Knock sensor -- how does it work and how do we test?

[shadango]

There is a screw-in sensor called the "knock/detonation sensor".

Almost looks like a temp gauge sensor.

When we rebuilt the Volare slant 6, we didnt replace that since it is a $38 part even at Rock auto.

But wondering if this booger could be the cause of low-load, light throttle pinging ?

Is there a way to test this sensor?

Why is it SOOOOO expensive?

https://www.rockauto.com/en/moreinfo.php?pk=40220&cc=1243561&jsn=1869

 

[volare 77]

do you still have the original spark control computer hooked up/working? Could it be the problem? Maybe but could be other things too. I actually read somewhere that you could actually rap on the manifold with a hammer and see if the timing retards. here it is:
Popular Mechanics

 

[volare 77]

marty has it for $20 plus ship 4318118 DETONATION SENSOR,PU U5213629,4686044,4700044,4671185
$20 here with free shipping make offer also

Ignition Knock (Detonation) Sensor Standard KS1 | eBay

 

[Cordoba1]

Hello! What it "is" is a microphone, believe it or not. It listens for that sound we all know, the ping! It's one of the 6 or 7 sensors (depending on year) of the Lean Burn system. When the system detects that sound, it's one of the many parameters Lean Burn uses to adjust timing. Other critical part of low-load timing for Lean Burn is the TPS: It's often at low-load that you change the throttle quickly, those few pings you get before the timing catches up. The computer uses the TPS to calculate rate-of-change on the throttle. During abrupt changes, the computer will very quickly retard the timing to reduce or eliminate pinging. Lean Burn carbs are set to an A/F of 18:1, which is quite lean (hence the name), and that alone introduces some pinging. Almost all contemporary tests of Lean Burn engines notices that there is some pinging even when everything is brand new. My Slant has an ever-so-slight ping when it is fully heated when stepping off from a stop. I've just learned to live with it. When I've tried to retard the timing to get rid of it, I get driveability problems.

 

[shadango]

do you still have the original spark control computer hooked up/working? Could it be the problem? Maybe but could be other things too. I actually read somewhere that you could actually rap on the manifold with a hammer and see if the timing retards. here it is:
Popular Mechanics

Nope.....just the ignition control box on the firewall.

 

[shadango]

Hello! What it "is" is a microphone, believe it or not. It listens for that sound we all know, the ping! It's one of the 6 or 7 sensors (depending on year) of the Lean Burn system. When the system detects that sound, it's one of the many parameters Lean Burn uses to adjust timing. Other critical part of low-load timing for Lean Burn is the TPS: It's often at low-load that you change the throttle quickly, those few pings you get before the timing catches up. The computer uses the TPS to calculate rate-of-change on the throttle. During abrupt changes, the computer will very quickly retard the timing to reduce or eliminate pinging. Lean Burn carbs are set to an A/F of 18:1, which is quite lean (hence the name), and that alone introduces some pinging. Almost all contemporary tests of Lean Burn engines notices that there is some pinging even when everything is brand new. My Slant has an ever-so-slight ping when it is fully heated when stepping off from a stop. I've just learned to live with it. When I've tried to retard the timing to get rid of it, I get driveability problems.

Lots of great info there....thanks. The carb , as far as I know is not a lean burn carb. Its an off-the-shelf cart BBD (?) 2 bbl. Its a rebuilt, but one from 20 years ago I was told...."when they were done right"....if thats true...LOL. Cars runs and drives fine as far as I can tell. Aside from getting 6-7 mpg around town (many short trips) and the pinging on light throttle.....

 

[shadango]

marty has it for $20 plus ship 4318118 DETONATION SENSOR,PU U5213629,4686044,4700044,4671185
$20 here with free shipping make offer also

Ignition Knock (Detonation) Sensor Standard KS1 | eBay

Thanks! A greta option if it looks like ours is bad....gonna try the hammer test method. LOL

 

[shadango]

Nope.....just the ignition control box on the firewall.

Wait a tick...

If I dont have the lean burn computer, is that knock sensor doing anything at all? What the heck is it connected to?

The car seemed stock when we got it.....it did NOT have the LBC.

 

[volare 77]

That was why I was asking because it shouldn`t come in to play if you no longer have the spark control computer.

 

[volare 77]

may be time for combustion chamber cleaner. it may help with the pinging.

https://www.amazon.com/Genuine-Chrysler-Accessories-4318001AD-Combustion/dp/B00BV4D97K

 

[shadango]

may be time for combustion chamber cleaner. it may help with the pinging.

https://www.amazon.com/Genuine-Chrysler-Accessories-4318001AD-Combustion/dp/B00BV4D97K

In our case, I dont think so....only a few thousand miles on a fresh rebuild....
The more I think on this, the more I think the sensor is moot...I seem to recall that the original air cleaner housing for the 1 bbl had a square cutout in it that was blocked off with a homemade plate of sorts....would have to dig it out....thinking that was where the lean burn may have been, and removed by the previous owner.

If that is the case then the sensor wouldnt do anything but take up room in the engine bay......because without the LBC, its just a typical old mopar spark box and ballast running stuff.

But I thought the hole in the air cleaner for the LBC was a lot bigger than what we had on ours.....attached a picture

 

[Cordoba1]

In our case, I dont think so....only a few thousand miles on a fresh rebuild....
The more I think on this, the more I think the sensor is moot...I seem to recall that the original air cleaner housing for the 1 bbl had a square cutout in it that was blocked off with a homemade plate of sorts....would have to dig it out....thinking that was where the lean burn may have been, and removed by the previous owner.

If that is the case then the sensor wouldnt do anything but take up room in the engine bay......because without the LBC, its just a typical old mopar spark box and ballast running stuff.

I think you're onto something. It is quite easy to convert from Lean Burn and have everything look stock. Heck, you can leave ALL of the Lean Burn wiring in place, and the standard issue electronic ignition would work just fine. If you don't have the LB computer on your air-cleaner, the anti-knock sensor is doing nothing. Look elsewhere for your problem. (Sounds like you already are!)

 

[shadango]

I think you're onto something. It is quite easy to convert from Lean Burn and have everything look stock. Heck, you can leave ALL of the Lean Burn wiring in place, and the standard issue electronic ignition would work just fine. If you don't have the LB computer on your air-cleaner, the anti-knock sensor is doing nothing. Look elsewhere for your problem. (Sounds like you already are!)

Ok, yeah....I guess the owner prior to us maybe removed it.

Talking with the son more, seems as he feels the pinging is more on light acceleration going up hill...1/4 throttle-ish.

I know he had tried tinkering with timing last fall and that didnt seem to help.....I forget what our base timing is but it is more advanced than the 2 degrees (?) stock....seems like it runs better with the higher timing.

Gonna have to break out the timing light I guess and check again......I keep telling the kiddo to keep a log of where stuff is at......I am getting too old to remember all the settings for every vehicle we play with...LOL

 

[volare 77]

I would set the timing for a earlier non lean burn slant six...... But I looked up a 75 slant six and it showed TDC. Is that right?

 

[BudW]

The item circled (above) is a block-off plate for cars without OSAC valve (which looks like part below). All it does reduces the rate of vacuum change to distributer vacuum advance – to reduce NOx emissions. Most people bypass it for better drivability (in states that allow that).

That block-off plate is hard to find and I’m sure someone would be willing to take it off your hands – if you elected to sell it . . .


The knock sensor needs to have a computer (Lean Burn, Spark Control Computer, or any of the other various names Chrysler has used) to control knocks/pings – which is one of the reasons to leave that system in place (especially if you use gasoline with varying levels of octane).
If you use a constant level of octane rating, then you can dispel that system (Lean Burn) altogether (which is N/A in your case) – with time spent on getting your ignition timing set properly.

Some of us, who use the low octane fuel for 90% of driving, then use the higher-octane fuel for racing – having a computer to control timing (and pinging) is a huge time saver.
Higher octane fuels can allow different spark timing – which in turn, helps engine run better. The cost of higher octane fuels is cost prohibitive for most driving.

Getting under hood to adjust distributer timing every other tank full – is a lot more time spent than I want to give . . .


In your case, ignition timing needs to be adjusted to eliminate the ping (or use higher octane fuel, which seams counterproductive with a /6).
If engine hadn’t been into recently, then a combustion chamber cleaning will help.

Keep in mind, every time you hear a “ping”, means the piston sustains damage as if you hit it with a ball-peen hammer, each and every time (ie: not good).
BudW