Valves tapping Avalon 2000 90,000 miles

You're correct when saying, "...The noise is caused because the air/fuel mixture in the combustion chamber is detonating prior to the spark plug firing. ...". My question is why does retarding the spark do anything helpful since the occurance of combustion is apparently unrelated to the occurance of a spark?

You're welcome!

Maybe pinging should be called premature detonation, then people will get all sorts of e-mails offering all sorts of fixes for it!

"Ray O" wrote: snip

All pretty well correct except for the fact that detonation ALWAYS occurs AFTER the spark.

Sometimes the parameters are so out of whack that the fuel/air charge will ignite well BEFORE the spark occurs but this is called 'PRE-IGNITION' and can destroy an engine in short order...some highly tuned racecar engines get into this trouble but it's pretty unusual in the run of the mill car unless the engine has been badly misused.

Ignition - That's the word I was trying to think of! Much more accurate description to what happens before the spark plug fires!

Not really John...'Pinging' refers to the sound that Detonation makes (not pre-ignition). pre-ignition is an altogether different cat than detonation.

Detonation ALWAYS occurs after the spark...Pre-ignition ALWAYS occurs before the spark (and is MUCH more deadly BTW)

I can't imagine that you can hear tappets at speed and under load. My guess is that you are hearing ping - pre-ignition - that is resulting from the cheap gas. I would fill the tank with high test - premium - for two or three tanks and take care to notice if the ping continues.

Since you are driving a 2000 model year, you might want to get a hold of the OBD II Code Reader tool to see if there are any codes floating around in the system that might tell you if the knock sensor is not working properly. The code reader can be found on eBay for around $90 - there are several models, some are more and some are less - or you can often times check them out from the auto parts store, similar to checking a book out from the library. If you want to check the tool out and use it in the parking lot, they will usually take your driver license. If you want to take the reader home and play with it overnight, they will sell you the tool on your credit card, but then give you a full refund when you take the tool back the next day. You need to check with the store to see if they offer this service, I am in California and AutoZone will let you buy the tool then bring it back for a refund, or use it in the parking lot while they hold your driver license.

It sounds like you may have combined the ideas of detonation and preignition.

Higher grade gas will fix this problem. The noise he is describing is not the valves at all, it is the engine knocking - also called ping and pre-ignition - caused by low octane fuel.

Try running some seafoam

Ray, I agree with everything you have said here except that I buy the idea that the term pre-detonation and pre-ignition might be used interchangably. I suppose the interchanging might be erroneous, but I accept that people will make the interchange and we all understand that the interchange is meant to convey the same meaning. I agree that the more correct term is pre-ignition, and if all you are suggesting is that one term is better than the other, then I am on the same page. But if somebody said pre-detonation to mean pre-ignition, I wouldn't be confused and I'd probably let it slide.

On another note, can the knock sensor fail in such a manner that the motor knocks, but there is no Check Light? I ask because I suggested in another post that the OP get himself a code reader to see what the car has to say about why it is knocking.

I saw your other post about the OP getting a code reader to see what the ECU has to say.

In general, the check engine has to come on, even intermittently, for any trouble codes to be stored. If the ECU stores a code, it will turn on the light. In some cases, the light will turn off if the trouble is fixed, i.e., loose fuel cap and the 3 trip test is passed but may still retain a code.

The OP didn't say that the check engine light came on so I doubt if there are any codes stored.

As far as whether a bad knock sensor will make the check engine light come on, I'm not sure. If I can remember to, I'll take a look at the factory repair manual tonight but my guess is that a bad knock sensor will not set a code.

If you think about those built-in igniters for barbeques, pushing the button compresses the piezo-electric crystal, which then sends a spark to the electrode. When you don't push the button, there is no spark.

For a knock sensor, if there is no knock, then there is no signal so the computer would look at the absence of a signal as a normal condition. In the case of a knock sensor, the sensor generates its own power and isn't powered by the ECU so there is no loop or continuous signal like most other sensors.

BTW, you can test a knock sensor with an oscilloscope - just take a hammer and bang on the block near the sensor and you'll see the signal on the scope.

It was my mistake for saying, I should have used the sarcasm brackets I suppose. Since there is no reason that I know of besides major oil starvation to make the valves 'ping' it was sort of a joke / sarcasm. This is why I asked in my first post why the owner thought it was valve ping. Instead of going off about what I said you could have tried actually diagnosing the situation.

Pre-ignition is /still/ detonation.This is why people sometimes say pre-detonation, really they mean detonation before ignition. If you want to see how widely that term is used, google it once.

IMO, one should not perpetuate the use of incorrect terms that are confusing or misleading, especially one who fancies themselves knowledgeable about cars.

For example, a "rim" is not a synonym for wheel. A rim is a part of a wheel. Manufacturers publish specs about wheel base, wheel alignment, wheel balance, wheel hop, etc. Not rim base, rim alignment, rim balance, rim hop. Try looking up "spinning rims" in the SAE database.

Cars are not equipped with emergency brakes, sometimes referred to as "E-brakes." Cars are equipped with parking brakes, which as the term implies, should be applied when parking.

I agree, the ebrake term does not bother me all that much, though.

Preignition is not exactly detonation. From

Pat

I remember having this whole conversation on the MR2 forums at one time. I guess it all depends on what your definition of it is. The definition of detonation is the explosion of gas, the definition of preignition is the ignition of fuel (just more specific as to what causes it), which is, an explosion of gas. So I guess its kind of a grey area there.

Whatever you say Josh...

"Josh" wrote: snip

Not grey at all, as Greywolf explained, a normal flamefront burns much more slowly, the pressure rise from it is useful because it's speed can move the piston efficiently where the sudden pressure spike of detonation is so sharp, high and short that most of it's energy is expended against the inertia of the moving parts of the engine therefore very little of that energy is extracted as useful work, most of it is lost as heat.

Sure...