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Old 09-29-2020, 09:03 AM   #1
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Workhorse knock sensors

Where are the knock sensors located on a 2003 8.1 L vortec. Can a exhaust leak cause them to fail.
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Old 09-29-2020, 09:20 AM   #2
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I believe they are under the intake manifold . But that could vary by year.

Are you getting a fault code ?

EDIT: Found this using the search function.

http://www.irv2.com/forums/f22/engin...or-165740.html
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Old 09-29-2020, 10:53 AM   #3
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Fault code P0332. I have researched the location and some place it at the rear of the engine and others place it under the intake manifold. I have a 2003. Dealer said that the sensor had been replaced once but check engine light cane back on and code is back up. Does not look like the intake had ever been removed at least not recently .
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Old 09-29-2020, 11:18 AM   #4
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Here's my experience with knock sensors.
I have a 2001 Class C with an 8.1 Vortec motor.
I read with interest the comments on the other thread regarding the subject.

My "Check Engine Soon" light started coming on about 3 years ago. At first I, (and especially DW!) were panicked and distraught and, when we found out the problem, hurried to get them replaced.
They both worked fine at first, then one went out so we took it back to the mechanic (we were on the road from Canada to AZ). He figured it must have been faulty and replaced it.

That worked for awhile, but it wasn't long before the light came back on. It didn't seem to affect the performance of the MH (I don't keep rigid track of the mpg) and then, wonder of wonders, one day while travelling the CES light just went out!

It stayed out for quite some time and then once in awhile it would come back on. I have it OBD'd occasionally and it always comes back with the knock sensor code. I now mostly ignore it. If it comes on and doesn't go off, and if the engine starts to act badly, I'll jump right in and get it looked at.

Bottom line (for me), I found that replacing the knock sensors did nothing to cure the CES problem. YMMV

O LLOYD
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Old 09-29-2020, 01:56 PM   #5
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Quote:
Originally Posted by lsalem View Post
Fault code P0332. I have researched the location and some place it at the rear of the engine and others place it under the intake manifold. I have a 2003. Dealer said that the sensor had been replaced once but check engine light cane back on and code is back up. Does not look like the intake had ever been removed at least not recently .
Did you read through the post that I linked in my other post , diagram in the post shows the sensors on the sides of the block , below the exhaust manifolds, with heat shields .
But as mentioned , placement could vary by year.
If you have a good look around on the sides of the block and don't see them , then check for wiring running under the intake manifold from the rear of the engine .
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Old 09-29-2020, 05:42 PM   #6
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Check this video:

It says they are on the side of the block. I have a 7.4 but when I've been under the MH, which has been way too much, I know I saw a sensor on each side and figured they were the knock sensors. The coolant temp sensor would not be down there.
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Old 09-29-2020, 06:17 PM   #7
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There are 2 Anti Knock sensors AKA: Detonation sensors. They screw into the engine block, one on each side, and also act as a coolant drain plug for the block.
Be sure to have a drain pan under the engine when you remove the sensor(s).
Lynn
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Old 09-30-2020, 06:16 AM   #8
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I'm not sure on the 8.1 but on my 7.4 hen I drained the coolant this spring there were separate plugs for the coolant. In the video I posted earlier he changed the sensors and there was no coolant loss. Upon reading on the internet it says the sensors have a microphone tuned to the right frequency to pick up the knock.
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Old 09-30-2020, 10:20 AM   #9
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Quote:
Originally Posted by LETMGROW View Post
There are 2 Anti Knock sensors AKA: Detonation sensors. They screw into the engine block, one on each side, and also act as a coolant drain plug for the block.
Be sure to have a drain pan under the engine when you remove the sensor(s).
Lynn
There are actually drain plugs (hex plug) on the engine block, at least on the 8.1.

The knock sensors are NOT drain plugs, when you remove a knock sensor there is no coolant that come out.


If you watch the video it will also show that the knock sensors do NOT provide a way to drain the coolant.
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Old 09-30-2020, 04:02 PM   #10
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Quote:
Originally Posted by lsalem View Post
Where are the knock sensors located on a 2003 8.1 L vortec. Can a exhaust leak cause them to fail.
The answer to your question is YES, it can make them miss read and give a false knock code& possible destroy them too.

I had a the exhaust "dognut" gasket lose about 1/2 inch chunk of gasket material and it was shooting hot exhaust right at the sensor. I bought two new knock sensors and when I got under the engine to replace them that's when I saw the gasket needed replacing too. Problem was gone but I didn't go back and try to isolate the precise fault.


When you replace the knock sensors be sure to NOT OVER-tighten as they are somewhat fragile inside. I think the torque is only 14 ft-lbs.
I never saw any coolant when I replaced mine.


Good luck,
Bill
Here's what I posted 7 yrs ago:
Knock Sensor Replacement

1. Disconnect the negative battery cable.
2. Remove the wiring harness connector from knock
sensor.
3. Remove the knock sensor from engine block.

Installation Procedure
Notice: Refer to Fastener Notice in Cautions and
Notices.
1. Install the knock sensor into the engine block.
Tighten
Tighten to 19 N-m (14 Ib ft).
sensor.
2. Install the wiring harness connector to the knock
3. Connect the negative battery cable.
Attached Thumbnails
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