What exactly causes KR? - Page 2 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 03-03-2007, 04:15 PM   #11
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Welcome to the club swifty! As Wilwren said above, KR is the enemy, though not necessarily evil. KNOCK, however, is pure evil and must be dealt with accordingly

My goal in this post is/was to name all the culprits that would cause the knock sensor to, well, pick up knock. But there are some cases that the sensor thinks something is a knock (or "ping" as others have heard it) and it actually isn't...one case, I listed, is my factory cat. converter going bad and rattling...otherwise known as "rattle cat".

Eliminate all forms of knock...be it legit knock or false knock...and you won't get knock retard, which makes the engine happy...which makes owners happy
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Old 03-03-2007, 08:23 PM   #12
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Quote:
Originally Posted by sandrock
Is it possible to do that? I thought the knock sensor grounded through the block...which is the reason why there is only one lead going to it.
You're right, the body of the sensor is the ground for us. Buff up a spot and solder a lead to it to serve as a ground. Of the V8'* , we just moved it to a different pipe plug hole in the block (like one of the shift linkage bosses) and put a few windings of teflon tape on the threads to deaden out the vibrations. Have to get a little more creative with the 3800. For the purposes of determining if you have detonation vs something else rattling, you can take it out and put a jumper wire to a ground source to finish the circuit.

Unfortunately, you can't just disconnect the sensor, since that will generate a 43 code in the ecm.

Anything that hits the right frequency can set it off. A bad harmonic balance, rod bearings, etc..the list from the service manual is a whole page.
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Old 03-03-2007, 08:42 PM   #13
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BTW, the whole reason behind my suggestion for deadening the knock sensor is just to try and troubleshoot the problem. The knock sensor circuitry is either working correctly and you are picking up actual noises or it is faulty.

If you deaded the knock sensor, you should see zero KR in all conditions.

If the KR is still there even with the sensor unable to physically hear a knock, then the problem is the sensor, the ecm, or the calibrator prom inside the ecm (the esc circuitry is inside the calibrator prom...that little circuit board over top of the resistor packs)
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Old 03-03-2007, 08:58 PM   #14
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So what frequency range does it listen to?
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Old 03-03-2007, 08:59 PM   #15
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Thanks for the tips Curt! I'm not going to deaden the sensor until I fix everything I listed...transmission being the first and foremost, and at the same time put a test pipe in place of the cat (and yes, this will be for test purposes only, as I plan on a full exhaust in the summer months), AND upgrade all the wiring at the fuel pump since it looks shot.

I'm ALSO going to build a knock indication circuit as well as a simple rich/stoich/lean (i.e. 3-light) a/f gauge, schematics of both are available online and will be a rainy-day or while-at-work-on-a-weekend project. This indicators will help me in keeping knock to a minimum on this engine.
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Old 03-03-2007, 09:06 PM   #16
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Brad, you won't want to run with the test-pipe for long. I did on my 95, and immediately lost some low-end grunt. Very obvious.
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Old 03-03-2007, 10:20 PM   #17
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I'm not planning on running a test pipe for too long...as I said before, I have no problem installing a new cat, but I want to do a full exhaust all at once. I'm sure you're right about the low-end loss as I went through the same thing with the Malibu. After removing the full factory exhaust and replacing it with 2.25" from manifolds on back (factory went anywhere from 1-5/8 to 2...that exhaust was a mess), I lost a noticeable amount of low-end power but I gained the same amount in mid-range.

But if my cat is broken and plugged, I'm losing flow (and power) anyway, so a test pipe, in respect to the cars current state of tune, won't have much if any effect. But what I hope will happen is that it will eliminate false knock coming from that area.

The more I think about it, the more probable it is that the cat is the biggest culprit in false knock. I discovered on S1 L67s, the knock sensor is located on the rear bank, near the exhaust. False knock comming from the cat could easily be picked up from that location. (For L27s, the knock sensor is on the front bank). You know, for testing purposes, I may very well lengthen the knock sensor lead and see what readings the front sensor gives when compared to the rear, as both sensors are installed on the block.
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Old 03-04-2007, 01:14 AM   #18
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Can restrictive exhaust manifolds cause KR? I've mentioned this before, but this goes back to my LN3, with the infamous restriction at the rear, behind the oxygen sensor hole.
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Old 03-04-2007, 01:18 AM   #19
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On a stock car, they should not.

On a modified car, they should be ported before or during mods.
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Old 03-04-2007, 02:05 AM   #20
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I just scanned today and I am getting 7 deg KR at WOT so I am interested in what to do too. I am running a little lean which could be a cause. I did the swap with my car and didn't change the fuel pump. Could that be a cause??
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