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Old 12-24-2015, 11:21 PM   #1
larry_g
 
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False knock help?

I am getting some fairly consistent knock retard (4-8*) around 3000 rpm and again around 5000 rpm during WOT runs in 3rd gear. This is happening with three different tunes, the stock 93 tune (SCT X4) and two mail order tunes from reputable vendors. Car is stock except for a Roto-Fab intake and a generic oil separator on the PCV line. Always use 93 octane.

I plan on trying an octane booster to see if that makes a difference, but I am beginning to agree with the suggestion that it might just be false knock, even though I am not seeing or hearing anything obviously loose.

Even if it is false knock, it's still pulling timing, and therefore not running to it's potential. Any thoughts on what I should be checking more closely as a source?
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Old 12-25-2015, 03:11 AM   #2
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Same thing here. Stock tune thought. I haven't found the issue on mine. Nothing over 5 degrees of timing for me.
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Old 12-25-2015, 09:24 PM   #3
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Try pulling some timing out of it and see if your still getting KR under wot. If you pull timing out of it and the knock goes away that could tell you that it's true knock. Could also be a bad sensor giving a false reading.
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Old 12-25-2015, 10:37 PM   #4
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I can't adjust the timing on the mail order tunes but I could on the stock one. I'll have to try that tomorrow.

The only thing I found loose was the vacuum pipe for the NPP exhaust. I zip tied it to the A/C line near it and the knock retard lowered but didn't go away completely.

I was also thinking that I've only seen it in 3rd gear. I didn't see it in 2nd and I haven't run it in 4th, but I'll need a different stretch of road to do that.
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Old 12-29-2015, 02:52 AM   #5
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3rd and 4th is where I get the higher knock readings. 2nd is really low at about 0.8.
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Old 12-29-2015, 02:49 PM   #6
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A couple of bottles of Lucas octane booster in a full tank of gas got rid of almost all of the knock retard on the tuner maps. My guess is that our 93 octane isn't that good so I'm going to see if tuning for 91 works better.
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Old 12-29-2015, 04:24 PM   #7
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I have the same exact problem. I'm running a 75 shot. I'm seeing around 8* knock retard at the very top of 3rd gear, right before the transmission shifts. I use 93 Octane and Royal Purple Octane booster or NOS Octane booster. Both claim to boost 3 FULL points.
I am thinking it is actually Burst Knock (Explained to me as follows: engine sees rpm flying up and predicts that knock is coming, so it initiates knock retard and pulls timing, like bracing yourself before being punched in the stomach).

I read that a lot of people zero out burst knock with hp tuners. Awaiting some extra $$$ so I can buy a tune...
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Old 12-31-2015, 11:26 PM   #8
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I'm surprised you haven't tried pulling timing already, that would be my first step, considering everything's tight and rattle free.


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Old 01-10-2016, 12:05 PM   #9
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Update: It looks like I have a problem with fuel pressure tapering off on WOT runs right when the knock retard is most intrusive. I was able to see this on more than one log. Once the weather gets better, I'm going to return it to the stock tune and see if the fuel pressure still tapers off. If it does, I'm thinking that it should still be eligible as a warranty repair as I have done nothing to the fuel system.

The thing I am still trying to figure out is the kPa to psi conversion on the data log. Using the google conversion calculator, the numbers on the chart make it look like I am only getting 20 psi and tapering off to 17. However, I found one thread where they mention that you have to take the SCT reading times 3 to get the actual pressure. This would mean it's running about 60 psi (normal) and tapering off to the low 50's (not normal). Does anyone have any experience with this?
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Old 01-11-2016, 08:21 PM   #10
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52 psi is normal at wot, the fpcm commands a lower pressure at higher rpm.
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Old 01-12-2016, 09:06 AM   #11
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Quote:
Originally Posted by Rhino79 View Post
52 psi is normal at wot, the fpcm commands a lower pressure at higher rpm.
When I was on tap-a-talk, I couldn't see that you are a tuner. I'm sure this won't come as a surprise, but I am getting conflicting information on this...

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Old 01-13-2016, 10:36 AM   #12
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make sure you're using GOOD gas, it makes a difference.. mobil, exxon, sunoco, amoco, bp, chevron are best brands to use, with mobil and exxon being the best..

NEVER use Shell, costco/bj's, mom-n-pop, or no-name brands, as it's crap gas that tends to cause a lot of knock retard...
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Old 01-13-2016, 07:25 PM   #13
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Quote:
Originally Posted by 2014CamaroSSRS View Post
make sure you're using GOOD gas, it makes a difference.. mobil, exxon, sunoco, amoco, bp, chevron are best brands to use, with mobil and exxon being the best..

NEVER use Shell, costco/bj's, mom-n-pop, or no-name brands, as it's crap gas that tends to cause a lot of knock retard...
How do you know that those 2 are the best? i want to know . Curious.
Thanks
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Old 01-14-2016, 10:44 AM   #14
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personal experience, along with several thousands of others that I've seen data logs for... can always tell when someone is using shell or other crap gas by their data logs.. lot of knock retard throughout the whole log...
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