Puzzling Knock Counts

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Aug 6, 2015 | 06:17 PM

C4ProjectCar

Thread Starter

Drifting

Joined: Jul 2014

Posts: 1,426

Likes: 46

From: Lynchburg, VA

Puzzling Knock Counts

I just datalogged a run on my new engine, and the knock counts steadily rose up to 128, which concerned me. I tried accelerating, decelerating, cruising in high gear, cruising in low gear, and nothing affected knock counts. Then as I was just cruising along, they instantaneously dropped to 2. The only change I can think of was that I turned on the AC 30 seconds or so before the counts fell. But after a while, without turning the AC off, they rose to 54 then dropped immediately to 0.

First off, why would the knock counts drop back down without any obvious change?
And second, how many knock counts are acceptable? I know that knock counts don't necessarily mean bad things, but I don't know how many are safe.

Pertinent info:

'90 6-speed coupe
383 stroker
Ostrich 2.0
New knock sensor

Aug 6, 2015 | 10:11 PM

FrankieD

Burning Brakes

Joined: Mar 2005

Posts: 1,083

Likes: 116

From: Richmond Hill Ontario

Sometimes a knock sensor can be sensitive if not torqued to proper specs. The main concern is that it is not retarding timing because of false sensitivity. Can you attach the datalog.

Aug 6, 2015 | 10:15 PM

C4ProjectCar

Thread Starter

Drifting

Joined: Jul 2014

Posts: 1,426

Likes: 46

From: Lynchburg, VA

I was certain to torque it exactly to spec (I think 14 lb-ft).

Here's the log:
http://www.filedropper.com/8615run5

Aug 7, 2015 | 08:11 AM

FrankieD

Burning Brakes

Joined: Mar 2005

Posts: 1,083

Likes: 116

From: Richmond Hill Ontario

Your Datalog indicates you have an "Error Code 42: EST Monitor Error" This is for Electronic Spark Timing . Your Datalog shows a lot of Spark Retard occurring. I would investigate what is causing Err42 first and then go for another Datalog.

Aug 10, 2015 | 04:53 PM

C4ProjectCar

Thread Starter

Drifting

Joined: Jul 2014

Posts: 1,426

Likes: 46

From: Lynchburg, VA

That's odd. I'll see if I can figure out what's causing that and post an update.

Aug 10, 2015 | 10:25 PM

C4ProjectCar

Thread Starter

Drifting

Joined: Jul 2014

Posts: 1,426

Likes: 46

From: Lynchburg, VA

Okay, I think the error 42 was from not disconnecting the battery after setting the timing.

Also, the issue with high knock counts seems to have gone away. Turns out my dad mixed up the #2 and #4 spark plug wires, and after putting them in their correct places I only got 26 knock counts on a 25 minute run.

Is 26 acceptable? Here's the data log.
http://www.filedropper.com/81015run6

Aug 11, 2015 | 08:30 AM

FrankieD

Burning Brakes

Joined: Mar 2005

Posts: 1,083

Likes: 116

From: Richmond Hill Ontario

Yes way better. You still have some spark retard during WOT. Here is a list of the events:
Rec# 4233, WOT, 3000 RPM, 5.6 Deg Spark Retard
Rec# 4639, WOT, 3375 RPM, 4.2 Deg Spark Retard
Rec# 5088, WOT, 3000 RPM, 4.6 Deg Spark Retard
Rec# 5188, WOT, 3150 RPM, 6.7 Deg Spark Retard
Rec# 5822, WOT, 2975 RPM, 2.6 Deg Spark Retard
Rec# 7021, WOT, 3100 RPM, 6.9 Deg Spark Retard
Rec# 7550, WOT, 3300 RPM, 7.7 Deg Spark Retard
Rec# 8018, WOT, 3950 RPM, 3.3 Deg Spark Retard

You should try and correct this area in the Tune.