On Sun, 7 Dec 2008 16:13:53 -0500, "Woody" wrote:
>
>> You don't need to drain the antifreeze if you plan it right. You will loose
>> a little antifreeze. Just have the new sensor ready to screw in and pull the
>> old one, hold a finger over the hole and then quickly insert the new one....
>> Make sure the radiator overflow tank has plenty of antifreeze in it and keep
>> a check on it for a week.
>
> 1. Open the radiator cap (tank cap) and relieve all pressure in the
> cooling system first.
>
> 2. Replace the cap and tighten it down.
>
> 3. Then follow the above instructions.

And if you want to make it even easier squeeze the lower radiator hose
and then put the cap on.

--
Steve W.
Near Cooperstown, New York


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 >> Stay informed about: Knock sensor? What does it do? 

"Gosi" wrote in message

> On 8 Dec, 07:15, letter....TakeThisOut@invalid.com wrote:
>> On Mon, 08 Dec 2008 01:05:50 GMT, "William R. Walsh"
>>
>>
>>
>> wrote:
>> >Hi!
>>
>> >> You don't need to drain the antifreeze if you plan it right. You will
>> >> loose a little antifreeze. Just have the new sensor ready to screw in
>> >> and pull the old one, hold a finger over the hole and then quickly
>> >> insert
>> >> the new one....
>>
>> >Only do this if you're very, very sure that you won't cross-thread the
>> >sensor. If you do that, you will be in trouble.
>>
>> >Draining the anti-freeze might seem like a pain, but if you're careful
>> >you
>> >can collect, filter (very important!) and reuse it. It's cheap insurance
>> >against having to rush through a job only to find out that in your
>> >haste,
>> >you cross-threaded the sensor.
>>
>> >William
>>
>> Thanks for all the replies.
>> It sounds like a pretty easy repair.
>
> It is not
>
> Get a new car

Gosi, if you want to make an ass of yourself by shoveling "I hate GM and
want it to die" post's into the group, that is one thing, but why don't you
leave the people alone who are simply asking for repair advise? We all know
you live on welfare, don't own a vehicle, never owned a GM, and live in
Europe. Seriously, this poster is only looking for an answer to his
question, he doesn't need your BS too.
 >> Stay informed about: Knock sensor? What does it do? 

> 1. Open the radiator cap (tank cap) and relieve all pressure in the
> cooling system first.
>
> 2. Replace the cap and tighten it down.
>
> 3. Then follow the above instructions.


Step 1/2. Allow engine to cool thoroughly.

I know it should be a given, but it couldn't hurt to mention...
 >> Stay informed about: Knock sensor? What does it do? 

On Mon, 08 Dec 2008 12:24:24 -0500, "Steve W."
wrote:

>PeterD wrote:
>> On Sun, 7 Dec 2008 16:13:53 -0500, "Woody" wrote:
>>
>>> You don't need to drain the antifreeze if you plan it right. You will loose
>>> a little antifreeze. Just have the new sensor ready to screw in and pull the
>>> old one, hold a finger over the hole and then quickly insert the new one....
>>> Make sure the radiator overflow tank has plenty of antifreeze in it and keep
>>> a check on it for a week.
>>
>> 1. Open the radiator cap (tank cap) and relieve all pressure in the
>> cooling system first.
>>
>> 2. Replace the cap and tighten it down.
>>
>> 3. Then follow the above instructions.
>
>And if you want to make it even easier squeeze the lower radiator hose
>and then put the cap on.

Good thought, a slight vacuum would be helful in the system...
 >> Stay informed about: Knock sensor? What does it do?