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Occasional Part-Throttle Detonation


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I posted this issue about a month ago and received some good suggestions. Unfortunately, the problem persists. Hopefully, somebody can shed some light on this baffling problem.

For quite some time, I have had an intermittant case of detonation on part-throttle acceleration. It only happens every once in a while so it's been very hard to track down.

I finally got a diagnostic customer snapshot of it.

The snapshot data said:

1. PD41 = 0 (The knock sensor did not detect any knocks even though my ears sure as hell did!)

2. PD40 = 0.00 (There was absolutely no spark retard resulting from knock sensor data this time. All snapshots I've taken when I wasn't hearing detonation showed between 1.5 and 9 degrees of knock sensor retard.)

3. PD08 = 23 (The spark was running about 5 to 8 degrees more advanced than any snapshots taken when I didn't hear detonation.)

Other pertinent information:

I give it a WOT at least 3 or 4 times a week (because it's fun).

I always use premium gas.

No codes are being set.

I replaced the EGR valve about 20,000 miles ago and cleaned out the passages and "mouse holes" in the intake and phenolic spacer shortly after that.

The car recently passed California's smog test.

The car has absolutely no drivability issues - it runs like a dream.

I've heard no detonation for, maybe, two or three months and thought the problem had gone away. All of a sudden, it's back. The only thing I can think of that's changed is the weather has warmed up a little.

From the snapshot, it seems that something in the knock sensor/spark retard circuit stops working for a moment causing the spark to run too advanced. I suspect the knock sensor is acting up because it wasn't reporting detonation yet I could hear it as plain as day!

I can get a new knock sensor from GMPartsDirect.com for about $45 including S&H. Book time to replace it is 3/4 hr. Total cost about $100.

I wouldn't mind replacing it but a bad knock sensor should set code P131 and knock sensor circuitry problems should set code P132. I have not gotten either of these codes, ever.

It's a real puzzle. I'm hoping somebody can help me find the answer.

Thanks in advance


Happiness is owning a Cadillac with no codes.

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That is puzzling. I suppose you already checked the plugs and wires. Would crack in the wire insulation cause something like this?

"Burns" rubber

" I've never considered myself to be all that conservative, but it seems the more liberal some people get the more conservative I become. "

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Plugs and wires were replaced with OEM about 20,000 miles ago. Head gaskets were replaced at that time. Did timeserts, all internal parts looked excellent, combustion chambers were clean, no carbon build-up.


Happiness is owning a Cadillac with no codes.

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Poobah, I have a very similar problem to yours. Even though I always run premium fuel, I can hear what I think is detonation during occassional mid-to-heavy throttle sometimes. It does it maybe a few times a month. I checked the connection to my knock sensor a while ago, but it was good, and the sensor was mounted tightly to the block. I'm not sure what else to do besides replace it. But the problem is so intermittent on mine, I haven't spent the time or money yet.

Jason(2001 STS, White Diamond)

"When you turn your car on...does it return the favor?"

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