What is the best way to test knock sensor?

[roswell998]

I have some slight pinging especially at slow speeds under light load both when cold and when at operating temp, however it is somewhat worse when cold.

I have an Actron CP9190 scanner so what is the best way to test the KS?

Both KOEO and KOER tests are 111. Cylinder balance test passed.

I read somewhere (perhaps on this forum but I can't find the thread now) that placing a socket extension near the sensor and tapping it lightly with a hammer should generate a knock signal, but how would you detect that signal? If the engine is running, would that generate a code?

Help will be appreciated

 

[roswell998]

Bump...

I've continued to search the forum but haven't uncovered the answer yet.

Any replies or if a link to a thread which covers the question is supplied, it will be appreciated.

 

[naval-avi8or]

I looked thru the Ford service CD. There was nothing in there to test a knock sensor. You either get a code during the Dia. test(s) or you don't. The knock sensor is set to a specific resonant freq and I can't see how you could produce the freq by tapping on the block with a socket extension.

 

[roswell998]

........The knock sensor is set to a specific resonant freq and I can't see how you could produce the freq by tapping on the block with a socket extension.

I agree with the above and did a little more research. The resonant freq is something in the range of 7 Khz.

It appears that when reading KOER codes, before the PCM calls for the "goose" test, it advances the spark to max which will induce pinging under engine acceleration while the PCM is looking for a signal from the KS. If it does not receive that signal it sets the 225 code.

So.........I'm not absolutely positive, but it appears that passing the "goose" test without a 225 code indicates a good sensor and wiring.

However, receiving the 225 code would not necessarily mean a bad sensor. It could be a bad connection or PCM.

 

[SHOZ123]

Mark the timing mark on the crank pulley with some whiteout correction fluid. Get a timing light. Start engine and watch the timing mark as you tap the block with a hard metal object. You should see the timing retard.

You can also do this with a data logger instead of a timing light if you have one.

 

[93rev2sev]

OR

Try super premium gas on your next fillup. 94 octane. See if your lugging knock goes away. I get the light load, low RPM knock too, but only since switching AWAY from super premium.

 

[SHOZ123]

But if you are not logging spark what will that really tell you?

 

[roswell998]

Well.......Here's the most current analysis/test results

1. Data logging with an Actron CP9190 scanner and placing a 1/4" straight steel rod about 1 foot long on the top of the KS right beside the connector and tapping lightly with a small ball peen hammer results in the spark being ******** from about 36 degrees to about 25 degrees. Note that a small piece of cardboard from a paper tablet was placed between the throttle butterfly valve set screw stop and the throttle stop which raised the engine speed up to about 1500 rpm. Otherwise the idle speed was about 700 rpm and the spark advance was only at about 10 degrees.

2. Also, when performing the test above, there was a noticeable drop in idle speed, so even without a scanner (or timing light) this test could be performed with audible observation and some valuable information related to the condition of the knock sensor and its associated circuitry could be gained.

3. Even though the KS is set to a tuned frequency, it appears that tapping on it will result in an output detectable by the PCM. I guess that much like a tuning fork, striking it will result in it being energized and it will vibrate at its resonant frequency.

4. All that said, it also appears that the KOER tests will detect lack of knock signal during the "goose" portion of the test and if the sensor or it's associated circuitry is bad, a code will be thrown. So, this test is probably redundant, but it does make me feel a bit better to actually observe the spark being ******** by inducing knock signals by tapping on the KS.

 

[hawkeye18]

If you goose the engine right during the goose test (stomping throttle to floor, starsky & hutch style), you will hear the knocking, much less the sensor detecting it. If you hear the knocking and you don't get the knock sensor code, the knock sensor is operating correctly, as this test tests both the quiescent state and the active state. If the sensor is talking when it shouldn't, it will set the code. If the knock sensor doesn't talk when it should (and you did the test right and heard the knocking), you will get the code. It's a very simple and very hardy sensor and doesn't fail often.

 

[somedude_001]

But if you are not logging spark what will that really tell you?

audible knock. mine always knocked on cheap gas so I have always run premium. not that I am turbo I have run 91 octang but I loose power so the knock sensor must be doing its job.