Knock sensor ?

[screwbaru2]

Does anyone know wether dielectric heat dissapating compound applied to the mating surfaces of a knock sensor would extend, shorten, or have no affect on the longevity of the knock sensor? I used to use it on the old GM ignition modules at every tuneup and it seemed to extend to life of those.

I seem to have a rash of knock sensor codes. The 96 imps code came back

the 99 imp has one now and my outback has one also. I feel like I'm getting knocked around here.

[OB99W]

Does anyone know wether dielectric heat dissapating compound applied to the mating surfaces of a knock sensor would extend, shorten, or have no affect on the longevity of the knock sensor? I used to use it on the old GM ignition modules at every tuneup and it seemed to extend to life of those.

Since I've never used the compound on a knock sensor, I don't have any hard data. However, I don't think your experience with the ignition modules can be applied to the sensors. The ignition modules generate heat, and dissipating it more readily should help extend their lives. However, the knock sensors are passive devices, and heat is likely their enemy. I suspect that using the compound wouldn't lengthen knock sensor life, although it probably wouldn't significantly shorten it either.

 

 

I seem to have a rash of knock sensor codes. The 96 imps code came back

the 99 imp has one now and my outback has one also. I feel like I'm getting knocked around here.

I'm going to give that a bit of thought, and post later.

[screwbaru2]

Thanks OB99W, I'm on my way out to replace the knock sensor in my 97 OB,

I'll use the compound on that. When I do my wifes 99 IMP I wouldn't use it.

Then when I do the 96 Imp I'll do it the regular way again. AAHH to be so lucky to be able to experiment lke this. Other people don't have the kind of luck it takes to have 3 cars with the same problem! :-\

[OB99W]

Good luck with the experiment, but just in case I didn't make my point, conducting heat into the sensor probably isn't advantageous. It is critical that the mounting area be clean and the bolt properly torqued, and the rotational angle of the wire lead can be important.

 

I have some thoughts on knock sensor trouble. Of course, sometimes the problem can be due to wiring/connection issues (anywhere from the sensor to the ECU), and not failure of the sensor itself. If the sensor is actually bad, you can often see cracks in the encapsulating material -- it may be that besides heat, ozone might play a part in that deterioration. Ozone is generated whenever there's a sufficiently high voltage discharge in air. While we'd all like to think our ignition systems have perfect connections and insulation, that's not very likely, so ozone is typically generated in at least small amounts.

 

The actual knock sensor is a piezoelectric device; cracking of the covering shouldn't directly cause the sensor to fail. However, cracks would expose the piezo element and internal connections to it to the potentially damaging kind of atmosphere found under a car's hood.

 

So, make sure it's not a connection or mounting problem before condemning the sensor. If you're getting frequent failures due to cracking, perhaps checking for ignition voltage leakage (tight connections at coil and plugs, no spark "leakage", etc.) might be worthwhile.

[screwbaru2]

Thanks OB99W, This 'perhaps checking for ignition voltage leakage ' is something that I will def. check on the 2 imps. The OB is a project car that I just finished and got the code after the 1st start up went to open loop. One Imp hasn't been driven and has a new Bosch sensor in it, which may itself be the problem. The wifes Imp has 160K on it and has been driven 150 miles a day 5 days a week + whatever other trips we do for the last 6 weeks. That's most likely worn out from times and miles, however her car is due for a minor tune up.

The OB is fixed I hope. I installed a used soob sensor from the 2.5 that was in it originally. This time I taped a piece of emery cloth onto the end of a old fishing pole handle and cleaned the mating surface on the block. Also shined up the sensor surface. Ran the motor up to open loop and no code.

[nipper]

Understand how sesnors work before you start experimenting.

 

The knock sensor is a pizo-electric device, like a microphone (which it is essentially). It listens for knock, and when it hears it it will generate a sharp AC signal and send that tiny ac voltage to the ECU. It needs a solid mechanical connection to the engine to operate. Since there are millions of these things on the road, just bolted to the the block, i would not do it. There are no electronics in the sensor, so it would have no value. Usually these things just fail due to age. Quartz itself is fairly heat resistant

 

 

nipper

[screwbaru2]

That experiment was cancelled. I think cleaning the mounting surface with emery cloth is helpful, clean contacts are important.