Knock sensor/CEL Flash mod checking

[Force Fed Mopar]

Is there a way to check the knock sensor to see if it's working? Can you read the voltage from it some way? I have the CEL Flash mod checked on my cal but I've never seen the light flash, even when I heard knock.

Is there a way to test if the CEL Flash mod is working? We've tried the "tap w/ a hammer" method and haven't seen any difference, and no flash.

[shelbymonster]

tap the intake with small metal object

[Force Fed Mopar]

tap the intake with small metal object

Is this a verified method? Will the engine change tune when you do it? If so then mine is bad, cause we whacked the shyte out of it right next to the knock sensor and it didn't change anything. Wonder what would cause a knock sensor to go bad? I 've never seen it much, but I guess most of them are 20+ years old now.

[DodgeZ]

If so then mine is bad,

prolly would explain why the check engine light randomly comes on.

[Force Fed Mopar]

Yeah but it doesn't flash though, is what gets me. Isn't it suppose to rapidly flash? Mine just comes on for like 3 secs, then goes out.

Stupid PITA car lol

[turbovanman²]

Yeah but it doesn't flash though, is what gets me. Isn't it suppose to rapidly flash? Mine just comes on for like 3 secs, then goes out.

Stupid PITA car lol

When it see's knock, the light comes on solid, then when the knock goes away, it turns off.

[Force Fed Mopar]

Ah okay, I though it blinked. So maybe it is a hosed-up knock sensor.

[ShadowFromHell]

I dont know what causes it, but the one in my NY went south. Cost me a HG when I upped the boost and kept adding timing with the log motor. I was watching the scanner, but nothing ever showed up.

[Force Fed Mopar]

Well I changed mine out, haven't seen any light yet (would randomly come on before) so we'll see.

[ShelGame]

It comes on whenever there is knock retard. Technically, it does flash. It typically just happens so fast that you can't see the individual flashes. If the knock level is really low, you might see the flashing, but probably the light will just seem dimmer.

It does not flash the same way the codes flash out. Maybe that's what you were thinking it would do?

[Force Fed Mopar]

No, I just thought it would be a rapid blinking that I could see whenever it knocked. Like, maybe a flash every 1/4 sec or something. I guess similar to the code flash yeah, just a lot faster and only when it knocked.

[Turboomni]

Years ago I had my knock sensor trip my Cal power loss light for no good reason. I had a bunch of old knock sensors on hand. I tested them out of the car with a voltmeter [digi} on AC . I then tapped them with a small screw driver to see the voltage. I was surprised to see the voltages sent out with me trying to tap them all close to the same way would vary abit from sensor to sensor. I then tested the knock sensor in my car and found it was hyper sensitive to the same tapping. A good bit higher the the others.
I averaged out the outputs of all the sensors I tested and put in the one that was in the middle output wise. Problem gone.
Basically the knock sensor is a Piezo type microphone and some put out more than others because of manufacture tolerances and age and they put out alternating current.

[Force Fed Mopar]

tap the intake with small metal object

Is this a verified method? Will the engine change tune when you do it? If so then mine is bad, cause we whacked the shyte out of it right next to the knock sensor and it didn't change anything. Wonder what would cause a knock sensor to go bad? I 've never seen it much, but I guess most of them are 20+ years old now.

prolly would explain why the check engine light randomly comes on.

Okay, so I replaced the knock sensor w/ another used one, light does not randomly come on anymore. However, it also does not light up when I tap on the intake next to it. Another bad one maybe? One extreme to another? Is tapping on the intake on sensor really a good way to test, or is it only supposed to work on a certain frequency? Need to get this working right before I crank the timing up too much more

[shackwrrr]

Okay, so I replaced the knock sensor w/ another used one, light does not randomly come on anymore. However, it also does not light up when I tap on the intake next to it. Another bad one maybe? One extreme to another? Is tapping on the intake on sensor really a good way to test, or is it only supposed to work on a certain frequency? Need to get this working right before I crank the timing up too much more

Doesn't the computer have a certain threshold of knock at different rpms? I would think the knock threshold is pretty high at idle. I would get a scan tool and actually look at the voltage it is producing. The computer may even ignore all knock at idle with the stock slider cam and all.

[Force Fed Mopar]

Hmm, quite possible. I'll see if I can hook it to the scanner this week. I have an OTC here at the house, but it only goes back to '89

[risen]

Doesn't the computer have a certain threshold of knock at different rpms? I would think the knock threshold is pretty high at idle. I would get a scan tool and actually look at the voltage it is producing. The computer may even ignore all knock at idle with the stock slider cam and all.

Give this man a cookie! You have to take it off idle for the sensor to have an active role in retard. I did the hammer test on mine, but I held it @ 2500 for a few secs while I tapped the intake lightly with a ball peen. I could hear the change in the engine when the retard came on and the light came on. There is a table for the volts vs rpm and a cutoff constant in the lm code. So the rpm has to be above the rpm constant and above the voltage level in the table in order to trigger the retard and light your cel.

[Force Fed Mopar]

Give this man a cookie! You have to take it off idle for the sensor to have an active role in retard. I did the hammer test on mine, but I held it @ 2500 for a few secs while I tapped the intake lightly with a ball peen. I could hear the change in the engine when the retard came on and the light came on. There is a table for the volts vs rpm and a cutoff constant in the lm code. So the rpm has to be above the rpm constant and above the voltage level in the table in order to trigger the retard and light your cel.

This is exactly what I needed to know, thanks!

[Force Fed Mopar]

Well I switched out my knock sensor again, as I was 99% positive I was hearing pinging under boost and no CEL flashing going on. The old sensor came apart when I unplugged it, in about 4 pieces I put another one in, and now the CEL is coming almost anytime I get on the gas. I am running 87 oct as I'm working on a tune for that, but it still seems pretty extreme. It pretty much just stays on anything over 1-2"Hg of vacuum. And it takes a second for the light to go out too when I lift, probably almost 2 secs. I am running bone stock T2 timing curves. In fact, the whole tune is stock other than scaling for 3-bar and +40s and turning the CEL Flash mod on. I dunno if I just have an over active sensor or what. I swear this stupid car is trying to drive me crazy

[moparman76_69]

I have a "hyper sensitive" knock sensor in the van, either that or a loud lifter tap. I had to adjust the knock sensor voltage table in the cal. The CEL would flash anytime I was out of boost or cruising over 2500 rpm even when I put straight CAM2 in it.

Try some higher octane to rule out actual knock and adjust the sensor voltage table to compensate.

[DodgeZ]

Well I switched out my knock sensor again, as I was 99% positive I was hearing pinging under boost and no CEL flashing going on. The old sensor came apart when I unplugged it, in about 4 pieces I put another one in, and now the CEL is coming almost anytime I get on the gas. I am running 87 oct as I'm working on a tune for that, but it still seems pretty extreme. It pretty much just stays on anything over 1-2"Hg of vacuum. And it takes a second for the light to go out too when I lift, probably almost 2 secs. I am running bone stock T2 timing curves. In fact, the whole tune is stock other than scaling for 3-bar and +40s and turning the CEL Flash mod on. I dunno if I just have an over active sensor or what. I swear this stupid car is trying to drive me crazy

stock 87 or StageII? try to pull some timing out. Maybe it is time to buy a new knock sensor.